Basement finishing in Denver goes through Community Planning and Development, the permitting arm of the City and County of Denver. The city's current code is the 2025 Denver Building Code, which adopts the 2024 International Residential Code with local amendments as the Denver Residential Code, alongside the 2021 IECC as the Denver Energy Code.
Denver's code even has a specific name for an old basement that was never built as living space. Before choosing finishes, it helps to know how the city will classify your project and what the existing space legally is.
When Denver Requires a Basement Permit
Denver's residential interior remodel page says a permit is needed when you alter the existing floor plan, change load-bearing structure, or add or relocate electrical or plumbing fixtures. New windows and egress windows need permits too. Like-for-like replacement of cabinets, countertops, flooring and fixtures doesn't, and neither does drywall repair smaller than one 4-by-8 sheet.
Applications go through e-permits. For the zoning, building and sewer (SUDP) review, you choose "building log" as the permit type, and trade permits for electrical, plumbing or mechanical work can be pulled separately as quick permits. Expect to provide a site plan, a floor plan labeling all existing and proposed rooms, and a framing plan with header information.
Sorting Basement Finishing in Denver by Size and Scope
Denver's permit classification policy, ADMIN 131A (effective January 24, 2025), determines which review track you land in.
- If the remodel is 1,000 sq ft or less
- It's classified as a Residential Express (walk-through) building log. Minor structural work, such as adding a beam, stays in this track.
- If it's larger than 1,000 sq ft
- It moves to Intermediate Residential, along with structural changes that aren't minor, such as relocating stairs.
- If you're digging out a crawlspace
- Crawlspace-to-basement conversion is its own Intermediate Residential category. The Denver Residential Code also applies its radon appendix to basement additions converted from crawl spaces, including a soil gas collection mat under the new slab.
- If the egress well lands in a side setback
- Denver's zoning administrator allows a window well to encroach into a side setback only if it serves emergency egress, and caps it at 3 feet wide by 6 feet long, measured inside the well. Side-by-side wells must be structurally separate.
- If you're adding a bar or second kitchen
- Denver's permitting checklist asks you to label it full or partial. A stove, cooktop, range, oven, 220-volt outlet or gas connection makes it a full kitchen.
- If you plan to do some work yourself
- Homeowner permits cover owner-occupied single-family homes only, and you must live there a year after the work. Electrical, plumbing and HVAC work requires passing a city exam unless you hold the trade license.
Older Denver Houses and the Cellar Definition
The Denver Residential Code defines a cellar as a basement built before 1990 that doesn't meet the code's minimum ceiling height and doesn't contain living space. If your house predates 1990, find out which side of that line your lower level falls on before planning rooms.
The existing-building provisions say living space created in an existing basement must meet the code's basement ceiling height section. They also say existing finished ceiling heights in basements without living space can't be reduced. In the IRC that basement standard is 7 feet, with beams and ducts allowed down to 6 feet 4 inches; confirm the Denver Residential Code's current wording with your plan reviewer.
Radon, Sewer Lines and Soil Under Denver Basements
Denver is a Zone 1 county on EPA's radon map, the group with the highest predicted indoor levels. EPA wants every home tested either way, and in a basement project the time to do it is before drywall.
Sewer use and drainage permits may come into play if the property is in a floodplain or the work digs within two feet of a sewer line, which is worth checking before digging a new window well. And the Colorado Geological Survey points to heaved, cracked basement slabs as a typical symptom of swelling clay, so walls and trim should be detailed to tolerate slab movement.
If a previous owner finished the basement, basement remodeling in Denver often starts with finding out what was permitted. See our basement remodeling approach, how we plan basement finishing, and nearby guidance for Lakewood basement finishing and basement finishing in Aurora.
