Drains Blocked After Heavy Rain in Snohomish County? Here’s Why

Heavy rain doesn’t usually block drains by itself. What it does is reveal blockages that were already there but didn’t make themselves known under normal conditions. Snohomish County averages about 41 inches of rain a year, and most of that arrives between October and May. By February or March, the sewer laterals and storm drains across Everett are taking on more water than they were designed for in any single 24-hour window — and the marginal ones fail first.

Five Reasons Heavy Rain Backs Up Drains in Everett Homes

In rough order of how often we see them:

1. Root intrusion in the sewer lateral. The most common cause in older Everett homes. Roots restrict normal flow by 20–40% before any symptoms show up; add the surge volume from a heavy rain and the line fails. Our walkthrough on spotting root intrusion in a sewer line covers the diagnosis.
2. Combined sewer overload. Some older Everett neighborhoods still have partially combined storm + sanitary sewer systems. During heavy rain, the city main fills, backflow valves engage, and homes downhill of the surcharge point see their drains slow or reverse.
3. Foundation drain overload. If your gutters tie into the foundation drain system (common in 1970s–80s splits around View Ridge and Mill Creek), heavy roof runoff goes into the same lines that handle groundwater. The system is designed for groundwater rates, not 40 GPM gutter flow.
4. Failed backflow prevention valve. If you have a backwater valve installed and it’s not seating properly, water can come back from the city main during surcharge. Failure modes include debris stuck in the flapper or simple wear.
5. Crushed or collapsed pipe section. Less common but worth ruling out. Heavy rain doesn’t cause this — it reveals it. We’ve found partial pipe collapses caused by ground settling that nobody noticed until the first heavy rain of fall.

What to Check Yourself Before Calling

Three quick checks. First — are your gutters and downspouts clear, and are they actually discharging away from the foundation? A lot of Everett homes have downspout extensions that have come loose over time, dumping roof water right against the foundation where it backs up the foundation drain. Free fix. Second — if you have a cleanout in your yard or basement, check whether water is sitting in it after rain. If yes, your lateral is restricted. Third — look at the storm grates near your property. If they’re choked with leaves or debris, the city’s drainage isn’t keeping up with the rain rate and your home is downstream of the problem.

If your interior fixtures are also slow during heavy rain — toilets gurgling, tubs draining slowly — that’s almost always the lateral, not the storm drain. The six signs of a clogged drain cover the diagnostic before we send a truck. Different problem requires different tool.

When This Becomes an Emergency

Water actively coming up through a basement floor drain or shower drain during heavy rain is an emergency. Call. Don’t try to plunge it, don’t try to pour anything down it. The water is coming up from the lateral or the city main, and the right move is to stop using water in the house until the lateral can be relieved. Same goes for sewage smell during or after rain — that’s the lateral, not weather, and the fix is mechanical not seasonal.

For the routine “my drains are slow during big rains” situation, our sewer line specialists can scope and clear the lateral so it can handle the surge volume. Or just reach our Everett-area drain service directly — we keep camera trucks rolling daily during the wet season for exactly this reason.