Prefabrication is a hot topic in Canada’s affordable-housing development community—and for good reason. Under this approach, a variety of specialized companies manufacture parts of a building’s structure remotely, then transport them to the job site for final assembly.
Prefabrication promises to increase the overall quality of buildings while reducing construction costs. It holds strong potential to accelerate timelines and dramatically reduce waste. And it’s already helping to grow a green business sector in Canada.
As BC Housing’s Vienna House nears completion, we’ve prepared this blog to highlight the project’s extensive use of prefabrication for walls, floors, ceilings, and balconies. Click or tap the sections next to the arrows below to learn how and why the team turned to off-site construction methods to craft what will be one of Canada’s most innovative and sustainable apartment buildings.
1. Walls
Click or tap here to explore how the Vienna House team turned to a Howe Sound–based off-site construction company to manufacture the building’s walls.
TAG Panels, a company in Squamish, B.C., assembled the building’s exterior walls, as well as all load-bearing interior walls—including the “party walls” that separate apartments and hide pipes, wires, and ducts.
- From the outside in, Vienna House’s prefabricated exterior walls consist of:
- A weather barrier;
- 13mm thick plywood sheathing;
- 235mm deep wood studs, with cavities filled with blown fiberglass batt insulation; and
- 15mm thick oriented strand board sheathing, sealed with tape to serve as the primary air barrier.
- Exterior walls arrived on the Vienna House site fully sealed from the TAG Panels factory. Meanwhile, the company shipped interior wall panels without sheathing, enabling plumbers, electricians, and other skilled trades workers to route their services where needed.
- By building the exterior walls indoors with exact measurements, the team believes it will be easier for Vienna House to meet its energy efficiency goals. That’s because cracks and seams allow indoor heat to escape a building, and when all the boards fit snugly together, that’s less of an issue.
2. Floors and Ceilings
What’s above and below? Click or tap to discover how layers of glued B.C. wood help hold Vienna House together from top to bottom.
Kalesnikoff, a Castlegar, B.C. company, manufactured 496 cross-laminated timber (CLT) panels of various shapes and sizes for Vienna House.
- CLTs are exceptionally strong and fire-resistant structural wood panels made by gluing together layers of dimensional lumber and alternating the direction of the wood grain with each layer. BC Housing’s Vienna House uses three-, five-, and seven-ply CLT panels. Picture a tightly compressed wood sandwich, and you get the idea.
- To minimize noise transfer between apartments and prepare for floor coverings, Public Architecture directed teams to add additional layers of material to the upper sides of the horizontal CLT panels. Workers first installed a thin acoustic isolation mat, then topped it with about four centimetres of concrete. Finally, tradespeople will install flooring that includes an integrated layer of sound-damping cork.
- These cross-laminated timber panels aren’t just sustainable, they showcase the natural beauty of locally sourced softwoods such as spruce, pine, and fir. Exposed natural wood has proven mental health benefits. To help residents feel calm, the design team chose to leave the material exposed on the ceilings in the main living areas.
3. Balconies
Prefab porches will not only provide semi-private outdoor space for Vienna House residents, they will also help advance energy efficiency. Here’s the inside story, with video.
Sapphire Balconies, a company based in Reading, England, supplied Vienna House with 70 balconies. The company manufactured them in Europe, shipped them to a Vancouver-area warehouse for final assembly, then delivered them to the project site via flatbed truck.
- Once on site, a Kindred Construction crane operator lifted the balconies off the truck and into position onto hooks and brackets previously installed on the side of the building. A second worker then attached stabilizer bars.
- The installation of the first balconies, from truck to installed on the brackets, took less than half an hour. Once the crews were familiar with the process, they only needed six minutes per porch.
- Because the Sapphire balconies attach to the building via hooks and brackets, they transfer very little heat to the outdoors. (For more on this, check out “Breaking the Thermal Bridge,” our December 2024 blog.)
- The Vienna House porches will lower the building’s maintenance costs and overall energy costs and will help the building meet its ambitious energy-efficiency goals.
- The Sapphire balconies are the first to be installed in a multi-family residential building in British Columbia. (The company recently published a case study of its work on Vienna House.)
Looking Ahead to Future Opportunities
As noted above, prefabrication has great potential to improve quality, reduce construction schedules, create jobs, and take advantage of sustainable Canadian resources. It’s proven an overwhelmingly positive experience at Vienna House.
That said, to ensure construction projects using prefabrication go as smoothly as this one has, affordable housing builders and developers may wish to keep a few things in mind:
- To ensure the puzzle pieces click together seamlessly on the site, all the various vendors and suppliers must carefully coordinate ahead of time in a digital format—long before anyone picks up a saw or hammer. This building information modelling (BIM) approach is especially useful for critical connections, such as those between the first floor of prefabricated walls and the foundation.
- Cranes are key! Project teams should plan their location, capacity, and schedule. The contractor should keep in mind not only the lifting capacity of their crane or cranes, but also its availability. You don’t want tradespeople unable to complete work while waiting for a given component to land on the site where they need it.
- When working in a temperate rainforest climate, like Vancouver, remember that prefabricated wood panels do not dry as quickly as dimensional lumber. Cross-laminated timber can stain with watermarks, if not dried quickly. Project teams need a moisture management plan to keep out winter rains, and a backup for longer stretches of wet weather.
BC Housing looks forward to applying the practices and solutions learned at Vienna House to future projects that it will develop elsewhere in the region and the province.
