Insulation Question - Knee Wall

[gpalmer77]

Slowly insulating my garage this winter, it is a nice project I can do a few pieces at a time when I get some spare time, evenings etc. I just got to the knee walls upstairs, it is a 2x4 wall about 6 ft high under the vertex of the gambrel roof, about 18" from the roof deck at the bottom, about 6" at the top. I have a small piece of styrene baffle at the top stapled to the back of the roof deck. My question is whether I need to put anything across the back of the knee wall to hold the insulation in, or is well fitted, stapled and taped Kraft paper facing enough to hold it all where I put it for years to come? Will the insulation stay attached to the paper over time, or deteriorate and fall out?

Thanks.

 

[Gerald O]

Assuming you are talking about fiberglass batt insulation, you need to install a rigid air barrier material on the back side of the knee wall studs. Besides needing it for support and to keep dirt and pests out, the fiberglass insulation needs to be enclosed on all sides by an air barrier to work properly.

 

[astroracer]

Instead of insulating the knee wall, consider insulating the roof behind it. That's what I did when we built my attached garage with loft trusses. Doing this allowed me to put doors on those 2' wide openings, an OSB floor in each one and create a number of built in bookcases and even a set of drawers. There is a LOT of storage going to waste behind those walls that is easily utilized with this method.
Mark

 

[gpalmer77]

Assuming you are talking about fiberglass batt insulation, you need to install a rigid air barrier material on the back side of the knee wall studs. Besides needing it for support and to keep dirt and pests out, the fiberglass insulation needs to be enclosed on all sides by an air barrier to work properly.

Thanks. I had read that somewhere else too. Only thing I don't get is how it's any different from air moving behind roof insulation, where the baffle is not a complete air barrier. Or insulation laid on an attic floor, which is often open to the cold air side.

 

[gpalmer77]

Instead of insulating the knee wall, consider insulating the roof behind it. That's what I did when we built my attached garage with loft trusses. Doing this allowed me to put doors on those 2' wide openings, an OSB floor in each one and create a number of built in bookcases and even a set of drawers. There is a LOT of storage going to waste behind those walls that is easily utilized with this method.
Mark

I did consider this, but it complicates a few things, as the framing is not conventional. One side has a 12 ft ceiling, the framing intersects about 2/3 of the way up the lower pitch of the gambrel. The knee wall in the attic on that side is about 2 ft high, and since it is crawl in storage, not worth the extra complications in terms of insulating the roof. The other side, which I'm working on right now, is an 8 ft ceiling with a full attic space above..... I did consider insulating the roof deck, but decided against it. I have two dormer windows in that run of wall, I'm gonna put doors in the sidewalls of those for cold storage of lesser used supplies, conduit, flashing etc in the skinny space behind.