Using WUFI to Prevent Moisture Problems

“Do I need a vapor barrier?” It’s a perennial question, but there’s no simple answer: heat and moisture interact with each other and with building assemblies in complicated ways, so the first thing you need is a vapor profile of the building assembly. This means looking at the vapor permeance of each material and ensuring it can dry should leaks or condensation occur.

You can take vapor profiling to a much more sophisticated level with a modeling tool known as WUFI—short for Wärme und Feuchte Instationär, or “Transient Heat and Moisture.” WUFI looks at both drying potential and wetting risk by predicting dynamic heat and moisture flows based on the site, climate, building materials, mechanical systems, and more. Although we’ve gotten by without such tools in the past, modeling hygrothermal performance (the interplay of heat and moisture) has become increasingly urgent as energy flows have radically decreased.