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Do Hardwood Floors Need Moisture Barrier?

Dear Bob and Betsy,
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. Do hardwood floors need moisture barrier if I’m installing them on grade? Thanks!
– 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.

Moisture barriers protect your flooring from below.

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.

Installation

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.

Wood Subfloors

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.

Attached Moisture Barriers to Underlayment

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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About Bob and Betsy

Bob and Betsy
Bob and Betsy are the dynamic duo that have all the answers for your flooring related questions! Don't hesitate to submit a question to them at support@bestlaminate.com!

45 comments

  1. Alana Kane

    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.

  2. Avatar

    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

  3. Alana Kane

    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!

  4. Avatar

    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!

  5. Alana Kane

    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.

  6. Avatar

    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

  7. Alana Kane

    Thanks Derek!

  8. Alana Kane

    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.

  9. Avatar

    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.

  10. Avatar

    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

  11. Alana Kane

    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.

  12. Avatar

    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.

  13. Alana Kane

    Hi Harold, thanks for the question. No, you will not need a moisture barrier for this situation.

  14. Avatar
    Hardwood Floor Refinishing Reston, VA

    Thanks for sharing. I have a question – is it really necessary to have a moisture barrier for the second floor of my house? There are no temperature differences or high humidity.

    Respectfully,
    Harold

  15. Alana Kane

    Hi Stuart, thanks for the question. I am assuming you are installing over a wood subfloor on a first floor. In that case, a moisture barrier isn’t needed and you can nail or glue right onto the subfloor. However, if you would like some added cushion and sound dampening, then an underlayment isn’t a bad idea! If you use an underlayment, you’ll need to nail the hardwood vs glue.

  16. Avatar

    I am in the process of laying hardwood floor on a subfloor (approx. 800 sq Ft.) and have received conflicting information about where i should use a moisture + sound barrier or glue down with nails w/o the moisture barrier. We have a basement that is unfinished and the subfloor is clean and clear of any problems. My question would be do i really need the moisture + sound barrier or just glue and nail down directly to the subfloor?

    PS. We live in OH for reference to climate

  17. Alana Kane

    Hi Lois, thanks for the question. Is the pine flooring in good shape and level? You can install over it, but if you need to fix or reinforce the subfloor, it’s best to remove it and fix the subfloor. For example, if you notice any areas that squeak or feels like there is give. You would want to look for a felt underlayment for hardwood flooring with either installation type.

  18. Avatar

    Question about the need for a moisture barrier: Old house on piers with a subfloor of center match with pine on top. Going to install red oak flooring. Do I need to remove the pine boards or can the oak be installed over the pine? Do I need to use a moisture barrier if installed over the pine? If I remove the pin e?

  19. Alana Kane

    Hi Christina, thanks for the question. Typically we worry more about the actual floor moving versus the subfloor. Your subfloor should be fine.

  20. Avatar

    Hi. I appreciate the information. I sealed my OSB subfloor for odors (cat urine) with an odor blocking primer. My husband thinks that now the subfloor will not expand and contract with the wood flooring we want to put down. Is it true that the subfloor needs to adjust with the flooring, and will the primer prevent this?

  21. Alana Kane

    Hi Halley, thanks for the question. I believe the Regard should do it for the waterproofing. I would double check with the requirements your building has set. You should do the whole concrete floor, as water could cause issues with a hardwood down the line.

  22. Avatar

    Hello! I live in an apartment with concrete subflooring and plan to install hardwood (parquet) tiles in the kitchen. My building requires both waterproofing and soundproofing. Can my contractor just use Redgard as the waterproofing membrane, then layer the soundproofing on top? Also, should the waterproofing cover the entire kitchen area or just near the sink and dishwasher? Thank you!

  23. Alana Kane

    Hi Michelle, thanks for your question. I would first check to see if your apartment has any specifications for sound dampening with your floors. Hardwood can be very loud for the tenants below you. You may be required to put some type of sound underlayment down. If they do not have a specification, you can glue the hardwood directly over concrete. I would read the manufacturer instructions on the adhesive and moisture coating they recommend.

