I have a line on some used EPS foam panels, 12'x8'x4" thick.  Yep, BIG panels.  For very cheap.  I am going to build a SIP shell with a conventional truss room.  I'd like to use the EPS panels inside the truss bays for insulation.  I think it could work very well, but I have some concerns that I hope some can shed some light on.

My initial thought would be to do a 'flash and batt', having a spray foam contractor shoot 1" of foam to air seal the ceiling, then rip down my panels to fit into the truss bays.  Do you think this approach would work well?  I'm thinking I'd like to go so far as to seal the panels against the trusses with a poly foam as well.  I wouldn't have enough R value to get my desired R60 roof, so I'd probably shoot cellulose over the top of the EPS. 

Is this a workable idea, or are there issues I can't see here?  By air sealing with the spray foam, I should be air/vapor barrier'ed, and as long as I get a decent fit with the cut insulation into the truss bays, then make sure odd areas are filled with foam or cellulose, it should work quite well, eh??

I can get these panels for $2 apiece, and there are enough to likely lay 2 layers in the attic.  it's hard to pass up the opportunity...


Thanks for any insight!!

At 2 dollars a panel, how many panels are there and can you send some to me? :)

When you say truss bays, I assume you're talking about a vented attic and insulating the attic floor? You've probably already read about the drawbacks to this approach.

75 and NOPE :-)  Well, if I have some leftover, feel free to come get them!

I know about vented and unvented attics - and my understanding that a vented attic is really my best option in my cold (9000 heating degree days) climate of northern Wisconsin.  I'm no expert, but it seems to me a properly constructed vented attic that is very well sealed to prevent air and subsequent moisture transfer from the heated to the unheated space will perform as well as an unvented or SIPs roof type.  Am I missing something though - please, educate me :-)

No, you're right, it's all about climate - forgot you were in the frigid north...

Are you the Rich or the Tiff half of the team?

My reservation would be that spraying to seal the ceiling might give an un-even bed to put the panels onto.  What if you cut the foam 1/2" or so narrow and and laid it into the bays, is there a wand that could inject low expansion foam between the panels and the trusses?  If so, then I'd lay the 2nd level parallel to the first but overlapped by half, cut shorter and notched to fit around the truss, then filled to seal and complete.

If the trusses are set carefully so that they're parallel, I'd cut the foam to width, force it down, and then foam the 1/2 X 1 1/2 slot that remains.  You could square off a 2x4 to the designed truss offsets, rip it in half, and use the pieces to space the trusses accurately and equally.  (Mark the spacers so they don't get trashed.)

Are you going to use a raised truss so you can run the foam all the way to outside edge?

This would be easier before the roof was decked.

I'll await the stones.  (grin)

Good luck,
Larry

richntiff are those the big 4x4x8 blocks they set boats on in winter? where are they? I am in Green Bay, not that I need any, more curious then anything.

First off, I'm the 'Rich' half of the team :-) My wife has no interest in building, I get to do all the fun stuff!


Brock - they are actually 8 feet x 12 feet x 4 inches thick!!! HUGE sheets, which is where I'm struggling with hauling/storing. They are located about 3 hrs from me, but very near my brother in law. The guy emailed me back and said they are actually 'yellow foam with a foil backing on one side'. Came out of a commercial freezer - I'm thinking they might actually by polyiso?