Arctic Wall is a new energy efficient construction option in the Interior
The Arctic Wall is a double-wall system with a thick layer of cellulose insulation that allows water vapor to diffuse through the wall while blocking air. It was designed by Fairbanks builder Thorsten Chlupp using the principles of the REMOTE wall—another super-insulated building technique that places the majority of the insulation outside the load-bearing wall.
Unlike most homes in Alaska, the wall system does not have a vapor barrier. While there is typically a sheet of polyethylene plastic along the inside the wall to keep water vapor from getting into the wall framing, it is virtually impossible to create a perfect vapor barrier without any holes or leaks. This is a known weak spot for conventional cold climate construction.
The Arctic Wall, on the other hand, allows water vapor to move through the wall with the seasons, creating a super-insulated wall that can also “breathe.”
The key components of the Arctic Wall include:
- an extremely tight building envelope to prevent air leakage through the wall, and the vapor that comes along with it
- the majority of the insulation outside the structural framing and air barrier
- a wall that is open to water vapor diffusion and has enough capacity within the insulation to absorb and release water vapor without succumbing to moisture damage
The Arctic Wall studied by CCHRC contains a 2×6 interior structural wall filled with blown-in cellulose with taped sheathing and a vapor-permeable air barrier (Tyvek HomeWrap) wrapped outside of that sheathing. A second 2×4 exterior wall is installed around the first wall with another air barrier membrane. The space between the two walls is filled with 12 more inches of blown-in cellulose (the spacing between the walls varies depending on how much total insulation is desired). Depending on thickness, this kind of superinsulated wall can attain R-values of 70 or more, more than three times a traditional 2×6 wall system.
CCHRC monitored the Arctic Wall’s performance over 13 months to see how moisture moved through the walls and whether it would grow mold. Data showed that both temperature and relative humidity levels in the walls were not sufficient to support mold growth. Neither side of the air barrier covering the exterior of the 2×6 structural wall ever approached the dew point (the point at which vapor condenses to water), indicating the structural framing was well protected from moisture.
The relative humidity of the bathroom wall (the one likely to see the most moisture) never exceeded 65%, staying well below the risk level for mold growth.
CCHRC also used moisture modeling software to predict how the walls would perform over a 9-year period, which showed that humidity levels and moisture content within the walls would not reach a level where mold growth would be a concern.
Also noteworthy was how moisture moved through the walls over the course of the year. Whereas a conventional wall can only dry to the outside, because of the vapor barrier on the inside, the Arctic wall was able to dry to the inside in the summer and the outside in the winter.
The Arctic Wall is a specific system that has to be carefully engineered and assembled to ensure that it works properly. Based on CCHRC’s testing, it has done very well in Interior Alaska and provided a new option for a super-insulated house design.