Short definition
A stub-out is a short pipe segment projecting through a wall or floor into a fixture rough-in, capped or terminated for later connection of an angle stop and a supply riser. It’s the universal residential rough-in detail — the 1/2-inch copper, PEX, or CPVC stub you see sticking out of the drywall behind every sink and toilet.
What it is
During rough-in plumbing (before drywall and finish), the plumber runs supply lines to each fixture location and terminates them with a short stub projecting about 2 to 4 inches past the eventual finished wall surface. The stub is capped while drywall and tile go in, then cut to flush during trim-out. An angle stop or compression-fitting valve slides over the stub, cinches down, and provides the shutoff valve and connection point for the fixture’s flexible supply riser.
For showerheads and tub spouts, the classic stub-out fitting is a drop-eared elbow with a short threaded nipple. For washer hookups, 3/4-inch stubs feed both hot and cold to a recessed washer box. Modern PEX systems use a brass or plastic stub-out elbow with a nailing flange that fastens to the framing.
UPC requires stub-outs to be properly secured against pull-out — strapped or clipped within 6 inches of the termination so an angle stop can be tightened without the stub moving in the wall.
Why it matters to a homeowner
You’ll encounter stub-outs whenever you replace an angle stop, a faucet, or a toilet. The cap or angle stop comes off, the stub is what’s left, and that’s the surface a new compression fitting needs to seal against. If the stub is loose behind the drywall (no strap), the angle stop wobbles when you turn the handle, and you may end up with a slow leak at the compression fitting that looks unfixable from outside.
Old galvanized stub-outs in homes from before the 1980s can corrode and refuse to seal a new angle stop — at which point the cure is replacing the stub with copper or PEX, which means opening the wall.
Common failure modes
- Loose stub-out. No strap behind the drywall; angle stop wobbles. Leak at compression fitting.
- Stub-out too short. Angle stop can’t seat past the wall plate. Extension required.
- Galvanized stub-out corroded. New angle stop won’t seal. Replace with copper or PEX.
Common variants
- Generic stub-out vs. PEX-specific stub-out elbow. PEX uses an elbow fitting with a nailing flange and a brass nipple.
- Stub-out vs. drop-eared elbow. Drop-eared is one common stub-out fitting.
- Stub-out vs. stub stack. Stub stack is vent-stack vocabulary, unrelated despite the shared word.