Minimum Air Gap On Metal Roof

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.

Minimum air gap on metal roof.

As it is i will probably be needing some insulation below the rafters to get down to the 0 2u but not needing the 50mm gap obviously helps reduce the size needed. Purlins parallel to the eave seem called for as the metal roof panels run perpendicular to the eave. The renovation is from the interior of an attic space room. The better option is to install 1x4 purlins creating a 3 4 thick air space.

This provides a path to exit for any leaks thru the metal roof but provides little ventilation beneath the metal roofing. In order for radiant heat to exist you must have this air gap. No air gap no radiant heat it won t work. Above sheathing ventilation asv is achieved by having continuous air flow between the roof sheathing and the metal panel system.

Metal roof coatings with solar reflectance can help building owners save substantially in annual cooling costs. It doesn t matter which side the air gap is on the foil will work the same whether it is using reflectivity or emissivity to block the heat transfer. An unvented roof assembly is possible only if you keep the roof sheathing warm enough to prevent conditioned air from condensing against it. The international energy conservation code prescribes the minimum r values of insulation based on climate zones and typically the required amounts for energy control also assure condensation control.

The beams are 2x6. On the south side of the roof there are solar pv tiles with an air gap under them and a ridge vent. As the metal roof heats up in the summer time the added air gap in between will act as a buffer instead of the the metal heating up the below shingle roof. Research has confirmed that creating an air space under a metal roofing system will increase energy savings during both summer and winter months.

Thanks for the info. Also on the south side the deck has an impermeable membrane red line in attachment. I m doing a renovation on an unusual roof. Metal panel roof systems require a minimum 3 8 air gap between the underside of the metal panel and the covered or uncovered insulation board.

So if you are installing under a roof or in a wall you must create an air gap.