Roof Rafter Depth For Ridged Foam Insulation

The 4 of rigid foam under the rafters at least give you r26.

Roof rafter depth for ridged foam insulation.

That would mean increasing the rafter depth to total of 9 5. At 5 even hfo blown closed cell foam is only r35 ish. For the same reason insulation shouldn t touch the roof s underside. 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.

2 measure and cut the foam boards as. Staple plastic or foam baffles to the roof sheathing near the eaves to keep the material away. The roof deck can be plywood metal concrete or wood planks. It provides an r value of 4 per inch of thickness and is the cheapest type of foam board insulation.

Products provide superior insulating properties. 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. 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 also can be installed above the roof sheathing in tandem with air permeable insulation between the rafters.

In this case the rigid foam can be thinner than when it s used alone. With a warm roof the usual process is to split the insulation into two layers. If they are full dimension 2x6 that s just 3 5 if milled 2x6 rare in 1900 it would be 4. Even small gaps can allow the passage of.

Eps is used under roofing over foundation walls and beneath siding. 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. This foam board insulation is the rigid pink or blue panels that can be found at home centers in many different thicknesses. 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.

Rigid foam on roof sheathing with air permeable insulation between the rafters. 2 would be to create the baffle in the 1st place. But at 4 would be sufficient dew point control to install r23 rock wool 5 5 to the interior side and you d be more like code minimum. 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. 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. Code specifies the minimum r value of the rigid foam layer.