Water expands by roughly 9% when it freezes. Inside a copper or PVC pipe, that expansion exerts pressures between 25,000 and 114,000 kPa — far beyond what any standard residential plumbing is rated to withstand. The result is a split pipe that, once it thaws, can release litres of water per minute into wall cavities, ceilings, and flooring before anyone notices.
In Canada, the Insurance Bureau of Canada estimates that water damage claims driven by frozen and burst pipes represent one of the most frequent causes of major home insurance payouts each year. The average payout regularly exceeds $10,000. The fixes are simple and inexpensive. The knowledge gaps are the problem.
Where Pipes Are Most Vulnerable
Pipes freeze where they are exposed to cold air without sufficient insulation or heat. In Canadian homes, this is usually one of five locations:
1. Exterior Walls
Pipes routed through exterior walls — often the case with kitchen sinks and bathroom vanities on outside walls — sit in a cavity that can reach outdoor temperatures during prolonged cold snaps. Building codes have tightened around this, but homes built before the 1990s frequently have supply lines running through poorly insulated exterior wall cavities.
2. Crawlspaces
Unheated crawlspaces are among the most common locations for frozen pipes. Without insulation on the crawlspace ceiling or along the foundation walls, cold air pools beneath the floor and can freeze any exposed pipe runs. The Health Canada resource on pipe safety notes that a crawlspace temperature of just −6 °C is enough to freeze uninsulated pipes within a few hours.
3. Garage Plumbing
Any water line running through or along an attached or detached garage wall is at high risk. Garage temperatures often track closely with outdoor temperatures, especially when the garage door is opened and closed repeatedly throughout the day.
4. Attic Supply Lines
Some homes — particularly those with bathrooms on upper floors — have supply lines that travel through attic space. These are extremely vulnerable and should be rerouted below the insulation line if at all possible. If rerouting isn't feasible, heat tape is a reasonable mitigation.
5. Basement Rim Joists
The rim joist — the band of framing that sits directly on top of the foundation wall — is frequently uninsulated in older homes. Cold air penetrates through small gaps, and any pipe running adjacent to this area is at risk.
How to Insulate Pipes
Pipe insulation comes in several forms. The most accessible is pre-slit foam pipe insulation, available at any hardware retailer. It is measured by interior diameter — measure your pipe before purchasing. Common residential pipe sizes are 12 mm (1/2 inch) and 19 mm (3/4 inch) for supply lines.
Foam Pipe Insulation
- Slip the pre-slit foam over the pipe and seal the slit with foil tape — not standard tape, which degrades in damp environments
- At corners and junctions, cut the insulation at a 45° angle to maintain coverage without gaps
- Minimum recommended thickness is 19 mm; 25 mm is better for locations near unheated exterior walls
Heat Tape (Electric Pipe Heating Cable)
Heat tape is appropriate for pipes that cannot be adequately insulated — in crawlspaces or along rim joists, for example. Look for CSA-certified self-regulating heat cable, which automatically adjusts its heat output based on the surrounding temperature and is safer than constant-wattage models. Always install it over the pipe first, then cover with foam insulation.
Key installation notes:
- Never overlap heat tape on itself — this creates hot spots that can ignite insulation material
- Use only on water supply pipes — not on pipes that carry gas
- Connect to a GFCI-protected outlet
- Check the cable condition each fall before activating — cracks in the jacket are a fire risk
Passive Measures During Cold Snaps
During extended cold periods when temperatures drop significantly below normal, a few low-effort measures reduce risk without requiring any new materials.
Let the Tap Drip
A slow trickle — roughly 1 drop per second — keeps water moving through a vulnerable pipe run. Moving water requires a significantly lower temperature to freeze than static water. This works best for overnight cold snaps rather than multi-day sustained cold, where continuous dripping adds up in water consumption.
Open Cabinet Doors
For kitchen and bathroom vanities on exterior walls, opening the cabinet doors allows heated indoor air to circulate around the pipes. This is particularly effective in kitchens where the sink cabinet is backed against an outside wall.
Keep the Heat On When Away
Setting the thermostat to 13 °C minimum when the home is unoccupied — even for a few days — is not optional in Canadian winter conditions. Dropping the thermostat below that point risks freezing pipes in the coldest zones of the house even if the main living areas remain above 0 °C. The cost of the extra heat runs $20–$50 for a week-long absence. A burst pipe costs orders of magnitude more.
If a Pipe Freezes
A frozen pipe typically presents as dramatically reduced or no water flow from a specific fixture. If you locate the frozen section:
- Turn off the main water supply valve immediately — if the pipe thaws while already cracked, water flows instantly
- Open the affected faucet to allow water and steam to escape as the ice melts
- Apply heat with a hair dryer, heat lamp, or electric heating pad — start at the faucet end and work toward the frozen section, not the other way around
- Never use an open flame — this damages the pipe material and creates fire risk in wall cavities
- Once thawed, restore water pressure slowly and inspect for cracks or weeping joints
If you cannot locate the frozen section or the pipe is inside a wall, contact a licensed plumber. Attempting to heat a section of pipe you cannot see or access directly causes more harm than good.
If a Pipe Bursts
Shut off the main water valve. For most homes, this is in the basement near where the service enters the foundation. Know where it is before winter — locating it while water is actively releasing into a ceiling is not the time to learn. After shutting the water off, contact a licensed plumber and document the damage immediately with photos for insurance purposes.