Bathroom leaking through the ceiling below

First, make it safe

• Electricity. If water is coming through or near a light fitting, fan or smoke alarm, switch off that circuit at the breaker panel. Do not touch the fitting or the switch while it is wet.
• A bulging ceiling. Drywall holding water can come down. Keep people out from under it. With the power to the room off, a small hole made at the lowest point of the bulge lets the water drain into a bucket in a controlled way.
• Catch the water with buckets and towels, and move furniture and rugs.
• Stop using the bathroom above until you know the cause.

Constant or occasional?

This is the most useful first question.

Dripping all the time, whether or not anyone is using the bathroom: a pressurised supply line is leaking. Shut off the main water valve, or the valves to the fixtures in that bathroom, and call a plumber.

Only when the bathroom is used: a drain, a seal or the waterproofing is leaking. You can narrow it down yourself.

Testing one fixture at a time

Leave the ceiling to stop dripping, then test each fixture separately, with a pause between, while someone watches below.

The toilet. Flush it several times. A leak that follows flushing points to the wax seal between the toilet and the drain. Other clues are a toilet that rocks, staining around its base, or a ceiling stain directly below it. Also check the supply line and the tank bolts for drips.

The tub or shower drain. Fill the tub a few centimetres and let it out, or pour a bucket of water straight down the shower drain without wetting the walls. A leak now is in the drain connection or the trap.

The tub overflow. Fill the tub up to the overflow plate. The gasket behind the plate perishes with age, and it leaks only when the tub is very full or someone is sitting in it.

The shower walls and door. Run the shower with the spray directed at the walls and the door, as in normal use. A leak now, when the drain test was dry, points to grout, caulking, the tile waterproofing or water escaping round the door or curtain onto the floor.

The shower valve and head. A leak only while the shower is running, even with water aimed straight at the drain, suggests the valve body or the connection behind the shower head.

The sink. Fill and drain it, and check the trap and supply lines in the vanity.

The floor. Water splashed on the floor by children, or a shower curtain left outside the tub, finds its way through at the tub edge and the toilet base. Failed caulking between tub and floor is a common, simple cause.

Common culprits

• Toilet wax seal
• Tub drain and overflow gaskets
• Cracked or missing caulking at the tub and shower
• Failed grout and waterproofing in a tiled shower
• A cracked shower base
• Supply line connections, particularly plastic fittings and braided hoses
• Pinholes in old copper pipe
• A shower valve leaking inside the wall

Fixing the source

Many of these are modest plumbing repairs: resetting a toilet on a new seal, replacing a drain gasket, recaulking. A failed tiled shower is a bigger job, because the waterproofing lies behind the tile and the shower usually has to be rebuilt.

Do not rely on a bead of caulk over failing grout as a permanent repair for a shower that is leaking through its walls.

What has happened inside the ceiling

Between the bathroom floor and the ceiling below is a cavity with joists, subfloor above and, sometimes, insulation. Water runs along the joists and pipes before it finds a way through the drywall, so the stain may not be directly under the source.

After a leak:

• The subfloor around the toilet or tub may be wet, swollen or rotted
• Insulation in the cavity is soaked
• The top side of the ceiling drywall is wet over a wider area than the stain
• Mold can begin within a day or two

Drying and repair

1. Assess the extent with a moisture meter, and thermal imaging where useful.
2. Open the ceiling where it is saturated, sagging or stained through. This also gives the plumber access.
3. Remove wet insulation.
4. Dry the joists, subfloor and remaining drywall with air movers and a dehumidifier, usually for a few days, until readings are normal.
5. Check the subfloor from below for rot. Soft subfloor around a toilet flange has to be replaced, which means working from the bathroom above.
6. Treat any mold.
7. Close up: new drywall, taping, priming with a stain-blocking primer and painting. Textured ceilings are hard to patch invisibly, and older textures should be tested for asbestos before they are cut.

If the leak was from a toilet seal or a drain, the water is not clean, and the wet drywall and insulation are replaced, not dried.

Painting over the stain

A water stain will bleed through ordinary paint. Once the leak is fixed and the ceiling is confirmed dry, use a stain-blocking primer, then paint. If the stain grows or returns, the leak is not fixed.

In a condo or apartment

If the bathroom above belongs to someone else, tell the neighbour and the property manager or landlord straight away, and take photographs. See condo water leaks: who is responsible.

Insurance

A sudden failure, such as a burst supply line or an overflowing toilet, is commonly covered for the resulting damage. A seal, grout or caulking that has leaked slowly over a long period is generally treated as maintenance or gradual damage. Report it promptly and keep photographs and the plumber’s findings.

More: water damage restoration.