Unvented Cold Pitched Roof

Unvented roofs also make a lot of sense in high wind or high fire areas where vents might admit drenching rains or embers.

Unvented cold pitched roof.

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. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. 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.

These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. 475 says their modelling shows these unvented roofs will work. Alternatively an unventilated pitched roof may be designed. 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. Cold roof voids are typically required to be ventilated. 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. 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.

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. 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. Four options for building an unvented roof assembly. The principle applied here is warm moist air rising from below is allowed to permeate through the roof membrane removing the need to fully ventilate the roof.

This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. Unvented roof here again the choice of what insulation to use and whether to install it over or under the roof deck depends on the condition of the present roof the depth of rafters the r value you must attain and cost.