Reclaimed polyiso over ICFs?
I am grateful for this forum, as most of the ideas discussed here are unfamiliar to the trades people I have encountered in my area (CZ5B, Eastern WA). Thanks in advance for your opinions and guidance.
Overview: New build, trying to think outside the box (but keep the air/heat in). Striving for performance, stability, longevity, air tight. Using the Pretty Good House theories and hoping to be close to 5/10/20/40/60.
2 story on slab, though because we are on a hill, a portion of the main level (4′) is essentially a daylight basement. One wall of the garage will double as a retaining wall, and will be almost entirely below grade. ICF, with PERSIST roof (1:12 shed, metal). EIFS finish. Dimpled wrap over the ICFs below grade.
When sourcing rigid foam for the roof, I came across 4″ reclaimed (insulation depot) fiber-faced sheets taken from a commercial re-roof. The facing is not “factory fresh” and has started to delaminate in spots. Initial thoughts were to build up 4 layers for the roof, cover with ice/water shield, and attach a vented, cold roof above 2x4s on edge (primarily to create the eaves). The price of the foam (and their desire to sell in truckloads) has me thinking about other uses.
Most of the local contractors try to discourage me from using ICF blocks in foam thickness above standard – they see it as “unnecessary.” But 5″ EPS won’t get me to the PGH R40 wall goal.
My (maybe not so) bright idea is to add a layer of this 4″ reclaimed polyiso to the exterior of the ICF, tape the seams, then EIFS over the top. It has left me with a few questions:
Is this feasible?
How would you attach the polyiso to the ICF EPS? Adhesive? Screws? If adhesive, would it be strong enough to support the weight of the EIFS?
Is the fact that the facing is not 100% intact an issue? Does the facing have to be to the outside? Or should (could) it be against the EPS? Do you foresee any issues taping the seams of the polyiso?
Would there be additional layers required to attach the EIFS (again, thinking of the degradation of the facing)?
Any precautions/methods that would allow me to continue the polyiso blanket on the “hill side” of the house (the portion that is below grade)?
Is this a fools errand in pursuit of an R value? Or is it the simple solution I have envisioned in my head?
I appreciate any advice you can give. Thanks.
Tyler
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Replies
Tyler,
To answer your last question first: Yes, I think it's a fool's errand. But I'll get back to that in a minute, after focusing on your roof.
I think you will find that it is almost impossible to fasten a 3.5-inch deep 2x4 on edge through Ice & Water Shield and 16 inches of rigid foam. That would require -- let me see -- screws that are at least 22 inches long, and a very fancy jig to keep the screws 90 degrees to the roof slope when attempting to find the rafters. Let's use simple English and call it impossible rather than almost impossible.
Perhaps you could achieve your goal if you included a layer of plywood above the rigid foam, because in that case you could fasten your 2x4s to the plywood (with the approval of an engineer, of course, who would determine the plywood thickness and fastener schedule). But it would still be tricky to fasten the plywood through 16 inches of rigid foam.
If you really wanted to fasten 4 inches of polyiso to the exterior of the ICFs, you would need to either (a) aim your fasteners at the embedded plastic strips that some ICF manufacturers provide for siding attachment (assuming, of course, that your brand of ICF has those plastic strips), or (b) Use very long TapCons and fasten the polyiso to the concrete core. Not fun.
And you still have the issue of EIFS attachment. The EIFS contractor may balk at your idea -- and you need a certified EIFS contractor to satisfy your insurance company.
If you have your heart set on ICFs, choose a manufacturer like Logix that makes high-R ICFs. (For more information on Logix ICFs, see New Green Building Products — January 2009.) Or you could consider building wood-framed walls. It's much easier to attached 4-inch polyiso to a wood-framed wall than it is to fasten 4-inch polyiso to an ICF wall.