Sewer Backwater Valve

When a property needs one:

• Water at the floor drain in storms. Sewage or gray water at basement drains in heavy rain, interior drains clear afterward. EPA counts about 700 US communities on combined sewers, which wet weather can overwhelm.
• Fixtures below the manhole cover. Any fixture on a floor below the cover of the next upstream manhole in the public sewer is inside the model codes' trigger, storm history or not.
• A valve nobody has opened. FEMA's retrofitting guide is blunt: debris can hold a check valve open. An uninspected valve is an unknown.

This page covers the inline valve protecting a whole lower level: the code trigger, assessing an existing valve, installation, repair, replacement and maintenance. It is not the drinking-water assembly covered under Backflow Prevention. Sewage on the floor now is Sewer Backup Emergency; the lateral defect behind a backup is Sewer Backup Repair; the floor drain body and its built-in flapper are Basement Drain Repair; a merely blocked drain is Floor Drain Cleaning; whether the water even comes from the sewer is decided on the Basement & Flood Prevention hub.

How the assessment runs:

• The code trigger, measured not guessed. The 2021 International Plumbing Code, Section 714.1, where adopted, protects fixtures on a floor whose finished floor elevation is below the manhole cover of the next upstream manhole in the public sewer; the 2021 International Residential Code, Section P3008.1, uses the fixtures' flood level rims.
• Locating and opening an existing valve. A round cover in the slab where the building drain leaves, or a lid outside between house and lateral. Cover off, in dry weather: debris on body and gate, the o-ring, free movement of the flapper. Hartford's MDC warns against opening it during rain; nothing protects while it is apart.
• Which fixtures pass through it. Only lower fixtures. IPC 2021 Section 714.1 bars fixtures above the manhole cover elevation from discharging through it in new work, with an exception for existing buildings; IRC 2021 Section P3008.2 lets upper fixtures pass only through a normally open type, with an exception for existing buildings. Sump and ejector discharge has its own check valve (Section 712.2 of Virginia's 2021 plumbing code, which adopts the 2021 IPC).

The work, and what writes the number:

• Installation. A listed valve (IPC 2021 Section 714.2: ASME A112.14.1, CSA B181.1 or CSA B181.2) in the building drain or the branch serving the lower fixtures, with access to the working parts (Section 714.3), a cleanout, and enough fall from the lowest fixture's flood rim. Slab cut inside, valve pit outside.
• Repair. A flapper held open by debris, a hinge that no longer swings, a cover seal that weeps in a surcharge: cleaned, re-seated or rebuilt where the body is sound.
• Replacement. A body cracked with the slab, an obsolete valve with no parts, or a valve taking upper fixtures it should not: replacement, normally open where upper fixtures keep passing through, the IRC 2021 Section P3008.2 rule, whose exception tolerates normally closed in existing buildings.
• Maintenance. No model code sets an interval. Hartford's MDC and Superior, WI say twice a year; NDSU Extension says annually; FEMA says regularly. Utilities from Philadelphia to Seattle leave upkeep with the owner.
• Municipal programs. DC Water's Backwater Valve Rebate Program reimburses in full up to a cap for combined-sewer-area owners with a documented backup. Philadelphia Water Department's Basement Backup Protection Program installs valves at no charge for qualifying customers with sewer backups.
• What writes the number. Pipe size and material, slab cut versus excavation, an existing cleanout or not, valve type, and the permit, which is local: DC Water says the District requires one obtained by a master plumber; Utah's Ashley Valley Water and Sewer Improvement District leaves installation to the owner.

• Basement Bathroom Plumbing
• Basement & Flood Prevention
• Sewer Backup Emergency
• Basement Drain Repair
• Backflow Prevention