Commercial Backwater Valve Installation in Phoenix

When any drain sits below the next upstream manhole cover in the public sewer. The 2024 IPC Section 714.1 puts it plainly: fixtures on a floor with a finished floor elevation below that manhole cover are protected by a backwater valve in the building drain or the horizontal branch serving them. The reasoning is simple. If the city main fills past capacity, sewage rises to its lowest outlet, and the lowest outlet in your building is the first to flood. Valley cities add their own measures. Mesa asks for a valve where the finished floor is less than 12 inches above the upstream manhole, and Scottsdale asks for one where the floor is not 12 inches higher. Both sit on private property. Our FAQ on when a backwater valve is required covers the rule in more detail.

Section 714.1 also contains a restriction that surprises owners: fixtures above that elevation may not discharge through a backwater valve in new work. A valve that is closed during a surcharge shuts off drainage for everything behind it, so upper fixtures are piped separately. Existing buildings are excepted from that restriction.

The installer cuts into the building drain and sets the valve in line, with access to the working parts. First, an elevation check settles whether the valve is required and which fixtures sit behind it. Second, the installer finds the drain and its slope, usually with a camera (see sewer camera inspection). Third, the slab is opened over the drain, the line is cut and the valve is set level with an access box or cover so the flap can be inspected and cleaned. A cleanout is often added upstream. The valve must be ASME- or CSA-listed, and the code requires that access be provided to its working parts. After the valve is set the line is tested, the slab is patched, and the permit is inspected. In Phoenix, new drain piping is permitted work and concealed piping may not be covered until it is inspected.

A valve protects everything upstream of it, and it also blocks drainage upstream of it when it closes. In a multi-tenant building one valve on the main building drain can serve every suite below the manhole line, so ownership and maintenance should be written down, because a valve that nobody opens and cleans is a valve that fails. The sequence after a backup is covered in multi-tenant sewer backups. Cleanouts, camera runs and routine cleaning keep debris from holding the flap open. The code says access must be provided to the working parts, so treat the access cover as a maintenance item, not a decoration.

Insurance is a separate question; see commercial water leak versus sewer backup coverage before you assume a policy pays for a sewer backup.

It protects fixtures that drain through the building drain below the valve's location. Floor drains, restroom fixtures, floor sinks and mop sinks on a low floor are the usual ones. It does not protect upper fixtures routed separately, and it does not replace indirect connections: a walk-in cooler floor drain protected by a valve must still discharge through an air break or air gap under Section 802.1.2. See floor sink versus floor drain for the difference.

A valve does not clear a stoppage in your own line. If the backup comes from a clog on your side of the cleanout, a valve changes nothing, and the answer is drain cleaning or a camera run. If every fixture is above the upstream manhole cover, the code does not call for a valve and may not allow new fixtures to drain through one. If the fixtures are too low for gravity drainage at all, the answer is an engineered pumped system, which is separate design work and not part of this service. And if the sewer is backing up often, ask the city about the main; a valve limits the damage but not the cause.

HQ installs backwater valves with free estimates and upfront pricing before work starts. Send us the address, the lowest floor drain location, your city and any as-built drawings with the street manhole elevation. Related: commercial plumbing, commercial sewer lateral repair and our sewer repair page.