Hidden wall leaks
Water leak behind a wall in Maple Valley, WA
Leaks inside walls rarely announce themselves. They show up as a baseboard that’s swollen, paint that’s bubbled, or a room that smells damp when nothing looks wet.
Tell us what you’re seeing on the wall; we’ll help you work out whether it’s a leak.
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The problem
What a leak inside a wall does
Walls are hollow boxes of framing, insulation and drywall with pipes, drains and wiring running through them. When a supply fitting drips or a drain joint weeps, the water runs down inside the cavity and collects at the bottom plate, where it wicks into the drywall, the baseboard and the subfloor.
A pressurized supply leak runs all the time and usually shows sooner. A drain leak only runs when that fixture is used, so it can go on for months. Water coming in from outside, around a window or through siding, shows up mainly during and after rain.
Signs
What people usually notice first
- Paint bubbling, peeling or discoloring low on a wall, or around a shower valve on the other side
- Baseboard swelling, separating from the wall or darkening at the bottom
- Carpet tack strip or flooring damp along one wall
- A musty smell concentrated in one room or closet
- A warm patch on a wall where a hot water line runs
- A water bill that climbs when your use hasn’t changed
A quick check: turn off every fixture and watch the water meter. If it keeps moving, water is going somewhere. That doesn’t say where, but it does say it’s supply water rather than rain or a drain.
A smell in one room and nothing to see? That’s worth a call.
Musty Smell in One Room? Call UsWhy here
Common causes in Maple Valley houses
Shower valves and supply connections
In the 1990s-onward houses that make up most of Maple Valley, the typical wall leak is at a shower or tub valve, a supply stub-out behind a toilet or vanity, or a fitting on the line to the fridge.
Drain joints behind tubs and showers
Tub overflow gaskets and drain connections loosen over time. They leak only when the tub is filled or drained, which is why the stain comes and goes.
Older plastic supply pipe
Some houses built before the mid-1990s were plumbed with gray polybutylene pipe. If you see it where lines enter the house or at the water heater, it’s worth having a plumber look at the whole system.
Wind-driven rain on exterior walls
Long rainy spells find gaps around windows, doors, deck ledgers and siding penetrations. The wet spot shows below a window or at an outside corner and gets worse in storms, not with water use.
Leak or rain?
Plumbing leak or water from outside?
It helps to know before anything is opened. A plumbing leak usually shows whether or not it’s raining, tracks with water use, and often appears on an interior wall. Rain intrusion comes and goes with the weather, is almost always on an exterior wall, and is often worse on the side of the house facing the prevailing wind.
If the wet spot is on an outside wall and appears during a storm, check the gutter and downspout above it too. An overflowing gutter can pour water down the siding and into gaps that stay dry the rest of the time. More on that under gutter and drainage intrusion.
We’ll help you narrow it down on the phone before anything gets opened.
Ask About Finding the LeakThe work
How a hidden wall leak is found and dried
Trace it without opening
Moisture meters, a thermal camera and, for supply plumbing, pressure testing narrow the wet area to a few feet. The goal is to open as little wall as possible.
Open the wall where it’s wet
Drywall is cut out along the wet area, usually a set height above the floor so the repair is a clean straight line. The baseboard comes off first and is saved if it can be.
Fix the source
A plumber repairs the fitting or drain, or the exterior gap is sealed and flashed. Nothing gets closed up until this is done.
Remove wet insulation
Wet fiberglass in an exterior wall holds water against the framing and sheathing. It’s removed, and replaced after drying.
Dry the cavity
Dehumidifiers and air directed into the open cavity dry the studs, bottom plate and subfloor. Readings are taken each visit until they match dry framing elsewhere.
Close and finish
New insulation, drywall, tape, texture and paint, then the baseboard goes back on.
Time and cost
What affects the time and the price
Finding the leak is often quicker than people expect. Drying the framing is what takes time, typically several days, and longer on an exterior wall in the wet season when the sheathing is already damp.
Price depends on how long the leak ran, how much wall has to be opened, whether insulation and flooring are involved, what the plumbing or exterior repair needs, and the finish work to match. You get the price up front, with no hidden fees.
Ask what finding and fixing this is likely to involve.
Get the Price Before We StartAfterward
Once the wall is closed
Watch the repaired area for a few weeks, and after the next heavy rain if the source was outside. If the cause was an old supply fitting, ask the plumber whether other fittings of the same age should be replaced while the wall is open.
Moisture left in framing and drywall can allow mold growth, commonly within a day or two under the right conditions, which is why the cavity is dried and measured before anything is closed.
If the leak was in a shared wall in a townhouse or condo, the neighbor’s side may need checking too. The crew can take readings on both sides if you can arrange access.
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Questions
Questions about leaks behind walls
Look for bubbling paint, swelling baseboard, damp flooring along one wall, or a musty smell in one room. Watching the water meter with everything off tells you whether supply water is escaping.
Usually the location can. Meters and a thermal camera narrow it to a small area. Some drywall normally has to come out to fix the source and dry the cavity.
Only the wet area plus a margin to reach dry material. On many jobs that means a strip along the bottom of the wall rather than whole sheets.
Drain leaks only run when that fixture is used, and rain intrusion only shows in wet weather. Both can come and go for months.
If it was wet briefly with clean water and the drywall is still firm, sometimes, with small holes behind the baseboard for airflow. If insulation is wet or it has been leaking a while, opening it is the reliable option.
Then the fix is sealing or flashing the exterior, and sometimes gutters or grading, not plumbing. The interior drying is much the same.
It’s an older plastic supply pipe with a mixed track record. If you have it, a plumber can check its condition and talk you through replacement options.
The crew can provide photos, moisture readings and written notes on what they found and the work performed, so you have a clear record for your own files.
When readings in the studs and bottom plate match dry framing elsewhere. That’s often several days, sometimes longer on an outside wall in winter.
Often. Taking off the toe kick, or drilling small holes behind it, lets the crew get air and meters into the space under the cabinets. If the cabinet bases have swollen or the wall behind is soaked, the affected cabinets may need to come out so the wall can dry.
Think there’s a leak behind the wall? Call and we’ll help find it.
Describe what you’re seeing. The crew traces the water, opens only what’s needed, dries it properly and puts the wall back.
Straight answers first, then as little wall opened as the job allows.
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