Sewage Backup in Denver Homes: Causes, Cleanup, Who Pays

Sewage backs up into a shower because the shower is the lowest drain in the house. When the main sewer line between the house and the street blocks, everything that goes down any drain comes up through the shower or the basement floor drain first. In Denver metro homes built before 1970, the block is almost always a clay sewer line cracked by expansive bentonite soil and invaded by tree roots.

This guide gives the cleanup steps, the Denver-specific causes, who pays when the block is in the city main, what a sewer scope and a repair cost, and what a backup means when the home is being bought or sold.

Why does sewage back up into the shower in Denver metro homes?

• Clay sewer lines. Homes built before 1970 in Denver, Englewood, Lakewood, Arvada, Wheat Ridge, and Littleton were plumbed with vitrified clay pipe in 3-foot sections. Each joint is a gap that roots find.
• Bentonite soil. Front Range clay soils swell when wet and shrink when dry. Every freeze-thaw and every wet spring shifts the pipe, opening joints and creating "bellies" where waste settles and rots.
• Tree roots. Silver maples, cottonwoods, and elms planted in the 1950s and 1960s send roots straight into the joints. A root ball in a 4-inch clay line blocks it in two to three years.
• Orangeburg pipe. Some 1950s and 1960s homes used tar-impregnated fiber pipe. It deforms into an oval and collapses at 50 to 60 years old, which is now.
• Grease, wipes, and paper. "Flushable" wipes do not break down. They catch on the first offset joint and build a dam.
• The city main. A block in the main under the street sends flow back up every service line on the block. This is the one case where the city pays.

What should I do in the first hour?

1. Stop using water. No flushing, no laundry, no dishwasher. Every gallon down a drain comes up in the shower.
2. Check the neighbors. If two or more houses on the block have the same backup, call the city or district. In Denver, call 311; in Aurora, call Aurora Water; in Highlands Ranch, call Centennial Water and Sanitation District.
3. Call a plumber with a camera. Ask for a main line clear and a sewer scope, $350 to $600 for both on a same-day call in the Denver metro.
4. Photograph everything before you touch it. Insurance and a city claim both need the pictures.
5. Keep people and pets out of the room until it is cleaned and disinfected.

How do I clean sewage backup in a shower, step by step?

1. Put on protective gear. Rubber gloves to the elbow, an N95 or better mask, goggles, rubber boots. Sewage carries E. coli, hepatitis A, and norovirus.
2. Ventilate. Open the window and run the bathroom fan. Dry Colorado air helps here; the room dries in hours, not days.
3. Remove standing water. Use a wet-dry vacuum with a filter you will throw away. Bail into a bucket and pour into a working toilet only after the line is cleared.
4. Remove solids and debris. Bag them in contractor bags, double-bagged, and put them in the trash, not the compost.
5. Clean the surfaces. Hot water and dish soap on the tile, grout, drain cover, and the shower door track. Rinse.
6. Disinfect. One part household bleach to ten parts water, applied to every surface the sewage touched, left wet for 10 minutes, then rinsed. Do not mix bleach with anything else.
7. Dry it completely. Fan for 24 hours. Pull the drain cover and clean under it; that is where the smell lives.
8. Throw out what touched sewage. Bath mats, loofahs, shower curtains, and anything porous. Towels wash on hot with bleach or go in the trash.
9. Wash yourself and your gear. Boots and goggles in the bleach solution; gloves and mask in the trash.

When do I call a professional instead?

• The water left the shower. Sewage on a floor with a subfloor, on drywall, or on carpet needs a remediation company. Wet drywall must be cut out 12 inches above the water line.
• It sat more than 24 hours. Bacteria and mold move into porous material inside a day.
• Anyone in the home is immunocompromised, pregnant, under 2, or over 75.
• It happened twice. A second backup in 12 months means the line has a defect, and a clear-out is a delay, not a fix. If you're facing frequent backups or have a damaged sewer line, professional sewer repair is the fix, and a camera inspection tells you which kind.

Remediation in the Denver metro runs $2,000 to $7,000 for a bathroom and adjoining floor, $7,000 to $15,000 for a finished basement.

Who pays: the city or the homeowner?

In Denver and every Front Range suburb, the homeowner owns the sewer service line from the house to the connection at the main, including the section under the sidewalk and the street. The city or sanitation district owns the main. So:

A city claim needs the plumber's report showing the service line was clear and the main was blocked, the photos, and the receipts. File within days, not months; the plumber's camera video is the evidence.

Does homeowners insurance cover sewer backup in Colorado?

