Holmes vs. FHB: Basement Floors
FHB has published two articles about making a floor over the concrete slab of your basement. While the two articles differed significantly, both stressed beginning the project with a layer of plastic laid atop the concrete.
I have recently begun watching “Holmes on Homes,” and he disagrees quite strongly with this method. He goes so far as to point out that his disagreement is contrary to the instructions that come with the ‘engineered wood’ floors.
Instead, Holmes places a ‘floating’ layer of rigid foam insulation, and tapes the seams. This has the effect of making the top of the foam the vapor barrier / retarder. It is his position that the sheet of plastic atop the concrete (that FHB advises) will only act to trap moisture, and create a mold / mildew / stink issue.
For a similar reason, he really likes a radiant heat mat as part of the follr (to dry off any moisture) and would just as soon not have ANY wood as part of the floor.
Holmes has a similar approach to concrete walls; a layer of foam, THEN the walls are built.
Well, Breaktimers …. has FHB been giving bad advice?
Replies
I think you'll get all sorts of arguments here, and precious few reliable facts to back them up.
First off, so what if moisture is trapped in the concrete? Go one inch into the concrete and there's plenty of moisture. Just make sure that there's no "food" for the mold beasties.
And if the foam is a moisture barrier, how is that not trapping moisture just as much as the plastic would?
But, on the other hand, there is no single scenarion for concrete walls/floor. Some are sopping wet, some bone dry, some wet only "in season". What works in one situation may not work in a different one.
Additionally, while the theory is that, once you get down 2-3 feet, the soil is always 50 degrees, I'm guessing that there's at least a ten degree variation on that, in either direction, again depending on the specific location and conditions. So the amount and type of insulation needs to vary accordingly.
And let's not forget that some people insist on a toasty warm floor while others are perfectly good with a floor that's a bit on the cool side.
>>Just make sure that there's
>>Just make sure that there's no "food" for the mold beasties.
I'm not sure is mold will ever grow on/in/in contact with concrete....
No, mold needs something organic for "food".
(I recall, after the Rushford MN flood, seeing a home owner vigorously "treating" efflorescence on a CMU foundation with a Clorox mixture to "kill" the "mold".)
.>>It is his position that
.>>It is his position that the sheet of plastic atop the concrete (that FHB advises) will only act to trap moisture, and create a mold / mildew / stink issue.
Trap the moisture under the plastic? Yep, that's what it's supposed to do. Mold won't grow in conact wih concrete, though, because of the alkaline (acid?) nature of concrete
Trap moisture on top of the plastic (under the flooring)?
Hmmmmm. In theory, more likely than with foam because of condensation temp issues.
OTOH, .....
I just watched that show too. The bottom line was that he, in spite of his promises to the homeowner, was unable to find the source of the moisture that was warping her wood floor. Since he is unconstrained by budgets he just switched gears, installed foam, radiant heat and tile. Problem solved and he's a hero. He very effectively hid the problem but didn't fix it at all. Did you see how quickly he changed his tune from, " the concrete has to come out" to "taking the concrete out is a waste of time" when he saw how hard it was going to be?
I posted this thread specifically to get all sorts of opinions. I am not ready to say that Holmes, or either of the FHB articles, is 'right.' It's your opinions I want.
There's a tendency to accept, as Gospel, anything that's printed, or we see an 'expert' expound on TV. This is one area where the sources seem to disagree.
As for "that episode:" I've seen Holmes discuss concrete floor on at least two separate episodes. He is correct in one thing: before you can solve a moisture problem, you need to find the source of the water. Is it coming from below (groundwater) or above (leaky roof)? That would be a critical bit of information.
I'm inclined to agree with Holmes as to not using a layer of plastic under foam. After all, the foam itself is a vapor barrier - and you want the 'seal' to be on the warm side of the barrier, which would be the inside face of the foam. That would address condensation.
