Back in 2016, our team started a multiyear experiment, sponsored by Building America, on unvented roofs without spray foam or exterior rigid insulation, using an instrumented test hut with multiple test bays. The experiment examined cellulose vs. fiberglass insulation, interior vapor control membranes, diffusion vents at the ridge, interior humidification, inward vapor drive issues, and the effect of air barrier imperfections. Some preliminary results were presented at BuildingEnergy Boston in early 2018. After three winters of experimentation, this is the rest of the story. We will give our take on what works, what is too risky, and what you might be able to get away with some of the time.
AIA 1.0 LU/HSW
BPI 1.0 hour
MA CSL 1.0 hour, Energy
- Explain the moisture risks inherent in unvented/compact roof assemblies with fibrous (air‐permeable) insulation
- Define the roles that vapor diffusion and air leakage have on moisture levels in roofs
- Explain the role that a vapor diffusion vent can have in ameliorating roof moisture risks
- Describe the risks of inward vapor drive in unvented roof assemblies