Frozen pipes

Short definition

Frozen pipes are water lines that have dropped below 32 °F long enough for the water inside to turn to ice. Because water expands roughly 9% when it freezes, the resulting pressure can split fittings or crack pipe — usually downstream of the ice plug, at the next closed valve or faucet. In Washington, frozen pipes spike during PNW deep-freeze events like January 2024 and December 2008.

What it is

When water freezes inside a closed section of pipe, the ice itself isn’t the immediate problem — the trapped water on the downstream side of the ice plug is. That trapped water has nowhere to go, and the ice keeps growing, so pressure climbs until something fails: a copper sweat joint, a galvanized threaded fitting, a CPVC mid-run, or a PEX expansion fitting.

Failure typically shows up at fittings (where stress concentrates), not along uniform pipe lengths. It may be immediate (audible burst, flooding when the line thaws) or delayed (a hairline crack that leaks slowly, sometimes for weeks before discovery).

The most-vulnerable runs in Washington homes:

• Uninsulated crawlspace — the single most common WA freeze location
• Garage interior wall to a kitchen or laundry stub-out
• Exterior-wall bathroom plumbing in older homes (any wall a plumber wouldn’t put plumbing in today)
• Attic runs over unconditioned spaces
• Outdoor sillcock with a garden hose still attached
• Tankless water heater during a power outage (built-in freeze protection requires AC power)

PEX tolerates several freeze-thaw cycles before fitting failure; copper bursts at sweat joints relatively early; galvanized iron splits at threaded joints; CPVC is the most brittle and often cracks along the length of the pipe.

Why it matters to a homeowner

Washington’s freeze events are infrequent but severe. The January 2024 deep freeze produced a wave of burst pipes across the Puget Sound region, with restoration contractors backed up for weeks. Average single-pipe burst with drywall and flooring repair runs $1,500–$8,000; a multi-pipe failure in a vacant home can total $25,000-plus once mold remediation is included.

The good news: freeze damage is among the most preventable failure modes in residential plumbing. A weekend of fall prep — disconnect garden hoses, insulate exposed pipes, add a heat tape on the most vulnerable run, plan a drip strategy for cold snaps — eliminates most of the risk for under $200.

If a pipe is already frozen but not yet burst, you have time. The wrong move (open flame, see never use open flame to thaw) burns down the house. The right move (gentle ambient heat, working from the faucet back) costs nothing.

What to do if a pipe is already frozen (no burst yet)

1. Open the faucet at the frozen fixture so meltwater has somewhere to go
2. Identify the frozen section — usually the coldest accessible run upstream
3. Apply gentle heat — hairdryer on low, warm towels, a heat lamp at safe distance
4. Work from the faucet back toward the freeze so meltwater can escape
5. Never use an open flame (propane torch, blowtorch, candle) — this is a leading cause of winter house fires

What to do if you suspect a burst

1. Shut off the main water valve immediately — know where it is before you need it
2. Drain the system by opening the lowest faucet in the house and a high faucet to break the vacuum
3. Document everything with photos for insurance
4. Call a plumber. Burst-pipe repair in finished walls is not a DIY job
5. Don’t restore power to a tankless water heater that froze until a plumber inspects the heat exchanger

Common failure modes

• Burst at a copper sweat fitting in an unheated crawlspace
• Burst at a galvanized threaded joint in pre-1970s WA homes
• PEX line cracked at a fitting after multiple freeze cycles
• CPVC cracked along the pipe length during severe freeze
• Outdoor sillcock split inside the wall when a garden hose was left attached
• Tankless heat exchanger damaged during a power outage in cold weather
• Vent stack frozen at the roof penetration (rare in WA but possible during sustained sub-20 °F with east winds)
• Toilet tank cracked from freezing in an unheated bathroom

Common variants and disambiguation

• Frozen pipe (no flow) vs. frozen pipe with burst — the first is recoverable; the second is a damage event
• Frozen supply line (under pressure) vs. frozen drain or vent stack — different problems, different fixes
• Pipe freezing is a near-synonym; older trade books use the phrase for the general phenomenon, “frozen pipes” is the homeowner-search term

Washington note

Washington’s freeze risk is uneven by region:

• Western WA / Puget Sound — typically mild winters but occasional Arctic intrusions push temps below 20 °F for multi-day periods. Pre-1980s housing stock often has copper supply lines in exterior walls and uninsulated crawlspaces.
• Eastern WA — sustained sub-zero conditions multiple times per winter; freeze prevention is routine, not exceptional.
• Cascade and Olympic foothills — second-home and cabin culture; vacant-home freeze is the dominant failure mode (see winterizing piping and how to winterize a Washington cabin).

The WA Energy Code (WSEC, WAC 51-11) requires minimum pipe insulation on hot-water lines in new construction and major remodels — this prevents some freeze events indirectly but is not aimed at freeze protection specifically. For an existing home, freeze prevention is on the homeowner.

FAQ

At what temperature do pipes freeze?

Water freezes at 32 °F, but pipes inside walls and crawlspaces don’t usually freeze until outdoor temperatures sit below about 20 °F for several hours, because building heat and insulation buffer the indoor pipe temperature. Wind exposure, lack of insulation, and sustained cold all lower this threshold. Plan freeze prevention for any forecast below 25 °F overnight.

How long does it take a pipe to freeze?

In an exposed, uninsulated run with sub-20 °F ambient air, freezing can start within 4–6 hours. Pipes in insulated walls or in heated spaces take much longer. The rule of thumb in WA: if a freeze warning calls for 25 °F or lower for two or more nights, the prep should already be done.

Will my insurance cover a burst pipe?

Most HO-3 / HO-5 policies cover sudden burst-pipe damage, with deductible. Common exclusions: vacancy clauses (homes empty beyond a stated period), unmaintained heat (some policies require minimum 55 °F when occupied), and damage from open-flame thawing. Read your policy and document any winter absences.