Keeping pipes from freezing overnight is a problem many people face when unusually cold temperatures arrive in an area. In most cases homes are built using methods that stand up to the typical winter in the area they are in but only get into freezing trouble only when unusually cold temperatures arrive.
Inside the home keeping the heat turned up high can help. If you turn down the heat to save heating costs it can come back to bite you in the form of frozen pipes. Fixtures located on exterior walls with pipes located in cabinets and vanities are in greater danger because the closed doors keep heat from reaching the pipes. Open the doors to allow warm air to reach the pipes.
Insulate the pipes when they run through unheated areas such as crawl spaces, outside, and in attics. Insulation will not stop the freezing process but will slow it down. Heat tape may be used in areas that are exposed and away from combustibles.
With crawl spaces if you have a floor hatch you may set up a fan blowing heated air from in your home into the crawlspace. Vents in the crawlspace can temporarily be sealed with Styrofoam insulation to eliminate cold drafts on the pipes. If the crawl space is large enough that portable space heaters could safely be used, they may raise the temperature enough to prevent pipes from freezing.
Some advocate leaving faucets trickling. This may lead to frozen drain lines, which can be very difficult to thaw. In a sense if the water volume is too small to maintain the temperature above freezing until it discharges from your drain it may freeze in the drainpipe. You may be better off frequently running high volumes of water intermittently than running water at a constant trickle.
When pipes do freeze a hairdryer may become an invaluable tool for thawing the pipe. The hot air can be directed towards the hole in the wall through where the pipe goes and will eventually make its way to the frozen section of the pipe thawing it.
If you have pipes that freeze often you may want to discuss your options for rerouting the pipes in a manner that will prevent them from freezing in the future. Quite often pipes that are exposed outside can be buried and brought inside before they go above ground. Buried pipes that freeze can be buried deeper where they will not freeze. Pipes that are in exterior walls can be relocated to come up from the floor instead of the wall.