Trenching in Denver: local operators and what it costs
Trenching around Denver is often for a sprinkler system, a water or power line to a garage or studio, a gas line to a fire pit or grill, or a drain pipe taking water away from a foundation. Two local facts shape every trench: the frost line sits deep, and much of the ground is clay that swells when it gets wet. This page covers both, the Colorado 811 rules, the city permits to ask about, and a typical local cost.
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What trenching costs in Denver
$8 to $32 a foot, or about $850 to $3,150 for a 100-foot run
Based on Pro Operator Network's national trenching cost guide, checked against published cost guides, and adjusted to the Denver-Aurora-Centennial metro area using its 2024 price level from the U.S. Bureau of Economic Analysis (105.8, where the U.S. average is 100).
A typical range, not a quote. Your own price depends on your property and is set by whoever takes on your project.
Deep enough to stay below the frost
Denver's building code sets the frost line at thirty-six inches below finished grade. Water lines and anything else that must not freeze are normally laid below that depth, which makes a Denver utility trench deeper than one in a warmer city and means more soil to move and put back. Sprinkler laterals are usually shallower and drained for winter instead.
Clay that swells
The Colorado Geological Survey explains that montmorillonite clays, often called bentonite, can expand by up to a fifth of their volume when they take on water, and CSU Extension notes that all of Colorado's major population centers sit partly on expansive soils. Backfilling a trench next to a foundation with loose wet clay invites settling and swelling against the wall. Compacting the backfill in layers and grading the surface to shed water away from the house helps.
Colorado 811 and private lines
Colorado law requires notice to Colorado 811 at least two business days ahead, not counting the day of the notice, and the marks are good while visible but no longer than thirty calendar days after the due date. Colorado 811 says the call is required even for a small project. It does not mark private lines, which are the owner's responsibility to locate before digging, such as an existing sprinkler system or a line to a detached garage.
Permits
Driveway, curb and other work in the public right-of-way needs a permit from the City Engineer, so a trench across the sidewalk or into the street is permitted work. No city permit rule for a trench that stays on a private lot was confirmed for this page; check with Denver before digging.
For your project post
Give the length and depth of the run, what it carries, where it starts and ends, and what it must cross, including private lines you know about. Mention the yard access and whether the soil should leave the site.
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