Building a home in a flood plain area with a high water table and I am trying to decide whether to install radiant tubing in the slab. The area will be used mainly for parking vehicles, main floor if 8′ above grade. This is in NH so it would be nice to be able to heat the area for freeze protection and if I evre decide to move there I could imagine doing a good bit of vehicle maintenance down there.
I know that heating a slab with no insulation is a poor idea but I am concerned about putting 2″ of eps foam that has pretty good flotation properties under the slab when I know that eventually I will have water in there. I plan to install drains in the slab floor to prvent hydraulic pressure under the slab. Am I concerned over nothing or should I skip the radiant slab idea altogether.
Tom
Douglasville, GA
Edited 10/5/2005 4:54 pm ET by TomW
Replies
Wow, no one here has an opinion on his one. I figured I would at least get someone telling me not to build at all in flood plain. Maybe my concern is not warranted. I guess the worst that will happen is a cracked/damaged slab that has to be busted out and replaced. I guess the weight of 4" of concrete should hold the foam down if we ever hit that stage again.
Tom
Douglasville, GA
You could submit this to David Letterman for a "Will it float" segment! Seriously while rigid styro will float it does not have a lot of boyancy. I would dig out about 12"-24" or so of the native soil, fill back in with 3/4" washed stone, compact, lay down the styro and pour your slab. I assume that rest of the structure is on footings? Perhaps a bit more information in that regard would be helpful. Roger
The omly reason I am asking is that the BI is giving me the impression that the slab is going to float on its own due to hydraulic pressure. The rest of the structure is on footings 4' below grade with 8' poured walls on top of them which will give me 4' of concrete wall above grade. There will be a knee wall on top of that and then first floor framing begins. I think the BI is going a little overboard with the issue and I can't find any reference to a problem with the slab in any of FEMA's literature but I figured it couldn't hurt to ask here. I will be installing flood vents in the wall as required by FEMAv guidelines.Tom
Douglasville, GA
Tom, I am certainly no hydraulic expert here but my in experience with underground fuel tanks (that we worry about bobbing out of the ground if they are empty) you not ought to worry. I would say that your 4" slab on 2" of foam is never going to float. I think the BI should watch the David Letterman show for more research. To make the BI happy tell him that concerte weights approx 4000 Lbs per cu yard which works out to nearly .086 lb per cubic inch. If you are pouring a 4" thick slab, take a 12" square of 2" dow styrofoam and place it in a pool of water. Put 50 lbs on top of it, and ask the question "Will it float?" I think not. However two beautiful models and the "grinder girl" may walk out from behind a curtain! On the otherhand if you or the BI never watch the David Letterman show. You will not find any humor in my response. Roger
To make the BI happy tell him that concerte weights approx 4000 Lbs per cu yard
Hmm, a 12 x 12 x 4 volume is .33 c.f. At 62.3#/cf, that's 20.7# of bouyancy by volume. At the 2t/cy weight, .33 cf of concrete weighs 49#. 49# > 21#, slab ought not float.
Now, that's just the slab, it can be possible for an entire slab to act like an upside-down water glass, the foundation edge defines the bouyant volume--but that's presuming a lot (like completely waterproof concrete, water well up the foundation walls, etc.)
Putting foam under ought (ought being the important key word here) not add to "bouyancy."
Could be a case of a BI seeing something that is not "typical," and responding accordingly. Or maybe the BI would be happier with some soils engineering from an actual engineer. Hard to read from here on the internet <g>.Occupational hazard of my occupation not being around (sorry Bubba)
CapnMac, you are correct, my simplistic attempt at a humous response did neglect the displacement of the actual volume of the concrete slab and styofoam. As you have shown it does subtract 20 lbs from my sack of potatoes sitting on a square foot of styrofoam. I agree it should not float. Roger
at a humous response did neglect the displacement ... I agree it should not float.
Was tryin' to help a bit <g>
All of those classes on bouyancy, damage control, hull design will catch up with a person, though . . . Occupational hazard of my occupation not being around (sorry Bubba)
Let me get this clear, you are in an area with BOTH a HIGH WATER TABLE and that is subject to FLOODING. Those are two distinct different conditions.
I would think that if the water table was high enough to get into the foam that it would be too high to even put in a driveway unless you did extensive work.