Building Performance in Bits and Pieces
A new wave of companies is assembling energy-efficient homes where it is always bright, warm, and dry.
The vast majority of residential construction follows a proven pattern that hasn’t changed much in more than a century. Pour a foundation, erect walls, pop in doors and windows, frame up rafters, nail on sheathing, insulate, add siding, plumbing, wiring, etc., and done!
But in British Columbia, a small group of builders are taking high-performance home construction to “the great indoors” and assembling extremely energy-efficient buildings—or pieces of them—inside shops and factories. The companies then either truck or barge the houses or components to a job site, where a crane lowers them into place, and a crew assembles them into a finished structure.
The approach is broadly called “off-site construction,” and it includes companies that produce prefabricated walls and floors, and those that sell complete plumbed and wired modular buildings.
[Tip: Scroll down for our off-site construction photo essay.]
As more communities begin referencing the BC Energy Step Code in their bylaws, and market demand for high-performance buildings begins to increase, off-site and modular construction companies may see a jump in demand.
Here are a few advantages that make this approach well-suited to the needs of high-performance buildings.
Inside an offsite-constrution shop, carpenters and trades have ready access to all their materials and tools. Crews move materials and completed walls around via an overhead gantry that lifts panels on and off assembly tables, dollies and, eventually, a flat bed truck.
“In the shop, all our tools are here, all the materials are here, and we’re working from a 3-D drawing; it is seamless. It’s still challenging, in a different way, but it is a really enjoyable experience,” says Rane Wardell, co-owner of Collective Carpentry, in Invermere B.C.
It’s the same deal for Metric Modular, formerly Britco.
“For us, it is all about standardization of practices, and you have a lot more consistency in a factory environment,” says Craig Mitchell, Metric’s director of innovative solutions.
“We have 93 quality-control check points in our factory, we check the details as the building modules move along.”
Off-site builders work in well-lit heated spaces, and carpenters do their thing at ground-level. There’s no dangling on a harness to tape up a joint between materials as the rain pours down around you. This is especially helpful in buildings built to the Upper Steps of the BC Energy Step Code, when the details really matter.
“When you are building on-site you are distracted by other factors, like weather, that can work against you,” says Rane Wardell.
“There’s no weather in the shop,” adds Matheo Dürfeld, CEO of BC Passive House, in Pemberton, B.C.
“We don’t have to carry boards up and down a job in ice and snow — we completely eliminate the impact of the elements on the material.”
Improved Materials Efficiency
Traditional builders will admit they head to the hardware store every other day or so. Off-site builders make that run once a week, or once a month.
“Everything is more thoroughly thought through,” says Collective Carpentry co-owner Jan Pratschke.
Matheo Dürfeld agrees. His team runs project drawing through an optimization program to produce a materials cut list. “With traditional on-site construction, waste is 15 to 20 percent, but with off-site can be as little 2.5 to 3 percent,” Dürfeld says.
Faster Construction Time
With off-site construction, a builder can be putting the components of a home together in the shop while concrete contractors are placing the foundation. “The approach is going to buy you a whole lot of time,” says Dürfeld.
The downsides? All three builders say the costs more or less balance out with on-site construction. The lead constraints are all transportation-related. Road restrictions restrict the size of completed prefab units to 16 feet by 70 feet. Off-site builders are also limited to locations where they can deliver units on a flat bed and crane them onto a site. They have to keep a careful eye on weight, to make sure they don’t max out crane capacity.
Still, it’s a proven approach for delivering high-performance buildings that will meet the requirements of the BC Energy Step Code.
“The more people that are building this way, the more we all benefit,” says Wardell. “We are all going to win.”
Glave Communications produced this post on behalf of the Training and Communications Subcommittee of the Energy Step Code Council, with resource support from BC Hydro. In an effort to increase awareness and understanding of the BC Energy Step Code, the Energy Step Code Council is sharing information on how and why builders and communities are using the new standard. Local governments may use the BC Energy Step Code, if they wish, to incentivize or require a level of energy efficiency in new construction that goes above and beyond the requirements of the BC Building Code.