Rigid Foam Insulation Between Rafters

Fiberglass insulation s many open cells allow entry to mold and mildew.

Rigid foam insulation between rafters.

How do you install rigid foam board. This foam board insulation is the rigid pink or blue panels that can be found at home centers in many different thicknesses. It is denser than eps and provides more r value with a rating of 5 per inch of thickness. I think you re wasting your time ripping every piece of foam to fit between rafters that are different distances apart.

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. Alternate fasteners may be used with the type and length as recommended by their. With the 4 below the rafters you would then be r 26 below the rafters and r 52 between no. Measure the length and width between two rafters in your attic and transfer the measurements to a 4 ft by 8 ft of rigid foam insulation board.

Rigid foam insulation is better at mitigating mold than fiberglass insulation. 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. If you do not plan on finishing your attic then the installation process will be straightforward. Seal any gaps inside the rafter space and rigid board with can foam i e great stuff as per the directions 4.

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. The 4 of rigid foam under the rafters at least give you r26. Rigid foam insulation is considered to be impervious to water. Foam boards treated with a borate compound prevent this problem.

Add r 15 kraft faced insulation to the rest of the rafter space 3 5. Trim and install one layer of 1 rigid polyisocyanurate foam sheathing between each rafter under the vent baffle 3. This foam board insulation is available with straight or tongue and groove edges to help limit air movement. But mold and mildew can still grow on the surface of rigid foam insulation.

Also you d have to stack a lot of pieces of foam on top of each other or add other insulation on top in order to get any real insulating value which would make the waste of time add up significantly. Measure the space between rafters and cut the board to fit. 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. Properly cut boards should friction fit between rafters without falling out.

2 snap a chalk line between the length measurements. Use a chalk line or t square to mark where it needs to be cut. Rigid polyisocyanurate pir foam insulation boards from celotex are among the most thermally efficient commonly available insulation materials on the market. The difference is that mold and mildew cannot enter rigid foam.