Question for HotRod (Starch)

John Starcher_4

Hotrod, I know you've done several installations using insultarp - what R value do you use when calculating your heating loads? I've never used this product, but have a potential application for it.

I'm looking at a job where we'll have approx. 2100 sq feet of basemtent floor, 9' below grade. I checked their website and they claim an R value of 10. In your experience, is that accurate? Foam is not an option, so the tarp would be great, but I'm concerned about calculating the loads correctly.

TIA,

Starch

hr

That is a tough question!

In reality it is only a half inch of actual "dead air" space. So 2.5 would be the "real" answer.

However my "seat of the pants" testing and dozens of monitored installs tell me it does perform as well as 1" foamboard. Not sure if that aluminumized layer does in fact make a difference, or the excellent vapor barrier qualities, or the fact it doesn't break into pieces as foam does on uneven ground, but....

Termites are a real and known threat around here. I have seen first hand what they do to un-treated foam in concrete application. That plays heavily into my choice of giving up some R value, knowing it will not be eaten away, rendering a R-0 after time goes by, as is the case with foamboard.

Also this far south my heating loads pale to nothern and mountain climates. That helps me rationalize the InsulTarp to some degree.

The soil below the slab makes a huge difference also. Not much granite around here as we had EVERYWHERE in the mountains of Utah. Most basements there had to be blasted into the earth!

I still use 1-1/2" or 2" for my edge insulation. By far the greatest loss is at thet perimeter detail. It is also a place where termite protection can be update. Unlike the center of a slab

I made a list of pros and cons when I made my decision. Do the same and consider involving the homeowner.

Good luck with you quandry.

hot rod

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John Starcher_4

Thanks!!!!

When I ran the numbers, I plugged in R5 to be conservative. It provided a nice btu/sq.ft. I'll take your advice on the edge insulation, as foam is doable there.

I appreciate your feedback!

Starch