Missing P-trap on an inspection report: sewer gas, cost

What happens if there is no P-trap?

With a missing P-trap, sewer gas can come up the drain into the house. A P-trap is the bend under a drain that holds a little water, and that water blocks sewer gas from rising into your living space (Done). With no trap, or a trap that has dried out, nothing stops it. Get a licensed plumber to confirm which one you have and price the fix before your inspection deadline.

Key takeaways

• A rotten-egg smell can also be a natural gas leak. If you can't tell which, leave the house and call the gas utility or 911.
• A dried-out trap lets gas in just like a missing one. Water in the drain may stop a dry one; have a plumber confirm a trap is there.
• Nothing replaces the trap itself. In a tight space the fix is a different trap style or a rerouted drain, and wall work is priced separately.

How much does a plumber charge to replace a P-trap?

What a plumber charges depends on the job, so compare your bid to the row with the same scope.

Kept prices every line of an inspection report for $79, usually under 4 hours.

The Homewyse figure is the trap at the fixture. It leaves out permit fees, sales tax, and any work to move or modify existing plumbing or finishes. HomeAdvisor notes that plumbing behind drywall means removing drywall, drilling through joists, and putting it all back. If the plumber has to open a wall or reroute a drain, get that as its own written line.

Say the report flags missing traps under two sinks. At Homewyse's range, two traps run 2 x $313 to 2 x $393, or $626 to $786, before permit fees and tax. Homewyse says the 2-hour labor minimum "can be applied to other tasks," so a plumber doing both traps in one visit may bid less than double. Ask for one bid covering both. Wall or drain work comes on top.

Is a sewer gas smell dangerous?

Sewer gas can be dangerous. Wisconsin's health department calls sewer gas "a complex mix of toxic and nontoxic gases" whose "highly toxic components" include hydrogen sulfide and ammonia (Wisconsin DHS). The Occupational Safety and Health Administration (OSHA) says of hydrogen sulfide that "exposure to very high concentrations can quickly lead to death" (OSHA). Wisconsin DHS adds that "methane and hydrogen sulfide gases are both flammable and highly explosive."

Don't trust your nose to size it. Hydrogen sulfide "smells like rotten eggs, even in low concentrations," but "at high concentrations, hydrogen sulfide can interfere with the sense of smell." Methane, also in sewer gas, has no smell at all.

What to do depends on what you're smelling:

• You think sewer gas is building up in a closed space. Wisconsin DHS says to "evacuate the building and call the fire department for help." Don't make a spark from an electrical appliance, a match, or a lighter.
• You're not sure it's sewer gas. Gas companies add a rotten-egg smelling chemical to natural gas so people can smell leaks (U.S. Energy Information Administration). Leave, then call the gas utility or 911, then a licensed plumber.
• The smell stays at one drain and nobody feels sick. Book the plumber inside your inspection window.

Could the smell just be a dry trap?

A dry trap can let the same gas in. A trap only works while it holds water, and in a drain nobody uses that water can evaporate. Wisconsin DHS tells homeowners to "flush floor and sink drains with water to prevent the traps in sewer pipes from drying out."

Its checklist for a smell: follow the odor to where it comes in, such as a basement floor drain. Then check the roof plumbing vent for leaves or nests. Adding water to the drain or clearing the vent may stop the gas. If the leak is behind a wall, you may need a plumber to find it.

A shower or floor drain needs a trap too; it just sits under the floor where you can't see it. A plumbing company in Memphis suggests shining a light into the drain to see whether water is sitting down there (Mr. Rooter Plumbing of Memphis). Before you touch fixtures in a house you don't own yet, ask your agent. No water can also mean a leak, so if the smell comes back after water goes in, that's a question for the plumber.

What can be used instead of a P-trap?

Nothing can be used instead of a trap, but a P-trap isn't the only kind. A Denver-area plumbing company says a tight space is no reason to leave the trap out (Done). The fixes it lists:

• A bottle trap, a compact trap common under vessel and wall-hung sinks in Europe and increasingly accepted by U.S. plumbing codes.
• Moving the drain stub-out in the wall a few inches to make room for a standard trap.
• Rerouting the drain line to get the depth a trap needs.

An air admittance valve (AAV) can solve a venting problem, but it does not replace the trap. Which fix fits is a call for a licensed plumber on site. Whether a setup meets code depends on the plumbing code your town adopted, so the local building department or a licensed plumber answers for this house.

Who can confirm it before my deadline?

A licensed plumber can confirm it. A home inspector working to the International Association of Certified Home Inspectors (InterNACHI) Standards of Practice checks the drain, waste and vent system. The same standards say the inspector does not have to "open sealed plumbing access panels" or judge "the proper design or sizing of any water, waste or venting components."

Ask the plumber for three things in writing: whether a trap is there, the scope of the fix at each fixture, and a price. How to get repair estimates during the inspection period covers booking that visit fast.

What should I ask the seller for?

Ask the seller for the fix by a licensed plumber, or a credit equal to the plumber's written bid. Name the fixture and the scope so there's nothing to argue about. A line like "Install a P-trap under the basement laundry sink, licensed plumber, per the attached written quote" does that. What to ask for after a home inspection shows how it fits with the rest of your list, and the buyer repair request letter template has the wording around it.

If the seller says no:

• Ask for the credit instead of the repair, backed by the same bid.
• Look again at the scope if the fix needs walls opened or a drain rerouted. Get that priced before you decide.
• Read [when to walk away after a home inspection](/guides/when-to-walk-away-after-a-home-inspection) if you can't get a figure before your deadline.

Your contract sets the exact dates and terms, so confirm them with your agent. If the report lists other plumbing items, plumbing findings on an inspection report covers them.

What are the first signs of sewer gas poisoning?

Signs of sewer gas poisoning at low levels, per Wisconsin DHS, include "eye and respiratory irritation" from hydrogen sulfide, plus dizziness, drowsiness, headaches, nausea, and nervousness. If you have these symptoms and suspect a sewer gas leak in the home, it says to see a doctor.

How do I know what the rest of my report is worth?

If the sewer smell is one line on a long report, upload the report to Kept and spend your remaining days on the plumber's visit, not on pricing the rest.

Sources

• Wisconsin Department of Health Services, Air: Sewer Gas
• OSHA, Hydrogen Sulfide: Hazards
• U.S. Energy Information Administration, Natural gas and the environment
• InterNACHI Standards of Practice
• Done, What if there's no room for a P-trap?
• Mr. Rooter Plumbing of Memphis, What in the world is a P-trap?
• Homewyse, Cost to install a sink trap
• HomeAdvisor, How much does it cost to hire a plumber?