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Dear Bob and Betsy,
Do hardwood floors need moisture barrier if I’m installing them on grade? I’ve read a lot about how dangerous water is to hardwood floors. I’m planning to install my new flooring “on grade” (not above), which I know is a little bit risky. I feel confident they won’t get damaged where I live.
– Susan C.
Dear Susan,
You’re right. Moisture can do serious damage to hardwood flooring if you’re not careful. If you were to install your flooring below grade, we’d caution you heavily against it. However, on grade installations can be safe as long as you’re confident that the moisture levels won’t damage your floors. We have compiled more information for you to help to decide what’s best for you. Cheers! Bob & Betsy
You are probably diligent about keeping your house clean and free of standing puddles. You might also have a plan in place for what to do if someone spills on your hardwood floor. Still, you can’t always know what’s lurking below the surface.
Although you check (and double check, and triple check) your subfloor for damage, such as cracks or dips, before you install, damage can still happen over time. After you’ve had your flooring for several years your subfloor might get a tiny crack that could let in just the right amount of moisture to harm your floors.
Moisture barriers protect your flooring from below. They keep your hardwood safe even if a little bit of moisture seeps up from the subfloor. This is the type of moisture you won’t know is lingering until it’s too late.
These benefits sound ideal but should you use a moisture barrier for your hardwood flooring installation? It depends on your subfloor and how you plan to install your flooring.
If you’re planning to nail down your hardwood floors, a moisture barrier is recommended.
If you’re planning to glue down your hardwood floors, things get a little trickier. Many solutions today require the use of a trowel spread barrier. Talk to your installers about this before they arrive at your house so you’re sure your flooring is protected correctly from below.
If you are installing an floating engineered hardwood flooring, you can use Aquabar underlayment to help control moisture.
Sometimes, a moisture barrier is not recommended. If you’re installing your hardwood floors over a wood subfloor, you should avoid using a moisture barrier.
Over time, moisture can get trapped between the moisture barrier protecting your hardwood flooring and the wood subfloor. This can cause the subfloor to warp and rot, promoting mold growth and causing serious damage to your home.
You might also be tempted to use underlayment with a moisture barrier attached. This type of underlayment is great for floating floors, such as some laminate and engineered hardwood flooring. However, it’s not recommended for solid hardwood flooring because you will either need to nail or glue down the floors when you’re installing.
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Hi there. I have an odd real wood flooring situation.. perhaps you can help. I’d like to put 3/4″ T&G Hickory Wood floor in my shop.
New construction project. I designed a Shop along with the house (it’s attached/part of the house). It has a 4″ concrete floor, and a full-sized garage style overhead door to the outside. The walls are 2×8, fully insulated. The garage door is insulated. The concrete was poured over 4″ of Owens Corning Foamular 400 rigid insulation, which was taped at the joints, and then a 6mil polyethylene plastic sheet over the foam, and taped at the concrete stem walls. The Shop room is heated (forced air) as part of the house.
I prefer to nail in real wood flooring, so that meant I needed some sub flooring under the Hickory. So I put down a series of (20) 4″ wide 1/4″ thick industrial rubber strips along the concrete, to act as sleepers under the subfloor so that the sub flooring could get some air circulation. Then we put down 1-1/8″ thick AdvanTech sub flooring T&G panels over the rubber sleepers. The subfloor was attached by drilling through the subfloor panels, and then switching to a concrete bit and drilling further into the concrete, and then screwing in concrete bolts. Only (6) per 4×8 panel though. The thinking was that the very thick subfloor panels would stay flat (Advantech 1-1/8″ panels are exceptional heavy on their own).
I went off to build the rest of the house, and planned on coming back to the Shop subfloor in a year, to put in the Hickory flooring. But 6 months later.. that’s when the problem occurred; The subfloor panels started to warp, assumably from moisture coming up from the concrete. I goofed up in thinking that the only source of moisture would be from the ground below the concrete (hence the taped poly sheet over the foam), but I didn’t realize that concrete seems to keep putting out its own vapor. I didn’t also liquid vapor barrier seal the concrete before putting down the rubber sleepers and subfloor panels. I left the panels 3/4″ short of reaching the stem walls, on all four sides, thinking that would provide airflow ‘channels’. Wasn’t enough. The panels are now warped up about 3/16″ along each edge of each panel.
It’s easy to say to myself; Hey, just pull all that subfloor out and start over. But that would be thousands.
I’m wondering if it is possible to continue to deny the root problem (mitigate it) by simply driving in more bolts to flatten the subfloor, then spread/paint on a vapor barrier, and then still put down the Hickory flooring? Or is the sub flooring doomed to continue to be damaged by vapor? … and possibly then also damage the eventual Hickory flooring as well? Any suggestions.
Thanks so much
Hi Rowan, thanks for the question. I think the root cause is coming from the concrete or water/moisture getting in from under the garage door. I’m not an expert on subflooring, but it’s usually not recommended to add a wood subfloor over a concrete one and also not recommended to install hardwood in a garage. Is it possible to consider an engineered hardwood that you can glue? You could coat the concrete with a sealant to prevent moisture and glue the flooring. I’m afraid moisture may always be an issue here.
Hello!
I’m planning to install 3/4” 5” hardwood floors on the first level that has concrete. I would like to glue and nail down the hardwood. Do I need to have a liner of some sort like someone mentioned felt? Also moisture barrier like Sika? Which needs to be done first? Pardon my questions as I’m trying to understand what is needed. Would like to install floors correctly since it’s my first time and for how expensive it is. Thanks so much for all your advice!
Hi Van, thanks for the question. You will need to glue your hardwoods over a concrete subfloor. You will not be able to nail into concrete. I hope this helps!
My dad told me that he would like to replace the floor of his house and he is trying to decide which material to choose from. I like how you said that moisture barriers protect your flooring from below. Thanks for sharing this article, I will recommend him to hire a professional company so that he does not have to worry about installing the new floor himself.
Thanks Derek!
Hi I’m installing plywood over a OSB Subfloor the subfloor has gaps where I can see the ground under the house do I need moisture barrier between the 2 layers of flooring
Thanks for the question. Usually, you would not need a vapor barrier with a wood subfloor, however, if you have no insulation or sealing under the subfloor, I would recommend it here.
i am wanting to install reall hardwood flooring over my wood sub-floor. What i have for a sub-floor is 1/2″ plywood then 30lb felt then 5/8″ plywood. I also have 6″ bat insulation on bottom being held up with chicken wire. i live in South East Texas it gets hot here so a/c runs a lot. Do i need a vapor barrier? i was also thinking of removing the bat insulation and replace it with close cell foam. Please advise what to do.
Hi Mark, thanks for the question. You don’t need a moisture barrier over wood subfloors. Just make sure your room stays at a consistent temperature and humidity, or you could experience gapping or buckling.
I have removed carpeting from the upstairs of my 20 year old house and mdf tongue and groove sheets are the subsurface. I live in Austin Tx. I plan on stapling half inch engineered wood to mdf. Do I need to install felt or a moisture barrier? Thanks. Tim
Hi Tim, thanks for the question. If your subfloor is in good shape and level, you can install right over it. You will only want to consider a vapor barrier if you’re installing over concrete, crawl space or if you have any type of water issues with the subflooring.