Unventilated Roof Construction

This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction.

Unventilated roof construction.

Together with not having to provide a ventilation pathway the technique permits insulation to be installed within the full depth of the rafter. Unventilated attics are common where roof assemblies are complex and it s difficult to create a sealed ceiling plane. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. Eliminating traditional ventilation and the potential condensation risk associated with large voids of cool air make this the optimum pitched roof solution.

Moisture content in roof structure must be less than 18 prior to covering. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. Eliminates large cool voids within the construction reducing thermal stress. 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.

Cold roof decks and external cladding or tiling. For designers the advantage of using unventilated construction comes from removing the necessity to provide a ventilated cavity below the sarking. Poorly insulated ducting can cause heat loss in colder months and the loss of conditioned air in the summer in vented attics.