Unvented Low Slope Roof

Drying of unvented roofing assemblies is by definition only provided to the interior.

Unvented low slope roof.

Five ways to insulate an unvented low slope roof of the various methods to insulate a shallow roof applying insulation to the exterior is easier than working in a space with limited access. While this fact adds some risk to these assemblies compared for example to a traditional vented unconditioned attic with asphalt shingles this type of roof is very common. The insulation can go below the roof deck above the roof deck or both. Like a wall that is severely out of plumb an unvented roof has insulation packed into the framing cavities aligned with the sheathing.

Low slope and steep slope unvented roof systems i e. In unvented flat or low slope roofs with parapets perform a full flood test to ensure leak free installation of roofing membrane. Whatever method is used the amounts of insulation must achieve r values mandated by local codes. Because the attic space is now inside the thermal envelope blowing a little heat up there is not like throwing twenty dollar bills out the window.

However architects of these compact roof assemblies must consider vapor permeance and arrangement of the materials to produce acceptable hygrothermal performance and low risk of condensation in the resulting conditioned attic space. Another approach is to build a cupola or ventilated doghouse in the middle of the low slope roof an approach championed by joe lstiburek.