What should you do about water under a pier and beam house?

Start by ruling out a plumbing leak, then look outside: downspouts emptying at the skirting and ground sloping toward the house cause most crawlspace water. Fix those, watch the next storm, and only then decide whether the crawlspace needs an interior drain to a sump. Rein Irving Drainage Company handles that outside-in drainage work.

First, find out whether it rained

The quickest clue is timing. Water under the house after a storm points to drainage. Water in dry weather, or a wet patch under a bathroom, kitchen or water heater, points to plumbing.

To check, turn off every fixture and the sprinkler system, read the water meter, and read it again an hour or two later. If the dial moved, water is leaking somewhere, and that is a job for a plumber before any drainage work. A leaking sprinkler line along the house can do the same thing from outside; check it with the controller off. The standing water page covers wet ground with no rain.

Then work from the outside in

Most water reaches a crawlspace the same way it reaches a slab: from the roof and the grade. Walk the house during or right after rain and check these in order.

1. Downspouts. Each inch of rain on 1,000 square feet of roof is about 620 gallons, delivered to a few corners. A downspout ending at the skirting puts that water right at the crawlspace wall. Piping it away in solid pipe is usually the first fix; see downspout drainage and whether downspouts should drain into perforated pipe.
2. Grade. The ground should fall away from the house, about 6 inches in the first 10 feet by the common standard. Beds, mulch and settled soil often reverse it. The slope guide shows how to check, and regrading covers the fix.
3. Vents and access openings. A vent or access door set at or below the surrounding ground lets surface water pour straight in. Look for silt lines below vents and at the access door.
4. Neighbors and paving. A patio, walk or driveway that drains toward the house, or water arriving from a higher lot, can feed one side.
5. Low spots along the skirting. Puddles that sit against the house after rain will find their way under it.

When the crawlspace sits lower than the yard

Some crawlspace floors sit below the soil outside. Even with good grade and roof water handled, water can move through the ground and seep in, especially on sandy topsoil over clay where water perches on the clay a few inches down. Parts of central Irving map that way in the USDA soil survey (about 15 inches of loamy fine sand over sandy clay loam at one sample point, not every lot).

That is the case for an interior perimeter drain: a shallow trench inside the foundation wall that collects the water and carries it to a sump basin at the low point, with a pump that lifts it out to an allowed outlet. The order matters. Fixing the outside first keeps the water reaching the pump small. The sump pump drainage page explains how the basin and pump are built, and where to discharge a sump pump covers where the water can go.

Why it is worth fixing promptly

Standing water under a floor keeps the air in the crawlspace damp. Over time that can soften wood framing and subfloor, soak insulation, encourage mold and rot, and send musty air into the house. Wet soil around piers can also soften, and on expansive clay, uneven wetting around a foundation is a cause of movement. The foundation moisture guide explains why.

If you see sagging floors, damaged joists or piers that have shifted, have a foundation engineer or structural professional look at the house. Drainage keeps water out; it does not repair framing or reset piers.

What not to do

• Do not pump water onto a neighbor’s lot. Texas Water Code section 11.086 makes it unlawful to divert surface water in a way that damages another property.
• Do not rely on a vapor barrier alone. It slows ground moisture but does nothing for standing water.
• Do not trench deep along the outside wall without a plan. On expansive clay, a deep gravel trench along one side can dry that side unevenly.

A practical next step

After the next storm, take photos under the house and of each downspout and the ground along the skirting. With those, a foundation drainage plan can start with the cheapest fixes. Send them with your address, or use the drainage assessment to sort the likely cause first.

Questions people ask

How can I tell if crawlspace water is from a plumbing leak?

Turn off every fixture and the irrigation, then read the water meter and read it again an hour or two later. If it moved, water is going somewhere. Water that appears in dry weather, or sits under a bathroom or kitchen, also points to plumbing.

Should crawlspace vents be closed when water gets in?

Vents set below the outside grade, or in a low corner where water runs, can let surface water in directly. Those need the ground lowered or a well around them. Whether vents should be open or sealed for moisture control is a separate question for the house as a whole.

Is a vapor barrier enough to fix water under the house?

No. A plastic ground cover slows moisture rising from damp soil, but standing water will sit on top of it or under it. The water has to be kept out or drained first.