How to insulate the wall between cathedral ceiling and attic?

[defranks]

I imagine someone here has run into this before and can offer some useful advice:

I'm building a house in eastern Tennessee, which is just about complete. I intend to use blown-in insulation in the attic, but I'm unsure how to insulate the wall that divides the attic from the great room, which has a cathedral ceiling. The wall is a roof truss with wood siding on the great room side, so the 2x4 framing members are turned 90-degrees to the direction that framing members usually face. In other words, the wall between the room with a cathedral ceiling and the attic is just 1 5/8 thick.

I'm thinking that spray foam might be the best bet, but wonder what others have experienced in this situation. Thanks in advance!

 

[oosik]

I have a cathedral ceilings throughout my house - Pan Abode. The insulation is RMax. Urethane sheets - 2" thick, 4' x 8' - with aluminum foil wrap. There are two staggered layers on the OUTSIDE of the roof.

I'll admit - I'm not quite sure what you have there. I get mixed images of what you are explaining. Perhaps a picture..........

 

[Topzide]

Spray foam would be the best solution. That way you get the best r-value you can and vapor seal all in one! I'd fill the void in 2it's and then go over them to prevent thermal transfer. JM2C

 

[defranks]

I have a cathedral ceilings throughout my house - Pan Abode. The insulation is RMax. Urethane sheets - 2" thick, 4' x 8' - with aluminum foil wrap. There are two staggered layers on the OUTSIDE of the roof.

I'll admit - I'm not quite sure what you have there. I get mixed images of what you are explaining. Perhaps a picture..........

Yeah, my ceilings are insulated with foam sheet insulation between the ceiling and the roof. I'm talking about the area between the attic and the room with the cathedral ceiling.

The cathedral ceiling extends over an 800 square foot area, but the remainder of the house has 8' ceilings. So there is one tall wall that consists of a roof truss with wood siding on the great-room side. The other side of that wall is the attic.

I'm leaning toward spray foam, but MAN that stuff is expensive. I've got about 200 square feet of wall there, so 400 board feet of foam insulation. Lowe's sells a 650 bf kit for nearly $800. I'll spend something around $1000 to blow insulation in on the other 1000 square feet of ceiling.

 

[defranks]

Spray foam would be the best solution. That way you get the best r-value you can and vapor seal all in one! I'd fill the void in 2it's and then go over them to prevent thermal transfer. JM2C

Was that a typo, or am I just missing something? I'm not at all sure what you mean by "2it's"

 

[/pine]

If you're actually "building it yourself"...?...Personally I would fit and hang R-30 bats on the wall with the craft paper against the living side...some cheap mesh webbing or light strapping etc. would keep it from sagging etc...much less trouble and expense than sprayed foam etc...

 

[oosik]

Yes - what /pine says...... I was thinking foil backed fibre glass roll insulation. If this didn't prove adequate - it could always be removed and you could use spray foam or something else.

Thanks for the further explanation.

 

[PEJ5]

Ouch, less than two inches. I would remove the interior boards and widen the gap to improve the insulation. We have some new 12:12 pitch ceilings that are roof trusses, but they are 16 inches deep - more than R60.

 

[dragoneggs]

We have a 8/12 cathedral ceiling in the center of our house flanked with 4/12 trusses extending to the sides. The rafters are blown in and the cathedral is batting. I like batting vs spray foam for remodel/routing of wiring for lighting, audio/video, security, etc later on. Sprayfoam makes that all a real pain.

 

[defranks]

Thanks all. Batting would be less expensive, but I was concerned about the fiberglass slowly pulling away from the backing. The mesh is a good idea to prevent that.

By the way,Dragoneggs, I moved from Union, WA to TN about a year and a half ago. Sounds like WA is still under a lot of stress with the CV. Here in my part of TN, we hardly know it exists except by reading the news.