Thermally Broken Balconies by Perkins&Will

January 2022

Thermally Broken Balconies Alternative Strategies for Low Carbon Buildings

“In certain complex assemblies, the research identified facades with as much as a 70% reduction in effective R-value [resulting from thermal bridging]” 1

Executive Summary Private outdoor space is a key part of a livable

of construction, structural integrity, fire safety,

home, and is an expectation widely held by those

constructability, and accessibility. Through a

looking to buy or rent a residential unit. Multi-

comparative analysis of eight balcony connection

unit residential buildings vary in scale, height,

details using these requirements, Part B of this

and construction typology, but the basic desire

report recommends a number of future proof

for outdoor space remains. Balconies have the

balcony connection details which significantly

practical function of providing occupants with

reduce the thermal bridge heat loss coefficient

access to semi-private outdoor space as part

and heat transfer through the building envelope.

of their suite and are an effective strategy for developers in attracting tenants and meeting amenity space requirements.

The balcony connection detail cannot be considered as an isolated element, and to fully understand its effect on the overall building

Despite recent efforts made to improve energy

performance a number of other design decisions,

efficiency and thermal performance of buildings,

such as form factor, effective R-value, window to

the balcony connection detail often remains

wall ratio, glazing specification, infiltration rate,

an unchallenged source of heat loss through

and HRV specification, must be considered. Part C

thermal bridging. Thermal bridging occurs when

of this report is a case study analysis that looks at

heat flow bypasses the insulated elements of the

the role that the balcony connection detail plays

building enclosure through penetrations or gaps

in relation to these other design decisions.

in the insulation. Currently, a typical balcony in mid to high-rise construction is built by extending the internal floor slab through the building envelope to form the balcony walking surface. Using this construction detail, the balcony slab becomes a significant source of thermal bridging. This type of thermal bridging leads to both additional heat loss and risk of condensation in the building due to lower internal surface temperatures relative to the ambient interior temperature—both of these implications not only impact occupant comfort but also the resiliency and durability of the building. Part A of this report considers the principles, methodologies, and design considerations related to thermal bridging in balconies.

Despite the fact that technical information is available regarding thermal bridging at balconies, and proprietary thermal break solutions have been available on the market for many years, there is still a knowledge gap related to the different strategies available, their impact on overall thermal performance, and the improved energy modelling standards required to reduce the gap between predicted and actual building performance. This report aims to distill the available information and overlay architectural guidance on balcony thermal bridging strategies with the goal of providing designers options for effective balcony design. This will ensure practitioners are in a position to design and construct buildings with

Efforts to improve the thermal performance

lower operational carbon footprints and meet

of balcony construction can be challenging

increasingly stringent energy performance

for designers and builders as they require

targets while achieving their architectural and

the successful resolution of often competing

design intent.

functional requirements. Alongside thermal performance, these requirements include cost

Acknowledgments This report was produced by Perkins&Will Architects with support from RDH Building Science and funding from BC Housing. We gratefully acknowledge the financial support of BC Housing through the Building Excellence Research & Education Grants Program. Authors: Marc Häberli, Senior Associate, Perkins&Will Architects Cillian Collins, Senior Architect, Perkins&Will Architects

Reviewers: Graham Finch, Principal, RDH Building Science Kathy Wardle, Principal, Perkins&Will Architects

Graphic Design: Karena Yeung, Marketing Coordinator, Perkins&Will Architects

Acknowledgment is extended to the following industry leaders who participated in an external review and workshop for this report: Sailen Black, City of Vancouver Tavis McAuley, McAuley Consulting Ian Boyle, Fast+Epp Structural Engineers William Loasby, Fast+Epp Structural Engineers Harshan Radhakrishnan, Engineers and Geoscientists BC Brent Olund, Urban One Builders Gino Matino, Axiom Builders Inc. Neil McGowan, BTY Thanks also to Westbank Corp for their participation in external reviews and workshops, in addition to allowing 5055 Joyce Street be used as a case study for this report. Additional thanks goes to the consultant and construction teams working on the project. Fast+Epp, Structural RDH Building Science, Envelope Integral Group, Energy Modelling George Third & Sons, Prefabrication Review Icon West Developments, Construction Manager Seiko, Curtain Wall Supplier

Table of Contents

Introduction

Report Assumptions and Structure

Part A: Understanding Balcony Thermal Bridging

A.1

Overview

A.2

Balcony Design Considerations

A.3

Rethinking the Status Quo

6 13

Part B: Balcony Types

B.1

Balcony Configuration

B.2

Balcony Types

B.3

Balcony Type Comparison

B.4

Balcony Type Recommendations

Part C: Case Study

C.1

Case Study Overview 43

C.2

Path B Performance Limits

C.3

Impact of Various Balcony Options

C.4

Case Study Outcome

Conclusion 53 References 54

↑ Exploded section of the thermally broken balcony connection for 5055 Joyce Street

Thermally Broken Balconies

Introduction Private outdoor space is a key part of a livable home, and

Report Assumptions and Structure

has become a sought after amenity in a residential unit.

The approaches presented in this guide are relevant to

The provision of balconies is not only an effective strategy

balconies of varying material in buildings at varying scales;

for developers in attracting tenants and meeting amenity

however, the primary focus of this report is for concrete

space requirements but it also has the practical function

construction for medium to high rise buildings. Building

of providing access to the outdoors which has a direct

performance requirements are specific to the regulations

correlation to quality of life, livability and mental health.

governing construction in the City of Vancouver but the

Balconies have become private havens for people living in

principles addressed are universally applicable. Refer to the

urban environments, and their value has been exponentially

local Authorities Having Jurisdiction for specific building

demonstrated in the recent pandemic where balconies

regulations and requirements.

have become a safe place to access the outdoors as well as platforms for community resilience and social connection.

Both imperial (IP) and metric (SI) R-values are used in this guide for indicating the thermal performance of

In recent construction there have been many advances in

base building assemblies. Metric (SI) units are used when

building envelope performance but the balcony connection

outlining thermal bridge performance values and regulatory

detail, and associated thermal bridging is often overlooked.

performance targets.

The impact of thermal bridging on overall building performance has been the focus of numerous studies and

This report is broken into three parts:

reports but the design and construction industry has been

Part A: Understanding Balcony Thermal Bridging

reticent to address this connection detail for a number

provides an overview of thermal bridging, balcony design

of reasons. As new building performance standards and

considerations and common concerns regarding thermal

requirements are introduced, the impact of the balcony

bridging specific to the balcony connection detail.

connection detail must be considered to achieve the

Part B: Balcony Types describes and compares several

increasingly stringent performance targets.

balcony construction options along with their associated

Although relatively new to North America, thermally broken

benefits and drawbacks.

balconies are common place in other countries around the world. Northern European countries, which experience

Part C: Case Study presents a case study that compares the

similar climatic conditions as Vancouver, have had to adapt

thermal performance of several balcony design options.

their design and construction practices to accommodate similar advances in building performance requirements. Thermally broken balconies are now standard practice in these countries, which demonstrates the feasibility for this type of progress and innovation within the local industry. To facilitate the transition to holistically higher performing buildings, this report focuses on understanding the impact of thermal bridging related to the balcony connection detail, its impact on the overall building performance, and provides a number of alternative solutions that address thermal bridging and allow for a more comprehensive improvement of the building envelope.

Part A

Understanding Balcony Thermal Bridging

Part A: Understanding Balcony Thermal Bridging

A.1 Overview As a basic principle, heat travels through the path of least resistance. In the context of balconies, these paths typically occur where highly conductive materials penetrate through the thermal barrier to provide structural support for a balcony. Mid and high-rise concrete buildings typically have balconies that are constructed as extensions of the building’s cast-in-place concrete floor slab. The effective R-value for such penetrations is approximately R-1 (0.2 RSI) where insulated opaque wall assemblies typically have effective R-values of R-5 to R-20 (0.9-3.5 RSI). The result is a path of least resistance for heat to escape through to the balcony slab.

“After accounting for windows and doors, exposed concrete slab edges and balconies can account for the second greatest source of thermal bridging in a multi-storey building.” 3

← Illustration of heat loss path through cantilevered balcony slab. The majority of heat loss is through the balcony slab and fenestration.

Thermally Broken Balconies

The impact of thermal bridging at balcony slabs is well understood and has been studied for many years using two and three dimensional heat flow simulation modelling.2, 3 Thermal bridging through cantilevered concrete floor structures increases heat loss and results in low interior surface temperatures which have the potential to cause a number of undesirable effects, including: ǌ Increased space heating and cooling requirements for the building; ǌ Condensation and mould growth due to colder interior surfaces; and, ǌ Occupant discomfort due to radiant heat loss to colder interior surfaces and convective air drafts. To mitigate these undesirable impacts and allow buildings to achieve more stringent building performance requirements, alternative balcony connection details must be considered. These details attempt to lessen heat loss by reducing the extent and conductivity of the materials penetrating the thermal barrier.

↑ Thermal imaging of a building with cantilevered concrete balconies. Red and white horizontal stripes on the right are indicative of thermal bridging and heat loss through the slabs at balcony locations.

← A thermal model of a cantilevered concrete balcony. Plume of green and yellow radiating inwards at balcony connection is indicative of thermal bridging occurring.