Not on the standard policy. Water that backs up through a drain is excluded on the base homeowners form sold in Colorado. Two add-ons fix that:

• Sewer and drain backup endorsement. $40 to $150 a year for $5,000 to $25,000 of coverage for the cleanup and the damaged finishes. Every Denver metro homeowner with a pre-1980 home should carry it; the deductible is the policy deductible.
• Service line coverage. An endorsement or a separate utility-partner plan, $5 to $15 a month, that pays for the repair or replacement of the line itself. Read the cap: $10,000 is common, and a full replacement under a Denver street costs more than that.

Our post on how insurance changes a Denver metro house payment lists the endorsements to price before you buy.

What is a sewer scope inspection and what does it cost?

A sewer scope is a camera on a cable, pushed from a cleanout through the service line to the main, recorded on video with a locator that marks the depth and position of any defect from the surface. It costs $150 to $300 in the Denver metro as an add-on to a home inspection, and it is the highest-return $200 a Colorado buyer spends. The camera finds:

• Root intrusion at the joints of a clay line.
• Offsets where bentonite movement pushed one section out of line with the next.
• Bellies where the pipe sags and holds standing water.
• Cracks and breaks, and collapsed Orangeburg.
• Pipe material and transitions: clay to cast iron, cast iron to PVC, and the age each one implies.

Order it on every home built before 1985 and on any home with mature trees between the house and the street. It is on our Denver home buyer verification checklist as a required item, and the inspection red flags that kill Denver home sales post shows why sellers order one too.

What does sewer line repair or replacement cost in the Denver metro?

A line that runs under a Denver street needs a right-of-way permit and a licensed contractor to cut and restore the pavement; that is the part that pushes a job above $15,000. Our post on spotting a clogged sewer line before replacing it covers the clear-versus-replace decision, and the warning signs a sewer line needs replacing lists what to watch for between scopes.

Who pays for a sewer repair found during a Colorado home sale?

Whoever the contract says. The buyer's inspection objection deadline in the Colorado contract is the moment: the buyer delivers the scope video and asks for a repair, a credit, or a price reduction. On a Denver metro resale, a full replacement gets split or credited more than half the time, because the next buyer's scope finds the same defect. A seller who scopes before listing and fixes or discloses the line keeps the deal on schedule; the plumbing prep before selling a Denver home post puts the scope in the first week, and the preparing and adding value before selling guide shows where the repair money comes back at closing.

How do I prevent sewer backups in a Denver home?

• Scope every 3 to 5 years on a clay line, every year if roots were found.
• Root treatment. A foaming root killer once a year, $30 to $50, on lines with known intrusion.
• Hydro-jet before it blocks. $300 to $500 every 2 to 3 years on an older line with trees.
• Install a backwater valve if the basement floor drain has backed up once.
• Nothing but toilet paper and waste goes down. No wipes, no grease, no coffee grounds, no cat litter.
• Replace before it fails. A planned trenchless lining at $10,000 beats an emergency open-cut at $20,000 plus a $5,000 basement cleanup.

Which Denver neighborhoods have clay sewer lines?

Any area built before 1970. In Denver that includes Park Hill, Washington Park, Congress Park, Berkeley, Sunnyside, Platt Park, Baker, Harvey Park, Bear Valley, and Virginia Village. Outside Denver: Englewood, older Littleton, Lakewood's east side, Wheat Ridge, Arvada's Olde Town blocks, Aurora's original streets near Colfax, and old town Golden. Homes in these areas are among the best-built brick ranches and bungalows on the Front Range, and the sewer line is the one item to check before you fall for the brick.

What a sewer backup means when buying or selling

For a buyer: a $200 scope, a written objection, and a repair credit. For a seller: a $200 scope before photos, a repair or a disclosure on the Colorado Seller's Property Disclosure, and a sale that closes on time. For either: a backup is a plumbing problem with a known fix and a known price, not a reason to walk away from a good house. Our Colorado home buyer resources page has the rest of the inspection list.

Where to go next

• Search every home for sale in Colorado
• Denver home buyer verification checklist
• Preparing and adding value before selling a Colorado home
• Hidden water damage signs Colorado buyers check before closing
• Explore Denver homes and neighborhoods
• Meet the Kenna Real Estate Group agents

Talk to the Kenna Real Estate Group

The Kenna Real Estate Group at Keller Williams DTC puts a sewer scope on every pre-1985 home our buyers inspect, negotiates the repair before the objection deadline, and helps sellers scope and fix the line before the listing goes live. Call or text 303-955-4220. A live person answers. Not a robot, not a phone tree. When you are ready to look, search every home for sale in Colorado.