What a rough-in is and why it can smell
A rough-in is drain and vent piping installed during construction and capped off for future use. In an unfinished basement, a cluster of capped pipes poking out of the slab in a corner usually marks where a bathroom was planned. When a later owner finishes the basement, those pipes are connected to a toilet, shower and sink, or sometimes buried behind drywall and left capped.
Sewer gas reaches a room when the barrier between the drain system and indoor air fails. A cap that was taped rather than properly fitted, a test plug that was never replaced, a cracked fitting under a vanity or a shower that sits unused for months can all let it through. In homes where the basement drains sit lower than the main sewer line, a sealed ejector or sewage pit collects waste and pumps it up; if its lid gasket or vent connection fails, the smell is unmistakable.
Basement bathrooms in family homes often see little use. A guest bath used a few times a year will lose the water in its traps, especially in winter when furnace-heated air is very dry.
Staircase with floor protection taped over the treads. A general example of this kind of work, not a photo of a particular home, business or job.
Basement plumbing points to inspect
- Every floor drain, including the one in the mechanical room
- Shower and tub drains in a basement bathroom, plus the sink and toilet
- Any capped pipes visible in storage or under stairs
- The lid, gasket and vent pipe of a sewage ejector pit, if present
- The laundry standpipe and any utility sink
- Cleanout plugs on the main stack
- Any wet bar sink in a basement entertainment area
What to do with what you find
- IfRunning water into a drain makes the smell fade within a dayThenA dry trap was the problem. Run water monthly, or ask a plumber about a trap primer or trap seal device for drains that rarely get used.
- IfA capped pipe is loose, taped or has a rubber test plugThenHave a plumber install a proper permanent cap. Tape and test plugs are not meant to be permanent.
- IfThe smell is around an ejector pit lidThenAsk a plumber to check the lid seal and the vent connection. Do not open a sewage pit yourself.
- IfOdor persists after traps are full and caps are soundThenA plumber can run a smoke test on the drain and vent system to show where gas is escaping, including behind finished walls.
Common questions
Is sewer gas dangerous?
At the faint levels usually noticed from a dry trap it is mainly a nuisance, but it should not be ignored. Strong or persistent odor, headaches or nausea are reasons to get a plumber in promptly and air out the space.
Does a radon mitigation system affect this?
It can interact with a sealed sump or pit lid. If your basement has both, ask the plumber and radon contractor to check that each lid and seal is intact.
General information for Highlands Ranch, not a quote or professional advice. In an emergency, call 911.