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Pipes Frozen Under the House or in the Crawl Space: Thaw and Prevent
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If a pipe under the house is frozen now
- Open the faucet served by that line. Texas A&M AgriLife Extension says water will begin to flow as you treat the frozen area. Howard County says to open the nearest cold-water faucet to relieve pressure.
- Know your main shut-off. Texas A&M says the frozen pipe may already be broken and will leak when it thaws. Shut the main valve if it does.
- Warm the pipe gently if you can safely reach it. Howard County suggests gentle heat such as a light bulb or hair dryer. Texas A&M lists a heating pad, hair dryer, portable space heater or towels soaked in hot water, with cords kept away from water.
- No open flame. Howard County and Texas A&M both say not to use one. Texas A&M says flames are a fire hazard and release lethal carbon monoxide.
- Call a licensed plumber if you can't locate the frozen area, can't reach it, or can't thaw it (Texas A&M). Our own safety note: do not go in if there is water near wiring.
How to protect pipes in a crawl space
- Close the foundation vents in extreme cold. Howard County says to close outside air vents located in the foundation wall during extremely cold temperatures.
- Seal the space. Indiana's OUCC says to seal basements and crawl spaces as tightly as possible to keep cold air out, using vents and doors to stop drafts. It also says to caulk, weather-strip and seal gaps.
- Insulate exposed pipes. Indiana's OUCC says to insulate exposed water pipes in cold areas, including basements, crawl spaces and attics, and to follow the maker's instructions for any insulation or heat tape. Howard County says to wrap or insulate exposed pipes.
- Add a heat source. The International Code Council, quoting IBHS, says insulation without a heat source cannot protect a pipe from freezing. Howard County suggests heat tape. Read our heat tape and pipe insulation guide.
- Drip a faucet in deep cold. Howard County says to let cold water trickle from a tap when temperatures drop below 15 °F, and never to leave running water unattended. Indiana's OUCC says on zero-degree days, let a pencil-sized stream run from a faucet, ideally on an exterior wall.
- Go away prepared. Indiana's OUCC says not to set the thermostat below 55 °F when traveling, and to have a neighbor check the home.
A longer-term option and a caution
The Building America Solution Center, a U.S. Department of Energy resource, describes an unvented crawlspace that is air-sealed, insulated and conditioned, with rigid foam on the perimeter walls and a polyethylene vapor retarder on the floor and walls. It says this can help protect plumbing pipes from freezing temperatures. It says to check with local authorities before installing the insulation and notes that residential codes require a drying mechanism, such as an exhaust fan or conditioned air supply. It also says vents can encourage condensation in humid climates. This is a project for a licensed contractor, not a weekend fix. Closing vents for a cold snap and changing the crawl space design are different things.
Will your pipes freeze tonight?
Answer four quick questions about tonight's low, where your pipes run, insulation and heat setting. Get a risk level and a short to-do list.
Open the freeze risk checkerProtect the pipes before the next cold snap
Pipe sleeves and UL-listed heat cable are the products Red Cross and extension services point to for exposed pipes. Read the label and follow the maker's instructions.
How to choose and use themSee pipe insulation and faucet coversSee UL-listed heat cableCommon questions
Why do pipes freeze in a crawl space?
Howard County's utilities bureau says water pipes in a crawlspace or on an outside wall are subjected to sub-freezing temperatures. Texas A&M AgriLife Extension and Missouri Extension both list crawl spaces among the unheated spaces where pipes are most at risk.
Should I close the crawl space vents in winter?
Howard County's utilities bureau says to close outside air vents located in the foundation wall during extremely cold temperatures. A U.S. Department of Energy resource (the Building America Solution Center) says that in humid climates vents can encourage condensation by letting warm, humid air in. Check local advice for your climate, and ask a pro before changing a crawl space permanently.
Is insulating the pipes enough?
No. The International Code Council, quoting IBHS, says insulation by itself (without a heat source) cannot protect a pipe from freezing. Indiana's OUCC says to seal basements and crawl spaces as tightly as possible to keep cold air out, and to insulate exposed pipes.
Can I use heat tape under the house?
Howard County's utilities bureau suggests heat tape as another way to prevent freezing, and Indiana's OUCC says to follow the manufacturer's instructions for any insulation or heat tape. Use only UL-listed products (Texas A&M) and have a licensed electrician check any wiring.
Is there a long-term fix?
A Department of Energy resource describes an unvented, air-sealed, insulated and conditioned crawlspace that it says can help protect plumbing pipes from freezing temperatures. It tells you to check with local authorities before installing the insulation, and notes that residential codes require a drying mechanism.
Related guides
- Howard County (Maryland) Bureau of Utilities: Water Pipes - Cold Weather Best Practices
- Indiana Office of Utility Consumer Counselor (OUCC): Preventing Frozen Pipes
- Building America Solution Center (U.S. Department of Energy; PNNL; updated Sept. 23, 2021): Unvented, Insulated Crawlspaces
- Texas A&M AgriLife Extension: Winter Storms: Preventing and Thawing Frozen Pipes
- International Code Council eNews: Build It to Code to Minimize Damage from Frozen Water Pipes (early 2014; quotes IBHS guidance)
Free printable: Frozen Pipe Night-Before Checklist
What to do before a cold night so your pipes survive it. Download the one-page PDF now, or get it by email along with a short series of five helpful emails.