Water in the crawl space: pumping, drying and keeping it out
A crawlspace is the part of the house nobody looks at until the floor feels soft or the furnace smells musty. Many Lexington-area homes sit over one, and the water that collects there is slow to show and slow to leave.
Referral service, not a contractor. Your request goes to an independent Lexington-area restoration company. We do not do the drying or repairs.
Four ways water ends up under the floor
Looks likeClear water pooling on the dirt floor, seeping in at the base of the foundation wall, sometimes days after the storm.
FirstCheck that the sump, if there is one, is running and discharging well away from the house.
Looks likeA hiss or spray under the floor, water running out a vent, the meter spinning with every tap closed. Common after a hard freeze.
FirstClose the main shutoff. Then call a plumber for the pipe.
Looks likeWet soil under a bathroom or kitchen, with a sewage smell that rises through the floor.
FirstStop using drains. Treat it as sewage, which changes the cleanup.
Looks likeMuddy water entering through vents or an access door after a downpour, where the yard slopes toward the house.
FirstLook at grading and downspouts once it is dry.
Why crawlspaces in the Inner Bluegrass get wet
The ground under central Kentucky moves water in ways that surprise people from elsewhere. The Kentucky Geological Survey's karst primer explains that rainwater sinks through fractures in the limestone and comes back to the surface at springs, which appear where the water table meets the land surface. After a wet stretch, that water table can sit close enough to the surface to show up under a house.
Timing matters as much as rainfall. In its study of the Sinking Creek karst basin south of Lexington, the KGS found flooding was more likely, and higher, when the soil was already near saturation before the storm (Currens and Graham, 1993). A crawlspace that stays dry through one storm may not stay dry through the second storm of a soggy week. The local karst and freeze guide covers the geology in more depth.
Frozen lines start under the floor
Kentucky American Water's winter advice, republished by the city in its frozen pipe tips, says frozen water lines typically occur in places like crawl spaces and along outside walls, where unprotected plumbing is most exposed. It suggests checking crawl spaces for uninsulated pipes, wrapping them in insulation sleeves, sealing cracks in foundations to keep cold air off the pipes, and keeping a slow trickle running through faucets fed by pipes in unheated spaces when temperatures drop below freezing.
A line that splits in a crawlspace can run for hours before anyone notices, because the water soaks into the soil first. If a winter water bill jumps, look under the house. The frozen pipe page has the shutoff steps.
How a crawlspace gets dried
- Pump the standing water. A submersible pump moves the bulk of it; a wet vacuum gets the low spots.
- Pull what is ruined. Fiberglass batts between the joists hold water against the subfloor and usually come out. A plastic ground cover with water trapped on top is usually cut out too.
- Dry the wood, not just the air. Dehumidifiers and air movers run in the crawlspace, sometimes with the vents closed so the machines are not drying the outdoors.
- Prove it is dry. Ask for moisture readings on the joists and subfloor at the start and again at the end, compared with a dry part of the house.
- Then close it up. New ground cover and insulation go in only after the readings say so.
If the water came from a drain or sewer line, the soil itself is contaminated and the work is closer to a sewage cleanup than a dry-out. And if the floor above was wet, the crew should check the finished rooms as well; the drying timeline page explains why speed matters.
Ground covers done properly
A plastic ground cover, or vapor retarder, is the most common fix for a damp crawlspace. A U.S. Department of Energy weatherization job aid sets out what a good one looks like:
- At least 6-mil plastic with a perm rating of 0.1 or less.
- Coverage of the whole floor, or as close as possible.
- Run at least 6 inches up walls, piers and columns, and attached securely.
- Seams overlapped at least 12 inches, lapped so water runs over them, not into them.
- Seams and penetrations sealed in unvented crawl spaces.
- No interference with the existing drainage.
The DOE notes that a well-installed retarder helps keep down ground moisture and soil gases such as radon. A ground cover does not stop flowing water, though. If water runs in, the fix is drainage, grading or a sump, and a plastic sheet laid over a wet floor just hides the problem.
For the air above it, the EPA's mold and moisture guide suggests keeping indoor humidity below 60 percent, ideally 30 to 50.
Crawl space questions
The crawlspace had water but it drained away on its own. Is it fine now?
Not necessarily. The soil may be dry on top while the joists, subfloor and insulation are still wet. Wet insulation pressed against wood keeps it wet for weeks. Have someone check with a moisture meter before deciding nothing needs doing.
Do I need a permit to encapsulate or add a sump?
It depends on the work and where you live. In Lexington, ask LFUCG Building Inspection at (859) 258-3770; in Wilmore or unincorporated Jessamine County, ask the joint planning office; elsewhere, ask your city. Drying alone usually involves no permit, but electrical or plumbing changes may.
Will a referral company handle the crawlspace and the rooms above?
Restoration companies that take water damage jobs generally dry both. On the form, mention that the water is under the floor, so the company comes ready to work in a tight space. The basement flooding page covers houses that have both.