Denver · typical $150–$450
Basement floor drains backing up in Denver
In older Denver homes the basement floor drain is the lowest opening in the house, usually by the furnace or laundry. When the main line downstream narrows, this is where you find out.
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Reading the floor drain
| What happens | Likely cause |
|---|---|
| Water rises only when the washer drains | Partial main line clog or lint in the laundry branch |
| Water rises when any toilet flushes | Main line blockage |
| Smell but no water | Dry trap in a rarely used drain |
| Water after heavy rain | Groundwater or a downspout tie-in, not a clog |
Backwater valves
Some older Denver homes are low enough relative to the city main that a backwater valve makes sense, so sewage from the street can't flow back into the basement during a main surcharge. It's a permitted plumbing job; ask the plumber whether your house is a candidate after the line is cleared.
Older Denver basements
In pre-war Denver homes, basements were often dug or finished after the house was built, and the floor drain may connect to the main in ways no current plan shows. Some still have an old clay or cast iron trap below the floor that cracks or fills with sediment over the decades. When a floor drain stays slow even after the main is cleared, a camera through the floor drain itself usually finds the reason.
If you're finishing an older Denver basement, it's worth having the floor drain and main scoped before the drywall goes up. Moving or adding a cleanout is far cheaper with the walls open.
Common questions
Why does my Denver floor drain back up during laundry?+
The washer sends a lot of water quickly, and a partial main line clog can't take it, so it comes up the lowest drain.
Is floor drain water safe to clean up?+
If it's sewage, treat it as contaminated. Keep children and pets away.
Can a plumber add a backwater valve?+
Yes, it typically requires a permit and is installed on the main line inside or outside the foundation.