Minimum Air Gap On Metal Roof

I thought there was supposed to be an air gap between the roof deck and the underside of the metal roofing to ventilate it and prevent condensation.

Minimum air gap on metal roof.

Metal roof coatings with solar reflectance can help building owners save substantially in annual cooling costs. An unvented roof assembly is possible only if you keep the roof sheathing warm enough to prevent conditioned air from condensing against it. 2 metal roofing with regular 7 16 osb decking then attic foil stapled to the bottom side of the rafters. The better option is to install 1x4 purlins creating a 3 4 thick air space.

I m doing a warm roof with breathable membrane so didn t think i needed this 50mm air gap. This provides a path to exit for any leaks thru the metal roof but provides little ventilation beneath the metal roofing. 1 metal roofing with 7 16 radiant barrier osb decking with the foil side down then attic foil stapled to the bottom of the roof rafters. Nonetheless if a layer of wood sheathing is placed directly on the insulation and then the metal roofing placed directly on top of that the metal roofing will tend to get warmer in the sun than in a ventilated condition.

No air gap no radiant heat it won t work. Plywood decking is never used to directly fasten metal roofing to. In order for radiant heat to exist you must have this air gap. Research has confirmed that creating an air space under a metal roofing system will increase energy savings during both summer and winter months.

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. 3 metal roofing with 7 16 radiant barrier osb decking and no attic foil on the rafters. Thanks for the info. So if you are installing under a roof or in a wall you must create an air gap.

For refurbishments where you may have a traditional bitumen based roofing felt which has high vapour resistance you show follow the guidance in the bs 5250 code of practice for control of condensation in buildings and leave a minimum 50 mm air gap underneath the membrane ventilated to external air. 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.