The topic is radiant slab heat and underslab insulation. How to prepare the base under the concrete slab. A contractor told me to put my 2 inches of insulation right under the slab (i.e. no gravel/sand over the insulation). Another contractor said put 2 inches of sand over the insulation prior to pouring my slab.
I’ve heard that a vapor barrier (e.g. the insulation) right under a slab will inhibit proper curing of the concrete, but the first contractor said he does it all the time. The second contractor also recommended visqueen under the insulation which seems to me to be a little redundant. … comments?
Replies
No comments other than I feel your pain. RIH is common here. Used in all custom/semicustom.
Have heard those two arguments, plus a third. The third says you need nothing at all. Some heat will leak from the slab to some portion of the ground....but it's not like it's going to warm the dirt down to China. The dirt warms up and becomes part of the heat sink.
I've done all three and can't tell the difference. Wish I knew the right answer.
ShelleyinNM
I've been in the energy business for 20+ years, now. From an energy standpoint, no insulation is probably not the way to go. yeah you warm up the earth and it acts as a buffer, but it costs you. Like the other guy said, you have 100 degF slab and the ground is 50. You may establish a gradient down several feet or more, but the energy result is still the same ... heat loss from 100 to 50 w/ no insulation in between. If you are trying to store heat on a bi annual basis (i.e. summer to winter) or if you have excess heat to store, no insulation may be the way to go, but if not, you really need some insulation.
Wally,
Try your question over at this site, they are the pro's
http://www.heatinghelp.com their forum is called The Wall
Jason
If you have a high water table, you should have insulation. At the price of energy, why would you want to heat mother earth. Infloor runs at say 100. The ground is at 50. A high water table makes the heat transfer faster.
The last house we did, vapor barrier, styrofoam, rebar,tubing, concrete. Makes for a neat job.
Heated indoor slabs I have done here in BC have spec'd compacted 3/4" minus crush with poly moisture barrier and rebar 24" o/c each way. Inside of foundation walls has 2" rigid styrofoam down to top of footing, exterior is dampproofed with tar-type coating. All typical for indoor slab on grade. Then add more 2" rigid insulation on the flat extending 24" in from foundation wall around building perimeter (remove some subgrade to retain consistent slab thickness across full width). Finally the heating tube is laid out according to manufaturer specs, typically in runs of 250' max with no more than 12" separation between outgoing and incoming tubes. Tubing is fastened to rebar with plastic zip ties.
Wally, we did ours the same way as Rich1, except we used some sort of square wire mesh instead of rebar. Our slab cured just fine. I think one of the hardest things as homeowners is Too Much Information. It can be overwhelming at times listening to everyone's different and comflicting opinions.
There's alot of information on this site http://www.radiantcompany.com .
It gives many different design situations and the rationale for them. Hope it helps you make a more informed decision.