How to Keep Pipes From Freezing in a Crawl Space

How do you keep pipes from freezing in a crawl space? Put foam sleeves on every supply line under the house. Before a hard freeze, close the foundation vents, cover the access door, and block any gap in the skirting where wind gets in. On the coldest nights, let the faucets on outside walls drip. The lines that freeze first run near a vent, by the access door, and along the north or windward wall. Put the sleeves on in October, not the afternoon the freeze warning goes out.

Motmot is a foundation company. We level pier and beam houses, set piers, shim beams, and replace rotted sills. We are not plumbers. If a line bursts, shut off the water at the main and call a licensed plumber. Our part comes afterward, when the water that soaked the clay under your piers shows up as sticking doors and dipping floors.

Why pipes under a raised floor freeze when slab pipes usually don't

On a slab house most of the plumbing runs under the concrete or through the walls of a heated house, and the ground under a slab holds its warmth through a cold night. The weak spots are the ones that stick out, like a hose bib or an attic line.

A pier and beam house hangs its supply lines in open air a couple of feet above the dirt. The crawl space is outside air with a floor over it. The vents in the skirting move air through on purpose, and most of the year that airflow helps dry the soil and the framing. In January the same openings pull freezing air across bare pipe, and a north wind pushes it in faster. Texas A&M AgriLife Extension lists crawl spaces among the places where exposed pipes are at risk, notes that pipes with northern exposure freeze more readily, and puts the burst danger at 20 degrees or colder outside, with precautions any time it drops below freezing.

Our mild winters make it easy to skip the prep. Then a hard front drops in after a dry summer, or a storm like Winter Storm Uri in February 2021 holds the state below freezing for days. A line that survives one cold night in an open crawl space may not survive three. Uri left burst pipes and slab leaks across Central Texas, and pier and beam houses with open skirting and bare lines were easy targets. PEX stretches more than copper before it splits, but its fittings and valves still crack, so treat every supply line under the house as one that can freeze.

Where the lines freeze first

Supply lines stay full and under pressure, so they are what bursts. Drain lines sit mostly empty between uses and rarely freeze.

Next to the foundation vents. Outside air comes through the opening and hits the nearest run first. A line within a few feet of a vent is the first one to sleeve and the first one to protect on a freeze night.

At the access door. Plenty of access panels are a piece of plywood leaned into the opening, and wind works through the gaps around it all night.

Along the north and windward walls. Our winter fronts come in from the north. The lines on that side cool first, along with the risers into a kitchen or bathroom on an outside wall.

Wherever the sleeve stops. Bare valves and elbows, a sleeve that slid down the pipe, the foot of line a repair left uncovered, and the runs out to a hose bib or in from the meter. One bare foot of pipe is enough.

Insulating the pipes, and when heat cable makes sense

Foam pipe sleeves are the base layer, and most homeowners can put them on if they can crawl the space safely. Buy the size that matches the pipe, usually half inch or three quarter inch, with the thickest wall the store carries. Tape every seam and every joint between sleeves, cut the ends at an angle so they meet tight at the elbows, and wrap valves and tees with foam tape or a fitted cover. A zip tie every couple of feet keeps a sleeve from sliding. Skip loose fiberglass wrap under a house. It soaks up crawl space moisture and does almost nothing once it is wet.

A sleeve adds no heat. It slows how fast the water in the pipe loses heat, which buys hours, and on most Central Texas freeze nights hours are enough. On a freeze that lasts days, a sleeved line in a wide open crawl space can still freeze, which is why the sleeves and a closed-up crawl space have to work together.

Check the sleeves every fall, because rodents chew them and anyone who works under the house can leave a gap. AgriLife also advises buying pipe insulation early, because supplies run short in the rush before a freeze.

Heat cable makes sense for a line that has frozen before, a run you cannot keep out of the wind, or a long stretch under an addition where the crawl space is open. Use self-regulating cable listed for pipe use, install it exactly as the maker says, and plug it into a GFCI-protected outlet. Heat cable also needs power, and a winter storm that takes out the grid takes out the cable with it, as happened in many Texas homes during Uri. It protects a problem line. It does not heat a crawl space.

Should you insulate the crawl space floor?

For comfort, often yes. For the pipes, it can backfire unless you plan for it. An uninsulated floor leaks house heat into the crawl space all winter, and on a freeze night that stray heat helps keep the lines above freezing. Insulate the floor and the rooms stay warmer while the crawl space gets colder. So either the pipes get their own sleeves, or the insulation goes in so the pipes end up on the house side of it.

The U.S. Department of Energy's consumer guide to home insulation suggests R-13 for an uninsulated floor in climate zone 2, where most of Central Texas sits, and R-19 one zone north. Under a house that usually means batts between the floor joists, held tight to the subfloor with wire supports or netting. The facing and the supports are an insulation contractor's call, and sealing and conditioning a crawl space is a different system that also brings in your HVAC contractor.

Old floor insulation is where the trouble starts. Batts that sag between the joists or lie on the dirt soak up moisture and hold it against the wood, insulating poorly and keeping sills and joists damp long enough to rot. If the batts under your house hang loose, the moisture problem comes first. Pull the wet material, find the water, and only then insulate again. Our crawl space moisture control page covers the drainage, vapor barrier, and ventilation side.

