The integrated truss home was born as an emergency housing solution for Alaska’s many natural disasters. When ice-jam flooding on the Kuskokwim River devastated the village of Crooked Creek in 2011, CCHRC was hired to design a fast, simple, low-cost home that could be built by volunteers. It also needed to be able to withstand the harsh conditions of the Bering Sea climate. The integrated truss consists of a prefabricated wall assembly that connects the roof, wall, and floor into a single structural piece that can be easily tipped into place.
How it’s put together
The trusses are made in a factory and shipped to a building site in full house-shaped pieces. The units are set and braced two feet apart in a straight line for the full length of the home. There are several benefits of this design. First, the truss system is easy to erect, even for unskilled crews that are often involved in rural builds. Second, it’s fast. The prebuilt trusses can be assembled in a single day rather than the week it typically takes to stick-frame a home, saving precious time during a short building season. Third, the truss system makes it easy to build a super energy efficient home, as the depth of the walls, roof, and floors can be scaled to accommodate as much insulation as desired. CCHRC has added as much as 18 inches of insulation on the North Slope and as little as seven inches in milder southwest communities. Furthermore, each piece of the truss is comprised of an inner and outer chord with webbing in between, which largely cuts down on conductive heat loss through the wood. Lastly, the trusses can be assembled without heavy equipment, which is lacking in many rural communities.
Variations in design
Because of its competitive cost and versatility, the integrated truss design has been used in more than a dozen housing projects across Alaska, from Utqiagvik to Bethel. Over time, CCHRC has experimented with different types of designs and insulation types. Early iterations used polyurethane spray foam because it was easy to ship and had a high R-value. In Atmautluak, for example, the walls, roof, and floor cavities were filled with 7 inches of polyurethane for an insulation value of R-45.
This was swapped out for cellulose insulation in Tanana, a village at the confluence of the Tanana and Yukon rivers. The same integrated truss wall was blown in with 18 inches of densely packed cellulose. Made of recycled cardboard, cellulose is comparatively easy to install and reduces air flow through the building assembly. However, air sealing is critical with this system to ensure a tight, energy efficient wall. One downside to cellulose is that it takes up a lot of space in transport; because there was an ice road to Tanana the crew was able to deliver the bags of insulation cost-effectively.
Yet another type of insulation was used in Mertarvik in 2019. This project was unique in that the entire village of Newtok was moving to a new site due to severe erosion that endangered the community. Because 13 new homes were needed in one season, the integrated truss was a fast and practical choice. Blown-in fiberglass insulation was chosen due to local shipping costs and its superior tolerance to moisture–there were concerns the product might be exposed to weather in transit and during construction. In addition, the Knauf insulation product used 70% recycled glass.
The diversity of climates, landscapes, and cultures in Alaska means that each building project requires a unique approach. The integrated truss design has worked very well in remote applications because it improves efficiency over a standard wall while saving cost and allowing for a degree of flexibility.