GPS beneath a slab with hydronic heat
joge2468
| Posted in Green Building Techniques on
I’m in NC climate zone 4A, self-contracting a gut remodel on a 50s ranch. Oddly, given how relatively progressive this area is, nobody uses anything but XPS here, and then only to a very limited degree. I mention this because I will need to travel to purchase polyiso or EPS.
I found a GPS product specifically marketed for beneath a slab (new pour) in TN. However, I haven’t seen any mention of its use on GBA. I’m wondering 1.) if the graphite has any impact on y’alls recommendation of EPS beneath the slab, and 2.) if there is any issue using it with a heated slab. Thank you in advance for your help.
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Replies
I think a big part of the reason you see XPS get used so much is that all the box stores stock it. Usually box stores will stock EPS in only one or two thicknesses, and it’s only type-I. I think people see the EPS and think “less R value than XPS so XPS is better”.
Polyiso is usually only stocked in 1/2” and 3/4” thicknesses if at all. That means around R3 and R5 at best, and it costs more than XPS so people think “thin expensive shiny stuff, must be for special purposes”, so they get XPS.
Those are my guesses anyway as to why you see XPS get used more often by many.
GPS is just graphite loaded EPS. I don’t see any reason it would be a problem in any area “regular” EPS will work. If the product (you don’t mention exactly what product you are looking at) is specifically marketed for use under slabs, then I’m inclined to think it won’t have any issues in that application, but can’t be sure unless you post a link or product name.
GPS isn’t mentioned often because it adds cost for only a small increase in R value per inch. Many on here likely just use either regular EPS to save money, or step up to polyiso to maximize the R value in whatever amount of space they have available. That doesn’t mean there is anything wrong with GPS, just that it isn’t as commonly used.
Bill