Preventing Frozen Pipes in the DC Area

Why do pipes freeze in a place with mild winters?

The DC area does not stay frozen for weeks the way northern cities do, and that is part of the problem. Many houses were never built with deep winter in mind, so a few nights in the teens find the weak spots quickly: a supply line inside an exterior wall, a hose bib on the north side, a pipe running through a garage or a vented crawl space. Water expands as it freezes, pressure builds between the ice and a closed faucet, and the pipe splits. Often nobody notices until the thaw, when the crack starts spraying.

Housing age matters too. The median home in the District was built in 1957, and the inner suburbs are not much younger, with median build years in the mid-1970s for Arlington and Alexandria. Older rowhouses and detached homes tend to have little wall insulation, drafty basement windows, and plumbing that was rerouted during past renovations through whatever space was handy. Utilities feel the cold as well: WSSC Water notes that main breaks tend to rise a few days after the Potomac River reaches a new low temperature, a reminder that the same weather is working on the pipes inside your house.

Which pipes in your house are most at risk?

Virginia American Water points out that snow over a meter pit acts as insulation, so there is no need to shovel it off. The same utility warns that replacing a frozen meter can cost more than $100, which is far more than a night of extra water use.

What should you do in the fall, before the first freeze?

1. Find and test the main shutoff. Both DC Water and WSSC Water put this first on their winter lists. Label it so anyone in the house can find it in the dark. In many rowhouses it sits low on the front basement wall where the service pipe comes in.
2. Winterize outdoor faucets. Remove hoses, close the shutoff for each outside faucet (it is inside the house), then open the outdoor tap so the line drains. Frost-free sillcocks still need the hose removed, or water trapped in the hose can freeze back into the valve.
3. Seal the drafts. Caulk gaps where pipes and cables pass through the foundation, replace broken basement window panes, and weatherstrip doors near plumbing.
4. Insulate exposed runs. Foam pipe sleeves are an easy fix in basements, crawl spaces and garages. If a line runs somewhere you cannot keep warm, UL-listed heat tape is an option, but Fairfax County Fire and Rescue warns that installing it even slightly outside the manufacturer's directions can start a fire.
5. Book a heating check. A furnace or boiler that quits on the coldest night is the most common way an otherwise safe house ends up with frozen pipes.

If your home has had the same pipe freeze more than once, it is worth having a plumber look at rerouting it through a warmer part of the house. A whole-house plumbing inspection before winter can flag the runs that are most exposed.

What should you do during a cold snap?

• Keep the thermostat at 55°F or higher, day and night, including when you are away. DC Water and WSSC Water both use that number.
• Let the most exposed faucet drip. A thin, steady trickle keeps water moving. Virginia American Water suggests running both hot and cold overnight. WSSC Water recommends dripping only while you are home, and Fairfax County Fire and Rescue cautions that you cannot count on dripping alone.
• Open cabinet doors under sinks on outside walls so room heat reaches the pipes.
• Keep garage doors closed if any water lines run through the garage.
• Check the basement once a day. A frosty pipe or a faucet that suddenly delivers only a trickle is an early warning.

Leaving town for the holidays?

An empty house is where most freeze damage gets serious, because a split pipe can run for days before anyone sees it. Leave the heat at 55°F or above and ask someone to check the house regularly. A freeze alarm, which Virginia American Water says costs under $100, can call a phone number if the indoor temperature drops below 45 degrees. For a longer absence, consider closing the main shutoff and draining the lines. This also matters for insurance: the National Association of Insurance Commissioners notes that policies generally expect a minimum indoor temperature and that a vacant home's water supply should typically be shut off. Read your own policy for the exact wording.

A pipe froze. What now?

Signs include a faucet that will not run or only sputters, frost on an exposed pipe, or a bulge in a copper line. Work through it in this order:

1. Close the water. Shut the main or the valve that feeds the frozen section before you start thawing, so a hidden crack cannot flood the room once the ice melts. If it is a hot water line, turn off power or gas to the water heater as well.
2. Open the faucet nearest the frozen spot so melting water and pressure have somewhere to go.
3. Warm it gently. A hair dryer, warm towels, or warming the room all work. Start near the faucet and move back toward the ice. Never use a torch or other open flame; Fairfax County Fire and Rescue warns it thaws the pipe too fast and weakens it. Keep space heaters away from anything that can burn and never leave them running unattended.
4. Turn the water back on slowly and look along the pipe for drips or spray.

If you cannot reach the frozen section, or it is inside a finished wall or ceiling, stop and call for help. If thawing reveals a split, our step-by-step page on what to do in the first minutes after a pipe bursts walks through the next moves, and you can be connected with a plumber for burst pipe repair in the District.

Is it your pipe or the utility's?

Inside the house it is yours. Outside, the dividing line depends on your water provider:

• DC Water handles the service pipe in public space; the section on private property belongs to the owner. Its 24-hour Emergency Command Center is 202-612-3400.
• WSSC Water, which serves Montgomery and Prince George's counties, is responsible for the part of the line that connects to the main; the customer owns the part from the property line into the home. Emergencies: 301-206-4002.
• Arlington County owns the line up to and including the meter; the owner has the rest. Its 24-hour hotline is 703-228-6555.
• Fairfax Water owns the meter and its setting, while the underground lateral from the meter to the house shutoff is the homeowner's plumbing.

Other providers, including Loudoun Water, Prince William Water, Virginia American Water and several city and town systems, have their own rules; the number to call is printed on your water bill. If the street has no water or you see water coming up through pavement, report it to the utility. If only your house is affected, a plumber is the right call. For an outdoor service line split by frost, see repairing a broken water line.

Local help across the region

Freeze calls come from every part of the area, from Capitol Hill rowhouses to split-levels in Annandale and older homes in Takoma Park. In Prince George's County, homeowners can start with plumbers in College Park, and in Northern Virginia, with emergency plumbers serving Arlington. A wet basement after a thaw can also overload drainage, so it is worth reading our guide to basement sump pumps in the DC area. When the water is pouring and you are not sure whether it can wait, our checklist on deciding between an emergency call and a regular appointment helps. You can also browse every community we cover.