Sewer Backwater Valve Installation in Van Nuys and Sherman Oaks: When Los Angeles Code Actually Requires One
A backwater valve is a one-way gate installed in your sewer lateral. Sewage from the house flows out through it. Sewage coming the other way, from a surcharged city main under the street, pushes a flapper shut and stays out. It is a small casting in a box at grade, it costs a fraction of what a flooded lower level costs to clean up, and on a fair number of Valley lots the plumbing code has required one since long before the house last changed hands.
Most homeowners in Van Nuys and Sherman Oaks learn about the valve standing in a garage with three quarters of an inch of water on the slab and a floor drain doing the opposite of its job. We have had that conversation in enough garages to write it down here instead.
The code test is one measurement, and you can check it yourself
California Plumbing Code Section 710.1 is the governing language, and Los Angeles adopts it. The test compares two elevations. If any fixture in the house has a flood level rim sitting below the cover of the next upstream manhole on the public sewer, that fixture has to be protected by an approved backwater valve. Flood level rim means the edge where the fixture would spill over: the lip of a shower pan, the top of a floor drain grate, the rim of a laundry sink.
Walk out to the street and find the manhole cover uphill of your house. Now look at your lowest drain. If that drain sits lower than the lid, the street is a reservoir and your shower is the overflow point. There is no hydraulic modelling and no calculation sheet behind the requirement, only those two elevations.
The houses that fail it in our service area fall into recognizable groups. Post-and-beam homes on the flats with a sunken living room or a step-down den. Anything with a basement, which in the Valley usually means a 1920s or 1930s house south of Ventura Boulevard. Garages built into a grade change, common on the streets climbing out of the Sherman Oaks flats toward Coldwater Canyon Avenue. And the duplexes and fourplexes along Sepulveda Boulevard and Van Nuys Boulevard where a laundry room was cut into the lowest corner of the building in the 1960s.
Why the Valley floor surcharges in the first place
Los Angeles runs a separate sanitary sewer system. Storm runoff is supposed to reach the storm drains, the washes and the Los Angeles River. Sewage is supposed to reach treatment, in our case mostly the Donald C. Tillman Water Reclamation Plant on Woodley Avenue and the outfall system beyond it. The two are not connected by design.
They get connected by defect. Cracked laterals under wet ground let groundwater in. Downspouts and area drains that somebody tied into the sewer 40 or 50 years ago, because the sewer was 30 feet closer than the street, let stormwater in. Manhole lids in low intersections take water over the rim. Add that up across a few thousand properties and the main under your street carries far more on the second day of a storm than it was sized for. Then it backs up and looks for the lowest opening it can find, which is frequently a floor drain a block and a half away.
Geography decides who gets it. The flats around Oxnard Street, Vanowen Street and Victory Boulevard sit low, the water table near Bull Creek and the Sepulveda Basin is shallow, and laterals running north out of Sherman Oaks toward the river channel have the least fall to work with. We see the same handful of blocks after every wet winter.
What the valve will not do, said plainly
A backwater valve protects you from the city's water coming in. It does nothing about your own.
If your backups come from roots in a 4-inch clay lateral, a bellied section holding water instead of draining at the quarter-inch-per-foot fall it was laid to, an offset joint left by the 1994 Northridge earthquake, or grease off a kitchen line, the valve is not the repair. It can mask the problem for a season and then fail at the wrong moment, because the same roots and grease that clog a pipe will hold a flapper open or jam it shut. We will not sell you a valve as a substitute for fixing the pipe, and anyone who does has not run a camera down it.
So the sequence matters. Camera first. If the lateral is sound and the water is coming from the street, the valve is the right answer and a cheap one. If the lateral is failing, repair or line it and add the valve during the same excavation while the trench is already open. Our sewer camera inspection is what tells us which of those two conversations we are having.
One more thing nobody mentions at the sale. While the valve is shut because the street is surcharged, your house has nowhere to drain either. Do not run laundry, skip the dishwasher, keep showers short. The valve buys you a dry floor, not unlimited capacity.
Where it goes, and what the work involves
The valve belongs outside the building, in the lateral, downstream of everything it protects and upstream of the city connection. In practice that means at or near the two-way cleanout by the property line, so one excavation serves both. It sits in an access box with a removable lid set flush to grade, because a valve nobody can reach is a valve nobody will ever service.
