Why do mobile home water lines freeze under the skirting?

The federal HUD standard treats freezing as a design problem the maker has to solve. It says "all piping and fixtures subject to freezing temperatures shall be insulated or protected to prevent freezing, under normal occupancy."

Why does freezing break a pipe? The American Red Cross explains that water "expands as it freezes," which "puts tremendous pressure on whatever is containing it, including metal or plastic pipes." It adds that "no matter the strength of a container, expanding water can cause pipes to break." The split often shows up later, when the ice melts and water runs out of the crack.

The Red Cross also lists the places most likely to freeze, including pipes that run against exterior walls with little or no insulation, and it says both hot and cold pipes in unheated areas should be insulated. A crawlspace under a home fits that description.

### Does skirting keep the pipes warm?

The federal rule on skirting is about air, not heat. It does not describe a sealed box: "a crawlspace with skirting must be provided with ventilation openings." The minimum area is one square foot of opening for every 150 square feet of floor, or one square foot for every 1,500 square feet where a vapor retarder covers the ground beneath the home. In areas subject to freezing, the standard says the vent covers "must also be of the adjustable type, permitting them to be in the open or closed position, depending on the climatic conditions."

So the vents are required, and they let air in. In freezing areas the standard wants covers that can be opened or closed to suit the weather. Because the same rule requires ventilation, a plumber or the installer should decide what is right for your home before you seal anything.

Two parts of the HUD rules matter.

At the factory. The standard says the maker must provide "written installation instructions for the method(s) required" for freeze protection, plus a statement that "if the heat tape or pipe heating cable is used, it must be listed or certified for its intended purpose." The maker must also provide "a receptacle outlet" that meets the electrical section of the standard.

At the site. The installation standard says the water line connections between sections of a multi-section home, made during installation, must be protected from freezing. It adds that in areas subject to freezing or subfreezing temperatures, exposed sections of water supply piping, shutoff valves and pipes in water heater compartments "must be insulated or otherwise protected from freezing." The same list also names devices on the supply line. It also says "only heat tape or pipe heating cable listed and certified for its intended purpose is permitted for use, and it must be installed in accordance with tape or cable manufacturer installation instructions."

There is one more detail for drains. A note in the same standard says fittings in the drainage system subject to freezing, "such as P-traps in the floor, are protected with insulation by the manufacturer," and that "insulation must be replaced if it is removed for access to the P-trap." If a repair took the insulation off, it needs to go back on.

### What else does the standard say about the piping under the home?

Several other rules bear on freezing. All piping, "except the fixture trap, shall be designed to allow drainage," which is what lets a line be emptied. Piping, pipe threads and supports exposed to the weather, water, mud and road hazard "shall be painted, coated, wrapped, or otherwise protected from deterioration." Exterior openings around piping and equipment "shall be sealed to resist the entrance of rodents." Separately, the Red Cross advises adding insulation to crawl spaces, which keeps those areas warmer. The Red Cross lists water supply pipes in unheated areas such as crawl spaces among the pipes that freeze most often.

### Which pipes freeze first?

The Red Cross lists two groups. The first is pipes "exposed to severe cold, like outdoor hose bibs, swimming pool supply lines, and water sprinkler lines." The second is "water supply pipes in unheated interior areas like basements and crawl spaces, attics, garages, or kitchen cabinets." A manufactured home has few of the interior spaces on that list, but it does have a crawlspace, an outdoor hose bib and often a sprinkler line. Check those first before a cold night.

The Red Cross also suggests looking at "other areas where water supply lines are located in unheated areas," including under kitchen and bathroom cabinets, and insulating both hot and cold pipes there. It says pipes that run against exterior walls with little or no insulation are at risk too, and a manufactured home has plenty of exterior wall.

Use the steps the Red Cross recommends, and follow the manufactured home rules above.

• Insulate exposed pipe. The Red Cross suggests pipe sleeves or UL-listed heat tape or heat cable on exposed water pipes. For a manufactured home, the federal rule says the tape or cable must be listed and installed to the maker's instructions.
• Let a faucet drip on a very cold night. The Red Cross says running water through the pipe, even at a trickle, helps prevent freezing. Choose a faucet served by exposed pipes.
• Handle hose bibs. Remove and drain outdoor hoses, and close the inside valve to an outdoor hose bib if there is one.
• Check the insulation on the water connection. The standard says the water connection must be wrapped or protected when it is subject to freezing.
• Know where the shutoff is. The installation standard requires an identified and accessible shutoff valve between the supply and the home, and the water riser for it must be underneath or adjacent to the home. If a pipe splits, turning that valve is the first move.

Our frozen pipes in Phoenix page covers the temperatures and general home tips.

The Red Cross says that if you turn on a faucet and only a trickle comes out, suspect a frozen pipe. It advises keeping the faucet open, since running water helps melt the ice as it thaws, and checking other faucets, because if one pipe freezes, others may too. The Red Cross says to thaw a pipe with a heating pad, hair dryer or space heater kept away from flammable materials, and not to use "a blowtorch, kerosene or propane heater, charcoal stove, or other open flame device."

If a pipe has split, shut off the water at the valve and call a plumber. The standard requires an access opening at least 18 inches wide and 24 inches high, located so any utility connections under the home can be reached.

Call if you are not sure what is under your home, if a line has split, or if insulation and heat tape look damaged. Heat tape must be listed, and a plumber can check what is installed. Our pipe materials in mobile homes page explains what may be under there, and the sewer and septic connection page covers the drain side.

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