Do Pipes Really Freeze in Fullerton? Foothill Freeze Nights in Bastanchury

Two effects, and they work in opposite directions on the same hillside.

Cold air is denser than warm air and drains downhill at night, pooling in low areas and valleys. That is why the coldest readings on a still winter night are often at the bottom of a slope rather than the top.

But elevation also means clearer skies, less urban heat retention, and more radiative cooling on a still night. The foothill neighbourhoods north of the city sit at the top of Fullerton's elevation range, and they are more exposed than the built-up flats.

In practice the coldest nights in Fullerton are clear, still, dry post-Santa Ana nights — when the offshore flow has scoured out humidity and there is no cloud cover to hold heat in.

Bastanchury sits at the highest ground in the city. Rolling Hills, the upper parts of Sunny Hills and the Coyote Hills ridge are in the same band.

Not your interior plumbing. These are the vulnerable points:

Water expands about nine percent when it freezes, and the burst mechanism is not what most people assume.

The pipe rarely splits where the ice forms. What happens is that ice forms at a cold point and blocks the pipe, and continued freezing behind it pushes water toward the closed tap. Pressure builds in the trapped section between the ice plug and the fixture, and the pipe fails at the weakest point in that section — which may be a considerable distance away.

The second thing people get wrong is the timing. The burst frequently does not release water while it is frozen, because ice is plugging it. It releases when everything thaws the following morning — which is why freeze damage is discovered at breakfast rather than overnight, and why a house left empty during a cold snap can be found flooded days later.

This is genuinely all it takes for a Fullerton house, done once before December.

Disconnect garden hoses and drain them. Fit inexpensive insulated foam covers on exterior hose bibs — a few dollars each and they solve the most common failure outright.

Insulate any accessible supply line running through the garage or an unheated space with foam pipe sleeve.

Insulate or wrap the irrigation backflow assembly, or shut it off and drain it if you are not irrigating through winter.

Then on a forecast night in the high twenties: open the cabinet doors under sinks on exterior walls so household heat reaches the pipes, and let one distant tap drip very slightly overnight. Moving water is far harder to freeze, and the drip relieves pressure if an ice plug does form.

The sign is a tap that produces nothing, or a trickle, on a cold morning while other taps work normally.

Leave the tap open. That gives melting water somewhere to go and relieves pressure as the plug releases.

Apply gentle heat to the accessible pipe — a hair dryer, warm towels, a space heater in the room. Work from the tap end toward the frozen section so meltwater can escape.

Never use an open flame, a torch or a heat gun. That is how frozen pipes become house fires, and it is a genuine annual occurrence in colder parts of the country.

And be ready for a burst on thaw. Know where your main shut-off is before you start warming anything, because if the pipe did split you will find out in the next few minutes.

Freeze damage is not the main water risk to a Fullerton home and it would be dishonest to suggest otherwise.

Across our work, slab leaks, water heaters, appliance connectors and storm intrusion account for the overwhelming majority of losses. Freezing is a handful of calls a year, almost all of them hose bibs and irrigation assemblies rather than interior plumbing.

The reason to do the prevention anyway is that it takes ten minutes and costs almost nothing. Foam covers on the hose bibs and a sleeve on the garage run is a very small investment against a burst at full household pressure into an unoccupied garage.

If you are travelling over the holidays, shutting the water off at the main is the complete answer to all of it.

The damage from a freeze is rarely apparent during the cold. It appears as the ice thaws and the split lets go, usually mid-morning as the sun hits the west and south walls.

That is the window to be paying attention. A split found while you are standing next to it is a valve turn; the same split found that evening has been running for eight hours.