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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!

21 comments

  1. 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

    • 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!

      • 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!

        • 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!

  2. 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?

    • 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.

  3. Avatar

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

  4. Avatar

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

  5. 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!

    • Tyler

      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.

  6. 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?

  7. 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

    • 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!

  8. 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

    • 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!

  9. 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

    • 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.

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