How To Replace Subfloor (AVOID Doing This!)

There are several reasons that a subfloor might need replacing, but in most cases, it is a result of water damage. A damaged subfloor will compromise the floor finish above it while potentially compromising the integrity of the house’s structure. It’s imperative, therefore, to replace your subfloor correctly to ensure the safety of all your home’s occupants.


The first step in replacing your subfloor will involve fixing the cause of the damage. Next, you will need to remove the floor finish and the old rotten subfloor. Once this is complete, you can start installing your new subfloor, and then you can install the floor finish of your choice.

Because most damaged subfloors result from water, your first task will be to find and repair the cause of the damage. This will prevent the new subfloor from being damaged once installed.

How To Replace Subfloor

The replacement of your subfloor is a process that involves several steps. Firstly, you will need to locate and address the water issue that has caused the damage in the first place. Only once you have located the main cause of the issue and ensured that it will not re-occur in the future can you proceed to the next steps.

Once you have removed the floor finish, you can proceed with removing the subfloor beneath it. This involves lifting up the plywood after having carefully identified the locations of all of the plumbing and electrical lines.

The next stage of replacing your subfloor will involve removing the old, damaged subfloor. This will require you to lift up the existing floor finish before proceeding. In certain cases, depending on the extent of the damage, you will not necessarily have to remove the entire floor before proceeding.

It can be difficult when replacing only a section of the subfloor to ensure that the new section and the old section are completely level. However, it can be achieved with some patience.

After carefully removing the rotting subfloor, you can clean up the edges and remove all nails or screws.

Now that you have a large hole in your floor, you need to measure how much plywood is needed for the new subfloor. In most cases, you must also add supports between the joists onto which you can attach the new subfloor. This will usually consist of pressure-treated lumber.

Once all the preparation work is done, you can start attaching your subfloor to the joists below using a combination of glue and screws to ensure secure fixing.

Fix The Source Of The Moisture

The moisture in the subfloor could result from a leak in the piping or drains. It could also be caused by water making its way through a window, door, or attic. Another major cause of moisture in the subflooring is the dampness that moves up from the ground. A plumber can help you to find and repair these issues.

If the subfloor rotted due to moisture making its way up from the ground, there are several ways to address the problem. Firstly, you can install a fan to increase the airflow in the crawlspace and reduce moisture overall.

Alternatively, you can redirect water away from the house through gutters and downpipes. Another option is to install a vapor barrier underneath the house’s floor. This will prevent moisture from making its way up into the subfloor from below.

Get Rid Of Rotten Subfloor

Perhaps the easiest way to remove your old subfloor is to cut it out one section at a time using a circular saw. You will first need to check the locations of any existing plumbing and electrical lines. You will also need to ensure that you don’t cut into the joists below the subfloor. This is extremely important, as the integrity of the joists will ensure the integrity of the entire floor structure.

By cutting the subfloor out one small section at a time, you will also make it far easier to transport the wood when throwing it out. Next, you will need to remove all the screws or nails fixing the old subfloor to the joists below.

It will also be extremely helpful to clean up the edges of the subfloor along the walls before proceeding. This can be done by using a reciprocating saw.

There are some materials that can help to waterproof your floors. This is essential if you install flooring near a shower.

Prepare For The New Subfloor Installation

To ensure sufficient support for the new subfloor, you must add additional lumber between the joists. Next, you must ensure that the joists are completely level.

Install Your New Subfloor: nails or screws

Once you have measured the area to determine the amount of plywood required, you can start placing as many full boards as possible. These should be placed perpendicular to the joists with the edges centered in the middle of the joists.

To prevent squeaking floors, add a bead of glue across each joist, ensuring that the subfloor doesn’t separate from the joists. Use 2” deck screws to fix the subfloor properly to the joists. Ensure that you leave a gap of 1/8” between plywood sections to allow for natural expansion.

You can use nails or screws for a subfloor (check your local code though!). Using nails goes a lot faster if you have a nail gun. Some professionals prefer to use screws though as they think that it is more stable. The materials that you work with also affect how easy it will be to work with nails or screws. If you use wide wood panels, screws might be easier as a nail gun might struggle with this. In the end, it all comes down to your preferences. Nails can lead to squeaky floors over time but they are faster to install.

Once you have filled the area with as many full pieces of plywood as possible, you will need to cut the remaining boards to fill the rest of the space. Once this is complete, your subfloor is ready to install the new floor finish.

Subfloor or drywall first? Subfloor before or after plumbing?

You might be preparing a renovation project and wondering if you should install the subfloor or drywall first. In most instances, the answer is to install the subfloor first. This will make it easier to install the drywall as you have a floor to walk on. Furthermore, the drywall might get dirty if you install the subfloor after this.

The plumbing rough-in should happen before installing the subfloor. This provides the plumber with more access and makes everything easier. Some of the final plumbing installations might happen after you have installed the subfloor though. Drains have to be installed precisely. This is why plumbers need a lot of space.

We don’t want to deal with damaged or dirty drywall so fixing the subfloor before you install the drywall is the way to go. We have outlined how you can carry drywall here.

If you work with different contractors, you have to make sure that you schedule them in the right order. This will avoid problems down the road.

Signs Your Subfloor Needs Replacing

There are several signs that your subfloor needs replacing. Because the subfloor is located below your floor finish, it is naturally more difficult to see if there are issues with it. As a result, you should pay attention to telltale signs of a failing subfloor.

If the floor squeaks or bounces significantly when you walk on it, this is a sure sign that there is an issue with the subfloor. Sinking sections of flooring will also naturally be a major sign that the subfloor is potentially failing. Your floorboards can become cupped, which is another sign that moisture is affecting the flooring, which in most cases means the subfloor is affected too.

Some other signs of a failing subfloor to look out for include a musty smell, bubbling linoleum, and leaking ceilings. In the case of tiled floors, any cracking or popping up of the tiles will be a sure sign of a subfloor issue that needs to be addressed.

Below are some tips on how to install subfloor on concrete:

How long can the subfloor be exposed?

The subfloor should get covered as soon as possible. Some people wait a while before they do this. You can technically live on a subfloor for a few months if you cover it properly. Check your local code though as this might not be allowed in your area.

It also increases the chances of damage. Subfloors shouldn’t get wet. During hot summers, moisture can build up around them as well and this can lead to mold.

For this reason, you should close the subfloor as soon as you can and only wait with this if you really can’t move forward faster. You have to be careful that you don’t damage the subfloor or plumbing systems in the meanwhile.


Replacing your subfloor may initially seem like an exceptionally daunting task, especially if you do not have a significant amount of prior DIY experience. However, by carefully following the guidelines mentioned above, you will be able to replace your subfloor without any major issues. It may be the perfect opportunity to install the floor finish you’ve always dreamed of.