Breathable buildings roadmap

1. Establish objectives

Determine the project goals and how they relate to a breathable building concept

9. Track in-use data

Use building system data and post-occupancy evaluation to ensure objectives are met and inform future development projects

8. Commission it right

Allow for a program of testing and verification over time, to tune the ventilation system in various scenarios

7. Prototype and tune

Build mockups and create computational simulations of the design to verify performance expectations

6. Develop integrated solutions

Set up dedicated breathability workshops to collaboratively develop solutions that mitigate identified risks

2. Engage the right team

Ensure the right specialist skills are available early in design and brief the team on breathable building objectives

3. Assess the local context

Conduct a climate assessment and review how the site surrounds may influence breathability

4. Develop a strategy

Decide the most appropriate approach to breathability – flow, openings, control

5. Identify risks

Work with consultants to identify challenges to solve through design or in operation

1. Establish objectives

As early as the business case/feasibility stage, it is important to establish a vision for the project and identify how a breathable buildings concept might contribute to — or become the centrepiece of — the achievement of project objectives. These goals may relate to climate resilience, prioritising health, and wellbeing, maximising the connection between indoor and outdoor spaces. The list goes on.

2. Engage the right team

Once you have established project objectives, it is far easier to engage a team with the right skills and experience to deliver that vision. For breathable buildings projects, it is important to consider specialist expertise in facade design, building services, airflow (fluid dynamics), and the selection of architecture, quantity surveying and construction professionals with relevant delivery experience. Importantly, the client must ensure objectives relating to breathability aspirations are clearly briefed and specialist studies are scoped.

4. Develop a strategy

Based on the local context assessment, the team should develop a breathability strategy that harnesses the characteristics of the site and the proposed building. This is the time to set direction on key parameters such as flow regime (cross or stack ventilation), system integration (natural ventilation or mixed-mode), openings (operable windows or discrete louvres) and control philosophy (occupant or building management system) — among other key decisions.

7. Prototype and tune

Assuming the previous steps have gone to plan, the design development phase provides an opportunity to fine-tune the proposed breathability approach. Use physical and/or virtual mock-ups to validate the design and reduce uncertainty. This might include physical prototypes to test opening actuators or computational fluid dynamics (CFD) to assess indoor airflow characteristics and predicted comfort levels. Ensure performance requirements are embedded in project specifications for appropriate testing and commissioning.

5. Identify Risks

Use the project consultants’ collective experience to identify risks associated with the breathability strategy, including condensation, airflow control, mechanism failures, occupant guidance, air leakage, noise, acoustic privacy, fire code compliance, etc. Create a risk register to track and navigate identified risks and develop integrated solutions.

3. Assess the local context

During concept design, the consultant team should assess the local context to inform possible breathability approaches. The assessment should include a climate study (considering air, solar radiation, moisture, precipitation, and wind at a minimum) and a review of site surroundings to understand the potential influence of adjacent buildings and/or topography. This assessment is often captured in the sustainability consultant’s scope but can also be delivered by the architect, facade engineer or mechanical engineer if they possess the relevant expertise.

6. Develop integrated solutions

Set aside dedicated breathability workshops with project consultants to collaboratively develop integrated solutions that mitigate identified risks. Some risks can be designed out while others will need to be managed through operational policies or tenant lease agreements. During concept design, focus on solutions that resolve challenges using simple rather than complicated interventions. For example, if condensation risk is high, consider Low Temperature Variable Air Volume (LTVAV) systems rather than chilled beams with condensation sensors.

8. Commission it right

Make allowances for specific commissioning of the operable components of the building (e.g., facade actuators), HVAC equipment and building management system (BMS) controls in their capacity to control the natural ventilation performance of the building. Ensure performance requirements are met through targeted testing, which may occur over time as the building is operated in various occupancy and weather scenarios.

9. Track in-use data

Use operational data to track building performance in relation to the breathable building systems. This may include the timing and duration of natural ventilation occurrences, the coincident indoor and outdoor environmental conditions, occupant behaviour, energy consumption, and frequency of maintenance calls. It is also recommended that postoccupancy evaluation surveys are conducted to assess how breathability is influencing the occupant experience. Finally, use this data and lessons learned in future development projects.

