Plumbing under a house on piers

Three things, mostly. Cold reaches pipes in the open air under the floor, old iron drains wear out, and a house that shifts on clay can strain the joints. You can see much of this from the access hatch. Repairs underneath belong to a licensed plumber.

19-1 Why this house is different from a slab

Chapter 18 dealt with pipes you never get to see. A house on piers gives you the opposite problem. The pipes are right there, hung under the floor in moving air, and you can look at them from the hatch.

Older country houses were often built up off the ground. Figure 19-1 is a Texas tenant farm from 1913, whose board house appears to sit up on blocks, and Figure 19-2 is a small farmhouse of unstated date, from Central Texas, not this region. Plumbing arrived in many such houses after they were built, so what is under the floor may be several generations of work laid on top of one another. Those two points are ordinary observation.

19-2 Cold comes from below

AgriLife says water pipes "have the potential to freeze and burst when the outside temperature reaches 20 °F or below," and it lists pipes in crawl spaces among the exposed ones.¹ On a pier house that is most of the supply line. AgriLife names a pipe sleeve and UL-listed heat tape as protection, and skirting around the house is ordinary practice on top of that. Chapter 28 sets out the rest before the cold, and Chapter 29 covers what to do once it has happened.

Do not crawl under a house in a storm to thaw anything. The state's review of the 2021 storm listed "engaging in outdoor repair activity during the storm" among the risk factors for hypothermia deaths.² And open flame under a wooden floor is out of the question at any time. AgriLife warns against a "blowtorch, kerosene or propane heater, charcoal stove, or other open flame devices."¹

19-3 Drains, slope and old iron

Drain pipes work by gravity. AgriLife describes the line from the house to the system as piping "on a slope to allow gravity to move the waste and water."³ So a drain depends on staying at its pitch, and on a pier house it hangs from a floor that may move.

The clay is the reason it may. The 1979 soil survey of Lamar and Delta counties says of its largest map unit that the soils "shrink and swell greatly with changes in moisture content," and it calls them "corrosive."⁴ Clay under a pier does the same as clay under a slab. The Texas Department of Licensing and Regulation says that soil with high moisture "will heave (swell), causing a building to be lifted," and low moisture will "collapse."⁵ No official source was found saying this breaks pipes under a pier house. It is an inference from the soil and the common experience of plumbers, and you should weigh it as that. Chapter 14 takes the same care with the long line.

Figure 19-3 is the view you want to learn to read. White plastic drain lines meet an old rusted iron stack, with a plastic sheet over the dirt below. Where iron meets plastic, the joint is often made with a banded coupling, and no-hub fittings (Plumbing Supply and More, run by the same team as this book) are one kind, sold at one place linked here so you can recognize the word. Knowing the name helps you follow what a plumber tells you. It is not a suggestion to do that joint yourself.

19-4 Looking, and stopping at the hatch

Look from the access opening with a good flashlight. That is the job this chapter gives you. What follows is ordinary practice.

The last row outranks everything here. Propane vapors "are heavier than air and may accumulate in low-lying areas," the Railroad Commission says, and a crawlspace is one.⁶ Chapter 33 has it in full.

Past the hatch, this book stops. It gives no instructions for crawling in, cutting pipe or re-hanging drains. The legal side runs the same way as under a slab. Chapter 31 quotes the homestead exemption and sets out who may do the rest.⁷ Gas piping counts as plumbing under the statute's definition, and this book's answer is that it goes to a licensed plumber or, for an LP gas system, a licensed LP gas installer.