As a member of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), I participate in technical committees that deal with building performance from a heat, air, and moisture perspective. One committee explores best practices for building envelope design. The committee focuses on how to manage heat, air, and moisture flow through assemblies.
At a recent forum, members discussed concern that in the rush to create air-tight building envelopes with high levels of energy efficiency, the long-term impact on durability due to these changes may be overlooked. Energy efficient, air-tight buildings have a greater potential to accumulate moisture and have less energy to dry out.
The Department of Energy is poised to support the energy efficiency retrofit of existing homes by improving air tightness and adding thermal insulation. This time, hopefully, the history of the 1980s and 1990s does will not repeat itself regarding the durability issues related to energy efficiency retrofits. Moisture related damage typically takes seven to 10 years after the retrofit of an existing home or construction of a new energy efficient home if measures are not taken to address moisture.
DOE recognizes the need to control interior humidity levels, as well as address combustion safety. If adjustments are not made to control humidity levels and circulate fresh air it could cause other problems like excess moisture which could result in mold.
Another concern is combustion safety. By making an assembly more air-tight, you have less air available for combustion events. For example, hot water heaters and furnaces that once relied on a building’s air leakage to supply enough air to the combustion process may backdraft if enough air is not available in a well sealed home. Direct ventilation may now be required to compensate for the retrofit.
DOE is recommending that energy retrofit contractors address moisture management issues and combustion safety by following guidelines outlined in ASHRAE Standard 62.2 as a way to insure proper indoor air quality for residential buildings and increase the durability of assemblies.
Americans have traditionally had access to inexpensive energy but that is changing. We do need to address retrofitting older buildings, but it is crucial to not create other problems while doing so.
Stan Gatland is Manager, Building Science Technologies for CertainTeed Corporation