Can You Install Drywall Over OSB? (Explained)

Drywall is the go-to material for building walls and ceilings. It comprises large rigid sheets that can be used to finish interior walls. Drywall is pretty easy to install and durable. Therefore you will find it in many homes these days.

On the other hand, OSB is a versatile engineered wood panel that can be used a wall sheathing, roof cover, floor underlayment, and even I-joists.

Considering that these two materials are used in the same place, one may wonder if it’s possible to install drywall over OSB.

This will be the focus of our discussion, and we will explore everything you need to know about installing drywall over OSB.


Is Installing Drywall Over OSB Possible?

You can install drywall over OSB. It’s a popular practice amongst both professional contractors and DIY builders. With OSB at the back, it will create reinforced support for drywall to be hung on.

Even though it’s doable, there are some risks and concerns associated with installing drywall over OSB. But before we look at these risks, let us highlight why you may consider installing drywall over OSB.

Reasons You May Be Interested in Installing Drywall Over OSB

1. You Prefer a Drywall Finish

The most common reason you may install drywall over OSB is that you want the finish of the former material. We can all agree that drywall leaves an impressive and smooth finish. Therefore, if you have moved to a home with an OSB floor, you may hang drywall to change the finish.

Hanging drywall over OSB is way easier than removing the OSB and then screwing the drywall directly to the joists.

2. You Want a More Rigid Wall

Nowadays, it’s become a standard practice for contractors to hang drywall directly to joists. Some builders refer to such structures as doll houses because the walls lack adequate support. When comparing the toughness between these two materials, drywall is no match for OSB.

With OSB at the back of your drywall, your walls will be more rigid and durable. If you are interested in reinforcing the structure of your walls or ceilings, you can install drywall over OSB. OSB behind drywall also makes it easier to fix the latter.

3. You are Interested in Enjoying the Insulation Properties of OSB

Besides improving your walls’ structural strength, OSB is also an excellent insulating material. OSB that has been properly installed in a wall will offer unrivaled insulation and air tightness.

Therefore, your room will be much warmer and your energy bills won’t be so high. If you live in an area that experiences cold weather, you should consider installing drywall over OSB.

4. You Want to Increase the Load Bearing Capacity of Your Walls

Another reason you may install drywall over OSB is to increase the load-bearing capacity of your walls. This mostly applies to commercial buildings or garages. Do you plan on hanging tools on a wall or mounting heavy fixtures?

Some mounts or tools can be too heavy to be held by drywall. That is why installing an OSB board behind will increase the structural load resistance of your wall. In this case, the mounted objects will be screwed past the drywall and to the studs behind the OSB.

These are all benefits that you can get from installing drywall over OSB. However, there are a couple of risk factors you need to keep in mind.

What Risks are Involved in Installing Drywall Over OSB?

1. OSB Expands and Contracts When Exposed to Moisture

OSB isn’t very different from other wood products. It’s still susceptible to expansion and contraction when used in high-moisture areas.

Assuming that you install drywall over OSB in a high-moisture room such as a shower or kitchen. There is a good chance that the OSB will damage the drywall as it expands. Therefore, resulting in drywall failure.

You need to be mindful of where you install drywall over OSB. The best place is a room that doesn’t experience a lot of moisture.

Alternatively, you may opt for water-resistant drywall instead of regular one. A good example would be green drywall. It’s also advisable not to tightly butt the drywall against the OSB. You should leave some room for expansion.

2. OSB Can Increase the Fire Potential of Your Walls

When you add OSB to your walls, you increase the fire potential because more materials will burn. OSB is flammable, like other wood materials.

There is no prevention or loophole on how you can avoid this. It’s something that you only need to keep in mind.

3. Mold May Develop on the OSB

If there is a lot of moisture passing through the walls, sandwiching OSB with drywall may create the perfect breeding ground for mold.

This is why I emphasize the importance of installing drywall over OSB in areas that experience little moisture. Because the mold growing on the OSB will be concealed by the drywall, it may take years for you to notice it.

4. It Will Extend Your Jambs

Another drawback of adding drywall over OSB is that it will affect your window and door trim. The extra sheet of drywall will extend the thickness of the walls. Therefore, you may have to do something about the door jambs.

Interior construction of housing project with drywall installed and patched without painting applied interior with drywall installation and construction work in progress

What Type of Drywall is Best for Installing Over OSB?

That will depend on the conditions experienced in that particular room. As you already know, there are different types of drywalls.

If you want to install it over OSB, you need to evaluate the moisture levels within that room. Take a shower, for example.

If you want to install drywall over OSB in such a high moisture area, you must use moisture-resistant drywall, such as the green version. It’s also advisable to invest in a waterproofing product such as RedGard.

However, if you are installing drywall on OSB in the living room or bedroom, you will do just fine with regular drywall. Before beginning this project, you must identify which type of drywall is best.

Can You Install Drywall Over Damaged OSB?

No, you shouldn’t. Drywall should only be installed on a structurally sound surface. If the OSB you plan to install drywall over is moist, spongy, or damaged, the screws won’t stick, and the drywall can fall off at any time. Installing drywall over damaged OSB is a huge risk and a hazard to homeowners and their families.

If the OSB is damaged, replace it with another. Or take it off and install the drywall directly to the studs without any OSB on the back.

Which Screws Should I Use to Install Drywall Over OSB?

Regular drywall screws can get the job done. But I would recommend longer drywall screws so they can pierce through the drywall, OSB, and the studs.

You will have a more structurally sound surface when you screw all these three materials together. After installing the OSB, you can mark the studs’ location for easier screwing.

Alternatively, you can screw the OSB first and then screw the drywall on top. You need to use the recommended screws because drywall is brittle. When you use regular screws, you risk damaging the drywall.

Why Do Some Builders Install OSB Behind Drywall?

In some scenarios, you may move into a new home and discover OSB behind the drywall. And be left questioning what is the reason why builders install OSB behind drywall.

It could be any of the four reasons we have listed earlier. However, in your case, the builder could be attempting to build a shear wall.

The presence of OSB can offer more structural support, thus enabling the walls to resist side-to-side forces.

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