A sewer backup occurs when something blocks or significantly restricts the main sewer line, causing wastewater to reverse direction and rise through the lowest drain points in the home — typically a basement floor drain, toilet, or tub. The most common causes in Denver-area homes are root intrusion in aging clay tile pipe, grease and debris accumulation, collapsed or offset pipe sections, and blockages caused by non-flushable items.

Root Intrusion

Root intrusion is the leading cause of sewer backups in the older neighborhoods of Denver, Aurora, and surrounding Front Range communities. Mature trees — cottonwoods, silver maples, willows — send roots toward the moisture in sewer lines, entering through the joints in clay tile pipe. Over years, roots grow into masses that fill the pipe diameter and eventually prevent waste from passing. Backups from root intrusion typically develop gradually — you’ll notice progressively slower drains before a full backup occurs. Hydrojetting removes root masses effectively, and a follow-up pipe lining seals the joint entry points to slow future regrowth.

Grease and Debris Accumulation

Kitchen grease is liquid when it leaves the drain but solidifies on cooler pipe walls as it cools. Over time it builds up into a coating, then a narrowing, then a blockage — often in combination with food debris, soap, and other material. This type of backup typically develops over months or years. Hair and soap buildup in bathroom drain lines causes the same kind of slow accumulation, though usually in individual fixture drains rather than the main line. The fix is professional drain cleaning — mechanical or hydrojetting service that removes the material from the pipe walls, not just punches a hole through the clog.

Pipe Damage from Soil Movement

Denver’s clay soils expand and contract with moisture changes — wet seasons swell the ground, dry stretches shrink it. This seasonal movement shifts underground pipes, causing joints to offset and creating belly sections where the pipe sags below the correct grade. An offset joint creates a ledge that catches debris. A belly holds standing water that speeds corrosion and accumulates solids. Both lead to backups, and neither can be fixed by drain cleaning alone — the pipe geometry needs to be corrected. A sewer camera inspection identifies these issues and determines whether spot excavation, pipe lining, or pipe bursting is the right repair.

Non-Flushable Items in the Line

“Flushable” wipes are one of the most common contributors to main line blockages. Unlike toilet paper, which disintegrates in water within minutes, wipes retain their fiber structure in the sewer line and accumulate into masses — often tangling with grease or other debris. Paper towels, cotton balls, feminine hygiene products, and dental floss cause similar problems. In the kitchen, coffee grounds and fibrous vegetable material from disposals contribute to drain line accumulation faster than most homeowners realize. If a backup follows a change in household habits — guests using the bathrooms, heavy cooking for a holiday — non-flushable material is worth considering as a contributing cause.

Municipal Sewer Line Issues

Not every sewer backup originates on the homeowner’s side of the line. If the city sewer main is blocked, damaged, or overwhelmed during a heavy rain event, wastewater can back up through the home’s connection into the private lateral. Municipal backups often affect multiple homes in the same block simultaneously, which is one differentiating sign. Reporting the issue to Denver Water or the relevant utility is the right first step for suspected municipal problems, though a camera inspection of your lateral can confirm whether the private line is contributing.

What to Do When a Backup Happens

Stop using all water-dependent fixtures immediately — every flush, every sink drain, every shower adds more volume to a line that can’t move it. Do not use chemical drain cleaners in a backed-up line; they won’t reach a main line blockage and can create a hazard for the technician who opens the cleanout. Call for emergency drain cleaning service. Done can typically dispatch quickly for active backups across the Denver metro.

  • Root intrusion through clay tile joints — most common in Denver’s older neighborhoods
  • Grease, soap, and debris accumulation in the main line
  • Offset joints or belly sections from clay-soil movement
  • “Flushable” wipes, paper towels, and other non-degrading materials
  • Collapsed pipe in aging clay tile or cast-iron lines
  • Municipal main blockage or overflow during heavy rain

If you’re dealing with an active sewer backup, call Done for emergency drain service. Once the line is clear, a camera inspection through our sewer services team identifies the root cause so the backup doesn’t repeat.