Unvented Low Slope Roof

In unvented flat or low slope roofs with parapets perform a full flood test to ensure leak free installation of roofing membrane.

Unvented low slope roof.

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. Drying of unvented roofing assemblies is by definition only provided to the interior. 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. Like a wall that is severely out of plumb an unvented roof has insulation packed into the framing cavities aligned with the sheathing.

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. Another approach is to build a cupola or ventilated doghouse in the middle of the low slope roof an approach championed by joe lstiburek. 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. Low slope and steep slope unvented roof systems i e.

If the upper edge of a low slope shed roof intersects a vertical wall the most logical approach in my opinion is to detail the roof as an unvented roof. Insulation and air barrier are applied directly to the underside of the roof deck are common in applications where designers are seeking cost effective and energy efficient roof assemblies.