This is my first post and I hope I have selected the right forum  for this topic....if not please advise where I should post. 
I am in the process of building a new house and have been thinking quite a bit about how I want to construct the basement floor.  The house is  a 2 story walkout and the less basement like I can make the lower floor the better in my opinion.  To start with I really dislike concrete floors in a living space.....I find them cold, hard and ugly and that's enough for me to seek an alternative.  So my plan has always been to create a wood floor environment without resorting to a poisonous p.t. foundation.  I'm planning for a radiant floor in this design so my approach is a little different than normal.  I was going to start with a V.B. under 4" of concrete than 2" of XPS foamboard with pex pipes layed on top between 1x6 boards glued directly to the foam board, topped off by a 3/4" finished wood floor.

I'm looking at a 1200 sq. ft. footprint and I estimate I'm going to end up spending $8-10,000 to pour that "never-to-be-seen" concrete layer.  I'm thinking that this probably isn't the best way to spend my money and thought perhaps I could replace the concrete layer with another material like well packed gravel, "roadbase" or even common sand and save around $8000.... if I do it myself.  In this case I would move the V.B. to the top of this alternate fill level directly below the 2" foam board.     I have searched the Web and have not been able to find any information or record of anyone creating a basement floor in this way so that has slowed my enthusiasm for this idea....a bit. 

Any thoughts or advice would be greatly appreciated.

Cheers!

you could float a wood floor over the concrete without sleepers. that would work better anyway.

I don't have any keen insight on the concrete substitution question though, sorry.

I can't fathom why you want to substitute. Concrete has been nearly perfect for construction for some thousands of years now.

First, to improve the creature comfort of any space you have to have windows. Windows are of course the antithesis of comfort often adding heating and cooling loads. But in a walkout properly done, the heating load is going to be added by the windows. The best way to meet the added heating load of any window is with a radiant surface nearby. Since concrete slabs are common, inexpensive and nearly perfect radiant emitters, you start with a heat load and PEX tubing in the slab.

All of this is available -sans the heat load perhaps - making it easy and affordable. With the heat load, a heat source and floor coverings can be considered. With the typically low heat loads for basements in most of North America, nearly any reasonable floor covering can be used. For instance in my own home I have used cork, 3/4" oak over 3/4" sub-floor, slab on grade covered with tile and tile over a slab removed insulated and tiled in my walk-out.

For snow melting we place XPS on a compacted base, staple tube to the XPS and fill with class 5 compacting lightly with stone over all.

If I were to do a primitive basement, I would start with a vapor barrier, XPS, PEX, class 5 and wood over all. As long as you control moisture from the walls I can't envision a problem. You may also consider a cork laminate as I did in my bathroom.

None of it without a heat load and experienced design help of course.

I agree - once you have windows, insulation, a floor covering and possibly dehumidification, you won't know it's underground. I suppose if you want a little spring in the floor, you could build the equivalent of a wood deck as a floor. It would fare better in the case of a water leak.

You might get the spring but you add the challenge of heating a suspended floor, but he has me thinking.

Naturally, some PEX manufacturers imagine all kinds of things that might happen to their tube in a compacted crushed rock environment, but my snow melted flag stone is still holding pressure. We also have down some veil barns with tube, rock and cattle...no problema.

Thanks for all the replies so far. I should mention that I think thermal mass is overated. Sorry but I'm just not a fan of "flywheel effect" or "thermal lag" that most see as a benefit. That is the reason the pex piping will be located above the 2" of rigid foam and not in the concrete or conrete substitute. I appreciate the history of concrete but I can see no real benefit to using it and as I mentioned I believe I could save around $8000 by using an alternative, which goes a long way towards other objectives when building a new house.

Five years ago when I built this part of the house I thought raiant in slab was the cat's meow but after living witht his setup day to day my opinion has changed and I prefer an alternative. I admit it's great during the heating season but once the heat is off I tend to strap on fleece to stay warm as I spend 8 hours a day typing in a basement office, the refreshingly cool effect only lasts about 30 minutes.

I should mention that I think thermal mass is overated.

It is what it is, regardless of how you perceive it. The concepts of "flywheel effect" and "thermal lag" don't have much relation to basement slabs. There isn't much effect with a floor which should see the same temperature on the underside regardless of whether it is morning noon or night and whose topside is affected by comfortable living space temps. Your plan to create a radiator using sheets of wood is a whole lot less efficient than radiators utilizing concrete which is a large part of the "benefit" of concrete.

You haven't described what "day to day setup" you are living with now so it is hard to make anything out of your fleece and refreshingly cool remarks.

While the direct loss out the bottom of the slab doesn't change much over time, having the slab fully within the thermal boundary of the house affects the time constant of the house, and when being used for radiation, the time constant of the heating system (for both good & ill.)

