There is no single answer. The federal HUD standard allows copper, brass, galvanized steel and listed plastics such as PEX, CPVC and polybutylene for water lines, and ABS, PVC, copper or cast iron for drains. What your home has depends on its age and maker, so a plumber should identify it.
What pipe materials does the federal standard allow?
Manufactured homes, which many people still call mobile homes, are built to a federal code written by HUD, the U.S. Department of Housing and Urban Development. The plumbing part of that code says that water pipe "shall be of standard weight brass, galvanized wrought iron, galvanized steel, Type K, L or M copper tubing, approved or listed plastic or other approved or listed material." It adds that "all plastic water piping and fittings in manufactured homes must be listed for use with hot water."
The code also keeps a list of the standards that pipe and fittings can meet. Under plastic pipe, that list includes CPVC hot and cold water systems, PEX tubing and PEX distribution systems, and polybutylene hot and cold water systems. For copper, it lists water tube standards. For drains, it lists ABS and PVC drain, waste and vent pipe, along with cast iron soil pipe.
So the answer is a range, and the standard does not say which material a given home has.
### What about the drain pipes?
Drain lines are a separate system from the water lines. The HUD standard says drainage piping "must be standard weight galvanized steel, brass, copper tube DWV, listed Scheduled 40 ABS plastic, listed Scheduled 40 PVC plastic, cast iron, or other listed or approved materials." In practice, black ABS or white PVC drain pipe is what most people see under a manufactured home.
### Is anything not allowed?
Yes. The standard says "used piping materials shall not be permitted," and it bars pipe dopes, solder, fluxes, oils, solvents and chemicals that are "toxic, corrosive, or otherwise detrimental to the water system." For homes that connect to a public water system, all water piping must be lead-free as defined in the Safe Drinking Water Act Amendments of 1986.
Does the age of the home matter?
Yes, and it matters more than the brand. The list of allowed materials is a list of what the code permits, not a promise of what your home has. It still names a polybutylene standard alongside CPVC and PEX. Polybutylene has its own history, and our polybutylene pipes page covers it and what to do if you have it.
If your home is older, do not assume anything about what is in the wall or under the floor. The HUD standard says "the material and design of fittings shall conform to the type of piping used," and that "special consideration shall be given to prevent corrosion when dissimilar metals are joined." Those rules apply to how the home was built, and they are a reminder that fittings and pipe have to match when a section is repaired.
We would not guess at what you have from a description. The safe way to find out is to have a plumber look at the pipe itself.
How do the lines connect, and what else does the standard say?
Two connections matter when you are thinking about pipes. The water connection is a threaded inlet. The standard calls for a "3/4 inch threaded inlet connection" on each home with a water distribution system, and it says the connection must be tagged or marked as the fresh water connection. The installation rules require an accessible shutoff valve between the water supply and the inlet, and say that when the local water pressure is over 80 psi, a pressure-reducing valve must be installed.
The drain connection is one outlet. The standard says "each manufactured home shall have only one drain outlet" and that the outlet and connector must be at least 3 inches inside diameter. Our page on how a manufactured home connects to sewer or septic explains what happens next.
### What is different about plastic pipe?
Plastic pipe has its own installation rules. The standard says plastic piping "shall not be exposed to heat in excess of manufacturers recommendation or radiation from heat producing appliances," and that all plastic water piping and fittings must be listed for use with hot water.
Two plastics get compared all the time. Our PEX vs CPVC page explains how they differ, and both appear in the federal list.
### What else does the standard say about how the pipe is installed?
The plumbing section has several rules that show up in repairs. Galvanized pipe "shall not be bent or welded." Cracks, holes or other imperfections in materials "shall not be concealed by welding, brazing, or soldering or by paint, wax, tar, or other leak-sealing or repairing agents." Joints in copper water tube must be made with approved fittings and solder that "contains no more than 0.2 percent lead." Piping and electrical wiring "shall not pass through the same holes in walls, floors or roofs."
The standard also says the maker must state that the home "has been designed for an inlet water pressure of 80 psi," and that where the water pressure exceeds 80 psi a pressure reducing valve should be installed. Outdoor hose bibs, where provided, must be protected by "a listed nonremovable backflow prevention device." These rules are why a repair that looks quick, such as a sealant on a crack, does not meet the standard.
### How is the pipe sized?
The standard sizes water piping by counting fixtures. You start at "the most remote outlet on any branch" and count toward the water service connection, adding up the fixtures each section supplies. It says a water heater, food waste disposal unit, evaporative cooler or ice maker "shall not be counted as a water-using fixture when computing pipe sizes." It also sets a floor for old-style threaded pipe: "no galvanized screw piping shall be less than 1/2 inch iron pipe size." Valves in the supply system, when fully open, must have an opening at least equal to the pipe's nominal size.
None of this tells you what is in your home today. It tells a plumber what a correct repair looks like, and it is one more reason to have the pipe identified before a section is cut out.
What should I do if I am not sure what I have?
Have the pipe identified before anyone cuts into it, and do not rely on a guess. These steps get you there safely.
- 1Look at the pipe where you can see it. Under the sink or at the water heater is a good place to start. Do not cut into anything.
- 2Write down what you see. Note the color, any printing and where the pipe runs, so a plumber has something to work from.
- 3Ask a plumber to identify it before any repair. The standard says fittings must match the type of piping used.
- 4Check freezing protection. Lines under the home need protection, and our frozen pipes under skirting page covers it.
HQ Plumbing & Air is licensed and insured, gives free estimates and upfront pricing, and answers 24/7. If you are planning a repipe, a plumber can tell you what your home has now and what the code allows for the replacement.