Cold floors in winter are why most people ask. On a pier and beam house they usually come from an uninsulated floor, air leaking in around the sill and through skirting gaps, and open vents on a windy night. Closing the vents on the coldest nights and sealing the skirting helps right away. Insulating the floor helps for good. A floor that feels cold and also bounces or slopes points at the framing and the supports, and that is our work, covered on our pier and beam foundation repair page.

What to do on a freeze night

Run this routine in daylight when the forecast calls for a hard freeze or any night in the 20s. The federal Ready.gov winter weather page puts pipe protection on the list of things to do before winter weather arrives.

Close the vents. Snap the vent covers shut, or press cut pieces of foam board into the openings. Our guide to whether crawl space vents should be open or closed covers the rest of the year, and in Central Texas the answer for most of it is open. One exception before you shut everything. If a gas furnace or water heater sits under the house, it may draw its combustion air through those vents, and closing them all can starve the burner. Leave that appliance's air supply open and ask an HVAC contractor how to protect the pipes near it.

Close the access door. Set the panel back in its opening, wedge it tight, and block the gaps around it. A sheet of foam board behind the panel helps.

Block the skirting gaps. Walk the whole perimeter. Loose panels, broken lattice, and the holes armadillos dig under the bottom edge all let wind in, and foam board or plywood is fine for the night. For lasting repairs, see our guide to skirting options for pier and beam homes.

Handle the outside faucets. Disconnect every hose, because a connected hose traps water at the wall, and cover the hose bibs.

Drip the faucets. Let the faucets on outside walls, and any fed by lines that run through the crawl space, drip slowly overnight, with a single-handle faucet set to the middle so hot and cold both move. Moving water is harder to freeze, and an open faucet relieves the pressure that builds behind an ice plug, which is what actually splits the pipe. Open the sink cabinets on outside walls and keep the thermostat steady all night.

Find the main shutoff before you need it. Know where your shutoff valve is and keep the tool that turns it where you can find it in the dark. Hunting for it while water sprays under the floor is how a small split becomes a soaked crawl space.

If a faucet gives only a trickle the next morning, a line has probably frozen. Leave that faucet open and call a plumber. Never thaw a pipe with a torch or any open flame, under a house or anywhere else.

When the freeze passes, open the vents again. A crawl space closed up for weeks traps moisture, and open vents help the ground and framing dry back out.

What happens after a line bursts under the house

Shut off the water at the main, open a faucet inside to drain the lines, and call a licensed plumber. If water is pooling near wiring, stay out from under the house until the power to that circuit is off. Photograph the split, the standing water, and the wet insulation before cleanup starts, because an insurance claim will need them.

The clay under the house is the next concern. A burst line can dump a lot of water straight onto the clay under the piers. Expansive clay swells when it gets wet, so the piers and pads near the leak can rise. As that soil dries back out over the following weeks they can drop again, and pads on softened clay can sink. That is why the foundation side of a freeze shows up late, as doors that stopped latching and a floor that humps in one room and dips in the next. After Uri, a lot of that damage did not surface until weeks after the pipes were fixed.

The wood takes a hit too. Sills and joists that stay soaked for days, especially under wet batts, can soften over the following months. Pull wet insulation down, open the vents once the freeze is over, and give the crawl space time to dry. Rotted sill runs and soft joists get cut out and replaced, as our guide to floor joist and sill repair explains.

Do not level the house while the clay is still wet. We measure the floor, check the piers, beams, and sills, and let the ground dry back toward normal before any re-shimming. When supports have moved for good, we reset them and add steel or hybrid piers where the soil calls for it. Our page on whether a hard freeze can damage a Texas foundation covers the slab side of the same story.

Who handles which part of the job

A licensed plumber repairs supply lines, installs heat cable on pipes, and handles anything that touches the water system, and an electrician handles the outlet the cable plugs into. An insulation contractor installs floor batts, and a sealed, conditioned crawl space is an HVAC and insulation job. Motmot handles the structure, meaning the piers, beams, shims, sills, joists, and the leveling. When one of our jobs needs plumbing work, we bring in a licensed master plumber, and our part is the access and the structure around it.

How insurance treats a frozen pipe under the floor

A pipe that bursts in a freeze is the classic sudden and accidental loss, so water damage to the subfloor, the insulation, and the flooring is the part a Texas homeowners policy most often pays. The split pipe usually is not. Slow leaks and rot fall on the excluded side, and so does foundation movement unless the policy carries a foundation or slab endorsement. After the 2021 storm, a Texas Department of Insurance bulletin pointed out that some policies cover freezing losses only when the owner took reasonable care to keep the heat on or to shut off and drain the water. Your freeze-night routine is part of your evidence. Our post on insurance coverage for pier and beam repairs has the details, and your own policy has the final word.

If your house is in Bexar, Travis, Williamson, Hays, Comal, Guadalupe, Kendall, Medina, Bastrop, or Caldwell County, our inspection is free. An ICC-certified inspector checks the piers, beams, and sills, measures the floor, and gives you the findings in writing. About a third of our inspections end with no repair needed. Book a free foundation inspection online, or call or text (210) 816-0034.