Part A: Understanding Balcony Thermal Bridging

A.2 Balcony Design Considerations The basic function of a balcony is to provide

exposure to rainwater, seawater, or other

private or semi-private outdoor space,

incompatible materials. Thermal bridging can

expanding the physical living space and

also lead to condensation buildup within the

range of activities possible in a dwelling unit.

connection posing a threat to the durability of

It is also a key part of the architect’s toolkit

the structural material.

when developing the overall aesthetic and composition of the building.

In addition to the balcony structure itself, it is important to understand the support

Although the primary focus of this report

requirements for balcony doors and glazing

is the thermal performance of the balcony

systems, and to ensure required support is

connection detail, thermal performance is

provided; for example, in high performance

just one of several considerations of balcony

building envelopes doors and glazing systems

design. There are other attributes in balcony

should be located in plane with the insulation

design, both in the construction of the balcony

in the opaque assembly, while other door and

itself and its impact on the overall building that

glazing systems may require continuous sill

need to be considered.

support. In balcony connection details where

Structure

structural material is not provided directly below the wall, door and glazing system,

The structural integrity of the balcony and

additional structure may be required to support

safety of its occupants is fundamental to

the sill of the door and glazing system (Figure 1).

the balcony design. The balcony generally

Thermal Performance, Occupant Comfort and Resilience

cantilevers or is connected laterally back to the building and must resist dead, live, and lateral loading as well as meeting local seismic

Most of the focus in discussions around thermal

requirements.

bridging mitigation is to quantify and reduce

The size of a balcony’s structural connection back to the building’s primary structure is directly related to its weight and loading requirements. By reducing the weight of a balcony, through its size, construction or materiality, the size of the structural connection back to the building can also be reduced.

the associated heat loss. While this is important in tackling the carbon footprint associated with buildings’ operation, of no less concern is the impact on both the building itself and its inhabitants due to the thermally compromised detail(s). These include: ǌ Thermal resilience—the ability to

This in turn decreases the amount of thermal

provide shelter despite power outages

bridging through the building envelope. When

or extreme weather events;

optimizing the balcony structural connection,

ǌ Occupant comfort—eliminating

the stability or perceived “bounce” of

discomfort due to radiant heat loss,

cantilevered balconies must also be taken into

removing the risk of mould growth and

consideration to ensure user comfort levels.

associated indoor air quality issues;

The durability of the connection materials

ǌ Building resilience—providing protection

must be considered when specifying a balcony

against rising energy and carbon

connection detail. Concrete or steel balconies

costs, and increasing overall durability

can be at risk of deterioration either through

by reducing condensation risk. 6

Thermally Broken Balconies

Door/glazing system Structural door or glazing support angle Structural thermal break

← Figure 1: Balcony detail demonstrating provision of an additional support angle to provide the required continuous sill support at base of balcony door and glazing system

Envelope Detailing By its nature, a balcony or a balcony’s structural support inevitably interrupts the continuity of the building envelope as it is required to tie into the building’s primary structure. When detailing the balcony connection, the associated building enclosure control layers including air, thermal, water, and vapor control must be maintained. Regardless of the balcony type, air barrier continuity must be maintained around balcony

A horizontal balcony surface must manage large amounts of rainwater which is important to prevent water ingress or damage to the balcony structure. Some balconies are sloped to allow water to drain off the balcony edge away from the building and some collect the water through a drain and direct it to an external or internal rainwater leader. It should be noted that routing a drain inside the building may add to the thermal bridging and associated heat loss.

interfaces and penetrations. This can be more

Ventilation

challenging with some connection details,

In-slab exhaust ductwork for ventilation

particularly where the air barrier is penetrated

systems and clothes dryers are often run

by structural connections. These details

through the slab to vent into the balcony soffit.

require attention to proper detailing, material

Conventional extended slab balcony’s allow

selection, and construction sequencing (e.g.

for this strategy but it becomes challenging to

use of air barrier membrane pre-stripping).

maintain a duct penetration when attempting

Within the wall assembly, the vapour control

to break the thermal continuity between

layer must also be maintained through

the interior floor slab and the balcony.

balcony interfaces.

Depending on the balcony connection detail alternative methods of ventilation may need to be considered. 7

Part A: Understanding Balcony Thermal Bridging

HEADER

CEILING

LOWER ELEVATION OF HEADER AND DOOR TRACK ASSEMBLY

LIVING AREA

1980mm MINIMUM HEADROOM

BALCONY OR PATIO AREA PATIO DOOR

UPPER ELEVATION OF STEP OVER AND DOOR TRACK ASSEMBLY MAX 200mm

BALCONY FLOOR LEVEL

MAX 200mm

← Figure 2: Step over requirements from City of Vancouver’s Balcony and Patio Doors in Houses and Dwelling Units Bulletin

FLOOR LEVEL STEP OVER

300mm MAX

Policy / Code

Accessibility

In order to encourage the provision of outdoor

Section 3.8 of the BCBC differentiates between

space, the City of Vancouver grants a floor

“accessible” dwelling units and “adaptable

space ratio (FSR) exemption of up to 12% of

dwelling units.” In fully “accessible” dwelling

the maximum gross area available for new

units, where people may be expected to be

buildings that provide balconies. The City of

confined to a wheelchair, the Vancouver

Vancouver has also published design guidelines

Building Bylaw (VBBL) and BCBC permit

on ‘enclosed balconies’ to extend the year-

a maximum 13 mm high threshold at the

round enjoyment of these outdoor spaces.4

balcony door.

Conventional approaches to constructing

Subsection 3.8.5 of the BCBC includes

continuous slab balconies required little

additional requirements to be incorporated

attention to Part 3 (Fire and Life Safety) of the

into “adaptable dwelling units” which

British Columbia Building Code (BCBC). Until

depending on the municipality may be

recently, accessibility to the balcony was not

required to be included in a building.

considered, however in recent years some

"Adaptable dwelling units" are designed to

jurisdictions have increasingly placed limits on

allow occupants to age in place or entertain

the step over threshold dimensions to improve

persons with mobility restrictions. In Vancouver,

accessibility for persons with limited mobility,

all dwelling units in new buildings are classified

and in some cases require a percentage of

as “adaptable dwelling units.”

units within a building to have wheelchair accessible balconies. 8

MIN M

1,10

MAX 200 MM

Thermally Broken Balconies

← Figure 3: Minimum height to guard railing from City of Vancouver’s Balcony and Patio Doors in Houses and Dwelling Units Bulletin

ADDITIONAL BY-LAW CONFORMING LANDING

A recently published bulletin specifies the

of non-combustible construction. However,

maximum step over threshold to be not

the exterior balcony structure is not required

more than 200 mm high and 300 mm wide.

to have a fire resistance rating. This means

Alternatively, the VBBL will permit a “step-

that exposed steel or other non-combustible

on threshold”; however, these may require

structural components of the balcony above

interior landings and in some cases landings

exterior space would not require minimum

to the exterior with resulting guardrail height

concrete cover or a fire protection system as

extensions to maintain the required minimum

would otherwise be required on the interior

1070 mm height. See illustrations (Figure 2

floor slabs.

and Figure 3) in Bulletin 2016-002-BU. These 5

threshold limitations and requirements should be considered in detailing the thermally broken balcony connection as well as the structural supports for the door and glazing systems described in the previous section.

The BCBC also requires additional fire protection in rain screen wall assemblies incorporating a drainage cavity in excess of 25 mm and containing combustible materials (cladding or insulation). To prevent the spread of fire within this cavity the code requires fire

While not impacting the performance of the

blocking at each floor level or at a maximum of

balcony, non-climbable guards of not less than

3 m vertically and 20 horizontally. In continuous

1070mm high are required by the building code

slab balcony construction—where the floor slab

on all balconies where the walking surface is

interrupts the envelope—this requirement is

more than 600mm above the adjacent surface.

met by the slab. However, where the balcony

Fire Protection

has intermittent connection back to the base structure, this firestopping must be maintained

Part 3 of the BCBC mandates that for buildings

by incorporating sheet metal flashing or

required to be of non-combustible construction,

non-combustible insulation within the

the balcony supporting structure must also be

drainage cavity. 9

Part A: Understanding Balcony Thermal Bridging

Constructability Most Canadian high-rise buildings are built using conventionally reinforced cast-in-place concrete construction, where the internal floor plate extends through the building envelope to form the balcony slab. This typical construction methodology is coming under scrutiny due to its inherent thermal bridging. However, developers and contractors favour the simplicity and uninterrupted construction sequencing that this methodology allows. Any alternative construction methodologies will have to take this into account. Some proprietary structural thermal break systems allow traditional construction methodology to be maintained with the

Daylighting and Shading

addition of a thermally broken structural

Through strategic placement of balconies, especially on the south face

slab edge. Other balcony connection options

of a building, solar gains can be mitigated as the balconies serve as a

required unique connection details and

shading device which reduces heating and cooling requirements. This

allow for off-site balcony prefabrication.

also has an impact on the daylighting levels within the building.

Prefabrication provides efficiencies in balcony construction and construction sequencing by allowing the building envelope to be completed prior to the installation of the balconies.

Environmental Balconies can be strategically designed to control environmental performance and improve the resiliency of a building. They can influence daylighting and shading, rainwater protection, wind, acoustics, and ventilation strategies, which all play a large role in building performance, occupant comfort, and a building’s marketability.

