Recent updates to energy codes continue the trend towards energy efficient building, with an increased emphasis on minimizing thermal loads and reducing heat flow through the building enclosure.
DuPont Building Scientist Maria Spinu, Ph.D., LEED AP observes that this can have unintended consequences for moisture management as well as the long-term durability of the building.
Recent energy code changes emphasize increased levels of thermal performance for the building enclosure. This includes increased R-value requirements, use of continuous insulation (ci) for framed construction, and tougher effective air leakage control requirements. While these measures can contribute to a more energy efficient building, the way in which additional insulation is added to a framed wall, as well as the chosen wall assembly design, are critical to long-term durability.
The last three versions of IECC and ASHRAE 90.1 show consistent trends towards including requirements to increase the R-value for walls. Continuous insulation is critical for reducing thermal bridging, which can significantly decrease the effective R-value of cavity insulation. Thermal bridges are regions of high thermal conductance that bypass insulation, and can lead to significant heat loss. Continuous insulation is often employed to balance this out, and to meet prescriptive energy code requirements.
A natural consequence of reduced heat flow is a slowdown in the wall’s ability to dry, which can raise the risk of mold and moisture-related damage. Moisture analysis can be helpful for estimating potential risk. One common tool for doing so is Wärme und Feuchte Instationär (WUFI) analysis, which is German for “Transient heat and moisture thermal dynamics transport.” WUFI is a dynamic simulation for coupled heat and moisture transport that uses hourly data and transient parameters.
The way in which thermal insulation is added to framed wall assemblies to increase thermal performance is critical to long-term durability. By simulating scenarios that can lead to condensation and long-term durability risks for wall assemblies, WUFI modeling provides a valuable means of analysis. It also allows relative comparison of the performance of different wall designs to help select lower-risk options.
For a more in-depth look at energy-efficient building, read the full article from DuPont Building Scientist Maria Spinu, Ph.D.