Structural Design

Figure 3: Canada’s Earth Tower Winter Garden View Looking North—with a series of suspended balconies at each end of the residential tower

Figure 4: Canada’s Earth Tower Interior View—showing mass timber structural members with timber balcony in the background

Purpose of Report and Key Research Questions

As a critical design component in residential buildings, balconies pose significant challenges for the successful execution of competing structural, fire and thermal requirements. These challenges are amplified in mass timber construction due to added new design difficulties regarding structural connections, building enclosure detailing, and proper waterproofing membrane application. Due to limited budgeting and given the repetitive nature of the balcony layout, this research project has selected a two-storey balcony structure from the Canada’s Earth Tower design proposal to use as a prototype to design and construct (Figures 5-8). The prototype will be used to analyze, document, and better understand its performance in a real world setting regarding thermally broken structural connection detailing, off-site timber pre-fabrication, and weather protection. Conventional strategies, in concrete or steel buildings, predominantly include projecting and inset balconies that are supported through direct extension of the floor structure. Although these conventional balcony construction methods provide a cost effective solution, the associated thermal bridging cannot be ignored as the increasingly stringent building energy requirements, i.e., the BC Energy Step Code, are introduced to achieve high-performance buildings with reduced carbon footprints. In tall mass timber buildings, the requirements to connect balconies to the structure and related building enclosures are relatively new and evolving. It comes with its own challenges. Perkins&Will and the design and construction team were commissioned to design a balcony mock-up that would overcome barriers, and provide solutions to address structure, durability and constructability for balconies in mid to high-rise mass timber buildings will improve the acceptance of timber as a competitive structural system.

The focus of this balcony mock-up research is to:

Balcony Mock-up: Structural Design

nj Investigate the use of timber as a structural material in a thermally broken balcony system—mass timber primary loading bearing structure, timber strut, timber deck, and timber unitized envelope system.

nj Evaluate balcony structure and materials for compatibility with timber building structure, considering weight, durability, and ease of construction.

nj Devise connection details to building structure that adequately accommodates all loads while enabling effective completion of a high-performance building enclosure.

Balcony Mock-up: Thermal Performance

nj Investigate the method of transferring load from the thermally broken balcony to the primary structure through the unitized cladding system.

Balcony Mock-up: Constructability

nj Evaluate constructability, methods of construction sequencing of the prefabricated balconies to avoid temporary scaffolding and bracing, and opportunities for prefabrication to support the broader goals of efficient and quick completion of the building envelope.

Balcony Mock-up: Accessibility

nj Investigate a zero threshold (no more than 13mm) balcony condition to accommodate universal accessibility.

Balcony Mock-up: Deck Construction

nj Mock-up and monitor the performance of two different types of timber balcony decks, i.e. dowel laminated timber (DLT) and cross-laminated timber (CLT), and two different membrane combinations, i.e. two-ply styrene-butadienestyrene (SBS) and a urethane membrane. Understanding the penetration of water through balcony edge details to explore how the final structure will handle water.

Balcony Mock-up: Deck Finishes

nj Test different types of engineered wood as decking material, exposing the underside of the engineered wood structure with a durable and clear coating, while maintaining a zero-threshold.

Balcony Mock-up: Durability & Weathering

nj Investigate durability and weathering. Install moisture monitoring sensors on the mock-up to log the moisture characteristics of the balcony timber components.

Balcony Mock-up: Code & Bylaw Acceptance

nj Investigate Code and Bylaw requirements related to climbability and occupant safety, acceptability of mass timber as decking material and fire rating requirements.

Balcony Mock-up: Cost Effectiveness

nj Evaluate cost effectiveness of prefabricated balconies.

nj This research supports the following Government of

Canada goals/directive/vision:

‒ The broader adoption and commercialization of wood-based products in the construction of high-rise buildings;

‒ The replication of demonstrated wood-base buildings; and

‒ Canada’s transition to a more wood-inclusive construction industry.