How Do I Know If There Is Water Damage Under My Bathroom Floor?

Short answer The most reliable signs are a soft or bouncy floor around the toilet or tub, a toilet that rocks, tile that cracks or comes loose, and stains on the ceiling below. If you see two or more of them, the subfloor is probably wet or already soft, and it is cheaper to open it now than after the rot reaches the joists.

The signs, from most to least serious

Soft or bouncy floor at the toilet or tub. Stand next to the toilet and shift your weight. If the floor gives, the plywood under the tile has been wet for a while.
A toilet that rocks. A failed wax seal leaks a little with every flush. The toilet starts to rock because the floor under it is no longer solid.
Stains on the ceiling below. A brown ring under the bathroom means water has already passed through the whole floor.
Loose, hollow or cracked tile. Tile cracks when the floor under it moves. Grout that keeps falling out of the same joints is the same signal.
Swollen baseboard or peeling paint at the bottom of the walls, usually near the tub or the toilet.
A musty smell that comes back a day after you clean.
Gaps between the tub and the floor or wall. Open caulk joints let shower water run down behind the tub every day.

One sign alone can be cosmetic. Two or more in the same corner of the room usually mean water is getting in.

What you can check yourself

Press the floor with your heel around the toilet, in front of the tub and at the shower curb. Push on the sides of the toilet bowl and see if it moves. Run a screwdriver handle along the tile and listen for a hollow sound.

Many Bay Area homes sit on a raised foundation with a crawl space. If yours does, look up at the bathroom from below with a flashlight. Dark or stained wood, white fuzz, or wood that a screwdriver sinks into are signs of rot. Do not go into a crawl space you are not comfortable in; we can look during a site visit.

Why waiting costs more

Water damage moves in one direction. First it soaks the subfloor, then it rots it, then it reaches the joists that hold up the floor. Replacing a section of plywood is a modest line in an estimate. Repairing or sistering joists adds framing work, more days and sometimes a permit. The tile on top has to come up in either case, so waiting does not save the tile.

What the repair involves

We remove the toilet and the tile around the damage, cut out wet or soft subfloor back to solid wood, and check the joists. Rotted framing is repaired the same way we repair dry rot on decks and balconies. Then we find and fix the source: the wax seal, a supply line, the shower pan or the caulk. New subfloor goes down only after everything is dry.

If we find more damage than the estimate covered, I photograph it and send you a price before anyone continues.

What we found under an older bathroom once the floor was open: old drain lines in the crawl space (left) and a corroded cast-iron fitting (right).

When a small repair is enough

If the floor is solid and the only problem is open caulk or a loose grab bar, you do not need a remodel. Jobs under $1,000 go through KST Handyman, our small-jobs service: $150 for the first hour, $100 for each hour after, materials at cost. If the floor is soft, re-caulking only hides the problem, and I will tell you so.

Can I just replace the wax ring?

If the floor around the toilet is still solid, yes, and that is a small job. If the floor gives when you stand next to the toilet, a new wax ring will not seal on a soft flange for long. The subfloor has to be repaired first.

Does a soft floor mean I need a full remodel?

Not always. A small soft area by the toilet can often be repaired with new tile in that section. If the damage runs under the tub or the shower, or the tile cannot be matched, a remodel is usually the more sensible spend. Send 2 or 3 photos and I will tell you which one it looks like.

How do I know if there is water damage under my bathroom floor?