Roof Rafter Depth For Ridged Foam Insulation

Code specifies the minimum r value of the rigid foam layer.

Roof rafter depth for ridged foam insulation.

The first step with roof installation is to prepare the roof deck by getting rid of all dirt dust and contaminants. That would mean increasing the rafter depth to total of 9 5. Think of the same example of a wall and attaching drywall with the tons of screws. 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.

The bottom layer of a single ply membrane roofing system is the roof deck or substrate. If they are full dimension 2x6 that s just 3 5 if milled 2x6 rare in 1900 it would be 4. 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. The roof deck can be plywood metal concrete or wood planks.

At 5 even hfo blown closed cell foam is only r35 ish. With a warm roof the usual process is to split the insulation into two layers. Foamular extruded polystyrene xps rigid foam insulation offers foamular extruded polystyrene xps rigid foam insulation offers a comprehensive line of products choose the strength you need from 15 to 60 psi and exceptional moisture resistance. In this case the rigid foam can be thinner than when it s used alone.

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. Rigid foam insulation installation prepare roof deck. The airflow from the soffits to the ridge vent keeps the roof cool and prevents ice dams and the material will block that flow. Rigid foam on roof sheathing with air permeable insulation between the rafters.

This foam board insulation is the rigid pink or blue panels that can be found at home centers in many different thicknesses. 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. 2 measure and cut the foam boards as.

It provides an r value of 4 per inch of thickness and is the cheapest type of foam board insulation. 2 would be to create the baffle in the 1st place. Eps is used under roofing over foundation walls and beneath siding. For the same reason insulation shouldn t touch the roof s underside.

The 4 of rigid foam under the rafters at least give you r26. Even small gaps can allow the passage of. Products provide superior insulating properties.