Unvented Low Slope Roof

Unvented low slope roofs are never designed to dry to the exterior because low slope roofing membranes are vapor barriers.

Unvented low slope roof.

Five ways to insulate an unvented low slope roof. Home roofing hybrid low slope unvented roof assembly in boise. Another approach is to build a cupola or ventilated doghouse in the middle of the low slope roof an approach championed by joe lstiburek. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.

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. 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. Air permeable insulation such as fiberglass batts dense packed cellulose or blown in fiberglass can t be used alone for an unvented assembly since these types of insulation can allow moist indoor air to reach the cold roof sheathing leading to condensation or moisture accumulation. 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.

An unvented assembly can perform well but it s important to get the details right to avoid sheathing rot. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. Of the various methods to insulate a shallow roof applying insulation to the exterior is easier than working in a space with limited access. Fall was quickly approaching and they knew that they had an urgent problem.

Low slope and steep slope unvented roof systems i e. How to do it right. Flat and low slope roof designs to avoid moisture condensation problems flat roofs call up a whole new breed of building moisture problems how to avoid moisture traps under flat roofs avoid mold rot caused by moisture trapped under un vented flat roofs questions answers about the cause cure prevention of moisture problems in flat roofs and similarly hard to ventilate structures. I was approached by a frantic client who had experienced a flood.

They were getting bids from every roofer in the book so to speak. However architects of these compact roof assemblies must consider vapor permeance and. Whatever method is used the amounts of insulation must achieve r values mandated by local codes.