Polyiso under EPDM: where to buy; vapor barrier?
I’m adding a 16×26 1-story addition w/ full basement on the north side of my house (E central OH). I want a flat (1/4″/ foot slope) roof.
EPDM in 20x 50′ .045 sheets is readily available at eg. Menards; also the various boots, washers, other accessories.
1) 3″ polyiso is NA locally (so far) & it isn’t clear what backing to use; and 2) there seems no definitive summary of best practice on building the roof structure.
1) Suggestions on where to buy 3″ (or thicker) polyiso in or near central OH. Backings available are none, foil, fiberglass. Only the foil is listed as a vapor barrier.
2) I’m getting conflicting stories about how to frame & install eg.
– Don’t use OSB as it has a vapor barrier and will trap moisture. Use plywood.
– spray insulation between the rafters to seal completely
– don’t spray insulation underneath as it will trap moisture
– use fiberglass backed (both sides) polyiso as it will let heat enter from the top
– don’t use white PVC as OH has more cold days and you want black to absorb sun
A local commercial roofer said they prefer: rafters on 16″ centers, 5/8″ plywood on that, 3″ high PT wood perimeter, and black EPDM.
I had hoped to do the job myself but I’ve not found any 3″ polyiso w/ fiberglass backing. I can drive 300 miles and buy unbacked (2nds) 3″ for $15/ sheet.
Why not more than 3″? 3″ is ~ R-18 and if I added eg. R30 fiberglass below …. I’d consider 4.5″ polyiso but if I can’t even get 3″ …. Local roofer said code here is 3″ and they use multiple layers if they go above 3″.
Replies
Any roofing supply house will have polyiso. Got any ABC's or Shelter's around?
ABC has it but ...
Thanks for the tip. I called ABC. They have some 3.3" ($42/sheet), don't sell much "commercial product", don't have 3" or 4" or ..... Rep I talked to wasn't familiar w/ the product, didn't know about backings, ....
I'll keep tryinng. So far I've found 1 local roofer who seems to know this product and a couple of suppliers who can get what I want but don't seem to do much with it.
I infer from feedback so far that polyiso under epdm/ pvc just isn't common here (OH).
(I found the same thing with concrete: in the 1970s poured walls were common on the East coast; in 1998 I had to look hard here to find someone who was doing it on a regular basis.)