Wind The placement and location of balconies on a building can not only change the way wind interacts with a building but also airflow patterns around a building. High wind speeds around tall buildings can cause occupant discomfort while using balcony spaces and even lift unsecured items off of balconies. Wind tunnel and/or computer model studies are recommended to ensure safe conditions and occupant comfort. 10

Thermally Broken Balconies

Acoustics The design of balconies can have a significant impact on noise penetration in residential units. Noise can be reduced through strategic balcony shaping, material choice, and the presence of a solid parapet at the edge of the balcony.6

Rainwater Protection Depending on their configuration, balconies can be used to protect spaces and building envelope systems below from rainwater and rainwater damage.

Mock-up of a thermally broken balcony for Delta Land Development Ltd.'s multi-storey timber Canada’s Earth Tower.

Thermally Broken Balconies

“Building envelope heat loss has historically been simplified due to past difficulties in cost-effectively providing more accuracy. This has generally led to overly optimistic assessments of building envelope performance by way of ignoring or underestimating the impact of thermal bridging.” 7

A.3 Rethinking the Status Quo Buildings and construction together account for 36% of global final energy use and 39% of energy-related carbon dioxide (CO2 ) emissions.8 Optimizing building energy use and reducing carbon emissions as they relate to balcony thermal bridging requires innovation and challenging the status quo in three main areas: 1. Introduction of higher performance requirements; 2. More accurate building performance energy modelling; and, 3. Understanding thermal bridging and updating traditional construction methodologies. The following sections address these three main areas as they relate to balcony design and constructability, as well as overall building performance.

Part A: Understanding Balcony Thermal Bridging

Introduction of Performance Targets With an increasing recognition of carbon emissions associated with buildings, there is a common drive towards carbon neutrality or zero emissions from buildings. Various policies and regulatory bodies are adopting performance-based targets with associated timelines for implementation, with zero emissions from new buildings by 2030 being a common goal.

“A key to meeting low thermal energy demand intensity (TEDI) for buildings is a holistic assessment of thermal bridging for thermal transmittance calculations. The biggest impact…is the quality of the details and design teams aggressively minimizing thermal bridging.” 9

This policy shift is evidenced at a variety of governmental levels: ǌ United Nations Framework Guidelines for Energy Efficiency Standards in Buildings; ǌ Canadian Federal Build Smart program; ǌ BC Energy Step Code; ǌ City of Vancouver Zero Emissions Plan for New Buildings Rezoning Policy; and, ǌ City of Toronto Zero Emissions Framework. A shared methodology for achieving these goals within the BC Energy Step Code and City of Vancouver Green Building Rezoning Policy is to place limits or thresholds on the Energy Use Intensity (EUI, measured in kWh/m²a) of a building, and a specific limit on the requirements for heating or cooling the building, known as Thermal Energy Demand Intensity (TEDI, measured in kWh/m²a).

Thermally Broken Balconies

Energy Modelling Guidelines The approach and methodology to assess building performance is changing as codes are becoming progressively more stringent. Traditionally building codes have been somewhat ambiguous about how to treat balconies (and thermal bridging in general) in terms of quantifying their impact on thermal performance. Previous versions of Canada’s National Energy Code for Buildings (NECB) (2011 and 2015) allowed the heat loss impacts of wall components encompassing a small percentage of the wall area to be ignored in code compliance calculations. The City of Vancouver and Province of British Columbia are addressing this by implementing performance-based standards, a move away from improvement as compared to a reference building or a prescriptive checklist approach. These absolute targets on energy performance are coupled with the comprehensive City of Vancouver Energy Modelling Guidelines in order to ensure accurate prediction of performance. These guidelines are referenced at both the Municipal and Provincial level. The Architectural Institute of British Columbia and

In terms of treatment of balconies, the City of Vancouver Energy Modelling Guidelines10 Section 3.1.2 outlines: Except where it can be proven to be insignificant, the calculation of the overall thermal transmittance of opaque building envelope assemblies shall include the thermal bridging effect of major structural penetrations, such as floor slabs, beams, girders, columns, curbs or structural penetrations on roofs and ornamentation or appendages that substantially or completely penetrate the insulation layer. In practice this means that the energy modeler will input an effective R-value of the external opaque wall assembly that must consider the thermal bridging of the balcony (and other thermal bridges). This modelled effective R-value, used for illustrating compliance with the performance targets and for guidance on design strategies, should allow closer prediction of eventual performance. This in turn means that the architect and design team must understand how thermal bridges are measured and how the effective R-value of an assembly is calculated.

Engineers and Geoscientists of British Columbia have also introduced the concept of an energy modelling supervisor and a qualified modeler who will sign and seal the energy model as a

“The contribution of details that are typically disregarded [in energy modeling] can result in the underestimation of 20% to 70% of the total heat flow through walls.” 11

means of ensuring quality control of the energy modelling process.

Part A: Understanding Balcony Thermal Bridging

Understanding Thermal Bridging Methodologies Thermal bridges are measured by assigning

BUILDING ENVELOPE THERMAL BRIDGING GUIDE v1.4

each penetration detail a thermal bridge loss coefficient. This is essentially an accounting  Point transmittance is the heat flow caused by thermal bridges that occur only at single, infrequent locations. This includes building components such as structural beam principle that compensates for the difference penetrations and intersections between linear details. The point transmittance is a single in heat loss between that which is modelled additive amount of heat, represented by chi ( ). based on assemblies alone and the actual heat loss through the detail. The actual heat loss is modelled in software such as THERM, HEAT 2 & 3 or Flixo or taken from a reference guide such as Building Envelope Thermal Bridging Guide. The Building Envelope Thermal Bridging Guide is used as the source document in this report. For linear thermal bridges, this value is known

6: Example clear field as the Psi (Ψ) value (W/mK). For Figure point thermal assembly

bridges, the correction factor is known as the

Figure 7: Example linear Example linear transmittance transmittance a floor slab detail of a floorofslab detail

Figure 8: Example point transmittance of Example point transmittance a beam penetrationdetail detail of a beam penetration

Chi (χ) value (W/K). The heat loss associated The overall U-value for any building envelope section is a simple addition and multiplication with thermal bridging of a balcony is process. a productIn straightforward terms this amounts to: ↑ of the linear length of balcony multiplied Examples of linear and point transmittance Heat flow through Heat flow through + Total Heat flow per area linear transmittances point transmittances Heat flow per area through connections, the number of point connections = + through Total Area of assembly clear field assembly multiplied by the Chi (χ) value. This allows for the overall assembly

by the Psi (Ψ) value or, in the case of point

subdivision of the balconies into categories;

those that result in linear thermal bridge versus Or, in mathematical terms: intermittent point thermal bridges. There are slightly different calculation methodologies depending on the guideline document or standard referenced e.g. Building Envelope Thermal Bridging Guide, ASHRAE-1365-RP, ISO 10211, ISO 14683 and Passive House Where: Institute (PHI). A comparison between the UT = different calculation methodologies is outlined Uo = in the BC Housing publication, Low Thermal Atotal = Energy Demand for Large Buildings.13

= Once the thermal bridge heat loss coefficient has been identified for a detail it needs L = to be included in the calculation of the

=

“U-value [or R-value] alone is a blunt instrument 𝛴𝛴( ∙ 𝐿𝐿) + 𝛴𝛴𝛴for ) gauging the thermal 𝑈𝑈𝑇𝑇 = + 𝑈𝑈𝑜𝑜 of a building” 12 performance 𝐴𝐴𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇

total effective assembly thermal transmittance (Btu/hr∙ft2∙oF or W/m2K) clear field thermal transmittance (Btu/hr∙ft2∙oF or W/m2K) the total opaque wall area (ft2 or m2) heat flow from linear thermal bridge (Btu/hr∙ft oF or W/mK) length of linear thermal bridge, i.e. slab width (ft or m) heat flow from point thermal bridge (Btu/hr∙ oF or W/K)

effective R-value. The impact of the thermal There are multiple types and quantities of linear and point transmittances, but they are all added to the clear field heat flow to get the overall heat flow of an area of the building envelope. The performance of different balcony connection length for the linear transmittance depends on the detail. For example, the length used in the details is illustrated in the Case Study in Part C calculation for a floor slab bypassing the thermal insulation could be the width of the building of this report. perimeter, if this slab detail occurs around the whole façade of the building. Alternatively, a corner 16

-11-

Thermally Broken Balconies

As an example, the thermal bridge heat loss

determine the heat flow through the detail but

coefficient for the most common continuous

additional hygrothermal modelling (via WUFI

slab balcony detail can be found in the Building

or other similar software) or calculation of the

Envelope Thermal Bridging Guide under

temperature correction factor (fRSI) may be

detail number 5.2.5 where a Psi (Ψ) value of

required to analyze condensation risk.

