Pipes in outside walls, unheated garages, crawl spaces and basements are the ones that freeze in a Treasure Valley winter, and water expands about 9 percent as it turns to ice. The leak often appears only when the pipe thaws. Shut off the main, call, and have a plumber repair the line.
Key takeaways
- Water expands about 9 percent as it freezes, and the pressure that splits a pipe builds between the ice and a closed faucet, not necessarily where the ice sits.
- Treasure Valley plumbers have described surges in frozen-pipe calls during sustained hard freezes, and pipes in outside walls, basements and crawl spaces are the most exposed.
- A split pipe often leaks only after the ice melts, so check ceilings, wall bases and cabinets after the thaw, not only during the freeze.
- Never thaw a pipe with a torch or open flame; slow, even warmth with the faucet open is safer, and a pipe inside a wall is a plumber's job.
- We found no sourced record of Boise freeze dates or temperatures, so this guide gives none; watch your own forecast and treat sustained lows below freezing as the signal to prepare.
Why does Boise get frozen pipes in a dry climate?
Because dryness and cold go together. Boise gets about 12 inches of precipitation a year, with December and January the wettest months, but clear winter nights lose heat fast. A house built for mild weather can have an exposed supply line a few degrees from freezing before anyone notices.
Climate normals put the valley near 12 inches of precipitation a year, with August the driest month at about two tenths of an inch and December and January the wettest at roughly an inch and a half to an inch and three quarters. Station figures vary between about 11.9 and 14.5 inches, so we quote the range. The point for pipes is the pattern: the coldest months are also the wettest, and sustained hard freezes are what local plumbers describe as the busiest stretch.
We did not find a sourced record of record lows or the dates of specific freezes, so we do not cite any. If you want to know how cold your own house gets, a cheap thermometer in the crawl space or garage tells you more than a regional average.
The takeaway for homeowners is practical rather than meteorological. A frozen pipe needs two things: cold air reaching the pipe and a pipe with little heat of its own. Moving a cabinet door, sealing a gap or wrapping a line changes one of those two things. None of it requires knowing the exact low temperature of a particular night, which is just as well, since a forecast can miss a cold pocket in a crawl space by many degrees.
Which pipes freeze first?
Pipes in outside walls, unheated garages, crawl spaces, basements and attics freeze first, along with lines to outdoor spigots. Local reporting on Treasure Valley freezes names outside walls, basements and crawl spaces as the most exposed spots. A kitchen or bath on an outside wall is a common place for a split.
Newer subdivisions in Meridian, Kuna and Star more often have plumbing under a crawl space, and the vents that keep that space dry in summer can let cold air in during a hard freeze. In older Boise neighborhoods, a supply line in an exterior wall is close to the cold side, and an unheated porch or back room can hold a line that nobody thinks about.
Outbuildings matter too. Garage apartments, detached shops, pump houses and farm buildings, which are common in Melba, Emmett and the edges of the valley, have plumbing that is only warm when someone is there.
Hose bibs deserve a special mention. A hose left attached through the first freeze holds water in the spigot and the short run of pipe behind it, and when that water freezes it can split the pipe inside the wall, where the damage shows only when the hose is reconnected in spring. Disconnecting hoses in autumn is a thirty-second job, and it is one of the few freeze precautions that costs nothing at all.
| Place | Why it is exposed | What helps |
|---|---|---|
| Crawl space | Cold air moves freely under many floors | Insulate pipes, close vents in a hard freeze |
| Unheated garage | No heat, and a washer or utility sink on the wall | Insulate the supply, keep the door closed |
| Outside wall | The wall is the coldest part of the house | Open cabinet doors under sinks, keep a slow trickle running |
| Outdoor spigot | Water left in the line freezes and splits it | Disconnect hoses, close the interior valve if present |
| Detached shop or shed | Heated only when in use | Drain the line or keep a safe low heat |
Why do leaks appear after the thaw?
Ice can plug a crack the way a stopper does. While the pipe is frozen, nothing flows. When the ice melts, water pushes through the crack at house pressure, often hours after the coldest night. That is why many freeze breaks flood a house when the weather warms.
The pressure that splits a pipe builds in the stretch between the ice plug and a closed fixture. The crack can be a lengthwise slit some distance from the frozen section, and a pipe that looks intact from outside can have a hairline split along its length.
After any hard freeze, walk the house with a flashlight. Look at ceilings below bathrooms, the bases of outside walls, cabinets under sinks on exterior walls and the crawl space if you can safely reach it. A damp patch or a drip you hear inside a wall is the cue to close the main and call.
How do you thaw a frozen pipe safely?
