Roof Venting With Rigid Foam

Rigid insulation is recommended in this roof assembly to raise the condensation potential above 50 percent rh at 70 degrees f.

Roof venting with rigid foam. In an un vented roof foam can serve as the air barrier and vapor retarder and prevent moisture from getting in to the roof cavities. Cathedral roofs especially need a lot more insulation between the ceiling and the rafters because there usually isn t any attic space. The rigid foam is cut to be 2 inches wider than the space between rafters then 1 inch of foam is scored and folded over on either side of the foam creating standoffs that hold the foam away from the roof sheathing providing a space for air to flow. Shop this collection 23.

Heat from the house rises up to the attic but when there isn t one the heat rises up to the roof. When rigid insulation is not present. Master flow 10 ft. Rigid insulation installed above roof deck.

If you want to put rigid foam on the exterior of your roof sheathing you will indeed need at least r 25 of rigid foam above your roof sheathing and r 11 25 of rigid foam on the exterior side of your wall sheathing assuming that you are using 2x6 studs. Owens corning ventsure 11 in. Roof ridge exhaust vent in black case 31 model 2018000 93 31 case. Rigid foam and spray foam are two of them.

If you have a vented attic it makes no sense to install rigid foam above the roof sheathing. Foam insulation can play an important role in both vented and un vented roof assemblies. A vented attic is basically outdoors so installing rigid foam above your roof sheathing is a waste of money and a waste of rigid foam. You might as well put the rigid foam in the branches of a tree in your back yard.

Gaf cobra rigid vent 3 11 5 in. The code also allows for air permeable insulation such as fiberglass or cellulose to be used under the roof deck as long as rigid foam is used above the roof sheathing. Wood has an r value of about one per inch of thickness. When set into place and sealed with spray foam the vent baffles are insulated and air sealed.

No potential for condensation on the underside of the roof sheathing until moisture levels exceed 40 percent rh at 70 degrees f. They range in style from 6 inch round stainless steel vent covers that are placed in the soffit between each rafter to continuous vents that run the entire length of the soffit. If spray foam is used a vent space may still be needed directly under the roof deck. These vents are installed in the soffit the enclosed portion under the roof overhang and permit air to flow up under the roof and into the attic.

This is not an issue specific to spray foam as much as it is a characteristic of peel and stick membranes. In a vented roof foam can seal the openings and serve as an air barrier and a vapor retarder in addition to its insulating function. Ridge vent rigid roll with weather protector moisture barrier. All insulation materials require proper venting.