Roof Rafter Depth For Rigid Foam Insulation

Eps is used under roofing over foundation walls and beneath siding.

Roof rafter depth for rigid foam insulation.

This foam board insulation is the rigid pink or blue panels that can be found at home centers in many different thicknesses. 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. If they are full dimension 2x6 that s just 3 5 if milled 2x6 rare in 1900 it would be 4. Convenience polyurethane or polystyrene spray foams can provide thorough coverage to roof rafters and attic walls in much less time than is needed for other materials.

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. Hitting amazing levels of 0 13w m will need 300mm of mineral wool or 180mm of rigid foam. Rigid polyisocyanurate pir foam insulation boards from celotex are among the most thermally efficient commonly available insulation materials on the market. 1 improve the structure of the roof and 2 allow more space for insulation.

It provides an r value of 4 per inch of thickness and is the cheapest type of foam board insulation. The current status is that we have 2x6 roof rafters actual 2x6 s the house was built in 1915 that are 20 o c. That would mean increasing the rafter depth to total of 9 5. For retrofit projects kingspan kooltherm k14 insulated plasterboard goes under the rafters.

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. So we need to do two things. At 5 even hfo blown closed cell foam is only r35 ish. Under a slate roof.

The 4 of rigid foam under the rafters at least give you r26. 2 would be to create the baffle in the 1st place. There will also be kooltherm k7 pitched roof board between the rafters image credit. Depending on the specifics of the roof it may be possible to fully fill the rafter depth or in most cases leave a 25mm or 50mm air gap between the top face of the insulation and the sarking membrane.