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.

Warm roof air gap.

This changes the dew point where warm and cold air streams merge and turn to liquid. Ventilation is not needed in a warm roof. Ventilation air follows exactly the opposite path. A warm roof uses solid pir insulation boards that sit above the roof deck topped by moisture tolerant boards.

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. 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. With a warm roof moisture is isolated before it can reach the roof deck meaning condensation can t form and weaken the structure.

There should be a ventilation gap created to allow air from the outside to be drawn into this space. A cold roof is where all of the insulation is placed either between and under or completely under the joists or deck.