What are acceptable moisture levels in a subfloor?

When it comes to installing floors, whether it is carpet or hardwood, you must make sure that the floor beneath your flooring, known as the subfloor, is at an acceptable moisture level. If it is too damp, this can lead to problems such as mold and mildew if you have carpet and warping, crowning, or cupping if you have hardwood installed. So, what is an acceptable moisture level for subfloors?

Your subfloor moisture level should be no greater than seven to nine percent when you are installing flooring. You can check for moisture by using a moisture meter. Since your subfloor may be concrete or wood, you should make sure you choose a meter that is specially designed for the specific element you are testing.

acceptable moisture levels in subfloor

It is essential to check for acceptable moisture levels with the subfloor before installing your flooring to prevent problems later once your flooring starts to expand and contract. But it is also important to keep floors moisture-free long after your carpet, hardwood, or tile flooring is installed. Ensure that spills or leaks are addressed as soon as possible so that the moisture from them won’t damage the subfloor, too.


How Subflooring Started

Subfloors weren’t always a part of the flooring process. In the past, homeowners would just have hardwood nailed directly into the joists without adding subfloor. Prior to the wide use of subfloors, homeowners would get the wood floor installed using tongue and groove wood flooring. This technique, made popular in 1885, uses interlocking pieces of wood, one with a tongue section that sticks out on one side of the wood and an opening on the other side of the wood. The tongue of another piece fits into the opening of another piece of wood.

For added security, the installer may tap the wood with a mallet to make sure the pieces fit firmly. Although the pieces are secured, the installer will still add a nail to ensure that the tongue and groove stay firmly in place.

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Plywood subfloors became more popular around the 1940s and 1950s and have been the subfloor material of choice. Oriented Strand Board (OSB) subfloors became popular in the 1970s. Although plywood remains the material of choice, the OSB board is much less expensive and more water-resistant.

Subfloors aren’t just a layer of the floor that is there for decorative purposes. It functions as a means of keeping you and your furniture and appliances from falling through the floor. Imagine laying carpet over joists alone. As a matter of fact, don’t imagine that because the thought of it is just as dangerous as the reality of it. Subfloors are thick and sturdy enough to support the weight of you and your furniture and support your flooring type, whether it is carpet, tile, vinyl, or hardwood.

How to Know It’s Time To Replace Your Subfloors

If you are planning a DIY flooring installation, you must not proceed with the project without making sure that your subfloor is good to go. Of course, you may be anxious to get rid of the dust-ridden, allergy-causing carpet that has been spreading germs around for years. However, replacing your floors with tile or hardwood isn’t as simple as removing the carpet and laying the new flooring down.

If you don’t know much about flooring, it may be best to hire a contractor. But if you want to go at the project on your own, here are some things to keep in mind about subfloor problems so you won’t end up covering them up instead of fixing them.

Your Floors Make You Feel Like You’re On a Kid’s Playground Slide

Clearly, this point is intended to make you laugh because if your floors feel like this, you may have more than subfloor issues. Your entire house may be about to cave in any second! But if you feel that there is a shift from one side of the room to the next, there is a problem.

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A quick test you can use to check for imbalance is to take a marble or something else small that rolls and sit it on the floor. If it moves without the help of any force, then your floor is uneven. Although replacing the subfloor may seem like bad news, in this instance could be good news. Far worse news will be if your house is unlevel. This problem could be far more expensive than replacing the subfloor because an unlevel house is usually associated with the foundation.

Squeaking Is Driving You Crazy

It’s natural to hear a slight squeaking with floorboards over time. However, if your floorboards sound like a symphony of odd noises every time you take a step, then you probably have bad subfloors that should be replaced. The squeaking that you hear will also be very loud. This noise that you hear is the warped subfloor rubbing against nails that have come undone.

Moisture is Causing All Kinds of Issues

If your subfloor needs to be replaced, you definitely will know if it is due to a moisture problem. For one, it will probably show because your hardwood floors may warp, cup, or crown. Another noticeable sign of a moisture issue with your subfloor will be a musty smell.

What Moist Subfloors Can Do To Your Flooring

Upon learning the signs of bad subfloors, you may have concluded that it’s time to get new ones. Therefore, you opt to get plywood subfloors to replace your damaged ones. However, when installing your new subfloors, you can’t just nail them into the joist and then immediately start laying your hardwood or carpet.

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You have to make sure that your new subfloors are at an acceptable moisture level before laying your new flooring on top. Or, within a short time, you will be facing the same problems you had before removing the old subfloor. Laying new carpet or hardwood over a new subfloor that is not dry enough will trap moisture between the plywood and the flooring and cause the hardwood to buckle and the carpet to start growing mildew or mold.

If your subfloor happens to be concrete, moisture can also be a problem. Although concrete seems like a dry substance, it can form condensation on it that is referred to as concrete sweating. The moisture from the concrete can cause the same problems that a wood subfloor can cause.

How to Check For Subfloor Moisture

To ensure that your subfloor is within the appropriate range of seven to nine percent, you will need to use a moisture meter. It is essential to get one for plywood if you are installing a wood subfloor or one for concrete if your subfloor is concrete. You should check the moisture variance by taking 20 readings every 1000 square feet. Once the subfloor is within the range for these readings, you can proceed with installing your new flooring.

If you can’t seem to get all your readings within the same range, it may be best for you to dry out the subfloor before installing your flooring. You can use fans or space heaters to bring the subfloor within acceptable ranges. Make sure that you keep the area aerated by opening windows or using a dehumidifier during this process so that the moisture isn’t going into the air and being redistributed back into the floor or into your drywall.