The pipes that freeze first

The places it actually starts

• Pipes in exterior walls. The worst case in residential plumbing. A supply line run in an outside wall has insulation only on the cold side at best, and often the pipe sits between the insulation and the sheathing where it is effectively outdoors. Kitchen sinks on outside walls are a frequent casualty.
• Unheated crawlspaces. Vented crawlspaces track outdoor temperature closely, and the plumbing runs along the joists where the cold air is.
• Hose bibs with a hose attached. A frost-free bib is designed to drain itself, and an attached hose stops that. This is the most common freeze failure of all, and the split happens inside the wall.
• Garages, especially where a water heater, utility sink or laundry has been put in an attached but unheated garage.
• Attic runs. Less common in Colorado than in warmer states, but when they exist they freeze fast.
• Unfinished basements along the rim joist, where cold air pours in through gaps at the sill plate.
• Vacant or barely heated spaces — a closed-off guest room, a shut-down vacation property, a room with the vents closed to save money.

Why north and west matter

Two reasons, and both are specific to our climate. South-facing walls get sun all day even in January, and at this altitude that sun has real intensity — a south wall can be meaningfully warmer than the air temperature. North walls get none of it.

West matters because of wind. Front Range winter wind comes predominantly from the west and northwest, sometimes hard. Wind does not lower the temperature of a pipe below the air temperature, but it dramatically increases the rate of heat loss, and it drives cold air through every gap in the envelope. A pipe in a wall cavity that a 20-degree still night would not trouble can freeze on a 25-degree windy one, because the cavity is being actively flushed with outside air.

That is why air sealing often does more for freeze protection than insulation. Insulation slows heat loss; sealing stops the cold air actually reaching the pipe.

The ten-minute walkthrough

1. Walk the perimeter of the basement or crawlspace with a flashlight. Look for daylight at the rim joist, and feel for drafts.
2. Note every pipe you can see running along an exterior wall or through an unheated space. Those are your candidates.
3. Open the cabinet doors under kitchen and bathroom sinks on exterior walls. Feel the back of the cabinet — if it is noticeably cold, that is where to leave the doors open on hard nights.
4. Check every hose bib for an attached hose.
5. Look at the garage: is there plumbing in it, and is the garage door seal intact?
6. Find the main shutoff and confirm it works. This is the one that matters if something does burst.

Before a hard freeze

• Seal air leaks at the rim joist, around pipe penetrations, and anywhere outside air enters a cavity with plumbing in it. Canned foam and caulk, cheap and effective.
• Insulate exposed pipe in crawlspaces, garages and unheated basements. Foam sleeves are inexpensive; the trick is covering the whole run including elbows, since the uncovered elbow is where it freezes.
• Open cabinet doors under sinks on exterior walls so room air reaches the pipe.
• Let a faucet drip on the coldest nights, on the fixture served by the most vulnerable run. Moving water resists freezing, and the open faucet relieves the pressure that actually bursts pipes.
• Keep the thermostat up, including when away. Dropping the house to 50 degrees to save money is a false economy if the pipes in the walls are relying on indoor heat.
• Keep the garage door closed, particularly if there is plumbing in there.
• Disconnect hoses, if you have not already. It bears repeating because it is the most common failure.

If a faucet runs dry on a cold morning

That is a frozen line, and you likely have a short window before it becomes a burst one.

1. Leave the faucet open. As the ice thaws, the water has somewhere to go, and that relieves the pressure.
2. Find the frozen section. Trace from the dry fixture back toward the main, through whichever unheated space the line passes. Frost or visible bulging on the pipe is the marker.
3. Apply gentle heat. A hair dryer, a heat lamp, warm towels, a space heater aimed at the area. Work from the faucet end back toward the frozen section so meltwater can escape.
4. Never use an open flame. No propane torch. It is a leading cause of house fires in freeze events, and it can boil water inside the pipe into steam and rupture it.
5. Open cabinets and let room heat in.
6. If you cannot find or reach it, or if more than one fixture is dry, call. Smith runs 24/7 emergency plumbing.

If it has already burst

Shut off the main immediately — that is the whole reason to know where it is. Open the lowest faucet in the house to drain the system down. If water is near electrical panels, outlets or equipment, kill power to that area before stepping in it. Then call. Damage from a burst pipe scales almost directly with how long the water runs, which is why the shutoff valve is the single most valuable thing in this article.

Our frozen pipe prevention guide has the full seasonal checklist, and outdoor winterization covers the irrigation side.

Frequently asked questions