Basement finishing in Longmont goes through one office, Building Services at the Development Services Center on Kimbark Street, and the city publishes its own single-family basement finish guide. That guide is specific about window wells, floated walls and inspection order. It's also dated January 2020, while the city's 2024 International Codes took effect July 1, 2026, so parts of it need a second check.
Longmont sits in both Boulder and Weld counties. The permit process below is the city's, and the decision matrix further down sorts the choices that most often change a Longmont plan.
Basement Finishing in Longmont Starts With a Full Floor Plan
The city's basement finish page lays out four steps. Review the Basement Finish Guidelines, complete a Residential Remodel/Addition Application, submit it with a full basement floor plan showing dimensions and room labels, then pay fees and pick up the approved plans. Submittals can go by email as PDFs or in person at the Development Services Center, 385 Kimbark Street. Your plan reviewer emails the fee amount.
The guide's floor plan checklist goes well past dimensions:
- Use of every room, plus furnace, water heater and plumbing fixture locations
- Outlets, lighting, fans, smoke and carbon monoxide detectors
- Window sizes, window wells and which openings are for emergency escape
- Heights of any dropped ceiling areas
- Insulation type and R-value for walls and ceiling
- Changes to posts, beams or floor joists
Approved plans must be on site for every inspection.
Which Code Year Covers Your Permit
Longmont's building codes page lists the 2024 International Codes, the 2024 Metro Cohort Model Code (an energy code based on the 2024 IECC) and the 2023 National Electrical Code as in effect as of July 1, 2026. The basement guide predates that adoption. It lists R-10 continuous or R-13 cavity insulation for below-grade perimeter walls, and that figure deserves confirmation at plan review under the newer energy code. Most Front Range jurisdictions adopt a version of the IRC; here, the edition matters when a reviewer reads your insulation and egress notes.
A Decision Matrix for Longmont Basements
- If you're cutting a new window or widening one in concrete
- The guide requires a letter from a licensed Colorado engineer that addresses the lintel or header.
- If you plan to reuse an existing window well
- New wells must project at least 36 inches from the house. Existing wells on houses built between March 30, 1986 and January 1, 1996 may be 30 inches, and on houses built before March 30, 1986, 24 inches.
- If a window well is deeper than 44 inches
- It needs a permanently affixed ladder.
- If the basement already has fire sprinklers
- Get the city's form for your sprinkler contractor and submit it with the plans.
- If the furnace and water heater will be enclosed
- Provide outside combustion air and keep 30 inches of clear working space in front of each appliance. Neither can open into a bedroom or bathroom unless it sits in a dedicated enclosure with outdoor combustion air and a self-closing, weather-stripped solid door.
- If your lot is in a mapped flood hazard area
- The city requires a floodplain development permit before construction begins. Its Floodplain Inquiry Map covers St. Vrain and Left Hand creeks.
Three Inspection Visits and What Each One Checks
The guide says most basement finishes need three inspection visits:
- Rough plumbing, mechanical and electrical, plus framing, fireblocking and bracing
- Fireblocking and insulation, with cavities checked before they're covered
- Final, with flooring installed and all trades complete
Separate framing or insulation inspections may be needed if walls or ceilings get covered before the inspector can see the structure. On the slab, the guide calls for non-bearing walls built to accommodate at least 1-1/2 inches of floor movement, with drywall held at least 1 inch above the concrete. Treat that gap as non-negotiable, since a wall pinned to a moving slab can't be fixed with trim.
Home Gyms and Basement Remodeling in Longmont
The 2020 guide sets habitable rooms at a minimum 7-foot ceiling, with beams, pipes and ducts allowed down to 6 feet 4 inches; ask plan review whether the 2024 codes changed that. That minimum is fine for a treadmill. It's tight for overhead presses or a pull-up bar, so we recommend planning a gym around the tallest clear bay and keeping duct runs out of it. Rubber flooring over the slab works with a floated wall as long as the drywall gap stays open.
If you're opening up an older finish instead of starting from bare concrete, our basement remodeling approach starts with what's behind the walls. For design ideas, see our basement finishing services.
Radon belongs in the plan too. Boulder County's health department reports an EPA Zone 1 ranking for Boulder County, and the state classifies every Colorado county, Weld included, as Zone 1. Neighbors in Boulder and Loveland work under different permit offices and code schedules.
