Basement finishing in Boulder comes with an extra layer of paperwork: the city's own energy code. Since December 1, 2024, work on existing homes inside city limits has answered to the 2024 City of Boulder Energy Conservation Code, known as CoBECC. It decides which checklist you submit and, on bigger projects, which heating equipment you can install.
This page covers who issues the permit, how the energy code sorts an alteration, the asbestos trigger, and flood and radon exposure below grade. For the order of operations, see how a project moves from layout to final inspection.
Basement Finishing in Boulder Starts at the City, Not the County
Homes inside city limits are permitted by the City of Boulder's Planning & Development Services, whose building code staff work at 1101 Arapahoe Avenue. Boulder County issues building permits only for unincorporated properties and tells city residents to contact their city. The county's basement handout is written for those parcels.
The city's Residential Alterations Criteria Guide covers interior work with no exterior scope. It requires a Scope of Work Form and floor plans showing existing and proposed conditions, and it may also call for the 2024 CoBECC Residential Mandatory Measures Checklist, an asbestos report or a plumbing fixture count form. Incomplete applications won't be accepted for review. Submittals go through the city's Customer Self-Service portal.
A new egress window cut into the foundation is exterior work, so ask intake staff which guide applies before plans are drawn.
How CoBECC Sorts a Basement Project
CoBECC classifies work on existing homes by alteration level, using definitions from the 2018 International Existing Building Code. The city's FAQ describes Level 2 as including the reconfiguration of space, adding or eliminating a door or window, and extending systems or adding equipment. Level 3 applies where the work exceeds 50% of the aggregate building area. When a project mixes scopes, the larger portion governs.
| Question | Level 1 or 2 alteration | Level 3 alteration |
|---|---|---|
| Trigger | Level 2 includes reconfiguring space, door or window changes, system extensions | Work exceeding 50% of the aggregate building area |
| Energy paperwork | Prescriptive checklist, or an ERI report plus performance checklist | Performance checklist plus an ERI of 50 or less, or a 30% ERI improvement over the existing home |
| Replacing a gas furnace | A new furnace can replace the old one | Allowed, but the space must be electric-ready; with substantial envelope work, new equipment must be all-electric |
| Blower door test on the existing home | Not required | Not required |
Most basement finishes reconfigure space and extend ducts and circuits, which reads like Level 2. A large basement under a modest house is where the 50% line deserves an early conversation with plan review, since Level 3 adds rater work.
Code Editions Behind Basement Remodeling in Boulder
City Council adopted the 2024 International Code Council suite with local amendments on March 20, 2025, effective August 1, 2025. Electrical work follows the 2023 National Electrical Code as amended by the city. Most Front Range jurisdictions adopt a version of the IRC, and Boulder sits on a recent edition, so check dimensions against the city's adopted text, not an older handout.
Egress size, sill height and ceiling clearance under beams and ducts are the numbers to confirm against that 2024 text before anyone commits to a soffit layout.
Reworking an older finish? Our basement remodeling page covers how we evaluate an existing space, and our overview of how we approach a finished basement explains the design side.
The Asbestos Trigger in Boulder's Checklists
The city's residential permit guides require an asbestos inspection report when a project disturbs potentially asbestos-containing materials at any of these levels:
- 32 square feet of surfaces
- 50 linear feet of pipe
- Waste equal in volume to a 55-gallon drum
A bare concrete basement may never get close. A space finished decades ago is different: pulling down an old ceiling or a wall of paneling can pass 32 square feet in an afternoon. Test suspect materials before demolition is scheduled, since the report belongs in the permit file.
Flood Maps and Radon Below Grade
The city states that Boulder has the highest risk of flash flooding in Colorado, with 14 tributaries feeding Boulder Creek. Its flooding guide notes that work on your property may need a floodplain or wetland permit, and the Floodplain Information Map shows mapped floodplains and conveyance zones by parcel. Check it before planning a bedroom below grade.
Radon is the other below-grade concern. Boulder County Public Health says the EPA ranks the county as Zone 1, meaning the average house will likely exceed the 4.0 pCi/L action level.
Family in Broomfield or north in Longmont deal with different permit offices.
