Signs of Water Damage in Walls: Drywall $1.50 to $3 a Sq Ft

Drywall and wall figures from each guide's water damage page. Finding and fixing the leak is billed separately.

Warning signs of water damage in walls that need a call today

• Call now: water running down a wall, a wet wall near outlets or switches, drywall that bulges, or water from a toilet or drain line inside the wall.
• This week: a stain that grows, a new musty smell, or baseboards that stay damp.
• Can wait a few days: an old, dry stain that has not changed. Still find out where it came from before you paint over it.

If a wet wall has an outlet or switch in it, turn that circuit off at the breaker only if you can reach the panel from a dry spot. Otherwise stay clear and call.

Visible signs of water damage in walls

The Minnesota Department of Health lists water stains, water leaks, condensation problems and standing water as the signs of a moisture problem, and says mold damage may look like discoloration or staining on the surface. Look for:

• Stains or discoloration that were not there before. Note where the stain is and what sits on the other side of the wall or above it; that is where the search for the leak starts.
• Swelling or split seams. The EPA uses these two signs to decide whether wet wallboard can be dried in place.
• A musty or earthy smell. The EPA says to suspect hidden mold if a room smells moldy but you cannot see the source, and Minnesota describes mold odors as musty or earthy.
• Standing water or damp flooring along the base of the wall, one of the moisture signs Minnesota lists.
• Spots of mold on the wall or behind furniture pushed against it. The EPA lists walls behind furniture, where condensation forms, among the places mold hides.

Water damage behind a wall: the hidden signs

A wall can look fine and still be wet. The EPA's mold guide for buildings gives the example of wallboard whose front side looks fine while the back side is covered with mold. It says vinyl wallpaper and wood paneling can act as vapor barriers that trap moisture underneath, and it lists pipe chases with leaking or condensing pipes among the hidden spots.

Do not start peeling things back to look. The EPA warns that removing wallpaper can release a massive amount of spores from mold growing underneath, and suggests an experienced professional if you suspect hidden mold. A higher water bill or a meter that moves with every tap off points to a supply leak; leak detection covers that test and what it costs.

How pros find water damage behind walls: moisture meters and thermal cameras

• Moisture meters. The EPA says moisture meters may be helpful for measuring the moisture content in building materials and for watching them dry. West Virginia University's facilities staff use a moisture meter to find wet materials and again after drying to confirm everything is dry.
• Thermal cameras. R&R Magazine's article on thermal imaging says an infrared camera shows surface temperature differences, not water, and that the top misconception is that all cold spots are moisture. It says the only way to fully confirm hidden moisture is with a moisture meter, and that the camera cannot see through walls.
• Leak detection tools. American Leak Detection, a leak detection company, says it uses thermal imaging cameras, snake cameras and acoustic sensors to find leaks without causing more damage.
• Small openings. West Virginia University's procedure removes the cove base and drills weep holes in wet wallboard. Alabama Extension describes removing baseboard and drilling holes between studs to drain a flooded wall.

Ask whoever comes out which of these they will use and whether readings will be written down each visit. A thermal image alone is not proof of a wet wall.

Water damaged drywall: dry it or cut it out?

Wallboard acts like a sponge when wet, NDSU Extension says, so the decision turns on how long it stayed wet and how dirty the water was:

EPA Table 1 is from its mold guide for schools and commercial buildings; the West Virginia University and NDSU rules come from a university safety office and an extension service.

Insulation is the other half. The EPA says wet cellulose and fiberglass insulation should be discarded and replaced, and NDSU says flood-damaged insulation will hold water for months. Plaster is different: NDSU says it usually does not need to be replaced, though it takes a very long time to dry. If sewage was in the wall, read Category 3 water damage first.

Water damaged drywall repair cost

HomeAdvisor, Fixr and Forbes Home all put drywall replacement after water damage at $1.50 to $3 per square foot, and HomeGuide at $1.50 to $3.50. HomeAdvisor puts a drywall repair job at $300 to $850, Forbes Home puts drywall replacement at $300 to $700, and Fixr's typical drywall project is $275 to $485. Fixr's range for a wall repaired after water damage runs from $275 to $2,200.

For scale: a 2 foot flood cut around a 12 by 12 foot room is 96 square feet of drywall, or $144 to $288 at the $1.50 to $3 rate, before taping, painting and any minimum charge. The drying, insulation and the leak repair come on top. The water damage cost calculator adds drywall to the drying estimate, and the water damage restoration cost guide has the rest.

Mold risk inside wet walls

The EPA says to dry water-damaged areas within 24 to 48 hours to prevent mold, and Minnesota's health department says materials dried in that window will often not have a chance to grow mold. West Virginia University's program says mold growth can occur 48 to 72 hours after water gets in if drying fails. The how fast mold grows timer counts from your start time.

If mold has started, the EPA says a homeowner can generally handle an area under about 10 square feet; larger areas or a lot of water damage call for professional guidance. HomeAdvisor lists mold removal within a water damage job at $1,100 to $3,400. See mold remediation for the full job.

Who to call, and does insurance pay?

Most wall jobs need two calls: one to stop the water and one to dry and rebuild. A plumber or leak detection company finds a pipe leak, a roofer finds a roof or flashing leak, and a water damage company dries the cavity and replaces the drywall. A stain on the ceiling below the wall points to the same leak; see ceiling water damage repair.

The Texas Department of Insurance says most homeowner policies cover sudden and accidental water damage but not gradual leaks or seepage, including the mold that follows. A pipe that burst inside a wall is usually the first kind; a slow drip that stained the wall over months is often the second. Photograph the wall before anything is cut, call your insurer, and never sign over the claim to a contractor. More in does homeowners insurance cover water damage.

Before the drywall comes out, get the company's license number if your state licenses this trade, and a copy of its insurance certificate. If a toilet or tub overflow soaked the wall, see toilet overflow cleanup; if the water ran under a wood floor, see water damage on hardwood floors.

What to do right now about a wet wall

1. Stop the water: close the fixture valve or the main shutoff if a pipe is leaking.
2. Turn off power to outlets in the wet wall at the breaker, only from a dry spot.
3. Photograph the stain and anything wet, with the date.
4. Move furniture away from the wall so air can reach it.
5. Do not peel wallpaper or open the wall to look for mold.
6. Call your insurer if you plan to claim it, then the water damage line.