Unvented Low Slope Roof

Fall was quickly approaching and they knew that they had an urgent problem.

Unvented low slope roof.

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. Five ways to insulate an unvented low slope roof. In some of the above areas where vented attics can be a challenge an alternative solution is an unvented roof assembly. 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.

I was approached by a frantic client who had experienced a flood. How to do it right. They were getting bids from every roofer in the book so to speak. This brings us full circle back to flat or low slope roofs being difficult to ventilate particularly if they re used as occupiable space such as a rooftop patio.

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. An unvented assembly can perform well but it s important to get the details right to avoid sheathing rot. 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. Another approach is to build a cupola or ventilated doghouse in the middle of the low slope roof an approach championed by joe lstiburek.

However architects of these compact roof assemblies must consider vapor permeance and. 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. Home roofing hybrid low slope unvented roof assembly in boise. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. Low slope and steep slope unvented roof systems i e. Unvented low slope roofs are never designed to dry to the exterior because low slope roofing membranes are vapor barriers.