If you find that your bathroom floor has rotted through, you will need to replace it. Sure, it will take you some work, but the end result is well worth the effort. Pick a time to do it, when the bathroom traffic will be lighter, like during the summer months when people are outside more, if possible, and get started. Here are a few tips to move the project in the right direction.
Turn off all the water to the bathroom. Remove all the bathroom fixtures including the toilet, sink, bathtub (if it is sitting on the floor) and shower stall. Save what you can of the appliances after cleaning them. Store them in your garage or spare room until ready for use.
Remove the old wax ring from the toilet drain and clean up around it. Place a rag in the opening to keep sewer odors from entering the room. Cover your sink and tub drains with an old sock or rag to keep debris from falling into them.
Rip out the old flooring. Use a crowbar, a hammer and lots of elbow grease to pull everything up until you get down to the studs. Make sure you wear good work gloves, eye protection and a dust mask, since you don't want to be breathing in the dust. Pull out any old nails that may be sticking out of the rafters. Try to save the walls from being damaged.
Vacuum and pick up all the debris that has fallen between the rafters. This is a good time to check on the insulation in the floor as well as the plumbing and any exposed wiring. Although you will probably find more damage if your floor was rotted, we will assume that only the floor has to be replaced.
Measure the floor and draw an outline of the room. Calculate the square footage by measuring the width and then multiplying it by the length of the room. This is how much plywood you will need to purchase.
Cut the plywood to fit your floor. Don't go cheap and by thinner plywood as you will need the support to hold the heavy appliances. You may have to use a jig saw to cut the holes for the plumbing and always measure twice before cutting.
Screw the plywood to the rafters or floor beams, sinking the screws into the wood. Once the plywood is firmly attached, you can decide what direction to go in next, depending on what kind of flooring you are planning on using. You may have to use a thin sheet of luan over the plywood to form a smooth surface for vinyl or vinyl tiled floors.