Key challenges

Occupant Experience

One surprising and powerful aspect of natural ventilation is that comfort can be achieved at higher temperatures than traditional systems. There are many examples of passive buildings where occupants report high satisfaction levels when it is 34°C outside and the windows are open. This is possible because our perception of comfort isn’t driven by air temperature alone, but is also influenced by humidity, sun exposure, surface temperatures and clothing.

While the opportunities and benefits are huge, designing buildings of this nature requires a fundamentally different way of thinking about comfort.

First, there is a fundamental prerequisite to block solar gain by reducing window-to-wall ratios and robust shading. This demands a departure from the heavily glazed buildings that many clients expect as the norm.

Second, the building must generate plenty of airflow and, ideally, exposed thermal mass. These are less strenuous demands but must be factored into the design at an early stage.

Finally, and arguably the greatest challenge, is that occupants must be convinced that temperature is misleading. Based on previous negative experiences in poorly designed buildings, many believe it is necessary to cool a space to 22°C on a hot, sunny day. We need more built examples, education, stakeholder willpower, and ultimately, a cultural shift to tip the scales back in favour of buildings that feel comfortable at higher temperatures.

Another key consideration in designing a breathable building is the occupant’s role in operating the natural ventilation system. It is worth developing a strategy in collaboration with the design team that addresses two primary decisions:

1. How conspicuous is the facade operability? Does the occupant experience operating windows, or are the openings concealed behind other features?

2. How much control does the occupant have? Are windows opened when they decide, or does the building management system automatically control operability?

Case In Point

Central Place Sydney is the centrepiece of a united vision to renew and transform the entire southern district of Sydney’s CBD into a burgeoning tech and innovation district “Tech Central”, attracting world-class tech and innovation talent to the city.

Introba facilitated collaborative design team workshops to develop the project’s natural ventilation approach. A key consideration was the occupant experience—how they will interact with the natural ventilation system and how they might better connect with the outdoor environment.

Generating Airflow

The goal from concept onwards is to generate robust airflow through all appropriate spaces. Given that most typologies can benefit from natural ventilation, this can include a significant portion of any building.

Six air change hours (ACH) is the typical target baseline ventilation rate on a warm day. The aim is to achieve comfort through the removal of heat, while 6ACH carries a further benefit in terms of dilution of air. Dilution is the rate at which airborne contaminants such as pathogens and exhaled carbon dioxide are removed from the space and replaced by outdoor air (OA). Traditional mechanical systems typically provide one to three ACH of OA, which corresponds with a 63% - 95% dilution rate. 6ACH provides 99.8%, which goes some way to explaining the improvement in cognitive function and reduction in colds and headaches associated with natural ventilation.

Guides such as the CIBSE Applications Manual 101 will walk a designer through the familiar options of single-sided and cross-ventilation. Stack-assisted ventilation is a reliable and economic way of generating plenty of airflow, provided a relatively centrally located central atria or chimney is available. Cross-ventilation is similarly efficient and effective, but a common challenge is that many spaces will be single-aspect. Single-sided natural ventilation is generally the least effective option. Openings must be significant in size, and the inclusion

1 https://www.cibse.org/knowledge-research/knowledgeportal/applications-manual-10-natural-ventilation-in-nondomestic-buildings-2005?id=a0q20000008I7m2AAC of bug screens will blunt airflow for all but the smallest spaces.

What emerges is the opportunity to harmonise building form with function; to shape the building itself in a way which responds to the site and generates airflow, while mitigating ingress of noise or poor air quality. It is vital that wind — which is far more powerful than the stack effect — complements the intended direction of airflow and can generate additional buoyancy under all prevailing directions. If this sounds like a balancing act, it can also be the most thrilling part of the design evolution of a building.

Case In Point

The Oakridge Centre Redevelopment in Vancouver, Canada, quadruples the scale of an existing shopping mall to offer a true mixed-use community centre, including retail, residential and civic uses.

