When the temperature starts dropping, unprotected pipes can start popping as water freezes and expands. And no one wants that.

The pipes most vulnerable to temperatures below 32 degrees are those not protected by a home’s insulation, in unheated areas such as attics, crawl spaces and outside walls. Holes in outside walls where TV, cable or phone lines enter also allow outside cold air to reach pipes.

Even if a home’s exposed pipes are already wrapped and the voids caulked, it’s common sense to do an annual check, and some preparations must be performed each year. In the spirit of keeping pipes safe, here’s a winterizing checklist.

Pipes can wear sleeves

In unheated areas, protect pipes with insulation. Pre-cut sleeves of foam rubber or fiberglass are convenient.

The big squeeze

Use caulk to seal holes and cracks in outside walls and foundations near interior pipes.

Check down under

If your house has a crawl space underneath, close all air vents in foundation walls.

Protect faucets

If possible, close inside valves supplying outdoor faucets. Keep the outside faucets open so any remaining water in the pipes can expand without causing the pipes to rupture. If no inside valve is available, let outside faucets drip during freezing weather.

What if a pipe freezes?

The first sign that a pipe is frozen usually happens when someone turns on a faucet and gets only a trickle of water or nothing at all. At that point, finding and gently thawing the frozen pipe before it can burst becomes crucial.

If the pipe has burst, immediately shut off water at the main or to the damaged portion of the plumbing system.

If water is flowing only to part of the house, the frozen pipe may be in a wall or crawl space. As an intermediate measure, open cabinets in the kitchen and bathroom to allow warm air to flow inside and warm the pipes. Next identify the affected area and track its supply pipe to where it is exposed to cold air, such as in a crawlspace or basement.

After the frozen pipe is located, This Old House suggests, open the affected faucet and all hot water taps in the house. Allow them to run until water begins to flow from the affected faucet, then close the other faucets down to a trickle. Let water run at the affected faucet until full pressure has returned.