Hi Folks,

  Some friends want me to insulate thier A-frame.  The walls/roof structure is twin 2X10s on 4' centers, 3/4 tounge and groove boards on top of that, then asphalt shingles.  They want to keep at least part of the rafters showing.  I'm thinking 2" thick 4'X8' rigid foam boards fit in between the rafters against the sheathing, covered with 1/2" drywall on 2X2 nailers.    (I have to cover the foam...right?)  Sound OK?  Any other ideas? (besides spray foam)

thanks!

Rich

What are the requirements for insulation values in your area? Foam board will give you a good r-value per inch.

From your post, it sounds like you don't want to use spray foam insulation. Why?
To my way of thinking, this would an ideal use of this product. The foam will seal out air infiltration, which a major concern with this type of construction. Also, you mention that the rafters are 4' on center. Have you planned on any type of blocking to stabilize your drywall? Even 5/8" drywall will deflect over that wide of a span. May I suggest 'ladder blocking' 2' on center between the rafters. In my market, 2x2's are basically the same price as 2x4's. Unless you intend to rip your own 2x2's, I would consider using 2x4's for your blocking. About the same price, and much stronger and easier to work with.

Hi Greentree,  this is northren South Carolina in a shady wooded setting.  Not much too much cooling load but some heating needed through the winter.

 

Thanks Wes,  Ladder framing sounds good.  I thought about nailers on the side of the rafters and long screws through the drywall, foam, and into the roofing boards (being careful not to go through) through the center.    Yes, spray foam would be good but expensive.  Also I thought spray foam would be messy for a furnished house and somewhat irregular where we want to keep part of the rafters exposed.  I've had one experience with spray foam on the underside of a floor and it wasn't good.  I think the installer put it on too heavy at first and as it expanded it sagged under it's own weight and created lots of voids.  

thanks for the replies

Rich