  24. Avatar

    Hello, I have a top floor apartment that currently has timber hardwood floors, we are taking these floors up and having them redone with pre-finished hardwood floors. Do we need to put a sub-floor down or can we just apply a moisture barrier coat and then glue the pre-finished hardwood directly to the slab?

  25. Avatar

    Will, thank you for replying!

  26. Alana Kane

    No problem Ryan! With your situation, I do not think you need anything under the floors. I am not an expert hardwood installer, but from what I have read, it is unnecessary for plywood applications. You can use the paper if you want, but it is not necessary. Be sure you consult with a professional if you’re doing a hardwood install!

  27. Avatar

    Thanks for the quick response Alana! Would you suggest putting anything down underneath hardwood floors that are being nailed to plywood subfloors? This would be on the main floor and there is a basement below. Thanks!

  28. Alana Kane

    Hi Ryan, thanks for the question. You only need to worry about the moisture barrier when it comes to a concrete subfloor, so you do not need one in this case. If you use one, it is no harm, but you don’t really need it. The felt paper is a good option for hardwood, but Since you’re nailing the hardwood down, you do not need a foam underlayment. Hope this helps!

  29. Avatar

    Hello!
    Im installing hardwood floors over plywood subfloors using the nail down method. Your article suggests using moisture barrier for nailing down hardwood, but then suggests NOT using moisture barrier when installing over plywood subfloors. Should I use moisture barrier? The recommended underlayment by Lumber Liquidators does not have a built in moisture barrier. Im also skeptical on buying the underlayment since I dont really care about the noise proof. Ive also read that 15 lb felt paper is a good moisture barrier for hardwood to plywood application. Thoughts or suggestions?? Thank you!
    Ryan

  30. Alana Kane

    Hi Marina, are you installing on the basement concrete or on the first floor above the basement? As long as you have a properly installed first floor subfloor, you can install the hardwood whichever way you prefer.

  31. Avatar

    Hi! we have basement without climate control . We are planning to install 5″ wide 3/4″ solid hardwood flooring in the house above that basement.
    We have installed insulation under the floor joist in that basement. Originally we had 5/8 plywood , installed extra 1/2′ new plywood on the top of it . Flooring contractors recommend ever full trout or partial trout glue/ nail down installation . I disagree. Even full trout glue/ nail down will create moisture barrier and We might have rot issues down the line.
    Yes, install will be more solid , but they care more not about rotting issues , but – they do not want to recieve a call backs for winter/summer flooring gaps/cupping/buckling and ets .
    Question – do we use full trout/ partial trout glue/nail down install or paper underlayment and nails/staples only?

  32. Alana Kane

    Hi Lizette, thanks for your question! Yes, you will still need to add a standard underlayment under your floors. Feel free to check out our standard underlayment here: https://www.bestlaminate.com/standard-3mm-underlayment/

  33. Avatar

    I’m looking to put laminate planks over tile and hardwood that is glued down, do I need to put something in between?

  34. Avatar

    Hello, underlayment is always necessary to put down underneath laminate!

  35. Avatar

    I’m looking to put laminate planks down in my living room of a manufactured home. Is underlayment necessary?

  36. Avatar

    In my opinion, just putting a vapor barrier down is like putting a bandaid on a lead. It may solve it for now, but long term will need more fixing. I would lean toward the cement, but this would be my opinion.

  37. Avatar

    Hello,

    I live in a 1930’s in the Denver area and have a unique (?) situation with a vinyl floor (Pergo with underlayment attached) I have laid in the basement. Two of the rooms have a slab that I laid the vinyl flooring on and they appear fine. The TV room had original hardwood under the carpet I ripped up and I put the vinyl in place of the carpet on the hardwood. Under the hardwood is a dirt/concrete mix of some sort that was used in 30’s. The issue I am having is now there is a bit of mold forming on top of the hardwood as any moisture from the ground is unable to escape, as it presumably did through the previous carpeting. My options are to either take it all up and lay a slab, or to put a vapor barrier down on top of the hardwood. Any thoughts?

    Much Appreciated!

