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The building envelope is one of the most important parts of a home; it is the barrier between the warm living space and varying outdoor conditions. A wall system must address multiple issues in a cold climate including minimizing heat loss via air flow through the envelope, reducing conduction through framing members, and managing water vapor within the wall assembly. Air flow can be the greatest heat loss mechanism from a home and a tight building envelope is imperative to minimize heat loss. However, a tight envelope will also minimize air exchanges which can lead to moisture problems (see ventilation). If humid indoor air is allowed to migrate into an exterior wall during the winter months, it will condense on any components that are below the dew point (the point at which vapor condenses, a function of temperature and relative humidity). Without an adequate drying path, this moisture buildup can lead to serious health and structural issues.
CCHRC has tested and developed a library of wall systems that are both energy efficient and address moisture related issues in the extreme and varied climates of Alaska.
The REMOTE Wall system (Residential Exterior Membrane Outside-insulation TEchnique) differs from a conventional wall in that the air barrier is applied to the outside of the sheathing, as opposed to the inside of the stud framing. Approximately 2/3 of the wall’s insulating value is then moved to the outside of the sheathing on top of the air barrier, while 1/3 of the insulation remains in the interior of the wall cavity. The reasoning is to install as much extra insulation as possible inside the heated envelope, while still keeping the dew point on the exterior of the air barrier. Warm to cold side insulation ratios are determined by the severity of the climate. The REMOTE wall is a cost-effective building technique that improves energy efficiency and solves moisture issues.
The Arctic Wall is a super-insulated double-wall system with cellulose insulation developed by Fairbanks builder Thorsten Chlupp. It is extremely airtight and does not include a vapor retarder, allowing the wall to dry to either the interior or the exterior. CCHRC tested the wall system to see if there was potential for moisture buildup and mold growth.
Integrated trusses combine the roof, walls and floor into a single structural assembly that can be tipped up to frame a house. They are manufactured at a truss plant and can be shipped in one piece. The trusses are set in rib-style construction to the desired length of the house. The advantages of the integrated trusses are simplicity and speed of assembly (a house can be framed in one day by unskilled labor). The depth of the floor and walls can be varied to accommodate different amounts and types of insulation. CCHRC used polyurethane spray foam insulation in the wall cavities in several prototype homes.
Super-insulated spray foam wall
CCHRC has experimented with a variety of walls using spray foam insulation. The Anaktuvuk Pass prototype used light-gauge steel studs with plywood sheathing on the inside and 9 inches of polyurethane foam sprayed from the outside. An elastomeric coating was sprayed as the exterior finish, a material similar to what is used in truck bed liners.
CCHRC developed a super-insulated wall with 4-inch steel studs and a 3.5-inch standoff wall connected by plastic bracing. The plastic spacer prevents heat from conducting through the metal to the outside, drastically reducing heat loss without the added material of double wall construction. The 7.5-inch wall cavity was filled with soy-based polyurethane spray foam insulation, a thick, tight building envelope with no thermal bridging.