http://www.insulationsolutions.com/products/insultarp/information.html

WHat are you using slab for, installing radiant? If so look at CreteHeat, it is the best insulation to use. If not using radiant would suggest you look at the Barrier, comes in 3/8 3/4 or 1 1/4 thickness.

Was thinking of radiant in basement slab, started a new thread on that. But will want to insulate slab anyway. The contractor uses INSULTARP and wanted to hear what was thought about this.

I use Crete-Heat with Helix, saves time and money

Smart wall, you might want to add Smart Floor also to your name. Crete-Heat is the best insulation to use under radiant, I tell people when you start with the Green Insulation you will save Green forever!

For use under a radiant slab Inusultarp & it's bubble-pack bretheren are crap- you need something that has the appropriate (for the climate & application) ASTM C 518 tested R value associated with it or you'll be paying for it every heating season. Reflective insulation needs to have both a high delta-T and an intervening air-gap far bigger than bubblewrap to deliver any significant reduction in heat transfer. It serves NO useful heat-loss reducing function under a heated concrete slab.

Subsoil temps and design-condition slab temps determine a reasonable minimum-R for cost-effectiveness, but for radiant slabs it starts at ~R10 for most of the US. If you start the center-slab numbers for your climate zone found on the right column of table 0.2 p 10 of this document and added ~R5 you'd be about right for most radiant slabs:

http://www.buildingscience.com/documents/reports/rr-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones

Crete-Heat is EPS, it has a real R value, and is a reasonable solution. But most radiant installers prefer to use XPS (any manufacturer) & staples for affixing the tubing.

I'd be a bit leery of any heating contractor recommending Insulatarp under a radiant slab. (If they screwed that up , I'd wonder how well they did on the rest of the design.) If it was a GC, not a heating contractor that came up with it I might be more forgiving. It's little more than a very expensive vapor barrier, and NOT appropriately called an insulation in that application.

Crete-heat is the one to use if you want real insulation that remains stable. XPS foam will loose up to 52% of original R value whereas EPS retains 92% of its. If you don't want to heat the ground due to cracks etc you will go with the best from the start.

...the overstatements of a vendor with a vested interest...

I too prefer EPS for under-slab insulation- primarily for cost-reasons. I wouldn't pay extra for it. The amount of long term moisture-saturation and loss of R value actually found in foams depends a lot on how well the slab is drained, the type of soil, and distance from the water table. For truly swampy conditions EPS is definitely a better choice, but presuming a 50% loss of long-term R for XPS would be atypical for most. Radiant installers prefer XPS since it retains tubing staples far better than EPS (ergo the molded-in knobs of Crete-Heat.)

Dana1 only partly true, am a vendor for Crete-Heat but also for the foil that installers used to put under slabs although I never recommend it, also for the Barrier product. There are a number of articles out there that show EPS retains heat better. I will not sell foil if gonna be used under a slab. We pride ourselves on suggesting only the best.

Look closely at the articles to find out the soil types & moisture conditions under which EPS has better long term performance. The differences not necessarily as distinct as the EPS Molders Association propaganda might indicate- they're cherry-picking test for extreme-moisture content clay soil conditions, particularly where freeze/thaw cycle can further damage the cell structure of foam that has taken on water. The EPS Molder primarily us results for sub-grade walls with zero-over hang roofs and poor surface drainage in cold or very-cold climates go figure... (They're not exactly an impartial source.) Much of this type of study got kicked off by Canadian studies in the early 1990s that were initially designed to find out whether EPS was even suitable for below-grade exterior applications (where it passed with flying colors.)

But if you're pouring your slab on clay without an intervening sand or gravel layer or adequate perimeter drainage, you're not even building to code. And if you're getting freeze thaw cycles in the XPS in your sub-standard pond-soaked radiant slab I daresay you have bigger problems than loss of R value to worry about, eh? ;-)

Sure, if you're going use it to float your dock on a lake, EPS is by far your best choice. With a properly drained slab, it matters not a bit. But show me the study that shows EPS has superior long term performance to XPS under drained slab that's consistently above the water table. The very long term (as in many decades) R value of XPS in non-pond-soaked conditions is pretty close to that of EPS at similar density, in part due to the slow dissipation of the hydrofluorocarbon blowing agents used in the XPS which give it both an initial and 25-year R-value edge over EPS. ( EPS uses pentane for a blowing agent which is gone after mere months, rather than decades for HFCs. )

If you need sump pumps to keep a lake from forming in the basement after periods of high rain due to a high water-table, EPS is the only way to go. If not, it pretty much doesn't matter.

Posted By Dana1 on 01 Jul 2011 12:04 PM
For use under a radiant slab Inusultarp & it's bubble-pack bretheren are crap- you need something that has the appropriate (for the climate & application) ASTM C 518 tested R value associated with it or you'll be paying for it every heating season. Reflective insulation needs to have both a high delta-T and an intervening air-gap far bigger than bubblewrap to deliver any significant reduction in heat transfer. It serves NO useful heat-loss reducing function under a heated concrete slab.

Subsoil temps and design-condition slab temps determine a reasonable minimum-R for cost-effectiveness, but for radiant slabs it starts at ~R10 for most of the US. If you start the center-slab numbers for your climate zone found on the right column of table 0.2 p 10 of this document and added ~R5 you'd be about right for most radiant slabs:

http://www.buildingscience.com/documents/reports/rr-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones

Crete-Heat is EPS, it has a real R value, and is a reasonable solution. But most radiant installers prefer to use XPS (any manufacturer) & staples for affixing the tubing.

I'd be a bit leery of any heating contractor recommending Insulatarp under a radiant slab. (If they screwed that up , I'd wonder how well they did on the rest of the design.) If it was a GC, not a heating contractor that came up with it I might be more forgiving. It's little more than a very expensive vapor barrier, and NOT appropriately called an insulation in that application.

Thanks for the reply! This was my opinion as well(GC uses it and attempted to convince me it was great stuff) but I have been out of the field of thermal engineering for so dang long my opinion is not worth much. Glad to hear from someone who knows.

Though I haven't tried INSULTARP,I heard the overall design of INSULTARP make it a very effective product for insulating under concrete slabs in Residential, Commercial and Agricultural radiant heating systems.