Rigid Foam Insulation Between Rafters

Rigid foam insulation is better at mitigating mold than fiberglass insulation.

Rigid foam insulation between rafters.

Use screws or nails with 1 inch minimum washers or caps. 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. 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. Rigid polyisocyanurate pir foam insulation boards from celotex are among the most thermally efficient commonly available insulation materials on the market.

If you do not plan on finishing your attic then the installation process will be straightforward. How do you install rigid foam board. 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. With the 4 below the rafters you would then be r 26 below the rafters and r 52 between no.

2 would be to create the baffle in the 1st place. 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. 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. It is denser than eps and provides more r value with a rating of 5 per inch of thickness.

The difference is that mold and mildew cannot enter rigid foam. Secure insulation boards between the rafters and seal board edges using one part canned foam. Fiberglass insulation s many open cells allow entry to mold and mildew. 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. Rigid foam insulation is considered to be impervious to water. 2 snap a chalk line between the length measurements. This foam board insulation is available with straight or tongue and groove edges to help limit air movement.

The 4 of rigid foam under the rafters at least give you r26. I think you re wasting your time ripping every piece of foam to fit between rafters that are different distances apart. Alternate fasteners may be used with the type and length as recommended by their. Properly cut boards should friction fit between rafters without falling out.

But mold and mildew can still grow on the surface of rigid foam insulation. Foam boards treated with a borate compound prevent this problem. Use a chalk line or t square to mark where it needs to be cut. 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.