Warm Roof Air Gap

A sealed warm roof construction can also be achieved by creating a 50mm ventilated air gap between the surface of the insulation and the undertile lining to allow water vapour to be safely removed from the roof construction.

Warm roof air gap.

The map at right which is based on table r806 4 of the irc lists the minimum r values required to prevent condensation in unvented assemblies in various climate zones. A cold roof can be cheaper as ridged warm roof insulation tends to be more expensive a warm roof is sometimes the only option when it is difficult to get the required cross ventilation rigid warm roof insulation can allow for smaller timber depths as the 50mm air gap does not have to be maintained. A cold roof is where all of the insulation is placed either between and under or completely under the joists or deck. There should be a ventilation gap created to allow air from the outside to be drawn into this space.

With a warm roof moisture is isolated before it can reach the roof deck meaning condensation can t form and weaken the structure. An unvented roof assembly is possible only if you keep the roof sheathing warm enough to prevent conditioned air from condensing against it. Ventilation is not needed in a warm roof. The amount of ventilation or air change needed can be calculated by.

Purlins at a 45 degree angle still provide sufficient support for installation of the metal roof panels. Ventilation air follows exactly the opposite path.