Introba provided multi-disciplinary services on the project, including computational studies to develop and validate the outdoor comfort and passive natural ventilation strategies.

Key challenges

To achieve natural ventilation during favourable external conditions while ensuring the building can be closed against extremes of external air temperature, pollution or wind, the facades of breathable buildings must have some operable elements that can be controlled.

The most common operable elements are horizontal louvres that pivot from the top to provide some resistance to rain while open. Using motors in the frame or by window actuators. Other forms and methods can be used but must balance the operational simplicity with the ability to protect from light weather and fully seal against extreme conditions.

For optimal performance, the facade operation needs to be controlled to respond to changes in air temperature, wind, heavy rain and even air quality. This requires an array of sensors linked to the building management system and coordinated with the mechanical systems.

From a system point of view, the operable systems typically incorporate multiple and additional smaller panels which require additional framing and associated gaskets. These are typically weak spots for both thermal performance and air permeability and consideration much be taken as to the impact of the elements on the overall facade performance. Other performance requirements such as safety, acoustics, and fire performance, can present challenges for specification and procurement if there is not a wide enough selection of products that have passed associated testing procedures.

From a system point of view, operable vents are typically incorporated as multiple smaller panels, requiring addition framing and introducing more joints compared to a sealed facade. This creates weak points for both thermal performance and air permeability, and consideration much be taken as to the impact on the overall facade performance. Other performance requirements such as safety, acoustics and fire performance, must also be considered and will impact the choice of opening type and position of vents in the facade. Examples of opening types in a curtain wall system are illustrated below.

The process of designing, coordinating and commissioning breathable buildings can also have its challenges, although through partnerships such the one in this study between Eckersley O’Callaghan and Introba, the close integration of facades and building services is being streamlined.

Case In Point

Atlassian Central will be the world’s tallest hybrid timber building. Located in Sydney, Australia, the building aligns with Atlassian’s commitment to operate on 100% renewable energy and reach net zero emissions by 2050.

Eckersley O’Callaghan is providing structural and facade design, including the building exoskeleton that supports mega floors with a mix of naturally ventilated indoor and outdoor spaces.

Controls

Controls are the final hurdle that makes or breaks a natural ventilation strategy. Unfortunately, many natural ventilation systems do not operate as they were intended, and this contributes to the common perception that natural ventilation is too complicated or cannot achieve comfort.

Where natural ventilation systems are solely responsible for achieving summertime ventilation and cooling, there tends to be greater end-user understanding out of necessity.

In an era of wildfire smoke and heatwaves, natural ventilation is often designed as part of a mixed-mode strategy, where it supplements mechanical systems, to improve health and save energy. In mixed mode setups, it is common for the natural ventilation elements to operate below their potential in terms of number of occupied hours with natural ventilation operating.

Indeed, there are many high-profile projects featuring a carefully designed natural ventilation system that does not operate at all. While in some cases, the design may have been at fault, it is more likely that the controls were too complex and the operators reverted to mechanical-only mode.

The challenge for designers, particularly in larger, interconnected buildings, is that the controls must dynamically respond to multiple live conditions, including wind direction and velocity, internal and external temperature, room CO₂ and humidity, rain and even air quality. Ideally, the openings will modulate such that the user experience is seamless. Meanwhile, at the user end, the controls must be simple, intuitive, and empowering to the occupant.

From a landlord’s perspective, it is important to design controls to protect the base build from any inadvertent tenant behaviour that would see facades open in extreme weather events. These scenarios may put base building energy performance contracts or certification at risk potentially damaging base building materials and finishes.

Case In Point

At completion in 2021, Clayton Community Centre was Canada’s largest Passive House building. The community hub integrates visual and performing arts, a neighbourhood library, indoor sports facilities and outdoor recreation spaces.

Introba designed the building’s carefully calibrated mixed mode system and led a “lessons learned1” exercise following the first year of operation to maximise the building’s potential.

1 https://issuu.com/deepgreenengineering/docs/ impact_fund_clayton_community_centre