Plumbing 101: Mobile Homes | Terry's plumbing

Plumbing 101: Mobile Homes

Mobile home plumbing is a bit different than plumbing in a site-built home. This article will help you learn how mobile home plumbing differs from a site-built home, and, of course, the most common mobile home plumbing issues you need to be on the lookout for.


Mobile homes use the same basics as site-built homes in their plumbing system designs, but there are a few obvious differences between the two. The list below dives deeper into those differences:

  • Supply Line Location – The plumbing system of a mobile home is simplified for easy transport and installation but that doesn’t mean it’s inferior in any way. The location of the supply lines is different in mobile homes simply because the homes are built differently. Supply lines are what the water travels through to reach each fixture. In site-built homes, they are typically running inside the walls. In mobile homes, they are almost always buried under the floor.
  • Cut-Off Valves – Another big difference is the lack of cut-off valves in mobile homes–though newer models have these implemented now. It’s smart to have cut-off valves at every water source (faucet, tubs, and toilets). However, in older style mobile homes there was only one main cut-off. So, if you had to repair or replace anything on a mobile home plumbing system you have to use the main valve–cutting off water to the entire home–to decrease pressure in the lines.
  • Pipe Sizes – Pipe size plays a big role in a plumbing system. Using a pipe that is too small for your venting can cause just as much trouble as using too small of a pipe for your waste line. Many mobile home builders install a smaller 3″ pipe for drainage and venting, while site-built homes would have 4″ pipe.

Common Plumbing Issues

Nasty smells – Ventilation issues are very common in mobile homes. Ventilation makes your pipes remain at neutral pressure. Without proper venting, your drainage slows and the water in your P-trap goes away, which in turn allows the nasty smells to escape into your home. Venting issues are hard to find. The easiest cases will either be a clogged vent stack, separation of a vent line somewhere, or a failed auto-vent under a sink.

Plumbing Leaks – Plumbing supply lines in mobile homes will rarely be inside a wall so you won’t need to worry too much about damage to walls. When there is a leak it’s usually the floors, sub-flooring, insulation, and HVAC ducts under the home that get damaged. If your flooring is made of composite wood or MDF it will soak water up like a sponge.

Clogged Sinks & Tubs – If there is a clog in your sink or tub, a plunger can work well. If you have a two-sided sink, close off one side by stuffing a rag into the drain and plunge the other side, then switch–continue this process until the clog is gone. If you have clog issues frequently, it may be time to find the underlying issue.

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