Roof Rafter Depth For Ridged Foam Insulation

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Roof rafter depth for ridged foam insulation.

The bottom layer of a single ply membrane roofing system is the roof deck or substrate. Code specifies the minimum r value of the rigid foam layer. If 180mm is to be installed then 100mm board might be introduced between the rafters there has to be a minimum 25mm air gap between the insulation and the underside of the tiles or slates with an 80mm board running across the rafters. Rigid foam also can be installed above the roof sheathing in tandem with air permeable insulation between the rafters.

The airflow from the soffits to the ridge vent keeps the roof cool and prevents ice dams and the material will block that flow. Select rigid foam insulation boards that are at least 1 2 inch less in thickness than the rafter space is deep if you plan to finish the attic as living space. This foam board insulation is the rigid pink or blue panels that can be found at home centers in many different thicknesses. At 5 even hfo blown closed cell foam is only r35 ish.

Rigid foam on roof sheathing with air permeable insulation between the rafters. Think of the same example of a wall and attaching drywall with the tons of screws. The first step with roof installation is to prepare the roof deck by getting rid of all dirt dust and contaminants. It provides an r value of 4 per inch of thickness and is the cheapest type of foam board insulation.

That would mean increasing the rafter depth to total of 9 5. 2 measure and cut the foam boards as. With a warm roof the usual process is to split the insulation into two layers. If you use open cell spray foam on your roof rafters you should cover the finished application with a paint or sealant that retards water vapor.

Other considerations to get the best performance out of spray foam insulation you must cover the roof rafters and surrounding areas as thoroughly as possible. But a 2x6 rafter with a 1 5 vent space would give you the ability to put 4 of rigid insulation r 26 in that space which was not filled. Eps is used under roofing over foundation walls and beneath siding. Staple plastic or foam baffles to the roof sheathing near the eaves to keep the material away.

Rigid foam insulation installation prepare roof deck. In this case the rigid foam can be thinner than when it s used alone. Even small gaps can allow the passage of. The roof deck can be plywood metal concrete or wood planks.

Products provide superior insulating properties. The 4 of rigid foam under the rafters at least give you r26. 2 would be to create the baffle in the 1st place.