The total time constant of the house is a function of the total thermal mass inside the insulation and the U-factors/R-values of the envelope, and the constant lengthens with both increased mass and lower U-factors. A long time constant on the house is in general quite a GOOD thing, since the interior temps are not quickly affected by outdoor temperatures, and the response time of the mechanicals can be quite slow without affecting comfort. In a high-mass/low-U house you can also undersize the mechanical system's peak output by a substantial amount, since even several hours of undershooting the instantaneous loads won't result in a big temperature shift.

But it's not worth paying 8 grand just for a modest thermal mass benefit, eh? If it's not required by code (some locations will require at least a non-structural rat-slab), it's your call.

thermal mass is oversold in some cases. however, if you are going to do radiant and you are doing a slab anyway, piping it directly should be a no-brainer decision in a basement. any problems with this kind of system are largely control problems that can be addressed, especially in a basement. the extra cost of doing radiant outside a slab that is being poured anyway could almost never justify itself in any but a part-time-heat situation.

Thermal mass is almost as magic as radiant barrier in some people's estimation, but increasing the time constant of the house with lower-U assemblies/windows/doors rather than increase mass provides comparable benefit independently of how it's achieved. Eight thousand Loonies can buy quite a bit of enhanced thermal performance, with a financial return much better than that of pouring concrete just for the thermal mass.

agreed. but I suspect by the time you're done figuring out an alternate floor method and all of its costs, you'll find the incremental cost is pretty damn small.

People do concrete basements for a reason. If you want to finish it, I doubt there is a way that is much cheaper. But hey, maybe.

Your plan to create a radiator using sheets of wood is a whole lot less efficient than radiators

I agree - unless there is some aluminum sheet involved. Then something like tile over wood can outperform concrete in both btu and responsiveness.

I was under the impression that Manitoba is high in the radon dept so having something well sealed and the room well ventilated is important. A 4" slab with tubing is pretty cheap to install and a floating floor after can run a from really cheap Ikea stuff to more pricey Brazilian cherry. I would use the mass then pick your covering.

Why reinvent the wheel?

Concrete slabs are used because it is a tried & true technology. I just don't understand the reasoning WHY you are so opposed to it. One can always places soft spongy carpeting or a floating wood flood over it if they don't like the "feel" of it.

No, I like his idea.

I generally don't like wheels and have never " willingly " poured a slab without the obvious benefits of PEX tubing. But, I would consider a vapor barrier, XPS, PEX, class 5 and any durable floor covering you like. It is a contradiction in terms to install concrete for a soft floor.

Dana astutely describes the benefits of thermal mass and crushes rock qualifies. Response time is affected but is not needed in a basement. I frankly don't see the down side. I will design it, if you will install it.

Posted By BadgerBoilerMN on 11 Jul 2012 07:37 PM
No, I like his idea.

I generally don't like wheels and have never " willingly " poured a slab without the obvious benefits of PEX tubing. But, I would consider a vapor barrier, XPS, PEX, class 5 and any durable floor covering you like. It is a contradiction in terms to install concrete for a soft floor.

Dana astutely describes the benefits of thermal mass and crushes rock qualifies. Response time is affected but is not needed in a basement. I frankly don't see the down side. I will design it, if you will install it.

Would you warrant tubing in crushed rock (which, in some cases means sharp gravel) because i wouldn't. I would if it was in soft sand as I have done many times in the past with snow melts. There is still the question of radon.....

I have PEX under a driveway with crushed limestone (no sand). I assume that with no trucks or cars, a basement is much easier on the PEX.

100%.

But, I don't make it. As a contractor, my exposure is much less. Sharp rock, shmart rock. I am not afraid. PEX is very tough stuff. It will generally take any abuse short of 200°F, but I didn't say that.

I used in my own sidewalk snow melting system and it held 60psi for two years. It is standard practice of snow melting under pavers. No doubt encasing PEX in concrete is the ultimate protection (in old days we had to convince people it would work and repair was not a problem).

Great replies, I appreciate the input. One clarification that most are missing is that I was intending to put the pex ABOVE the thermal mass and separate it by a V.B. and 2" of rigid foam. In this situation it wouldn't be any different than staple up under an upper floor (low mass). I have that setup in my current house along with pex in the slab in my basement and I actually like the staple up more. A well sealed V.B. should take care of any radon or moisture issues...and I'm pretty much sitting on shale rock with no clay to speak of. So I take it crushed stone or compacted sand would be two cheaper alternatives that would be stable enough to replace concrete? Again this is more about me trying to save money on a concrete floor that has no function "as I see it" rather than trying to perfect my radiant heating system. I already accept the cost of the wooden floor above so that money is already accounted forand will be spent regardless. i suppose the original question would have been better posted in a foundation discussion forum somewhere!

Badger. What are you refering to as "class 5"?

Thanks!

A concrete floor in a basement with structural wall has supports nothing but the occupants and there stuff. Why not?

As for the order of components, you will need to secure tube and figure output.

Class 5 is crushed rock typical in sub-slab construction.