Replace a Bathroom Subfloor

If your bathroom subfloor is plywood, chances are that at one point or the other you are going to have some water damage to it.

Why? Think of all the possibilities for a water leak in a bathroom – sink leaks, bathtub overflows, toilet overflows or leaking wax ring; you get the idea. When this happens, your choice is obvious. You must know how to replace a bathroom subfloor.

First Things First – Dismantle the Bathroom

The bathroom is a fairly small area to hold so many devices. Consider, a bathtub/shower, a toilet, a sink, etc. The first thing to do is remove all of these things. Leave the bathtub for last. You don’t want to fool with that if the subfloor around it is stable.

You will also want to take up your existing finish flooring, obviously. Chances of saving anything here are minimal so don’t waste your time on it. Just rip it up!

Get some help getting the toilet out. These things are so heavy and awkward you can strain your back. If you have a large vanity you may be able to set it in the tub. Or, if the subfloor is stable around it leave it in.

Survey the Subfloor Damage

Is it just one spot of the subfloor that went bad? If it is a small section you may get away with a patch job. If the damage is large enough it will warrant ripping up and replacing it all (other than the areas we discussed previously).

Remove the Subfloor

Mark out the lines you will be cutting with a chalk line. If you keep your cuts square you will be simplifying the task of installing the new subfloor.
To remove the subfloor you will need a circular saw, safety glasses, a claw hammer, a crowbar, and a chisel.

Begin by cutting out the subfloor with the circular saw. Take caution not to run over any nails. Set the depth of the blade just a hair deeper than the thickness of the subfloor. Get out as much as you can with the saw. At some point you will have to resort to the hammer and chisel.

When cutting parallel to a floor joist, cut down the center of one so you will have something to nail to. Pull these nails so you will not cut through them with the saw.

After the subfloor is out, take a look at the floor joists. If any are damaged you will have to sister them. Remember to use the same size and length of lumber as the one you connect to.

Install the New Subfloor

Now it is time to reinstall your bathroom subfloor. If you are planning to go back with ceramic tile as a finish floor, consider installing backer board and skimming it with thin set.

Otherwise, use either pressure treated or marine plywood of the same thickness as the original. Nail down or screw with deck screws? I prefer the screws. They have a better hold and are more moisture tolerant.

Once that task is done, install the finish floor of your choice. Just remember that laminate flooring is not a choice in a bathroom environment. If you want that look use real wood and two coats of polyurethane.

Finally, put the vanity, toilet, and anything else back in place. Don’t forget to use a new wax ring on the toilet!