Open the faucet so melting ice has an outlet, then warm the pipe slowly with a hair dryer, a heating pad or warm towels, working from the faucet back toward the ice. Never use a torch or open flame. If the pipe is inside a wall or you see water, close the main and call a plumber.
Slow, even warmth lets melting water escape instead of building pressure behind a plug. If you cannot find the frozen spot, follow the cold line from the fixture toward the outside wall. A pipe you cannot see is a plumber's job, because cutting into drywall risks hitting wiring and other lines.
If water appears, do not keep trying. Close the main, open a low faucet to relieve pressure, and call. A thaw that turns into a burst is a different problem from a frozen pipe, and it is covered on the burst pipe page.
- Open the faucet before you start
- Use a hair dryer or warm towels, never a flame
- Work from the tap end toward the frozen section
- Close the main and call if you see water
What do you do when a pipe has burst?
Close the main water valve, stay out of any room where water has reached outlets or fixtures, open a low faucet to drain the line, photograph the damage and call. A plumber repairs the pipe, and a restoration crew removes the water and dries the structure. Do not mop and carry on, because hidden water keeps spreading.
The first minutes matter because a supply line carries water at house pressure. If you cannot find the main, close the valve at the water heater or the nearest isolation valve, and note which fixtures are still running.
The EPA advises drying water-damaged materials within 24 to 48 hours to prevent mold, and wet insulation inside an outside wall dries slowly in winter. Call early, and tell the dispatcher when you think the break began. Whether insurance applies is your insurer's decision, and photographs, a moisture log and the plumber's invoice are the records that help.
How do you keep pipes from freezing next winter?
Insulate exposed lines in crawl spaces and garages, disconnect hoses before the first hard freeze, open cabinet doors on outside walls during extreme cold, keep a slow trickle on lines you worry about, and leave the heat on at a modest setting when you travel. These steps cost far less than the cleanup.
Seal gaps where pipes pass through walls and foundations, since a small draft can freeze a pipe in a warm house. Know where your main shut-off is, and test it once on a dry day so that it turns when you need it.
If you will be away, ask a neighbor to check the house, or set the heat to a safe level. A house that cools to the outdoor temperature will freeze its pipes, and the damage is discovered only when you return. For crawl-space plumbing, see the crawl space page, and for a house that has already thawed and leaks, frozen pipe water damage.
Renters and landlords have a shared interest here. A tenant who knows where the main is and who reports a drip early saves the owner a ceiling, and a landlord who insulates the crawl-space lines saves the tenant a month in a hotel. Put the shut-off location on the fridge or in a note for house sitters, because the person who finds a burst pipe at midnight is not always the one who knows the house.
What should you check after a hard freeze?
Walk the house on the first warm day. Look at ceilings under bathrooms, the base of outside walls, cabinets under sinks on exterior walls, the garage and the crawl space. Listen for dripping inside walls and watch the water meter with every fixture off. Early detection limits the damage from a hidden split.
Hidden splits are the expensive ones. A pinhole in a line behind a wall can run for days, and the first sign may be a stain, a smell or a bill. A meter that moves with everything off is the clearest signal that water is going somewhere.
Check outbuildings and seasonal spaces as well. A detached shop, a guest cottage or a rarely used bathroom can sit for weeks without a visitor, and a split in one of them floods quietly.
If you find damp materials, note the date and photograph them before touching anything. A meter reading from a restoration crew shows how far the water traveled, which is not always where the stain is.
- Check ceilings below bathrooms and kitchens
- Look at cabinets under sinks on outside walls
- Watch the water meter with every fixture off
- Visit outbuildings and rarely used rooms
Frequently asked questions
At what temperature do pipes freeze?
Water freezes at 32 degrees, but a pipe in a protected space may stay above freezing while the air outside is colder. We found no sourced Boise threshold. Treat sustained lows below freezing as the signal to prepare exposed lines.
Should I leave a faucet dripping?
A slow trickle on a line at risk can help, since moving water freezes less readily and an open tap relieves pressure. It is a precaution during extreme cold, not a guarantee.
Can I turn the heat down when I travel?
Yes, but not off. Keep the house at a modest temperature, open cabinet doors on outside walls and have someone check the house during a hard freeze.
Will insurance cover a burst pipe?
That depends on your policy and the cause. Sudden pipe failures are often treated differently from groundwater or flood. Your insurer decides, and we cannot predict the outcome.
Who repairs a split pipe and who dries the house?
A licensed plumber repairs the pipe, and a restoration crew removes water and dries the structure. Plan the two together so the house is not wet again when the drying equipment leaves.
Sources
This guide is general information for Ada County homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.