  38. Alana Kane

    Hi Glen, sounds like an exciting project! For engineered hardwood, here are some good options for you: https://www.bestlaminate.com/kronoswiss-provent-3-in-1-silent-vapor-flooring-underlayment-3mm-215-sf/ or https://www.bestlaminate.com/floor-muffler-ultraseal-2mm-underlayment/. From what you’re saying, I think the Kronoswiss Provent will be perfect!

  39. Avatar

    We’re renovating an 1845 home that we lifted off its foundation and rebuilt it. The ‘basement’ will have 11’ finished ceilings. We insulated under slab (2” foam and 16 mil vapor barrier). We insulated exterior walls (blue skin/dimple board/2” foam; wrapped footings and drylocked bond from footing to walls) basement has own hvac system, top two main floors – 2 zone. Basement walls interior have 1” foam and built out 2×4 walls to get further fiberglass batt before 1/2” green board. We are encapsulating all exterior walls and roof with closed cell foam. With such a tight building envelope (also adding batt between floors for sound and to keep temps consistent)… what would be a good underlayment for an engineered hardwood? I’m leaning toward wanting the floors to ‘breath’ more as we spent a lot of effort on the exterior envelope. Any suggestions on best underlayment being used on green built homes?

  40. Avatar

    Hi Frank – We would recommend AquaBar B underlayment. It is specifically made for hardwood flooring. As for the spacing, we would recommend checking your floor’s installation guide to see what is the proper expansion gap. If it recommends 3/4″ around the perimeter of your home, you should go by the installation instructions to avoid voiding your warranty and potentially creating issues with buckling or warping of your floor because of an inappropriate expansion gap, in later years. If you have any further questions, please reply to this comment! Happy installing!

  41. Avatar

    Removing carpeting and installing 3/4 Oak Flooring strips, 2 1/4 wide. Subfloor is sob, dry and in good shape. What underlayment should be used. I sold a 3 in 1, however reading your website it seems a paper underlayment would be adequate.

    Spacing: The new baseboard is narrower than 3/4″. Can spacing be 3/8″.

    Thanks

    Frank

  42. Avatar

    Hi Bethany. I will certainly answer your question, but I have some other concerns about your installation that I would like to point out first.

    First, I would really recommend that you do not install a wood floor in an space that has no temperature regulation, unless you live in an area that is very steady in its climate and humidity. Wood flooring (laminate, solid hardwood, and engineered hardwood) will expand and contract due to temperature and humidity conditions. If you live in an area where this fluctuates dramatically with season changes, your floor could buckle or warp due to these changes – ruining your floor. Consider COREtec flooring, which is a WPC + vinyl engineered floor, which is 100% waterproof and does not expand and contract the same way that wood flooring does, making it a better option for spaces that are not temperature controlled.

    Second, is the vinyl glued down or is it floating? If it is a vinyl that was glued down, then you can go ahead and install your new floor on top if the vinyl is even. If the glued down vinyl is not even, or if your vinyl was installed as a floating vinyl, you should uninstall it and install your new floor on top of the subfloor beneath. You can read all about subfloor preparation on our Help Pages.

    Now for your original question, you can use the same type of underlayment on top of both surfaces. Now you just have to decide if you need cushioning, added warmth, or if you just need a simple vapor block.

    If you need any additional help, please feel free to email us at support@bestlaminate.com or call us at 1-800-520-0961!

  43. Avatar

    Hello

    I would like to lay a wood floor (by floating) in a cabin that is not temperature regulated throughout the year. I will be using tongue and groove pine wood. Part of the new floor will sit on top of plywood and the rest will be installed on top of vinyl. What do you recommend for vapor barrier/moisture barrier for these two different surfaces?

    Thanks

  44. Alana Kane

    Hi Margaret! The most important thing you would need to do is have a level and sturdy subfloor before installing any type of wood flooring. This would include adding OSB or plywood to your existing surface if it is not level.

  45. Avatar

    Part of our home is over 100 yr old cabin. The logs were cut with a hew. The wall are all different in dept. The floor is very cold even though there is a basement under it. Could we use a laminate flooring. Also our kitchen floor has a dip in it . The laminate floor we put down keeps pupping up. What can we do to help. Thank you

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