Basement finishing services in Castle Rock

Basement finishing

Finishing turns unfinished space into living area. In Castle Rock, the permit application needs a floor plan of the entire basement showing room dimensions and uses, the furnace, water heater and stairs, every window and window well (with egress window sizes), and the total finished and unfinished square footage¹.

Basement stairs need lighting for the treads and landings, a switch at the top and bottom where there are 6 or more risers, at least 6'-8" of headroom, risers no taller than 7¾ inches, treads at least 10 inches deep and a continuous graspable handrail 34 to 38 inches high¹.

Basement remodeling

Remodels of finished basements also need a permit in Castle Rock; the Town lists both basement finishes and remodels among common projects that require one². If a project adds a kitchen, a ¾ or full bathroom, a sleeping area and physical separation from the main home, the Town treats it as an accessory dwelling unit (ADU), which brings extra requirements, including a deed restriction and development impact fees¹.

Basement bathrooms

• A bathroom needs an exhaust fan vented outdoors at 50 cfm or more through a duct at least 4 inches across, unless it has an openable window of at least 1.5 sq. ft.¹
• Showers need at least 900 square inches of floor, at least 30 by 30 inches, with a ceiling at least 70 inches above the drain. Hinged shower doors must open outward¹.
• Toilets and sinks need 21 inches of clear space in front; showers need 24 inches in front of the opening¹.
• Bathroom receptacles need a dedicated 20-amp circuit and GFCI protection¹.

Egress windows and window wells

Basement bedrooms must have an emergency escape opening: a window or door to the outside, a window into a window well, or a door to a bulkhead¹.

• Escape windows: at least 5.7 sq. ft. clear opening, at least 24 inches high and 20 inches wide, sill 44 inches or less above the floor, and openable from inside without keys or tools¹.
• Window wells: at least 9 sq. ft. with at least 36 inches of projection and width. Wells deeper than 44 inches need a permanently attached ladder or steps¹.
• Cutting a new opening in an existing basement wall needs a stamped structural engineered plan with the permit submission¹.

Full egress and permit details.

Framing and insulation

• Non-bearing walls on the slab must be built to allow 3 inches of expansion at the top or bottom, because of Castle Rock's expansive soils¹.
• Basement exterior walls need at least R-15 continuous blanket insulation or R-19 batts in the stud cavities, full height and length¹.
• Fire blocking is required at the ceiling and floor level of stud walls, at 10-foot intervals, at soffits and drop ceilings, and around vents, pipes and ducts¹.
• Furnaces and water heaters need a 30-by-30-inch clear space in front, and finishing the basement requires additional return air of at least 100 sq. in.¹

Moisture and radon checks

The Colorado Department of Public Health and Environment (CDPHE) says radon is found at elevated levels in one out of every two Colorado homes. It recommends testing in the lowest level of the home, including an unfinished basement, and says a mitigation system in Colorado usually costs about $1,000 to $2,000³. Colorado residents can order a free test kit through Douglas County's radon page⁴.

Any signs of water should be dealt with before finishing. Ask your contractor how they'll handle it.

Ready to plan your basement?

Call (720) 918-0175 or send a quote request. We pass it to a local basement contractor serving Castle Rock.

Sources

1. Town of Castle Rock, Residential Basement Finish Guide (revised 6/25/2026). Accessed October 25, 2026.
2. Town of Castle Rock, Homeowners Building Permits. Accessed October 25, 2026.
3. Colorado Department of Public Health and Environment, Testing and mitigating your home for radon. Accessed October 25, 2026.
4. Douglas County Health Department, Radon. Accessed October 25, 2026.