Experience / evaluation of GMX Thermal Drain?
Our builder proposed GMX Thermal Drain for below-ground foundation insulation. Thermal Drain appears to be softer and more flexible than ComforBoard 80 or rigid foam. The builder want to use 1 1/4 in Thermal Drain (R5; versus the R10 2″ foam we specified; these walls will have 1″ foam + 2×4 w/ batts inside; Climate Zone 6B). Use of Thermal Drain will significantly reduce the U-value at the top of the wall/subfloor due to an unusual design (floor joists set on an inset concrete ledge, to get the house close to grade (yes, I know – negotiation with wife …). I found no certifications or post-application reviews of this product other than the draining ability (which is excellent).
Do you have experience, knowledge, or recommendations of/for Thermal Drain? Do mice and other vermin like it (more than other products), does it compress unduly when backfilled? It would be installed over bituminous fluid-applied waterproofing. Is it likely worth holding out for the thicker foam or ComfortBoard (likely with delays and costs)?
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Have same dilemma w/GMX Thermal Drain board in Climate Zone 6A. When I asked GMX about compressibility and the impact on U-value / R-value, they answered that there is not standard test method to measure this....which didn't help my confidence in the product. As alluded to above.....it seems like it would function well as a drainage plane, but I am sketchy if it is an effective insulator after backfill....impacted by compression and water.
johngfc - what did you find out / what are you doing? Did you receive any feedback on the performance of the GMX Drain Board?
Any other feedback on climate zone 6A/6B best practices for foundation insulation products?
I pushed the builder and we're going with 2" of rigid foam, as was specified in our plans and will certainly provide more insulation. This is only necessary (IMHO) for the near-surface part of the basement, but it's not that expensive and will contribute to a super-insulated basement. I never found any independent reviews of the GMX product, which surprised me, and I don't know the cost differences. If you use it, please post a review.
Thanks johngfc! Assuming you will be using 2" of XPS as insulation and drainage plane? No dimple mat, EnkaDrain, or similar mesh product outboard of the rigid foam to promote drainage to tile drains at footings? Thanks.
Juan - No, but we're in Colorado where it's generally dry, and the site are such that I really don't anticipate a problem. Apparently, foundations around here frequently don't even get a waterproof coating and people tell me they're fine. We do of course have footer drains to daylight, and the waterproofing included a really good seal at the footer-foundation wall joint.
No experience with Thermal Drain here. But, as far as other products, I have written down in my notes something called "FoundationPRO" by PFT. It is a Neopor (GPS) foam wrapped in some sort of vinyl covering. It doesn't need a finishing coat applied on the top, it works both above and below grade. I have no idea how much it costs.
There is a GBA article about it here: https://www.greenbuildingadvisor.com/article/a-new-vinyl-laminated-exterior-foam-foundation-insulation
Looks like a better solution than CertiStud or products w/similar concept. Comparative costs would be interesting!
I had gmx sprayed on my foundation 2 weeks ago. They thought I wanted the r10 thermal drain even though I didn’t. Regardless I got to play feel and check it out. Once you backfill, the r10 board would end up 1/4” thick and offer almost no insulation. It is VERY soft. I didn’t want it because I thought over time that sediment would fill the pores and render it useless. Glad I installed eps instead.
Thanks tdbaugha. So you applied the GMX waterproofing and EPS, and skipped the Thermal Drain! I likely will do the same! Your assessment of the amount of compressibility on the Thermal Drain is exactly my concern!
Yeah I installed 3” of 15psi EPS. That was also less than 1/2 the price of thermal drain as well. The other consideration is there is almost no thermal benefit of installing thermal drain below grade and nothing above grade. The exposed concrete above grade will transfer cold right around and into the below grade space very easily since concrete is a pretty good conductor. I’m running the eps all the way to the top of the wall, and doing a parge coat over it where exposed above grade.