Rigid Foam Insulation Rafters

2 snap a chalk line between the length measurements.

Rigid foam insulation rafters.

The 4 of rigid foam under the rafters at least give you r26. However rigid foam insulation must be covered with a fire rated material when used on the interior of a building. 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. I would also like to attach 4 x8 sheets of rigid foam at least 1 2 inch thick to the lower edge of the rafters to prevent thermal bridging.

There are currently three types of rigid foam board. You can also add rigid foam insulation under the rafters which adds r value and eliminates thermal bridging through wood rafters. Meps is a rigid board formed by molding polystyrene into boards. Polystyrene can be fashioned into various items including shipping materials such as packing peanuts and coffee cups as well as sheets of foam board insulation.

Think of the same example of a wall and attaching drywall with the tons of screws. Molded expanded polystyrene foam board. Rigid foam insulation also known as insulating boards provide high r values. You can even place it under the foundation slab.

2 would be to create the baffle in the 1st place. The rafters are 2 6 so there is 5 5 of depth under the roof deck to put layers of rigid foam into as a stack of pancakes between the rafters. Consider using high density r 30 batts which are as thick as r 25 batts but fit into 2x10 framing. They keep your home at a comfortable temperature without the need to crank your heat.