Signs of water damage behind walls

Why hidden leaks do so much damage

A burst pipe announces itself. A pinhole in a copper line, a weeping joint or a failed shower valve does not. It wets the inside of the wall a little at a time, for weeks or months. By the time it shows on the surface, the insulation is soaked, the back of the drywall is moldy and the framing may be starting to rot.

Slow leaks are also the kind insurers question, because policies cover sudden events and generally exclude gradual damage. Catching one early matters in both ways.

What to look for

Stains. Yellow or brown marks, often with a darker ring at the edge. On a wall they tend to run downwards from the source. Below a bathroom they appear on the ceiling.

Paint and wallpaper. Bubbling, blistering, peeling or flaking paint. Wallpaper lifting at the seams.

Texture changes. Drywall that is soft, swollen, crumbling or bowed. Tape lines and nail heads that suddenly show.

Baseboards and trim. Swelling, warping, gaps opening at the joints, or paint cracking along the top edge. Water runs down inside the wall and collects at the bottom.

Floors. Staining, lifting or cupping at the foot of a wall. Damp carpet along one edge of a room.

Mold. Spots or patches on the wall, especially low down, in a corner or behind furniture. Mold on the surface often means much more on the hidden side.

Smell. A persistent musty, earthy odour in one room or cupboard, stronger when the room has been closed.

Sound. Dripping, hissing or running water when nothing is turned on.

Temperature. A warm patch on a wall or floor can be a hot water leak.

The water bill. An increase with no change in use.

The water meter test

1. Turn off every tap and water-using appliance. Do not flush.
2. Find the meter and note the reading, or watch the small leak indicator dial if it has one.
3. Wait one to two hours without using any water.
4. Read it again.

If the reading has changed, water is going somewhere. A running toilet is the commonest cause, so check those first by putting a few drops of food colouring in the tank and seeing whether it appears in the bowl. This test only finds leaks on the pressurised supply side. Drain leaks and rain leaks do not register.

Likely sources by location

• Behind a shower or tub: the valve, the shower arm connection, failed grout, caulking or the waterproofing behind the tile
• Below a bathroom: the toilet seal, the tub or shower drain and overflow, supply lines
• Kitchen walls: sink supply and drain, dishwasher line, fridge water line
• Laundry: supply valves, the drain standpipe
• Outside walls: windows, flashing, siding, a hose bib that froze and split inside the wall
• Top floor ceilings and walls: the roof, flashing, ice dams, attic condensation
• Basement walls: foundation seepage, window wells
• Near air conditioning or a furnace: a blocked condensate drain

When the stain appears tells you something. After rain points to the building envelope. After a shower points to the bathroom. All the time points to a supply line.

How a leak is found without tearing everything open

• Moisture meters. Pin and pinless meters read the moisture in drywall and wood and map how far the wet area extends.
• Thermal imaging. An infrared camera shows temperature differences. Wet areas usually appear cooler because of evaporation. It shows patterns, not water itself, so readings are confirmed with a meter.
• Small inspection holes and borescopes. A camera on a flexible lead looks inside the cavity through a small hole.
• Pressure testing and isolation of plumbing lines by a plumber.
• Acoustic listening for leaks in pressurised pipes.
• Controlled water testing of windows, showers and roofs.

What to do if you suspect one

1. Photograph what you see, with the date.
2. Do the meter test.
3. If the leak is on a supply line and you can identify it, shut off the valve to that fixture, or the main if needed.
4. Stop using the suspect shower or fixture.
5. Call a plumber to find and repair the source, and a restoration contractor to assess and dry the wall.
6. Tell your insurer or broker promptly.
7. Keep the failed part.

Do not paint over a stain and wait to see if it comes back.

What the repair involves

• The source is repaired
• Wet drywall is cut out to reach the cavity. Drywall that is merely damp and structurally sound can sometimes be dried in place by drilling small holes behind the baseboard and forcing air through.
• Wet insulation is removed. It does not dry reliably inside a wall.
• The framing is dried with air movers and dehumidifiers until moisture readings are normal
• Mold, if present, is dealt with under containment appropriate to the area affected
• The wall is rebuilt, primed and painted

In houses with finishes from before the mid-1980s, drywall compound and plaster may contain asbestos, and should be tested before cutting.

Why opening the wall is usually necessary

It is tempting to dry from the outside and avoid the mess. But insulation holds water, the back of drywall grows mold before the front shows anything, and nobody can see the condition of the framing without looking. A small, clean opening now is cheaper than a mold job later.

Insurance

Policies generally cover sudden and accidental escape of water and exclude continuous or repeated leakage. Whether a hidden leak is covered often turns on how long it was going on and whether you could have known. Prompt reporting, photographs, the plumber’s report and the failed part all help. Some policies cover the cost of opening the wall to reach the pipe, but not the pipe repair itself.

More: water damage restoration.