Most Poway homes from the 1970s on sit on a concrete slab. The floor of your living room is that slab, with carpet, tile or wood laid on top. Along every outside wall, the slab edge meets the wood wall framing, the stucco and the soil outside, all within a few inches of each other. When water shows up inside along an outside wall, that junction is the first place to look.
The good news is that a lot of these leaks have simple causes outside. The bad news is that they can go on quietly for a long time before anyone notices.
What it looks like inside
Owners usually notice one of these first:
- Carpet that feels damp or cold near an outside wall.
- Tack strip or pad that has rusted or rotted along one edge of a room.
- Baseboards that swell, separate or stain at the bottom.
- Paint or drywall bubbling just above the floor.
- A musty smell in a closet on an outside wall.
- White, chalky deposits on the slab when you pull the carpet back.
Note when it happens. Water that shows up only after rain or after the sprinklers run points outside. Water that is there all the time, in dry weather too, points to plumbing.
Outside first: grade and hard surfaces
The California Residential Code, section R401.3, says the ground next to a foundation should fall at least 6 inches within the first 10 feet. Patios, walks and other hard surfaces within 10 feet of the building should slope at least 2 percent away.
Over the years, that slope disappears on a lot of Poway lots. Planters get built up with fresh soil and mulch. A patio slab settles and tips back toward the house. Decomposed granite gets raked against the wall. Do this:
- Walk the outside of the problem wall and look at which way the ground runs.
- Hose the area gently and watch where the water goes.
- Look for downspouts that empty right next to the wall.
- Check for sprinkler heads that spray the stucco.
Don’t pile new soil or mulch against the house to “fix” a low spot. That usually makes it worse.
The weep screed line
At the bottom of most stucco walls is a metal strip called a weep screed. It lets water that gets behind the stucco drain out at the base. The Residential Code, R703.7.2.1, places it at or below the foundation plate line, and at least 4 inches above the earth or 2 inches above paved areas.
When soil, mulch, DG or a later patio pour covers that screed, two things go wrong. Water behind the stucco can’t get out, and water outside can wick or run right into the wall at slab level. Both feed the wet baseboard inside.
- Do: look for the screed. If you can’t see it, something is probably buried against it.
- Do: pull back soil or mulch to clear it where you can.
- Don’t: caulk or seal the screed shut. It is there to drain.
Up through the slab
Water can also come up through the concrete itself. The Residential Code calls for a vapor retarder under slabs in living spaces (R506.3.3), and where one is required, a capillary break under the slab per the state’s green building code (R506.3.3.1). Older slabs may have thinner or damaged sheeting, or none at all in rooms that were once a garage or patio.
Moisture that comes up through the slab usually shows as a general dampness, flooring adhesive letting go, or white deposits spread across the floor, rather than a wet strip along one wall.
Poway ground makes it harder
Poway’s Safety Element describes expansive clays in the Friars Formation and settlement in poorly compacted fill. It names triggers like prolonged rain, over-irrigation, leaking pools or pipes, and leach line discharge saturating weak material. Wet clay against a slab edge does not just let water in. It swells, and as it dries it shrinks, which can open a gap between the slab and the soil or crack the slab edge.
So a slab-edge leak is worth fixing even if the water inside seems minor. On a lot with clay, keeping the soil along the house at a steady, modest moisture level is the goal. Big swings between soaked and bone dry are what move the slab edge, and they are usually driven by how the yard is watered and drained, not by the weather alone.
Rule out the pipes
Before blaming drainage, rule out plumbing:
- Turn off everything that uses water and watch the meter for movement.
- Check for a hose bib, irrigation valve or water heater line near the wet area.
- Look at the water bill history for a jump.
A slow supply leak under or near the slab can look exactly like a drainage problem from inside.
Mold and drying out
The EPA’s mold guide says the key to mold control is moisture control, and recommends keeping indoor humidity below 60 percent, ideally between 30 and 50 percent. Dry wet carpet and pad promptly, and replace materials that stay wet. If you see mold on drywall or framing, deal with it before closing anything back up.
When it becomes a structural question
Most slab-edge water is a drainage and building-envelope issue. It becomes a foundation issue when you also see:
- A crack in the slab running out to the wet wall.
- Stucco cracking or a step at the slab edge outside.
- Doors that started to stick near the wet area.
- A floor that feels lower at that wall.
At that point, an evaluation should look at the slab and the soil, not just the water. We coordinate with licensed engineers as needed when soils or structural design come into it. If repairs change structure, City Building Services handles the permit.
What sizes the fix
We don’t post prices. These are the drivers:
- Grade, drainage and screed fixes outside.
- Plumbing repair, if a leak is found.
- Removing and drying flooring and drywall.
- Any slab or foundation repair tied to soil movement.
If you are anywhere in Poway and water keeps showing up at an outside wall, request a Free Quote. More on foundation drainage and slab foundation repair is on this site.