1.059 W/mK is given.2 The introduction of a

This guide uses the simple comparison of

proprietary thermal break to this detail can

thermal bridge heat loss coefficients to

reduce this value to 0.4 W/mK whereas Passive

underscore the importance of challenging

House projects generally aim for thermal

current balcony construction methodologies

bridge free design where the Psi (Ψ) value is less

and understanding alternative balcony

than 0.01 W/mK.

connection details and their impact on the

To ensure occupant comfort, the thermal

overall building performance.

envelope needs to be as homogeneous as possible, to maintain even internal surface Appendix A: Catalogue Material Data Sheets temperatures of the building fabric as close

BUILDING ENVELOPE THERMAL BRIDGING GUIDE v1.4

to the average ambient room temperature

and Interior Insulated 3 5/8” x 1 5/8” Steel Stud (16” o.c.) Detail 5.2.5 Wall Assembly with Horizontal Z-girts (24” o.c.) Supporting Metal quantifying the Ψ (Psi)-value in W/mK will Exterior as possible. Thermal bridge calculations

Cladding – Uninsulated Intermediate Floor Intersection with Uninsulated Curb

Balcony Stepdown Detail Balcony Stepdown Detail

ID 1

Component Interior Film1

Thickness Inches (mm) -

Conductivity Btu∙in / ft2∙hr∙oF (W/m K) 17

↑ Specific Building Envelope Thermal Bridging Guide² Nominal Resistance Density Heat pg.767—Detail 5.2.5 Uninsulated Intermediate hr∙ft2∙oF/Btu lb/ft3 o Btu/lb∙ Floor Intersection with CurbF 2 3 Uninsulated (m K/W) (kg/m ) (J/kg K) R-0.6 to R-0.9 (0.11 RSI to 0.16 RSI)

Part B

Balcony Types

Part B: Balcony Types

B.1 Balcony Configuration Balconies can be organized broadly into two categories, external, projecting balconies or internal, inset balconies. Within these two classifications there are a number of connection details that can be used to support the balcony. It is important to understand the implications to a building design, massing and thermal performance associated with these two balcony types.

1. External Balconies External balconies are characterized as balconies that project beyond the predominant face of the building. These balconies are fastened rigidly at the edge of the building

The expression of internal balconies is defined not only by their size, shape, and the composition of the guard but also by the massing of, and relationship to the building form.

and extend out from the face of the building.

The thermal bridging that results from the

All structural loads from the balcony are

structural balcony connection is fundamentally

transferred back to the rigid connection at the

a result of the area or linear length of thermal

edge of the building.

transmittance. Since inset balconies are

The expression of external balconies is defined by their size, shape, and the composition of the guard.

typically connected to the primary structure on two or three sides of the balcony, the length of thermal bridge, or number of structural connections is typically two to three times that

2. Internal Balconies

of the external balcony which is only connected

Internal balconies are open-air, outdoor

the area of thermal transmittance for internal

spaces configured to be in plane or behind the predominant face of the building. For this type of balcony configuration, the balcony is inset in a recessed façade articulation or internal

to the primary structure on one side. Therefore, balconies is typically larger which may result in more thermal bridging depending on the type of structural connection.

corner. The structure for internal balconies can be connected to the building’s primary structure along multiple perimeter walls. This type of balcony is popular because they provide a more protected outdoor space with privacy for occupants and more opportunities for doors to access the balcony.

Thermally Broken Balconies

A B

External Balcony (Connected on One Side)

Thermal Bridge = A

A B

Internal Balcony (Connected on Two Sides) Thermal Bridge = A + B

Internal Balcony (Connected on Three Sides) Thermal Bridge = A + B + C

Inset Balconies at Shannon Estate Vancouver, BC

Thermally Broken Balconies

B.2 Balcony Types There are a number of connection details that can be used in residential balcony construction in either an external or internal configuration. The following section describes eight balcony connection details: 1. Continuous slab; 2. Continuous slab with intermittent concrete; 3. Continuous slab with structural thermal break; 4. Continuous slab with wrapped insulation; 5. Discrete moment or knife plate connection; 6. Discrete connection with suspension/compression; 7. Simply supported; 8. Self supported. Each of the connection details are evaluated on thermal performance, constructability, resilience and occupant comfort, and cost efficiency on a scale of one to five, one being the worst and five being the best. For the purposes of this report this is a simplified scale to allow comparison across the connection details. In practice each connection type will have a range within these evaluation categories. Specific thermal performance values for each of these balcony types is dependent on a number factors and can be found in the Building Envelope Thermal Bridging Guide2. The case study in section C compares and evaluates different balcony types in relation to each other to better understand their impact on the overall building performance.

Part B: Balcony Types

1.0 Continuous Slab Continuous slab balconies are formed by extending the

Thermal Performance

primary structural concrete floor system through the building

Concrete and embedded steel reinforcing penetrating the building envelope are conductive to heat flow and represent a significant thermal bridge. Thermal performance is directly tied to the length and thickness of balcony connection.

envelope to form the balcony slab. Currently, this is the most common method of balcony construction but is susceptible to significant thermal bridging where the slab penetrates the exterior envelope. The concrete slab is typically covered with

Constructability

a water-resistant membrane which protects the concrete and acts as the finished walking surface. Because there are

Continuous slab balconies are the simplest balcony type to construct. By extending the formwork required for a building’s floor

typically no penetrations in the slab, the balcony provides

slabs the concrete can be poured in the same manner and at the same time as the primary building structure.

good weather protection for units below.

Achieving a fully accessible balcony in regard to maximum door threshold height is challenging without stepping down the balcony slab.

Design Considerations ǌ Balcony slab depth is based on structural

Resilience and Occupant Comfort

reinforcement and whether mild steel or a post-tensioned system are used.

The significant thermal bridging of this detail leads to low internal surface temperatures on the internal junction as the external wall meets the concrete slab, increasing risk of condensation and potential for mould growth.

ǌ Balcony slabs can typically be used for in-slab exhaust strategies.

Cost Efficiency This is a well-known construction method and contractors and designers are familiar and comfortable with the associated construction details. Since the concrete slab which creates the balcony is an extension of the primary structural system there are no additional cost associated with additional materials, trades or labour to form or pour the balconies. As the thermal performance of this balcony type is poor, there will be additional cost to improve other parts of the building envelope to meet building performance requirements.

Thermally Broken Balconies

Continuous concrete slab

Part B: Balcony Types

2.0 Continuous Slab with Intermittent Concrete Continuous slab balconies with intermittent concrete

Thermal Performance

are formed by concentrating the structural slab and slab

Although structural reinforcement is concentrated in smaller areas of the slab, the same total amount of slab reinforcement, typically mild steel, is required to support the balcony whether it is concentrated or disbursed. Since the embedded steel reinforcing is the most conductive material there are only minimal thermal performance gains attributed to this balcony type.

reinforcement to isolated locations along the length of the balcony to support the cantilevered balcony. The void spaces between the reinforced floor slab are insulated, reducing the length of thermal bridging through the slab. For a typical balcony, the reinforced structural slab can be reduced to approximately 40% of the balcony length

Constructability

allowing for 60% of the balcony connection to be insulated.

Concentrated reinforcements and void spaces require complex formwork and structural reinforcement layout. It limits the opportunity for in slab exhaust and ventilation strategies, and requires unique waterproofing details around the insulated void spaces.

The concrete slab is typically covered with a water-resistant membrane which acts as the finished walking surface. If the insulated voids in the slab are properly waterproofed and tied into the building envelope, the balcony provides weather protection for the unit below.

Insulation in the void space must be non-combustible and incorporate a fire block at the floor level if the wall cavity contains combustible elements and the drainage cavity is more than 25mm.

Design Considerations

Achieving a fully accessible balcony in regard to maximum door threshold height is challenging without stepping down the balcony slab.

ǌ Balcony slab depth and size of concentrated structural reinforcement is based on loading and cantilever requirements.

Resilience and Occupant Comfort

ǌ In-slab exhaust and ventilation strategies are possible with

The intermittent nature of the insulation means that thermal bridging is still present where the concrete continues to penetrate the envelope. This leads to localized lower internal surface temperatures. To guarantee a comfortable environment, the thermal envelope needs to be as homogeneous as possible to avoid temperature asymmetry across the internal surfaces.

this balcony type, but additional coordination is required with the structural engineer. In-slab ducts are required to be routed through the insulated void spaces to avoid conflict with the structural reinforcements. This introduces a thermal bridge through the insulation, reducing the overall performance of the balcony connection.

Cost Efficiency

ǌ To optimize alignment of doors and glazing within the

Additional engineering and coordination is required to design the concentrated structural systems. Additional labour and materials are also required on site to build the additional formwork needed to create and insulate the voids in the slab.

wall system additional structure may be required to provide continuous sill support above insulation.

Thermally Broken Balconies

1 2

Mineral wool insulation in slab void spaces Continuous concrete slab

Part B: Balcony Types

3.0 Continuous Slab with Structural Thermal Break Continuous slab balconies with structural thermal breaks

Thermal Performance

use proprietary thermally broken element to connect a

A proprietary structural thermal break system typically has an effective insulation value of R-2 to R-5 IP (0.35 -0.9 RSI) depending on size, type, and balcony loading. The less thermally conductive polystyrene thermal break decouples the interior and exterior concrete slab and represents a significant thermal improvement over typical cantilevered concrete balconies even when penetrated by steel reinforcing. The greater the balcony depth and higher the

cantilevered balcony slab to the primary structural concrete floor system. The insulated thermal break is formed from rigid polystyrene, mild steel or stainless steel reinforcing, and proprietary compression blocks to create a separation between the interior and exterior structure. When the concrete formwork is in place the thermal break

seismic loads the more steel that will be required which lowers the overall thermal performance.

is placed within the formwork prior to pouring concrete between the balcony and the interior floor slab. Concrete

Constructability

is then poured to form the interior suspended slab and

The use of these systems requires additional engineering, coordination, and input from the manufacturer although this effort is minimal due to the limited number of products available on the market and their use of standardized details. Placement of the thermal break adds an additional step to the formwork process and slight complexity to slab reinforcement layout. Waterproofing details are similar to continuous slab balconies.

balcony slab. The concrete slab is typically covered with a water-resistant membrane which acts as the finished walking surface.

