Unvented Roof Construction

Ventilation becomes more difficult the more complicated a roof s construction is.

Unvented roof construction.

Moisture content in roof structure must be less than 18 prior to covering. In order for an un vented roof assembly to function properly the following conditions must be in place. Control construction moisture content with tenting or temporary roofing when necessary. As a result unvented roofs have become popular in homes with feature dense roofs think multiple skylights dormers and other aesthetic flourishes.

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 roofs operate by the principle that venting is not necessary to control moisture accumulation. Designs and houses with unvented roof insulation systems have also been developed and constructed in cold and mixed climates. This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction.

Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof. However insulation placement in roof assemblies requires careful review to achieve acceptable hygrothermal performance levels and limit the potential for condensation within the system. Unvented roofs have a number of advantages. 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.

These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. Attic space enclosed rafter or joist space above normally occupied and conditioned interior space assemblies as an economical arrangement of roofing and insulation materials. They are designed without ventilation openings and the attic is conditioned like the rest of the living space. 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.

Designers may view unvented attic i e. The optimum systems developed to date are dependent on the climate location. In pitched roof construction thermal insulation can be placed horizontally at ceiling level cold roof. 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.