Passive House Case Study: Superinsulated Foundation and Vapor Diffusion-Open Walls
The Cold Climate Housing Research Center (CCHRC) monitored the performance of Fairbanks builder Thorsten Chlupp’s super low-energy home over one year. The superinsulated house demonstrates innovative building and mechanical systems, with a super-insulated foundation, integrated heat storage system, and an open wall design that allows vapor to diffuse through. This home shows that buildings can perform well without traditional heating systems even in a subarctic climate, and provides a new option for high-efficiency construction. The goal is to learn how to optimize this integrated heating system to make it more cost-effective in the future.
The wall design does not include a vapor barrier, allowing the wall to dry to either the interior or the exterior, and places an air barrier between two dense-pack cellulose masses. Sensors placed in the wall recorded temperature, relative humidity, and moisture accumulation in the walls for 13 months.
The primary concern of the wall system is the potential for moisture buildup and, subsequently, mold growth. A data analysis revealed that the humidity and moisture content in the wall do not experience the levels and duration required for mold growth. In addition, moisture does not appear to build up in the wall over time. Rather, moisture is transient, and the direction of moisture transport varies seasonally and diurnally, which supports the basis of the wall design.
The R-60 rigid insulation around the foundation was intended to reduce energy loss from the building to the ground. This study looked at how well the insulation prevents heat loss and whether it causes frost heaving of the ground. Temperature sensors were located in the soils beneath and next to the house.
Monitoring showed that the insulation in the foundation was not enough to completely thermally isolate the house from the ground. However the soil temperatures down to 7 feet never froze, which mitigates potential for frost heaving.
Read more about the house on Thorsten Chlupp's website here.