Design Considerations ǌ Balcony slab depth and choice of structural thermal

Depending on the product, additional assessment and certification or standardized testing may be required to comply with local building regulations and codes.

break product is based on structural reinforcement strategy, loading and cantilever requirements and must be coordinated with manufacturers specifications.

Achieving a fully accessible balcony in regards to maximum door threshold height is challenging without stepping down the balcony slab.

ǌ Attention should be given to the use of membranes or sealants on balcony surfaces which must be

Resilience and Occupant Comfort

compatible with materials used in the thermal break.

The use of thermal breaks transfer load and maintain full structural integrity, while at the same time maintaining inner surface area temperatures well above those likely to cause mould formation and condensation.

ǌ In-slab exhaust strategies are possible with this balcony type, but additional coordination is required with the structural engineer and thermal break manufacturer. The in-slab ducts introduce a

Cost Efficiency

thermal bridge into the detail reducing the overall performance of the balcony connection.

There are additional costs associated with the use of a proprietary product as well as additional engineering, coordination, and labour required to design the structural slab and install the thermal break and associated reinforcements into the formwork.

Thermally Broken Balconies

Structural thermal break

Part B: Balcony Types

4.0 Continuous Slab with Wrapped Insulation Wrapped balconies are formed by cantilevering the primary

Thermal Performance

structural concrete floor system beyond the building

Despite the additional insulation, the thermal performance of this balcony type is still quite poor due to the large surface area of heat loss from the cantilevered balcony.

envelope and entirely encapsulating them in insulation to address thermal bridging. Once the concrete slab has been cast and waterproofing

Constructability

membrane has been applied, the insulation is installed

The structural system and construction process for the wrapped balconies is similar to a conventional continuous slab balcony but

on the top, underside, and sides of the balcony. Pavers or removable exterior flooring tiles must be installed above

there may be additional complexity in formwork construction and concrete pouring if the slab is required to step down. The additional build up of the insulation and walking surface may require a step down of the structural concrete balcony slab to meet the local jurisdiction’s maximum threshold stepover height and accessibility requirements. Achieving a cantilevered balcony with a stepped slab poses some structural challenges and requires coordination with a structural engineer. This, in addition to the installation of the insulation, walking surface and unique guardrails requires additional construction time, trades, and labour.

the insulation and filter fabric to form the walking surface similar to a roof deck assembly. This additional buildup adds material, complexity, and additional requirements for fire protection.

Design Considerations ǌ Balcony slab depth is based on structural reinforcement strategy, loading and cantilever requirements.

This approach requires the use of non-combustible insulation on the bottom, front and sides of the balcony surfaces as they are susceptible to exposure to flames from below. Extruded polystyrene (XPS) can be used on the top of the slab to support the walking surface.

ǌ Buildup of insulation and walking surface creates a thick balcony assembly and edge profile. This can be challenging to accommodate with standard ceiling heights and must be considered from an

Resilience and Occupant Comfort

architectural and aesthetic perspective.

The addition of continuous insulation wrapping the balcony reduces heat flow through the junction. This will help keep internal surface temperatures above what they would be in an otherwise unmitigated condition. Detailed condensation risk analysis may be required to assess comfort and durability criteria.

ǌ The impacts of the stepped slab and insulation thickness must also be taken into consideration as it relates to the glazing and ceiling heights below. ǌ Unique guard connection details are required to accommodate the thickness of the wrapped insulation.

Cost Efficiency

ǌ Additional coordination is required for in-

The thermal benefit versus cost effectiveness of a balcony wrapped in insulation is relatively poor. A significant amount of extra construction materials (insulation, pavers/floor tiles, soffit) and additional construction time and labour are required to insulate and finish balconies which can equate to a significant cost premium.

slab exhaust and ventilation strategies.

Thermally Broken Balconies

1 2 3 4 5 6

1 2 3

5 6

1 2 3 4 5 6

Balcony walking surface on pedestals Protection board Rigid insulation Continuous concrete slab Mineral wool insulation Finished soffit material

Part B: Balcony Types

5.0 Discrete Moment or Knife Plate Connection Discrete moment or knife plate connection balconies are

Thermal Performance

supported by intermittent steel supports that are fastened or

This balcony system allows for a significant improvement in thermal performance by reducing thermal bridging connection points to each balcony. The performance of this connection can be further improved with the use of a structural thermal break.

cast into the buildings primary structural slab. Balconies can be fabricated from precast concrete or steel and installed once the building envelope is complete. There are a number of proprietary systems available on the market for this type

Constructability

of balcony construction.

Balcony structural elements must be connected back to the primary structure which requires coordination of embed plate locations and additional tolerances when pouring the concrete floor slabs.

Design Considerations

Additional waterproofing details must be considered at discrete structural connections. Since balconies are installed after the building envelope is complete, the building envelope and cladding is easily accessed during construction.

ǌ Balcony prefabrication allows for flexibility in the shape and design as well as superior quality in balcony construction. ǌ Balcony structural depth and size of steel connection

Balconies can be prefabricated off site which allows for efficiencies in construction scheduling. Installation of balconies requires access to a hoist or crane on site.

is based on loading and cantilever requirements. ǌ The dissociation of the interior slab from the balcony

Additional fire stopping may be required in the drainage cavity of a rain screen system at the balcony connection to prevent flame spread behind the cladding system.

through the steel connection detail allows for the height of the balcony to be designed to minimize stepover height and accommodate accessible threshold requirements.

Resilience and Occupant Comfort

ǌ Structural steel connections and balcony detailing

The reduction of the structural connection back to the building's primary structure from a linear connection to thermally optimized point connections reduces thermal bridging and ensures the internal surface temperature is closer to the internal average room temperature, reducing the risk of condensation and mould growth.

must accommodate movement and differential thermal expansion and contraction. ǌ To optimize alignment of doors and glazing within the wall system additional structure may be required to provide continuous sill support above insulation.

Cost Efficiency

ǌ Discontinuity of the balcony and interior

Additional coordination and structural calculations are needed to design and locate connections and embed plates into structural concrete slab. Cost savings may be realized through the use of prefabricated balconies but the cost for the use of a hoist or crane to install the balconies must also be considered.

slab eliminates the opportunity for in-slab exhaust and ventilation strategies. ǌ Bolted or welded structural connection must be carefully detailed to prevent water ingress

Several proprietary structural thermal breaks are available to increase the thermal performance of this type of balcony. Each of these systems are able to increase the overall thermal performance of the system but there is a cost associated with their use.

and may require periodic inspection.

Thermally Broken Balconies

Concrete Balcony

Steel Balcony

4 1

2 4

1 2 3 4

3 4

Discrete structural connection with structural thermal break Precast concrete balcony Prefabricated steel balcony Mineral wool insulation

Part B: Balcony Types

6.0 Discrete Connection with Suspension/Compression Suspended or compression balconies are supported off

Thermal Performance

the primary structure with a discrete steel connection at

The size and number of connection points back to the primary structure can be reduced by the addition of suspension or compression elements. This reduction in size of the structural connections represents a significant reduction in thermal bridging at the balcony connection. The performance of this connection can be further improved with the use of a structural thermal break.

the inner edge of the balcony and in tension from above or in compression from below at the exterior edge. The suspension or compression member prevents the balcony from buckling at the steel connection. This balcony strategy functions and performs in a similar manner to the discrete moment or knife plate connection; however, the cantilevered

Constructability

load of the balcony can be picked up by the suspension or

Embed plates must be coordinated in the floor slab as well as supports for the suspension or compression members.

compression members reducing the size of the structural connection back to the building’s primary structure.

Balconies can be fabricated from precast concrete or steel and installed once the building envelope is complete.

Design Considerations

Balconies can be prefabricated off site which allows for efficiencies in construction scheduling. Installation of balconies requires access to a hoist or crane on site.

ǌ Balcony prefabrication allows for flexibility in the shape and design as well as superior

Additional fire stopping may be required in the drainage cavity of a rain screen system at the balcony connection to prevent flame spread behind the cladding system.

quality in balcony construction. ǌ Additional coordination is required to design and locate embed plates in concrete slab and structural

All diagonal members must be designed to meet local code requirements regrading climbability and occupant safety.

supports in wall to support suspension or compression structural elements. Bolted or welded structural

Resilience and Occupant Comfort

connections must be carefully detailed to prevent

The further reduction of the structural connection back to the building's primary structure reduces thermal bridging and ensures the internal surface temperature is closer to the internal average room temperature, reducing the risk of condensation and mould growth.

water ingress and may require periodic inspection. ǌ Balcony structural depth and size of steel connection is based on loading and span requirements. ǌ The dissociation of the interior slab from the balcony

Cost Efficiency

through the steel connection detail allows for the height of the balcony to be designed to minimize stepover height.

Additional coordination and structural calculations are needed to design and construct the embed plates into the structural concrete slab as well as suspension or compression structural elements and tiebacks to the building. Cost savings may be realized through the use of prefabricated balconies but cost for the use of a hoist or crane to install the balconies must also be considered.

