To stuff or not to stuff

[davidforhim]

I'm finishing an attic space and had the framer fur down the rafter sections (the angled ceiling parts) to a 9" depth. I'm installing ventilation channels in each one losing about 1" of depth.

Will I get a higher effective R value stuffing an R30 batt in (9.5" to 8") or using an R25 batt (8")?

At the large retail outlets (Lo's HD) I haven't found faced R25 batts which I want to have. (Will be looking into the building supply stores - Carter's, Wycke's etc.)

Thanks for your feedback.
David

[Wgoodrich]

The insulation in a roof ceiling assembly should be installed 1" less than the depth of your ceiling cavity to allow for the 1" air gap. DO NOT STUFF. Compressed insulation loses R value as it is compressed. Insulation is to be fluffy not compressed.

If you are short of enough room then fur out again on the bottom of the rafter to gain the inches you need so that you need no shutes installed except at top of wall plate allowing the insulation to be stapled to the bottom of the roof/ceiling joist leaving the one inch air gap the entire length of that roof decking cavity thus not compressing your fiberglass.

My best advice

Wg