I live in Saskatchewan Canada, and have a icf house both the basement and main floor.  The basement is roughly 6 feet in the ground (9' basement).  I am just going to be installing the concrete basement floor, I am going to be installing 6 mil vapour barrier over the 8 inch of gravel and then above that 2" xps 30 psi foam board.  The question I have is whether or not I should be putting the foam over my footings that protrude past the inside of the icf wall.  I will be installing radiant heat loops for heating in the basement.

I thought I should install the foam over the footings, but a contractor I have worked with for parts of the build said he has been told not to and does not do it, because it will ensure that if frost ever does get down to the footings the heat will ensure the ground around the footings never freezes.  In my area water lines are typically dug to 10 feet to ensure no freezing occurs so my house is above what would generally be considered the frost line.

Please provide any thoughts.

Why don't you use our 3 inch thick CreteHeat as a vapour barrier and insulator plus it holds the radiant tubing. It will give you an R 14!! Let me know if you would like more info or go to www.barrett-inc.com/creteheat.php

I already have everything purchased, plus not sure on the vapour barrier of your product for my needs.  The reason I am using vapour barrier is for Radon protection, otherwise the foam I am using is a type iv which is effective for moisture migration as well.

typically you want the radiant slab poured in an "insulation bowl" that is continuous on 5 sides.

how to deal with frost in your area is a question i can't answer, however.

The propagation of frost heaves is in the direction of the heat loss, and as long as the basement is heated the direction will be away from the footing, not toward it, and the it won't heave, even if that heat loss has been much reduced in magnitude by the insulation. It's a much bigger problem in unheated buildings. See:

http://www.buildingscience.com/documents/insights/bsi-045-double-rubble-toil-trouble

thanks Dana1, I read the article it primarily talks about insulated walls not slabs, but I would expect that the principles are the same so from that it states I should be able to cover the footings and have no problems with frost heave.

As long as it's well-drained and heated you shouldn't have an issue, despite being above the design frost line for your area. If the foundation hasn't been backfilled and you have the material you can add wing-insulation to better earth-couple it, but it isn't really necessary. With R10 foam and a heated slab the heat loss to the soil proximate to the footing is still pretty substantial, and in the right direction.

BTW: A subtle (non-disaster issue even if you flip it) that comes up, when you put the poly below the slab insulation it takes longer for the excess moisture from the poured concrete to dry, since the excess water will find it's way down to pockets/bubbles between the rigid foam and flexible poly as liquid water. If you put the poly above the foam, the water stays in the concrete which helps it cure faster and the excess moisture gets out quicker since it isn't impeded by the vapor retardency of the foam, drying through the highly permeable concrete.

the problem with the vapor barrier on top of the foam is that the radiant tube will be stapled to the foam which would create holes everywhere in the vapour barrier thereby eliminating its purpose

Posted By jojo12 on 23 Oct 2012 01:45 PM
the problem with the vapor barrier on top of the foam is that the radiant tube will be stapled to the foam which would create holes everywhere in the vapour barrier thereby eliminating its purpose

A vapor barrier with a bunch of staple holes is still a very good vapor barrier (but not an air barrier.)  Moisture transfer via vapor diffusion is a vapor pressure times area sort of thing, and the staple holes are mostly filled with staple, and even the inevitable small tears don't add up to more than a handful of square centimeters for the whole slab, and the foam it's stapled to is also fairly vapor retardent.

I agree but as I mentioned earlier the reason I am putting the poly down is for radon protection, not vapor permanence as the xps is type 4 and will be taped so for moisture I dont believe I would even need the poly.

And how much radon leakage do you anticipate through a handful of square centimeters of rip-hole that is being held tight to the foam? A radon atom has a larger cross section than a water molecule, and the radon permeance of a material would be comparable to (but somewhat less than) it's water vapor permeance. As long as the air tightness of the assembly is good,water vapor permeance & radon permeance are the same type of problem, a vapor pressure times area kind of deal, where miniscule holes make very little difference.

http://www.aarst.org/proceedings/2010/03_EXPERIMENTAL_DETERMINATION_OF_THE_EFFECTIVENESS_OF_RADON_BARRIERS.pdf

I'd argue that with the poly protected between and tigth to both the concrete & foam the air-tightness is more assured over the long term, reducing it strictly to a radon-diffusion problem rather than an air/gas leakage problem.

As long as the air tightness of the assembly is good

That's the key - any air flow at all is a radon problem, even right through the concrete. If something is going to be putting holes in your poly, relocate the poly. And make an airtight seal at the wall-floor intersection. Both issues are covered here:

http://www.aarst.org/proceedings/2010/09_DESIGNING_EFFICIENT_SUB_SLAB_VENTING_AND_VAPOR_BARRIER_SYSTEMS_FOR_SCHOOLS_AND_LARGE_BUILDINGS.pdf

I may be dead wrong on this as I do not know but the thought of punching all those holes in the poly just seems wrong to me.  As for the initial reason that Dana1 gave for putting the poly above the foam was to stop the pockets of water being trapped away from the concrete in depressions in the gravel or base, I think that is somewhat minimized by the fact that the foam will all be taped and is  supposed to have low water transmittance. so unless I mess up on placing and taping the foam the water should be next to the concrete anyway and I also avoid the holes in the poly.

If I am missing something please let me know.  I do not assume I know all of this, just doing my research.  I plan on laying the vapour barrier and foam in the next couple of days when the plumbers are complete. 

Second question.  I am planning on putting a 3" pvc or abs Tee in the crushed rock base below the poly with a 3" line venting through the roof.  Is there any other current recommendations for radon remediation.  I should note that I do not think I have a radon problem, and it is not common in my area, but from what I can see putting the measures in place now is very cheap compared to doing it later.  I should also note that my footings have 2 inch pipes running through it at 2' centers and I have inside the footings a crushed rock base of roughly 8" and the exterior is backfilled with about 12" crushed rock about 2 feet out from the footings, and then backfilled with a sand clay mixture, probably 80% sand.

Thanks

punching holes in the poly is no big deal for all the reasons already noted. vapor transmission is related to area of exposure. holes are small and filled with stuff. not much transmission there.

Jojo, Put in the TEE under the concrete, bring it up about 10" and cap it. If you need it, finish it off later. Since is is largely a preasure effect, adding a underslab drain that goes to daylight can do alot for you also, and insures water under the slab is not a problem Cheap insurance. Cheers, Eric

BTW: For the record, it turns out the diffusion cross sectional or diameter of radon is even bigger than O2 or N2 molecules (I had always assumed it to be somewhat smaller than the diatomic gases, but was corrected on that on another forum) so there's even more AIR diffusing through the poly than radon, who knew? :-)

But it's still a diffusion issue, not a leakage issue- all about the total exposed area, which is miniscule.

I disagree - it's a leakage issue. Which is why the above reference repeatably says "no holes".

Use 2 layers of foam under the slab and put the vapor barrier between them.