ǌ Discontinuity of the balcony and interior slab eliminates the opportunity for in-slab exhaust and ventilation strategies. ǌ Structural steel connections and balcony detailing must accommodate movement and differential

thermal expansion and contraction. ǌ To optimize alignment of doors and glazing within the wall system additional structure may be required to provide continuous sill support above insulation. 34

Thermally Broken Balconies

Concrete Balcony

Steel Balcony

5 1

4 1

1 2 3 4 5

3 4

Discrete structural connection with structural thermal break Precast concrete balcony Prefabricated steel balcony Mineral wool insulation Structural tension rod

Part B: Balcony Types

7.0 Simply Supported Simply supported balconies are pinned back to the building’s

Thermal Performance

primary structural system and supported by independent

The size and number of the connection points back to the primary structure can be reduced by the addition of columns or structural supports on the outer edge of the balcony. This reduction in size of the structural connections represents a significant reduction in thermal bridging at the balcony connection. The performance of this connection can be further improved with the use of a structural thermal break.

columns or posts on the balcony’s outer edge. Structural loads are transferred from the balcony slab to both the primary structure and the exterior columns reducing the size of the connection back to the primary structural system. Balconies can be fabricated from precast concrete or steel and installed once the building envelope is complete. When considering this balcony type as an internal balcony,

Constructability

the outer columns can be replaced with a discrete steel

Embed plates must be coordinated in the floor slab as well as foundations, structural support and connection at outer columns.

connection on flanking walls—similar to the connection detail shown to the base building—to pick up the load at the

outer edge of the balcony.

Design Considerations

Balconies can be prefabricated off site which allows for efficiencies in construction scheduling. Installation of balconies requires access to a hoist or crane on site.

ǌ Balcony prefabrication allows for flexibility in the shape and design as well as superior

If the columns on the exterior edge of the balcony only support balconies, they are not required to be fire rated.

quality in balcony construction. ǌ Additional coordination is required to design and locate

Additional fire stopping may be required in the drainage cavity of a rain screen system at the balcony connection to prevent flame spread behind the cladding system.

embed plates in concrete slab and construct footings for support columns. Structural steel connections and balcony detailing must accommodate movement and differential thermal expansion and contraction. Bolted or welded

Resilience and Occupant Comfort

structural connections must be carefully detailed to

The limited connection back to the building's primary structure reduces heat flow at the connection and ensures the internal surface temperature is closer to the internal average room temperature, reducing the risk of condensation and mould growth.

prevent water ingress and may require periodic inspection. ǌ Balcony structural depth and size of steel connection is based on loading and span requirements.

Cost Efficiency

ǌ The dissociation of the interior slab from the balcony

Additional coordination and structural calculations are needed to design and construct the embed plates into the structural concrete slab, as well as the structural connections to the outer supporting columns. In addition, extensions of the building foundation or independent footings are required to support the outer columns. Cost savings may be realized through the use of prefabricated balconies but cost for the use of a hoist or crane to install the balconies must also be considered.

through the steel connection detail allows for the height of the balcony to be designed to minimize stepover height. ǌ To optimize alignment of doors and glazing within the wall system additional structure may be required to provide continuous sill support above insulation. ǌ This balcony type is more common in external balcony configurations.

Thermally Broken Balconies

Concrete Balcony

Steel Balcony

4 1

5 2

5 3

1 2 3 4 5

3 4

Discrete structural connection with structural thermal break Precast concrete balcony Prefabricated steel balcony Mineral wool insulation Structural support column

Part B: Balcony Types

8.0 Self Supported Self supported or freestanding balconies are fully supported

Thermal Performance

by exterior posts or columns that are independent from

Self supported balconies provide the highest thermal performance by minimizing the structural connection and therefore thermal bridging to the primary structural system. The performance of this connection can be further improved with the use of a structural thermal break.

the buildings primary structural system. Only minimal connections are provided to the primary structure to resist lateral loading. Balconies are prefabricated off site from steel or precast concrete and installed after the building envelope is complete. This balcony strategy is typically used

Constructability

in low rise construction.

In addition to requiring embed plates in the floor slab to connect back to the primary structural system, this balcony strategy requires the construction of an independent structure and foundation outside of the primary structural system.

Design Considerations ǌ Balcony prefabrication allows for flexibility

in the shape and design as well as superior quality in balcony construction. ǌ Additional coordination is required to design and locate

Balconies can be prefabricated off site which allows for efficiencies in construction scheduling. Installation of balconies requires access to a hoist or crane on site.

embed plates in concrete slab and construct footings for support columns. Structural steel connections and balcony detailing must accommodate movement and differential

If the balcony columns only support balconies they are not required to be fire rated.

thermal expansion and contraction. Bolted or welded structural connection must be carefully detailed to prevent water ingress and may require periodic inspection.

Additional fire stopping may be required in the drainage cavity of a rain screen system at the balcony connection to prevent flame spread behind the cladding system.

ǌ Balcony structural depth and size of steel connection is based on loading and span requirements.

Resilience and Occupant Comfort

ǌ The dissociation of the interior slab from the balcony

The elimination of the structural connection back to the building's primary structure ensures internal surface temperature is not compromised locally and is consistent the internal average room temperature. This removes the risk of condensation and mould growth.

through the steel connection detail allows for the height of the balcony to be designed to minimize stepover height. ǌ Discontinuity of the balcony and interior slab eliminates the opportunity for in-slab exhaust and ventilation strategies.

Cost Efficiency

ǌ To optimize alignment of doors and glazing within the

Additional coordination and structural calculations are needed to design and construct the embed plates and connections to the structural concrete slab, as well as the structural connections to the supporting columns. In addition, extensions of the building foundation or independent footings are required to support the columns. Cost savings may be realized through the use of prefabricated balconies but cost for the use of a hoist or crane to install the balconies must also be considered.

wall system additional structure may be required to provide continuous sill support above insulation. ǌ This balcony type is more common in external balcony configurations.

Thermally Broken Balconies

Concrete Balcony

Steel Balcony

4 1

5 2 5

1 2 3 4 5

5 3 5

3 4

Discrete structural connection with structural thermal break Precast concrete balcony Prefabricated steel balcony Mineral wool insulation Structural support column

Part B: Balcony Types

B.3 Balcony Type Comparison The following chart demonstrates the performance of each balcony type using all of the evaluation criteria and provides a total score per balcony. This total score, based out of twenty provides an empirical understanding of how each balcony types performs holistically relative to each other based on the evaluation criteria.

Total Score

1.0 Continuous Slab

2.0 Continuous Slab with Intermittent Concrete

3.0 Continuous Slab with Structural Thermal Break

4.0 Continuous Slab with Wrapped Insulation

5.0 Discrete Moment or Knife Plate Connection

6.0 Discrete Connection with Suspension / Compression

7.0 Simply Supported

11.5

8.0 Self Supported

 Thermal Performance

 Resilience and Occupant Comfort

 Constructability

 Cost Efficiency

Thermally Broken Balconies

B.4 Balcony Type Recommendations Through this analysis and comparison it is

Option 3, 5 and 6 on the other hand allow

evident that continuous slab balconies are the

for the highest performance targets and

most cost effective and simplest to construct.

a more balanced approach for improving

At the same time they provide the poorest

the overall building performance. These

score for thermal performance, resilience and

balcony types can be used in conjunction with

occupant comfort of all balcony types. As the

incremental improvements to other building

structural connection between the balcony and

components and systems to achieve higher

the building’s primary structure is minimized

performance targets rather than relying on

the amount of thermal bridging is reduced.

the other components to compensate for poor

Each of the eight connection details have their

performance related to thermal bridging.

own individual characteristics and associated strengths and weaknesses. Decisions on which connection detail to use should be made using a holistic understanding of each detail.

Option 6 scores the highest as it allows for the distribution of structural loads back to the building to more but smaller connections. This reduction in connection size equates to less

By our assessment and understanding of

thermal bridging allowing this balcony type to

performance requirements, balcony types 1,

achieve a slightly higher thermal performance,

2, 4, 7 and 8 do not qualify as robust future

and resilience and occupant comfort score.

proof systems.

Between these three recommended balcony

Balcony types 1, 2 and 4 are only able to meet

types, cost, structural constraints, designer

required TEDI targets at the expense of the

and contractor familiarity and architectural

other dependent building systems which are

expression of the balcony can inform which

required to compensate for their inefficiency.

type is best suited for an individual project.

With increasing performance target

In Europe, the extensive use of proprietary

requirements, using these balcony types and

systems has driven the price down and

this compensating approach is only viable to a

allowed designers and contractors to

certain point. The R-value of a wall can only be

become more familiar with the systems.

increased, or the window to wall ratio can only

Once these proprietary systems become

be decreased to a certain point to compensate

more common North America, they will likely

for thermal bridging before it becomes

become the favored detail type due to their

commercially or economically inefficient.

compatibility with existing construction

Options 7 and 8 have the potential to perform well on low to mid-rise buildings but are not

techniques and detailing as is evidenced in the European market.

a feasible solution in high rise construction. Since they rely on a self supported structure, independent of the building this becomes increasingly challenging the higher the building becomes.

