When you are installing a finished flooring like hardwood or carpeting, you will need an underlayment.
Underlayment smooths out imperfections in the subfloor and gives you a solid base to lay flooring onto. By adding this layer, you can be sure that your finished flooring will be level and even.
Underlayment can also help protect the finished flooring from moisture, mold, and mildew.
Plywood is a great underlayment to install over a subfloor. It is strong and durable and often very smooth without a lot of imperfections or knots.
Key Takeaways
Here are the basic steps:
- Choose plywood made from multiple strands if possible.
- Remove the molding and baseboards and remember where they went.
- Sweep and dust your subfloor and remove moisture. Check for cracks.
- Bring plywood into the room so it can acclimatize. Leave for 72 hours to avoid swollen flooring.
- Lay the plywood on the subfloor with screws 18 inches apart.
- Leave around an eighth-inch between the wall and underlayment.
Installing Plywood Over a Subfloor: Basic Idea
Installing plywood over a subfloor is relatively simple and doesn’t require much expertise. However, there are a few steps that you should follow to make sure it’s done properly.
These steps are:
- Remove baseboards and other trim
- Prepare the subfloor
- Acclimatize the plywood underlayment
- Lay down the underlayment
Best Type of Plywood for Installing Over a Subfloor
There are a few different types of plywood and you will have to choose one for your underlayment. Knowing what these different types are made of and how they perform can help you make your decision.
Instead, you can use plywood that has been put together with several different strands of wood. These strands are glued or waxed together and then pressed into boards.
This type is called OSB, or oriented strand board. While it is not as pretty as standard plywood, it is still fairly strong and will make a good underlayment.
Since you are not going to be seeing this underlayment, it doesn’t really matter what it looks like. You’ll be better off saving a few dollars and using OSB, then installing your finished floor.
Remove Baseboards and Moulding
Your first step to installing plywood over your subfloor is to remove any pieces of trim. Depending on how high your plywood is, you may have to reinstall these pieces.
For example, your baseboards may have to be reinstalled ¾” higher than they were. This is to accommodate the height of the plywood underlayment.
Be sure to remember which trim and moulding pieces go where. This will help you when you go to reinstall them.
Prepare the Subfloor
After you have removed all the trim pieces, you will have to prepare your subfloor.
Generally, this means sweeping and making sure that all dust and debris is removed. If this isn’t done, you could end up with an uneven underlayment that isn’t level with the subfloor.
Advice from the Expert: In my experience, always double-check your measurements before you start installing the underlayment. And remember, it’s better to cut slightly big than too small – you can always trim excess later, but you can’t add more if you cut it too short. Don’t forget to account for the expansion gap
You should also take the time to make sure that there is no moisture that has seeped up.
Sometimes, groundwater can make its way through the subfloor over time. Make sure any moisture is dry before installing the underlayment.
Acclimatize the Plywood
After you have prepared the subfloor, you should acclimatize your plywood. This means bringing the wood into the room and letting it get used to the climate.
Advice from the Expert: One important point I want to emphasize is the need to let your plywood acclimate to your room’s climate before installation. I’ve seen many instances where skipping this step resulted in warped flooring. It might take a day or two, but trust me, it will save you a lot of trouble in the long run.
This is an all-important step. Because plywood is sensitive to things like moisture and temperature, it tends to change with fluctuations.
Bringing the plywood into the room where it will be laid down will help it get used to the atmosphere.
If this step is ignored, you could end up with cracked or swollen flooring after installation.
Lay Down the Plywood
Now that the wood is acclimatized, you can install it.
You should also make sure that you are leaving about ⅛” between the underlayment and the wall. This will give the wood room to breathe if it needs to and prevent the finished flooring from warping.
Advice from the Expert: I always recommend screwing the plywood onto the subfloor, as mentioned in the guide. I attempted nailing in the past, but nails have a tendency to pop out over time, causing all sorts of problems. Screws might take a bit longer to install, but the peace of mind is worth it. Also, use screws specifically designed for subfloor installation – they’ll have a coating designed to prevent rust, which is vital in high-moisture areas like bathrooms or kitchens.
After your underlayment is installed, you are ready to lay down your carpeting, tile, or hardwood flooring.
F.A.Q.
- Is MDF stronger than plywood?
MDF is not stronger than plywood. MDF is made of many particles that are pressed together.
Plywood, on the other hand, is made of long sheets that have a more cohesive structure.
- How can I waterproof plywood?
You can waterproof plywood by sealing it with an epoxy sealant.
While you don’t need to do this if you are using plywood as an underlayment, you absolutely can. If nothing else, it will help block moisture from coming up through the top or getting underneath.
- Is it better to nail or screw a subfloor?
It is always better to screw in a subfloor. Nails do not stand up to warping very well.
Screws give a better hold and your local building codes may even require their use.
Conclusion
Installing a plywood underlayment over a subfloor is a great way to give your flooring a solid base. It can give you many more years of longevity with your floor.
By following the above steps, you can be sure it’s done correctly and won’t warp or crack over time.
