Wood Flooring Over Concrete
kennebecwoodworks
| Posted in General Questions on
I’m building my own house, its on a monolithic slab with 2″ foam underneath and around the perimeter. My plan was to install strapping and then 3/4 plywood and then hardwood flooring. I was wondering if there were any possible flaws with this design or better approaches.
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Replies
Mark,
Here's some relevant information from the American Hardwood Information Center:
http://www.hardwoodinfo.com/articles/view/pro/28/241/
Have you looked into either a glue down or engineered floating floor? The floating floors are not bouncy like they used to be.
Concrete has tons of water in it, so time is your friend. That means you may want to wait months to put anything over your concrete. Painting a garage floor for instance they say to wait 30-60 days, and paint is cheap.
Some of the glue down adhesives are vapor barriers as well
I mostly concur with Keith. Concrete loses 80-90% of its water in the first 28 days. The last 10-20% of water is lost very, very slowly.
You'll need to deal with a surface that is almost perpetually emitting some small amount of moisture.
I'd refer you to PCA, but they decided technical support is not something they're overly interested in anymore. I would link to their FAQs, but the GBA spam filter is preventing me from doing so. For a live human, you may want to call NRMCA.
Good luck. Let us know what you choose to do.
Thanks for the posts, it seems like most information says that a vapor barrier should be installed over the concrete, which I don't really understand. I have a vapor barrier and rigid foam insulation underneath the concrete, so wouldn't I want the concrete to at least dry in one direction and not trap moisture? Also is creating a 3/4 inch space between concrete and a subfloor plywood a bad idea where it may be cool, moist and dark? Seems like those are good conditions for mold.
I did this, but as a retrofit to a 30-yr-old house. I leveled the floor, then put down 1/2" high-density foam (I assumed there was no underslab insulation) then heavy poly, then underfloor heating "foil", then more poly and then engineered wood flooring. It's been fine. I would have liked more insulation, but that's all I had room for.
Mark - I would definitely install the vapor barrier over the top of the slab - even though it seems redundant, you have no idea how moisture may enter the slab in the future and very cheap insurance. I recently had to replace an entire houseof hardwoods installed over a slab without a vapor barrier - floors were over 10 years old and never had an issue until recently. I contacted Huber to see if they would provide their warranty in this application - they said they would and sent me installation guidelines. We screwed directly to the floor since it was a retrofit and had existing doors and thresholds to deal with. The furring strips, if space allows will help keep the floor level if the slab is not. I did a lot of reseach and saw some people recommend installing the subfloor on a diagonal which we did. Another reason I prefer Advantech over plywood is the floor we had to remove was over plywood and it was the plywood that actually buckled, not the hardwoods themselves.
I've done this a couple of different ways. Typically we wait as long as possible with one or two dehumidifiers running during working hours and then put down 6 mil poly and the PT 1x4 sleepers and then the ply and wood flooring but I've also pulled long 1x4 southern yellow pine flooring off the truck straight from the mill, lightly sanded and varnished it outdoors and then nailed it directly to the sleepers over poly and skip the plywood. In this application we just buffed it with a screen disk on a floor buffer and hei it with another coat of poly. (I like Hood Everlast)
I've also done radiant heat this way with the tubing running between the sleepers and pine flooring nailed to the sleepers in pretty much direct contact with the tubes. It takes a little care at the loops near the wall but you would run 100 PSI in it during install typically so as to get direct notification of any leaks.
I too will be putting wood floors over a new insulated slab foundation. My builder is recommending engineered wood flooring. What should go between the slab and the floating floor. Will using engineered flooring prevent moisture problems coming from a new slab?
Whatever floor you choose will have very specific instructions for installation over concrete if permitted. Select a floor type, go the their website and download the instructions and read them carefully. Since they usually provide a warranty, the instructions are normally very detailed.
I would use a floating floor. If you go with an attached floor, stay away from high density woods or strand bamboos which seem to be very moisture sensitive due to the density of the product. Some very expensive and well known products have a humidity range of 40% to 60%. I put down floating floors over concrete over a very tight vapor barrier 20 years ago and have never had any problems.
An engineered product over a vapor barrier or one that has it built in is the best. Installing a radon mitigation system will increase the durability as well.
Daniel Glickman
Sustainable Construction