Unvented Hot Roof Design

Unvented roof assemblies should be insulated either with air impermeable insulation rigid foam or spray polyurethane foam or with a combination of foam and air permeable insulation.

Unvented hot roof design. What type of foam is best. This type of roof assembly is sometimes called a hot roof. Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs. As a result unvented roofs have become popular in homes with feature dense roofs think multiple skylights dormers and other aesthetic flourishes.

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. An unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation. Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof. The disadvantagesof unvented roofs have to a certain degree been overstated in hot climates the extra heat gain from unvented roofs rarely exceeds a couple of degrees celsius.

An understanding of heat air and moisture as well as the causes of condensation is critical in detailing unvented roof assemblies. Unvented roofs operate by the principle that venting is not necessary to control moisture accumulation. This definition allows simple unvented roof design just don t install vents in a previously recognizable climate zone ashrae s hot humid zone. Unvented roofs unvented roofs are increasingly common due to design priorities.

Practicality is also enhanced. Any type of rigid foam can be used above roof sheathing. A powerful argument can be made for unvented roof construction in hot humid climates in order to control interior moisture. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.

Four options for building an unvented roof assembly. If you don t want to use sips or nailbase there are four basic approaches. Hot roof designs aka dense packed insulated sloped roofs. They are designed without ventilation openings and the attic is conditioned like the rest of the living space.