Bodies come in cast iron and in PVC, sized 4-inch for a house lateral and 6-inch where a fourplex or a commercial building runs a larger line. On a residential lateral we generally set a PVC-bodied unit with a flapper on a stainless pin, coupled into SDR 35 or Schedule 40 with proper transition fittings where the existing pipe is clay, cast iron or Orangeburg from before 1972. Whatever the material, it has to be an approved type listed for sewage service, it has to stay accessible, and it has to be bedded so the flapper seats level. A valve set out of plumb leaks past the seat and you have paid for nothing.
The on-property work takes a plumbing permit from LADBS. If the valve or cleanout lands in the parkway or under the sidewalk, that portion falls to the Bureau of Engineering and needs its own authorization. We pull both. In the City of Los Angeles the owner is responsible for the lateral all the way to the main, including the run in the public right of way, so there is no version of this where the paperwork belongs to somebody else. Most installs are a two to four foot trench at the property line, located with a camera and sonde first and backfilled the same day.
Maintenance, which is the part that gets skipped
Open the lid once a year, before the rain, and look. The flapper should swing freely and drop closed. Wipe the seat. Pull out any rag, wipe or root hair caught on the hinge. If the box has filled with soil, dig it out and find where the soil is coming from.
Buildings with a commercial kitchen need this quarterly. Grease sets up on a flapper hinge faster than anything else we see, and a greased-open flapper is a straight pipe.
If your line is already on a cleaning interval for roots, ask the crew to check the valve on the same visit. It takes four minutes. For the rest of the pre-winter list, see our guide on preventing sewer backups, and if you are smelling sewer gas after storms rather than seeing water, that is a different diagnosis with a different fix.
Not sure whether your house needs one?
We will check the elevations, camera the lateral, and tell you straight whether a backwater valve is the fix or a distraction. Van Nuys, Sherman Oaks and the whole San Fernando Valley, 7 days a week.
Call 818-280-9135Frequently asked questions
Does Los Angeles require a backwater valve on my house?
Only if you fail the elevation test in California Plumbing Code Section 710.1, which Los Angeles adopts. If any fixture's flood level rim sits below the cover of the next upstream manhole on the public sewer, that fixture must be protected by an approved backwater valve. Sunken rooms, basements, garage floor drains and lowest-level laundry rooms are the usual candidates. Houses whose lowest drain sits above that manhole lid are not required to have one and generally do not benefit from one. We check the elevations on site before quoting.
Will a backwater valve stop my drains from backing up?
It stops sewage from the city main entering your house when the street surcharges. It does nothing about a clog inside your own lateral. If the cause is root intrusion, a bellied or offset section, or grease, the valve is not the repair and can hide the real problem for a season. Run a camera down the line first. If the lateral is sound and the water is coming from the street, the valve is the right fix. If the lateral is failing, repair it and add the valve while the trench is open.
Where does the backwater valve get installed?
Outside the building, in the sewer lateral, downstream of every fixture it protects and upstream of the connection to the city main. In practice that usually means at or near the two-way cleanout by the property line, so one excavation serves both, with the valve in an access box set flush to grade for servicing. The trench is typically two to four feet deep and most residential installs are backfilled the same day. Placement is confirmed with a camera and sonde locate so the box lands where digging is least destructive.
How often does a backwater valve need to be serviced?
Inspect it once a year, before the rainy season. Open the lid, confirm the flapper swings freely and seats closed, wipe the seat, and clear any rag, wipe or root hair on the hinge. Properties with a commercial kitchen should do this quarterly, because grease builds on the hinge and a flapper held open by grease is no better than plain pipe. If the line is already on a root-cutting or jetting schedule, have the crew check the valve on the same visit.
More reading: how a sewer cleanout works and why yours matters, or see our frequently asked questions for scheduling and what we do and do not work on.
BBC Rooter & Plumbing is a sewer and underground pipe specialist at 8635 Yolanda Ave #6 in Northridge, CSLB license #720343. We do sewer laterals, trenchless repair, hydrojetting, camera inspection, root removal and backwater valves. We do not do water heaters, fixtures, repiping or gas lines, and we say so on the phone rather than after we arrive.