CoreLogic, the real estate analytics firm, specializes in crunching numbers. This spring, they're adding a new product to their risk mapping portfolio: a nationwide database that estimates the risk of a sewer backup at any given property. "The Sewer Backup Risk Score identifies the potential risk of sewer backup and basement flooding with unique location-specific analysis," reports insurance news website Claims Journal (see: "CoreLogic Discusses Launch of Risk Analytics for Sewer Backup," by Denise Johnson).

That's information any homeowner or contractor would like to have. Unfortunately, CoreLogic's customer isn't the builder or homeowner: it's the insurance industry. Even if they get quoted a higher rate for their insurance policies because of the sewer backup risk, homeowners probably won't be aware of the connection between their insurance rate and the particular hazard to their property.

For insurance companies, the information is a big deal: "Sewer backup claims are expensive," reports Claims Journal: "a typical claim averages in the mid $30,000's."

"Lindene Patton, vice president and global head of Hazard Products at Corelogic … said sewer backup claims are increasing due to converging circumstances like increased urbanization, an aging infrastructure, more frequent and severe claim events, and the continued migration to coastal areas of the U.S which includes both lakes and oceans," Claims Journal reported.

In 2012's Hurricane Sandy, flooding created sewage problems on a community scale, not just an individual property scale. Storm surge waters inundated low-lying sewage treatment plants, causing massive spills into streams, rivers, and the ocean. Thousands of homes were flooded and contaminated. The New York Times covered that story at the time (see: "Sewage Flows After Hurricane Sandy Exposing Flaws in System," by Michael Schwirtz). "At least six sewage plants in the New York region shut down completely during the storm, and many more were crippled by storm surges that swamped motors and caused short circuits in electrical equipment," the Times reported.

Billions of gallons of untreated sewage spilled into waterways or contaminated neighborhoods and homes, nonprofit group Climate Central estimated (see: "Report Cites Large Release of Sewage From Hurricane," by Michael Schwirtz).

But it doesn't take a superstorm to cause a backup: much smaller events can send sewage flooding into a home through the main drain. The summer after Sandy struck, the Staten Island Advance reported on a New York renter's second experience of storm-flood sewer failure (see: "Hurricane Sandy victim after last week's flooding: I lost everything -- again," by Deborah Young). Angela Smith, a young working mother flooded out of her last apartment by Sandy, had just moved into another apartment after six months in temporary lodgings. But then came the remnants of Tropical Storm Andrea. "As Ms. Smith cuddled with her children on their brand new couch listening to the drops pelt the windows, she heard a sickening, gurgling sound," the Advance reported. "Sewage water began flooding out of the toilets, the tub and drains, rising so quickly it sent the family fleeing to Ms. Smith's parents' place. Water still covered the floor when they returned to the apartment at 482 Mason Ave. the next morning; the water mark was nearly 4 feet high, and a sour smell filled the air, Ms. Smith said."

Ms. Smith turned to her renter's insurance for relief, but to no avail. "Ms. Smith said she called Allstate," the Advance reports, "expecting her renter's insurance would pay at least part of the cost of replacing the furniture, washer and dryer, clothing and other items she bought with her savings and the $4,600 she got from FEMA after Sandy destroyed her Naughton Avenue apartment. But she was told the policy doesn't cover sewage backups. A spokeswoman for Allstate confirmed the policy does not cover the damage, calling the renter's policy a 'peril policy' with sewage not included among the named perils."

A continent's width away, homeowner (and licensed general contractor) Joey Roche has a similar story, reports the Portland Oregonian (see: "What one homeowner learned from 15,000 gallons of raw sewage," by Dana Tims). Roche and his wife returned from a five-week family trip to find their house a disaster area. A municipal sewer line downhill from the home had been blocked by a scrap of 2x4 during maintenance work; sewage from uphill homes had backed up in the line and found its way into the Roches' house. "The couple had paid $265,000 for the house a few months earlier," reports the Oregonian. "Everything they owned, from new furniture they'd bought to family heirlooms and crucial business documents, lay buried beneath 4 feet of human waste, which for weeks had been baking in daytime temperatures exceeding 100 degrees."

Covered by insurance? Not so much, reports the paper. The family's homeowners' insurance capped sewer backup damage at $10,000 (and that, only because of a rider that Roche had purchased separately). Comments Oregon Insurance Division official Ron Frederickson: "I get calls every single day from people who are outraged to find out that they simply aren't covered for things they thought they were. In the end, unfortunately, there's usually not much I can do for them."

Independent insurance adjuster Dick Tutwiler blogged about sewer backup coverage in May of 2013 (see: "Super Storm Sandy and the "S" word…SEWAGE, Over Ten Billion Gallons of Raw Sewage release. Are you covered?" by Dick Tutwiler). In some cases, Tutwiler says, insurance policies cover drain backup damages if the blockage occurred inside the house — but not if the sewer outside the house (or rising water from a storm) causes the failure. (Obviously, sewage generated inside a home that floods the building because it can't exit the premises is nothing like the catastrophe of a municipal sewer pipe sending a whole neighborhood's flow into your basement.) But some policies don't cover sewage no matter where it comes from — while a few lucky Sandy homeowners, Tutwiler says, had very generous coverage in place for sewer backups, receiving full replacement value for their damaged goods and for cleanup and repair.

As for prevention, Tutwiler advises homeowners to look into having a plumber install a backflow preventer on the main drain of their house. This won't help you if six feet of contaminated water is surging through your street; but it could protect your house if the only problem is a sewer line backing up into your drain.

After Hurricane Sandy, New York City authorities offered advice for homeowners about backflow preventers (see: "Install a Sewer Backflow Valve"). According to the city, installing a backflow valve should cost from $600 to $1400 (including excavation and backfill), depending on the type of valve.