Recycled EPS foam for roof, under slab, and vertically on exterior and interior foundation in Zone 5a
Hey everyone,
I’m building a home in Northern Illinois this year, and I’m looking at picking up some recycled EPS foam salvaged from a commercial roof for use in the home’s foundation and roofing insulation in order to save some money.
I’m planning to add radiant heat to the slab, so I was going to try to get R20 under the slab and as close as I can get to that at the interior stem wall, on the exterior side walls, and on the exterior rear wall, which is 4 feet below grade.
I’m also planning to build an unvented roof with R20 above deck and r30 faced batts between the rafters, with gypsum to the rafters.
My question is, how can I best utilize 3.5″ thick EPS in 4’×4′ boards? For all locations, I was thinking I’d add 1-1.5″ of xps below or above the EPS. Is there any benefit to putting one over the other in any location, especially considering the boards are 4’×4′?
Does anyone see any downsides? The savings would be significant, so I just want to make sure before pulling the trigger.
Thanks in advance,
Chris
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Replies
Hi Chris -
What is different between EPS and XPS that could make a difference in your assembly performance? Vapor permeability, contraction/expansion over time, ease of taping or sealing for air tightness?
I think the most important issue is quality of air sealing; and I am going to say that taping the new XPS for airtightness is going to be much easier than taping the recycled EPS. I don't think the other properties have enough difference to affect the placement of the two.
If it were my house, I would put the XPS down first, tape it for air barrier continuity and then consider taping the exterior EPS as well, all layers with staggered joints of course.
Others think of issues I may not have?
Peter
Thank you, Peter. I appreciate the advice and having zero experience with taping rigid insulation, it's good to know.
Tapes don’t always stick particularly well to XPS. I’d try to get some 3” or 4” wire tape to seal the edges. The wider tape will be less likely to peel off, and will help to bridge any imperfect edges which are common with used foam, especially used EPS foam. Wider tape also requires less precision when applying compared with the more common 2” tape.
Bill
For the sub-slab insulation adding 1.5" of EPS gets you the same long term R-value as 1.5" of XPS, at a much lower environmental impact. The vapor barrier between the slab & foam is more than adequate air sealing.
On the roof 1.5" of polyiso give you MORE R-value than 1.5" of XPS, also at a much lower environmental impact. If reclaimed roofing polyiso, put the polyiso between the structural roof deck and EPS and tape the seams with housewrap tape. If foil faced polyiso put above the EPS and tape the seams with a temperature rated foil tape.
There are multiple foam reclaimers with 1-3" polyiso in N. IL, some of which advertise here:
https://chicago.craigslist.org/search/sss?query=rigid+insulation