Unvented Roof Construction

Over the past five years several unvented roof insulation systems have been developed by the building science consortium for use primarily in hot dry and hot humid climate zones.

Unvented roof construction.

Unvented roofs have a number of advantages. Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof. Because the drying capacity of unvented roof assemblies is inherently lower than vented ones it is especially critical to control built in moisture during construction. Ventilation becomes more difficult the more complicated a roof s construction is.

Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. Designers may view unvented attic i e. This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction.

Designs and houses with unvented roof insulation systems have also been developed and constructed in cold and mixed climates. Unvented roofs operate by the principle that venting is not necessary to control moisture accumulation. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. In order for an un vented roof assembly to function properly the following conditions must be in place.

In pitched roof construction thermal insulation can be placed horizontally at ceiling level cold roof. Un vented roofs operate on the principle that moisture entering the roof assembly can be controlled and that there is no need for venting to control moisture accumulation. They are designed without ventilation openings and the attic is conditioned like the rest of the living space. The optimum systems developed to date are dependent on the climate location.

An unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation. However insulation placement in roof assemblies requires careful review to achieve acceptable hygrothermal performance levels and limit the potential for condensation within the system. Moisture content in roof structure must be less than 18 prior to covering. Inclined along the line of rafters warm roof or positioned within the roof structure to form an insulated void room in roof which can result in warm and cold roof areas.