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Do Hardwood Floors Need Moisture Barrier?

by Bob and Betsy
51 comments 5 minutes read

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

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.


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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Beth Geiger March 11, 2023 - 6:21 am

I need help and advice on installing a vinyl floor or linoleum tile in my kitchen. I have already removed eight layers of the linoleum sheets. It is a unfinished hardwood floor. I would like to know what is the best subfloor I can use. I would like it to be water resistant and easy to clean. What would you recommend?

Rachel Vahcic March 13, 2023 - 3:58 pm

Thanks for your question, Beth. We would suggest installing a vinyl plank flooring in your kitchen because of all the amazing qualities it has! Vinyl flooring is 100% waterproof, extremely durable, and it is beautiful! You can also install vinyl plank flooring directly over your existing hardwood flooring.

John January 6, 2023 - 6:06 pm

Flooring option – Damp subfloor – PLZ HELP
HI guys, I have an old house ~100 years old and it has a front verandah converted into an indoor space – like a study.

It currently has a carpet, and when checked underneath, the subfloor timber (pinewood) is damp. I am getting mechanical subfloor ventilation installed for the whole subfloor but even then, I was told that this converted verandah will likely stay a bit damp (better than now however).

My question is, what will be the best flooring option when the subfloor might continue to be a bit damper than usual ?

One of the flooring guy suggested possibly hybrid flooring +/- subfloor insulation but I do not know whether this is a good idea as I am afraid it will trap moisture ? I do not know how it works.

Please help/advise !! Thanks

Rachel Vahcic January 11, 2023 - 11:08 am

Thank you for your question, John. We would suggest correcting any moisture from subfloor before laying any type of floating flooring. Placing a new subfloor can help with this. After the subfloor is fixed and tested for moisture, vinyl plank flooring would be a great option for a room like this. Trying to work around the subfloor may lead to future issues so we would advise to get the subfloor replaced for best results.

Stephen in Texas October 2, 2022 - 12:45 pm

Hi, Thank you for the great article. Here’s a question I hope you cna answer. Our 2 car attached garage was converted into a living space by the previous owner. Unfortunatley the PO did not use a vapor barrierm and used regular yellow pine for sleepers, and untreated OSB for decking. Within a couple of years the moisture trapped in the bubflooring caused all of the wood to compeltely rot. So, we are ripping the old floor up and starting from scratch. The garage floor has a 2.5″ stepdown coming out of the house, which tapers to 4″5″ at the gagage doors. I have already put a 6 mil vapor barrier down, then we put sleepers down (ground contact 2-by ripped to provide a even surface), then 3/4 ground contact plywood on top. The sleepers are attached directly to the concrete via concrete anchors. QUestion is, does that all sound ok, and do we need another vapor barier between the wood sub-floor and the finsh floor (floating laminate type).

Thank You,

Rachel Vahcic October 14, 2022 - 3:11 pm

Thanks for your question, Stephen. The vapor barrier is only essential over a concrete subfloor. You would be okay to install flooring on top of plywood without a vapor barrier, as long as you use underlayment or it has an attached underlayment. However, it is not recommended to install any floating floor in an area that is not temperature controlled. As long as this garage space has a controlled temperature, you are good to go!

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