Part C

Case Study

Part C: Case Study

↑ Exploded axonometric detail of the thermally broken balcony connection for 5055 Joyce Street

Thermally Broken Balconies

C.1 Case Study Overview In order to understand the thermal performance of a balcony design and its related impact on meeting increasingly stringent federal, provincial and municipal building performance requirements, the balcony design has to be considered in the context of the total building performance. In this section the thermal performance implications of different balcony connection details are examined through a case study analysis to understand their impact on achieving real world energy performance targets. The case study analysis examines a rezoning submission for a 35 storey mixed-use retail and residential high-rise tower at 5055 Joyce Street in Vancouver, BC being designed by Perkins&Will Architects for Westbank Corp.

38mm STEEL ROD

152x102x9.5 HSS

CONCRETE COLUMN

EMBED PLATE IN CONCRETE

50mm FIBRE-REINFORCED CONCRETE DECK WITH 100mmx100mm D/S @1000mm

CONCRETE SLAB

CAST STEEL NODE

C150x19

1000mm (TYP.)

←

THERMAL BREAK CONNECTION

Structural section of 5055 Joyce Street balcony connection detail

BALCONY SECTION

       

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        

  



5055 JOYCE STREET

BALCONY SECTION AND DETAIL





NTS



MJM





9 JAN 2018



2406-PU 

SSK-003 (6/6)

Part C: Case Study

The proposal includes seventeen 3m wide and 1.5m deep thermally broken balconies per floor organized on a staggered grid bay pattern. The design intent is for a suspended series of interconnected structures consisting of precast balcony slabs and lightweight steel outriggers to be suspended by a network of steel rods with minimal connections back to the base building. Similar to the discrete connection with suspension/compression balcony type, the balcony was designed to minimize the structural connection to the primary structure and therefore thermal bridging through the envelope. The offset and staggered balcony pattern creates a double height space at each balcony. It also provides a unique connection to adjacent balconies which is intended to encourage the creation of vertical communities for the tower’s residents.

↓ Rendering of thermally broken hanging balconies at 5055 Joyce Street

Thermally Broken Balconies

C.2 Path B Performance Limits In accordance with the City of Vancouver Energy Modeling Guidelines the project aims to comply with the Path B targets of the Green Building Policy for Rezoning, which sets performance limits for total energy use (TEUI), heat loss (TEDI), and greenhouse gas emissions (GHGI) limits. The table below indicates the targets and the modeled values as part of the rezoning application.

City of Vancouver Zero Emissions Plan for New Buildings: Path B Rezoning Performance Requirements TEUI (kWh/m 2a)

TEDI (kWh/m 2a)

GHGI (kgCO2/m 2)

Path B Performance Limit*

121

29.8

5.9

Rezoning Application Energy Model

98.2

28.7

4.2

* Limits are determined by an area weighted average of the Residential 7+ storey and Retail occupancy performance limits

The thermal energy demand intensity (TEDI) target provides

Glazing: Both the specification of the glazing units

a measure of the amount of energy a building requires

themselves and the amount of glass as per the window

to maintain an indoor temperature that is thermally

to wall ratio (WWR).

comfortable for occupants, per meter of conditioned floor area per year; It is a measure of the annual heat loss from a building’s envelope and ventilation, after accounting for all

Level of infiltration or airtightness of the building.

The use of a heat recovery ventilator (HRV).

passive heat gains and losses . Thus the performance of the 14

building envelope, and therefore any heat loss through the

To meet the Path B rezoning performance requirements

balcony connection detail, is critical to meeting this target.

the following targets were determined for this project. The proposed design will:

Per the City of Vancouver rezoning submission requirements under the Zero Emissions Plan for New Buildings, an energy

Have a simplified compact form;

model must be undertaken and the results form part of

Have an effective R15 opaque assembly (including all

the Sustainable Design Strategy Report for the rezoning

thermal bridging);

application submission.

Use good quality windows (triple pane fixed glazing

Listed below are the main areas under the designer’s control

and double pane operable/doors) with a 45% window

that will dictate how the project will perform in meeting the

to wall ratio;

TEDI performance limit, four of which are envelope related: 1.

Form / Massing: A more articulated building results in

of Vancouver target of 2.0L.s/m2@75Pa; and,

greater heat loss area, and therefore, more difficult to

meet the targets. 2.

Have a presumed infiltration rate as per the defined City

Use a 78% effective heat recovery ventilator (HRV).

Of these five targets two are impacted by the balcony

Effective R-values of assemblies, accounting for all

connection detail: compactness of form and the effective

thermal bridging.

R-value of a wall system.

Part C: Case Study

Impact of Form As described in section B.1, the form of a building and configuration of balconies can

form versus a simplified form with the same floor plate area illustrates the impact that compactness has on a project.

have a significant impact on the amount or

As an example, a multi-unit residential building

length of thermal bridging associated with a

with a simplified compact form has a VFAR of

balcony. Above and beyond thermal bridging,

0.49 whereas a more articulated version of the

building form and articulation is a significant

building with the same total floor area has a

factor affecting a building’s ability to meet

VFAR of 0.7.

TEDI performance targets. In general, a more compact building is more energy efficient, making it easier and less expensive to achieve the performance targets.

The articulated version nearly doubles the linear length of thermal bridging related to the balcony connection and adds 4500m2 of additional wall area. This addition of wall

The compactness of a building form can be

area reduces the window to wall ratio by

measured using the ratio of a building’s vertical

over 10 percent without reducing the amount

surface area to floor area ratio (VFAR). A case

of glazing as the ratio is based on surface

study which compares an articulated building

area of wall.

↓ Impact of building form and articulation

VFAR: 0.49

VFAR: 0.7

Total Floor Area: 17,400 m2

Wall Area: 5,320 m2

Wall Area: 9,835 m2

Window to Wall Ratio: 45%

Window to Wall Ratio: 32%

Length—Balcony Thermal Bridging: 1,634 m

Length—Balcony Thermal Bridging: 3,145 m 48

Thermally Broken Balconies

Building Envelope Thermal Bridging Guide

V E R S I O N 1 .1

2016

← Building Envelope Thermal Bridging Guide2

Thermal Bridging and the Effective R Value

THERM, HEAT 2 & 3 or Flixo.

The effective R value of a wall system is calculated through a 2.

combination of three values: 1.

The methodology for calculating an effective R value for an assembly through a combination of the clear field

Linear transmittance: Additional heat flow caused by

effective R-Value of the assemblies and any thermal

details that are linear, represented by Psi (Ψ). 3.

The values can be taken from a reference guide such as Building Envelope Thermal Bridging Guide2.

Clear field transmittance: The heat flow from the wall, floor or roof assembly represented by a u-value.

The detail can be modelled in a software such as

bridging (balcony, parapets etc.) is outlined in the extensive

Point transmittance: Heat flow caused by thermal

supporting documentation accompanying the Building

bridges that occur only at single, infrequent locations,

Envelope Thermal Bridging Guide2. A spreadsheet calculator

represented by Chi (χ).

(Enhanced Thermal Performance Spreadsheet) is included in the Building Envelope Thermal Bridging Guide2 to assist

Clear field transmittance can be calculated based on values

in this calculation. Once the effective R value has been

listed in the Building Envelope Thermal Bridging Guide2,

calculated, the wall, floor and roof assemblies (clear field

but to understand the thermal bridging calculation, the

transmittance) and the thermal bridging details (linear and

thermal bridge linear transmittance value (known as the Psi

point transmittance) can be adjusted to achieve the target

Ѱ-value), or the point transmittance value (known as Chi χ)

effective R-value.

of the detail needs to be determined. There are two main ways of doing this: 49

Part C: Case Study

C.3 Impact of Various Balcony Options For the purposes of this report, four of the

Thermal Performance Spread Sheet is used to

most common balcony types from Part B are

calculate the effective R-value of the overall

examined to determine their impact on the

opaque assembly. Typical values are assumed

TEDI targets. Thermal transmittance values

for other potential thermal bridging present

from similar reference details from the Building

in the vertical enclosure elements in the

Envelope Thermal Bridging Guide are used.

project (parapet, mechanical penetrations,

Where the guide provided multiple or a

slab on grade), and are common to all four

range of transmittance values for a detail,

options reviewed.

the values were averaged to provide one linear transmittance (Psi, Ψ) value. Similarly, for details with a point connection, the point transmittance value (Chi, χ) was converted to a linear transmittance (Psi, Ψ) for ease of comparison.

Impact on Effective R-Value Comparing the thermal bridge heat loss

When the effective R-value is calculated using the Psi (Ψ) value for each balcony types the impact of the balcony connection thermal bridging becomes apparent. This also allows for the calculation of the percentage of the total heat loss through the vertical enclosure that takes place through balcony connection thermal bridge.

coefficient Psi (Ψ) values of each of the balcony

The overall TEDI target, and the impact of

types demonstrates the impact that the

the different balcony connection options in

thermal bridging of the balcony connection has

meeting this target is unique to this case study.

on the overall effective R-value to be used in

The TEDI target of 29.8 kWh/m2a is a weighted

the rezoning compliance model.

average of the City targets for the retail and

A clear field wall R-value of R-22 (IP)(U-value of 0.26 W/m2K), was assumed in the energy model, achieved using 150 mm (6”) of mineral wool insulation with thermally broken cladding attachment clips.

residential components within the building. The weight of impact of the changing effective R-values (due to the balcony connection options) on this TEDI target is also influenced by other parameters within the Rezoning energy model at the time of modelling such as

For the purposes of this report Psi (Ψ) values

ventilation rates for high occupancy amenity

for each of the detail connection options are

spaces. Other projects may have other baseline

taken from the Building Envelope Thermal

requirements and therefore the impacts on the

Bridging Guide. The associated Enhanced

TEDI targets will vary project to project.

