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Can You Use OSB For Subfloor? (How To)

When doing any flooring project, some attention must be given to the subfloor. Is it okay to use OSB as the subfloor material?

OSB is suitable for subfloor under tile, hardwood, and carpeting. Maintaining a 1/8-inch gap between the panels is essential, as any moisture could cause the OSB edges to swell, resulting in buckling.

Man working on the OSB

A few options are available for the subfloor, and it is always of concern to the homeowner as to which one will be used. OSB is a good choice because it is good quality and less expensive than plywood.

As a flooring contractor, I often get asked about using OSB because many assume they must use plywood. OSB got a bad reputation when manufacturers started making it, but it has come a long way since then.

The OSB subfloor panels have a tongue and groove and are easy to install. As long as you continue to maintain a gap to allow for swelling, OSB can be used to save money and provide you with a quality subfloor.

It is a good idea to look at other options. The primary option compared to OSB is plywood. The main difference between the two is cost, but they are also made differently.

Plywood is made from thin sheets of veneer attached in layers using adhesive. Different types of wood are used for plywood, resulting in various grades of plywood.

OSB, which is short for oriented strand board, uses smaller pieces of wood, which are the strands, and glues them together using a compression method. OSB is usually made with softer wood but can also be made using hardwood.

Ultimately, you have a much more consistent product when you use OSB. It also can be more durable than plywood, as lower-grade plywood may have knot holes that could be problematic.

When you use OSB as a subfloor, you don’t have to worry about special preparation before applying it. It is applied to the floor similarly to plywood or any other material. We will discuss that further in this article.

You also have the advantage of better insulation, which is less important in an interior application. It can reduce heat transfer between floors, affecting your energy bill.

Essentially, the OSB used for the subfloor has the approval of The Engineered Wood Association, the APA. They consider OSB very similar to plywood, so you can use it as a building material without concern.

Should You Use OSB For a Subfloor?

Man working on the OSB

Now that we have established that OSB is suitable as a subfloor, it’s important to consider some issues that can also arise. These are not going to be a problem in every installation, but they could be problematic in the right situation.

Moisture – One of the most significant issues with OSB is that it soaks in water and holds onto it for a long time. This isn’t as big of a problem in an interior setting, but changes in humidity or any accidental flooding could be problematic.

It’s important to note that both OSB and plywood absorb water. Plywood absorbs water much faster than OSB but also releases it faster.

This isn’t something that will be of big concern to anyone installing OSB as a subfloor for an interior floor. At the same time, however, you should never install wet OSB and then put the flooring down without giving it adequate time to dry.

Swelling – Moisture can cause multiple issues with OSB, including swelling. Swelling is also an issue with OSB. Both OSB and plywood swell, but plywood swells evenly across the entire board, while OSB tends to swell on the edges.

That is why it is recommended to leave a 1/8-inch gap when installing OSB as a subfloor. The actual OSB subfloor that has tongue and groove allows for it.

If the edges of the OSB swell, they will not return to their original shape and size after the wood dries. This is perhaps the biggest downfall of OSB, but it will rarely cause problems in flooring.

Strength – When you compare the strength of plywood and OSB, plywood will come out on top. The strength of OSB is not typically a problem with a subfloor application, but it is something to consider, depending on how you will be using the room.

Loads – OSB provides plenty of strength when handling loads but still does not handle loads in the same way as plywood. If you use it as a subfloor in areas with heavy loads, you may need to change to plywood.

This is more of an issue when using OSB for roofing or other types of material. Even then, OSB provides a suitable material for all of your construction needs.

Weight – This is another thing to consider, and it may be a problem, depending on how you attach the OSB.

Copyright article owner is ReadyToDiy.com for this article. This post was first published on March 25, 2023.

Keep in mind that there are limits as to how much weight can be handled by the floor joists. If you are stacking floors rather than removing the old floor, you will add extra weight if you use OSB compared to plywood.

If you are running close to the limit, switching to plywood or another lightweight material may be best. You might also consider removing the old floor, which has benefits as well.

What Preparations Do You Need To Use OSB For Subfloor

Man working on the OSB

We will now consider some ways to prepare for an OSB subfloor. When you prepare correctly, you can get through the job and do so in the best way possible.

1. Check the Moisture – If you don’t have a moisture reader, it’s a good idea to obtain one. You should check the moisture of the existing floor and the OSB before installing it.

Installing OSB over a high moisture area can be problematic because the OSB edges would swell. You also must allow sufficient time for the OSB to dry if it has become saturated.

2. Check the Building Code – Before doing any construction project at home, it’s essential to check with the local AHJ and any building codes. You might be surprised to learn that they have something to say about the type of subfloor you can use.

In a stable area, it is perfectly acceptable to use OSB. That being said, you may still see a lot of plywood subfloors once you start looking into it.

3. Preparing Loose Areas – If you are installing OSB as a subfloor over an existing floor, such as plywood or hardwood, you need to tighten things up in advance. If there are any squeaks or creeks in the existing floor, they will simply transfer through the OSB.

Work your way around the room and check for any loose areas. These should be fixed before installing the new subfloor.

4. High Spots and Low Spots – Any high points or low points in the existing floor should be leveled out before you install the OSB subfloor.

The easiest way to fix a low spot is to float the floor with some flooring compound. As flooring contractors, we always preferred Ardex, a well-known and quality product.

High spots can typically be sanded down.

5. Clean and Clean Again – Check the floor for any loose screws or nails that may be slightly protruding. You should then sweep the floor clean and sweep it again.

When you have the floor perfectly clean, you will have fewer issues after installing the OSB subfloor.

How To Use OSB For Subfloor

OSB Board

Now that everything is prepared, you can install your new subfloor and finish your project. Take the following steps when doing so:

1. Use Construction Adhesive – It is essential to use suitable nails or screws when attaching the subfloor. It would be best if you also used construction adhesive to attach it to the area underneath, such as floor joists or an existing subfloor.

The construction adhesive will form a strong bond and keep the OSB from shifting or lifting.

2. Use Tongue and Groove – True OSB subfloor is tongue and groove, making it much easier to install the subfloor properly. You should use the tongue and groove as intended but also allow for the 1/8 inch gap between panels in case they get wet and swell on the edges.

3. Stagger – Be cautious not to set up a pattern that would weaken the subfloor. Staggering the panels on the existing joists makes it a much stronger subfloor that will stand the test of time.

4. Attach – Attach the OSB subfloor using 10d nails or a #10 wood screw. It would also be appropriate to check with the manufacturer for any suggestions they have on how to attach the floor. Always follow the manufacturer’s directions.

OSB is an excellent choice for a subfloor if you leave a 1/8-inch gap between panels for any swelling. You can save money using OSB, but it also is a strong material that works well under hardwood, tile, and carpeting.f

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ReadyToDIY is the owner of this article. This post was published on March 25, 2023.

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