Unvented Hot Roof Design

Hot roof designs aka dense packed insulated sloped roofs.

Unvented hot roof design.

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. Any type of rigid foam can be used above roof sheathing. Practicality is also enhanced. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.

They are designed without ventilation openings and the attic is conditioned like the rest of the living space. This definition allows simple unvented roof design just don t install vents in a previously recognizable climate zone ashrae s hot humid zone. Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof. Potential pitfalls to avoid include.

If you don t want to use sips or nailbase there are four basic approaches. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. An understanding of heat air and moisture as well as the causes of condensation is critical in detailing unvented roof assemblies. Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs.

The drawing shows exterior foam over an unvented conditioned attic but the details are similar for cathedral ceilings. 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. What type of foam is best. An unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation.

A powerful argument can be made for unvented roof construction in hot humid climates in order to control interior moisture. This article describes various cold climate building solutions for un vented cathedral ceilings and similar under roof spaces offering advice on how to avoid condensation leaks attic mold structural damage when roof venting is not possible. This type of roof assembly is sometimes called a hot roof. Four options for building an unvented roof assembly.