As for water coming through the floor itself, I doubt a plastic sheet will work. Water will enter through whatever seams or holes there might be - then be trapped. As concrete is porous, I'd just as soon let the moisture drain back out.
Again, I am inclined to think Holmes is on the right track with his use of radiant heating in these floors. Whatever moisture, from whatever source, gets in the floor will be driven out by the gentle heat. Ixnay on the mold potential.
Having dealt last Fall with the $13,000 damage a half-inch of water (or less) caused in a finished basement, this is a problem dear to me. Cleaning up after such an event, it is critival that you be thorough. For the one Holmes episode, it was possible that a roof leak had let the water in - and the water that had seeped under the flooring had never been adequately removed. Going over the floor with a vacuum for a few seconds wasn't enough. I'll give Holmes credit for thoroughly investigating other possible sources, by opening up both the walls and the floor.
In electrical work, we don't always succeed in keeping all water out. We get better results when we provide a means for the water to escape. I suspect that this approach is the better one when you lay a floor atop a concrete slab.
PS: I want to thank everyone for replying. I cannot visit this site very often, as internet access isn't all that common in these parts. I have to -literally- drive into town to get on anothers' network. Have a good Holiday, and I'll be back soon!
wood over concrete
I've seen/had it done several ways in the past. All but one worked just fine, in the years since. Maybe lucky, maybe there's more than one OK way.
1. Plastic sheeting over the entire floor, then the flooring. Seemed to work, but I always was afraid that friction/weight would cause the rough surface of the concrete to eventually degrade the plastic, then you have nothing.
2. Tar paper, with troweled mastic at the joints. (smooth). Floating floor. Mastic must be very dry, or thin plastic sheet over it.
3. Either tarpaper or plastic sheet under exterior plywood. Seemed a little odd because of the tapcons holding the plywood. This was for 3/4 hard maple, nailed. It did work though.
4. Closed cell foam, with taped joints, then the floating floor.
Of the above, #1 seemed to fail, because the floor buckled a lot. Not sure if they blew it on the perimeter clearance, or did the plastic degrade somehow and let moisture up through. Tough job to figure for the floor guys though, 60 ft. from a large river, and I'd say the basement slab was maybe 18" above the water level of the river. This failure was just in that one instance though, none anywhere else. Perimeter clearance should be larger when doing floating flooring over concrete. Use quarter round instead of shoe mold.
Dave
In this case Holmes himself showed that the moisture that cupped the floor did not come through the concrete and that the plastic vapor barrier worked just fine so any argument about plastic vapor barriers in this particular case are moot. In spite of his own evidence he kept up with the "moisture coming through the concrete" routine until it became obvious to everyone else that they were wasting time. Why he continued to argue that the plastic vapor barrier didn't work when he just stated that it had baffles me. I don't doubt that sealed foam, radiant heat, and tile is a better option for damp floors but of course fails to explain why the floor was wet in the first place and isn't an option for anyone restrained by finances.
amish.....
i'd keep the poly vapor barrier in the case you sited
but.... if we're building the floor system ... we start with 10 - 12" crushed 3/4 " stone....inside the footing... with a 4" pipe drainage system leading to a drain to daylight .....or....
if a drain to daylight is impossible then the pipe system leads to a sump
over the stone we install 2" of high density foam... then pour our slab ... either with rfh or without..
the slab can be the finish floor or get any finish floor installed over it
with a drain to daylight i'd be inclined to let the homeowner do a finish floor... with just a sump... i'd assume the pump will fail just when it shouldn"t... and the finish floor will be ruined
wet basements...
seems like a lot of people have trouble with run-off water pooling ....seeping down .... and leaking thru the wall
but ... most of the problems i've seen were not from run-off but from rising ground water...
so the problem is intercepting the ground water... i've already described our base system... but another pretty successful one .... if the houses are relatively close together... make sure your basement slab is at a higher elevation than your neighbors
they will pump the watertable below your slab... they will fight the good fight every wet season and keep you dry