Thermally Broken Balconies

Thermal Bridge Heat Loss Coefficient Psi (Ψ)

Assigned Clear Field R Value = R22 IP (3.9 RSI)

Total Vertical Enclosure Heat Loss Through Balcony Thermal Bridge

1.059 W/mK

Effective R Value R9.1

51%

0.496 W/mK

Effective R Value R12.6

34%

0.252 W/mK

Effective R Value R15.1

21%

0.089 W/mK

Effective R Value R17.5

Continuous Stab

Continuous Slab with Wrapped Insulation

Continuous Slab with Structural Thermal Break

Discrete Connection with Suspension / Compression

Part C: Case Study

To achieve a TEDI target of 29.8 kWh/m2a as per the City of Vancouver Zero Emissions Plan for New Buildings there are three parameters related to the effective R-value of a wall system that can be adjusted: the balcony connection detail, window to wall ratio, and the opaque wall insulation value. Each of the following scenarios demonstrates the resulting impacts of adjusting only one of the three parameters using the four balcony connection details.

By maintaining the window to wall ratio of 45% and opaque wall insulation of R-22, the following TEDI numbers are realized using the different balcony connection details.

Balcony Connection Detail

TEDI (kWh/m 2a)

Meets Target?

Continuous Slab

33.4 kWh/m2a

Continuous Slab with Wrapped Insulation

30.5 kWh/m2a

Continuous Slab with Structural Thermal Break

28.7 kWh/m2a

Yes

Discrete Connection with Suspension / Compression

27.6 kWh/m2a

Yes

By maintaining the opaque wall insulation of R-22, the following window to wall ratios would be required to achieve the TEDI target of 29.8 kWh/m2a using the different balcony connection details: (The minimum window to wall ratio specified by the client was 45%).

Window to Wall Ratio

Meets Target?

Continuous Slab

30%

Continuous Slab with Wrapped Insulation

40%

Continuous Slab with Structural Thermal Break

45%

Yes

Discrete Connection with Suspension / Compression

50%

Yes

By maintaining the window to wall ratio at 45%, the following opaque wall R-values would be required to meet the TEDI target of 29.8 kWh/m2a using the different balcony connection details:

Wall Insulation

R-Value

Achievable?

Continuous Slab

R-190 (33.5 RSI)

Continuous Slab with Wrapped Insulation

R-31 (5.5 RSI)

Challenging to Achieve

Continuous Slab with Structural Thermal Break

R-22 (3.9 RSI)

Yes

Discrete Connection with Suspension / Compression

R-18 IP (3.2 RSI)

Yes

Thermally Broken Balconies

C.4 Case Study Outcome By using a balcony connection detail which

The multistorey prefabrication of the balcony

minimized structural penetrations back

and strategy for construction sequencing

to the base building, a simplified building

allows for a quality product to be installed in

form and high performance assembly that

an efficient and cost-effective manner. The

focuses on reducing thermal bridging, the

point connection system, which incorporates

5055 Joyce Street project was able to meet

structural thermal breaks reduces thermal

the 29.8 kWh/m2a TEDI target. This case study

transmittance through the building envelope

demonstrates that performance targets can

equating to an improved overall building

be achieved by using a balanced approach

performance and allowing for a high level

to incrementally improving all components

of resilience and occupant comfort to

of a building envelope including the balcony

be achieved.

connection detail.

← Exploded axonometric of the thermally broken balcony for 5055 Joyce Street

Alternative balcony solutions reduce thermal bridging and contribute to a more efficient building envelope—improving thermal performance, occupant comfort, and the building's resilience.

Thermally Broken Balconies

Conclusion Thermal bridging related to the balcony

While the status quo currently in North

connection can have a significant impact on

America—the typical continuous slab balcony

building performance and must be addressed

connection detail—is the most cost effective

as more stringent building performance policy

and simple to construct, it provides the poorest

targets are mandated. More accurate energy

thermal performance, occupancy comfort and

modelling guidelines are leading to a reduction

resilience of all balcony types. As regulatory

in the gap between predicted and actual

policies and frameworks are updated to

building performance but require a holistic

demand improved performance this traditional

approach to understanding the building

methodology will be rendered obsolete.

envelope as an interlinked system rather than as individual parts.

As we look towards a low carbon future and shifting the human impact on climate change

The balcony connection detail needs to be

from negative to positive, it is clear that

considered within this framework and not as an

significant reductions of carbon emissions from

isolated condition. In addition to the balcony

buildings are required. As presented in this

connection details outlined in this report, there

report and through the case study, a number

are a number of building details and design

of alternative balcony solutions are available

decisions such as form factor, effective R-value,

that have been tested and are in use around

window to wall ratio, glazing specification,

the world today. These alternative details,

infiltration rate, and HRV specification which

which rely on discrete structural connections

must be considered holistically to truly

or proprietary structural break systems

understand the overall building performance.

provide the opportunity to significantly reduce

While the heat loss associated with a poorly

thermal bridging at the balcony connection.

performing balcony connection detail can be

This contributes to a more efficient overall

mitigated by improving the performance of

building envelope, reducing the operational

other parts of the building, other considerations

carbon emissions of the building and provides

such as building resilience and occupant

long term resilience and security to both the

comfort need to be kept in mind.

inhabitants and the building itself.

References

Works Cited 1

Payette, “Thermal Performance of Facades.” 2012 AIA Upjohn Grant Research Initiative Final Report, 2014, pg. 1.

Hershfield, Morrison. “Building Envelope Thermal Bridging Guide.” Version 1.3, 2019.

RDH Building Science. “The Importance of Slab Edge & Balcony Thermal Bridges.” Report #4, 2013.

“Balcony Enclosure Guidelines.” City of Vancouver, 1996.

“Bulletin 2013-002-BU Balcony and Patio Doors in Houses and Dwelling Units.” City of Vancouver, 2016.

H. Hossam El Dien, P. Woloszyn. "The acoustical influence of balcony depth and parapet form: experiments and simulations." Applied Acoustics, Volume 66, Issue 5, 2005, pg. 533-551.

"Energy Efficiency Report Submission & Modelling Guidelines." City of Toronto, 2018, pg. 19.

UN Environment and International Energy Agency. "Towards a zero-emission, efficient, and resilient buildings and construction sector. Global Status Report 2017." 2017.

Hershfield, Morrison. “Guide to Low Thermal Energy Demand for Large Buildings.” BC Housing, 2018, pg. 10.

10 “Energy Modelling Guidelines.” City of Vancouver, 2018. 11

Hershfield, Morrison. “Building Envelope Thermal Bridging Guide.” Version 1.3, 2019, pg. 1.

Little, Joseph. "Thermal Bridging." Passive House Plus Magazine, 2011, passivehouseplus.ie/articles/heating/ thermal-bridging.

Hershfield, Morrison. “Guide to Low Thermal Energy Demand for Large Buildings.” BC Housing, 2018.

“Understanding TEDI.” Zero Carbon Building Energy Modelling Guidelines, CaGBC, 2017.

Thermally Broken Balconies

Image Sources Cover Page—Rendering of 5055 Joyce Street Source: Perkins&Will

Page 17—Uninsulated intermediate floor intersection with uninsulated curb Source: BC Housing, Building Envelope Thermal Bridging Guide, Page 767

Page 2-3—Rendering of Delta Land Development Ltd.'s Canada’s Earth Tower Source: Perkins&Will

Page 18-19—Rendering of Broadway + Commercial Source: Perkins&Will

Page 5—Thermal imaging of a building with cantilevered concrete balconies Source: RDH Building Science

Page 22—Shannon Mews Source: Michael Elkan

Page 5—Thermal model of a cantilevered concrete balcony Source: RDH Building Science

Page 42—Rendering of 5055 Joyce Street Source: Perkins&Will

Page 8, Figure 2—Headroom requirements for residential balcony doors Source: https://vancouver.ca/files/cov/2016-002-balconyand-patio-doors-in-houses-and-dwelling-units.pdf

Page 44—Exploded axonometric of 5055 Joyce Street balcony connection detail Source Perkins&Will Page 45—Rendering of 5055 Joyce Street Source Perkins&Will

Page 9, Figure 3, —Minimum height to guard railing Source: https://vancouver.ca/files/cov/2016-002-balconyand-patio-doors-in-houses-and-dwelling-units.pdf

Page 48—Building Envelope Thermal Bridging Guide Source: Morrison Hershfield (See work cited)

Page 12—Balcony mock-up for Delta Land Development Ltd.'s Canada’s Earth Tower Source: Perkins&Will

Page 52—Exploded axonometric of 5055 Joyce Street balcony Source Perkins&Will

Page 16—Linear and point transmittance Source: BC Housing, Building Envelope Thermal Bridging Guide, Page 16

All other drawings, diagrams and renderings by Perkins&Will.

Vancouver Studio 1220 Homer Street Vancouver, British Columbia V6B 2Y5

Calgary Studio 1550–5th Street SW, Suite 401 Calgary, Alberta T2R 1K3

Thermally Broken Balconies

Articles inside

C.2 Path B Performance Limits

Report Assumptions and Structure

B.4 Balcony Type Recommendations

A.2 Balcony Design Considerations

B.1 Balcony Configuration

A.1 Overview

A.3 Rethinking the Status Quo