Unvented Cold Pitched Roof

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

Unvented cold pitched roof.

Four options for building an unvented roof assembly. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. Alternatively an unventilated pitched roof may be designed. Cold roof voids are typically required to be ventilated.

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. 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. The code doesn t say if you do a good job of those you can disregard the other requirements for the assemblies. 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.

Every roof here vented or unvented is required to incorporate a warm side vapour barrier and an effective air barrier. Unvented roofs also make a lot of sense in high wind or high fire areas where vents might admit drenching rains or embers. The more reflective a high emmissivity roof covering is to the solar spectrum the lower the average roof temp resulting in a colder average temp at the roof deck and in the attic below. 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.

If you don t want to use sips or nailbase there are four basic approaches. 475 says their modelling shows these unvented roofs will work. The sealed cold roof system does not need the provision of ventilation directly into the loft space and works on the principle of a monarperm vapour open or permeable underlay being used under the roof tiles simply allowing vapour drive to diffuse any water vapour harmlessly into the batten space and the external atmosphere beyond. However where vapour permeable underlays are specified this requirement may be relaxed.

In pitched roof construction thermal insulation can be placed horizontally at ceiling level cold roof. But the nightly low temp is barely affected by the daily peak temp usually limited from going colder than the dew point of the proximate air.