Plumbing a Metal Shop or Barndominium: From the Sewer Trench to the Shower

By the licensed master plumbers at Honest Choice Plumbing · TX Master Plumber License M-44120 · Published October 1, 2026

Sewer line trench running to a new metal shop building

Metal shops and barndominiums are everywhere in the North Texas counties we serve. Here's how the plumbing comes together on one, step by step.

1. The sewer line trench

First, a trench for the sewer line from the building to the septic system or city connection. Slope matters here. Too flat and waste sits in the pipe. Too steep and water outruns the solids.

2. Slab rough-in

The drains for bathrooms, kitchens, and utility sinks are laid out and roughed in through the slab. On this job, the slab was cut to run new drains.

3. Top-out

Once walls are framed, drains and vents run up through the studs, and the water supply lines go in. We used PEX for the water supply.

4. Trim-ready

Valves and drains are set, like this shower valve and drain, so the finish trades can close up walls and tile.

The biggest mistake we see

Owners pour the slab first and figure out plumbing later. Cutting a slab after the fact costs far more than laying out drains before the concrete. If you're planning a shop or barndo, bring a plumber in before the pour.

Slab cut open for new drain rough-in inside a metal building
Framed walls with PVC drains, vents, and PEX water lines in a metal building
Shower valve with PEX supply lines and new shower drain rough-in

Frequently Asked Questions

When should a plumber be involved in a barndominium build?

Before the slab is poured. Drain locations need to be planned and roughed in ahead of the concrete.

Can you add a bathroom to an existing metal building?

Yes. It usually means cutting the slab to run new drains, like the photos in this post.

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