Finishing a Denver Basement: Egress, Radon, and Resale

Finishing a basement in Denver is one of the cleanest ways to add usable space. It can also lift your resale if you do it right. The big levers are simple: safe exits for bedrooms, smart radon planning, and a permitted build that buyers and appraisers will trust. This guide covers what to know about egress, radon, permits, costs, and ROI. At the end, you’ll find a step‑by‑step checklist to move from idea to action.

Is Finishing Your Basement Right for You? Quick Pros & Cons

Before you dive in, get clear on your goal. Is this for family use, a future guest suite, a long‑term rental, or a flip?

Pros

• More livable square footage for daily life
• Potential for a bedroom suite, rec space, office, gym, or rental
• Better marketability at resale when work is permitted and documented

Cons

• Upfront cost and time for permits and inspections
• Egress upgrades for any basement bedroom
• Radon risk is common in Colorado and must be managed
• Moisture and ceiling height can limit design options

Tip: If you plan to add a bedroom, focus early on egress feasibility and radon testing. Those two items shape layout, budget, schedule, and buyer confidence.

Egress Essentials: Making a Basement Safe and Code‑Compliant

Egress is a code‑required way to escape a sleeping room in an emergency. In basements, that usually means a properly sized egress window with a window well that someone can climb through. If a basement has a sleeping room, it needs its own compliant egress opening. Appraisers and buyers look for this because it affects safety and whether a room counts as a legal bedroom.

What makes an egress opening “compliant”? The International Residential Code sets minimum clear opening sizes and heights, and Denver enforces these rules during permitting and inspection. Summaries align on these key points: a minimum net clear opening of 5.7 square feet for most openings, a minimum height and width, a maximum sill height of 44 inches above the floor, and it must open from the inside without keys or tools. These are net clear measurements, not glass size. A small 20 by 24 inch window is not big enough to meet area requirements. See detailed code summaries here: IRC egress basics and a practical explanation of why tiny windows don’t meet area rules here.

Common egress solutions

• Egress window with window well. Most common choice. If the sill is below grade, you need a properly sized well. Wells must usually provide at least 9 square feet of clear area with 36 inches minimum in both directions, and a ladder is required if the well is deeper than 44 inches. Covers are fine if they open easily from inside. Review an overview of well requirements here.
• Exterior stair or bulkhead door. Great for walk‑out basements or when you already have a door to grade. This can be pricier and may need more structural work.
• Enlarging an existing opening. If you already have a window in the right spot, you can cut the foundation to widen or lower it. That usually needs structural review and a permit.

Key factors to evaluate

• Wall area and foundation type. Can you fit the required width and height where you want the bedroom?
• Lot grading and drainage. Window wells need proper drainage so you avoid water issues.
• Landscaping conflicts. Plan for excavation access and well placement.
• Layout and ceiling height. Egress placement can steer where a bedroom goes and how furniture fits.

When does egress trigger permits or structural work?

• Cutting a foundation, installing a new well, or changing window size typically requires a permit and inspection. Denver uses an e‑permits system and asks for plans that show room use, window dimensions, and well details. Start here: Denver homeowner permits. Denver has adopted updated building codes with effective dates tied to submission timing, so confirm which code edition applies to your project at submittal.

Radon: Testing, Mitigation Options, and Decision Points

Radon is a colorless gas that can build up indoors. Colorado has some of the highest radon potential in the country, and about half of homes test at or above the EPA action level of 4.0 pCi/L. The only way to know your level is to test. Denver and state health agencies advise that all homes should be tested. Learn more here: EPA radon zones and Denver’s radon guidance.

How and when to test

• Start early. Do a short‑term test before design is final, so you can plan mitigation if needed.
• Short‑term kits run 48 to 120 hours and cost about 10 to 50 dollars. Long‑term tests run 3 months or more and better reflect year‑round levels. If a short‑term result is near 4.0 pCi/L, confirm with another test. See testing steps here: CDPHE radon testing.

Mitigation basics

• The most common solution is active sub‑slab depressurization. A contractor runs pipe from beneath the slab to a fan that vents outdoors, often reducing radon by more than 90 percent when installed correctly. Typical professional costs in Colorado run about 1,000 to 3,000 dollars. If a passive system exists, adding a fan is often cheaper. Details here: CDPHE mitigation overview.
• Plan routing early. It is easier and cleaner to run pipe and power for a fan before drywall.
• Hire licensed pros. Since July 1, 2022, Colorado requires radon measurement and mitigation contractors to be licensed. Verify status here: DORA licensure notice.

Real estate angle

• Colorado law requires sellers to disclose known radon test results and mitigation. Keep test reports, invoices, and post‑mitigation results for your future buyer. See C.R.S. 38‑35.7‑112 here: radon disclosure statute.

Permits, Inspections, and Working with Local Authorities

In Denver, most basement finishing that involves structural changes, egress, electrical, plumbing, or HVAC needs permits and inspections. The typical sequence is simple: plan and drawings, permit submittal, rough work, rough inspections, insulation/air‑barrier inspection, drywall and finishes, then final inspections. Clear plans help reviewers approve faster. If you are cutting a foundation, changing load paths, or adding a bath, consider adding an architect or engineer. Start your research here: Denver homeowner permits and Denver building codes and guides.

Also plan for required smoke and carbon monoxide alarms inside bedrooms, outside sleeping areas, and on every level including the basement. See local safety guidance from Denver Fire here.

Budgeting & Typical Cost Drivers

Every basement is different, but a few line items drive most budgets:

Major components

• Framing, insulation, drywall, doors, and trim
• Electrical, lighting, outlets, and panel upgrades if needed
• Plumbing for baths or wet bars, plus a sewage ejector if the main line is higher
• HVAC tweaks for supply and return air
• Flooring, paint, cabinets, and finishes
• Egress windows and window wells where bedrooms are planned
• Radon testing and mitigation if needed
• Permits, plan review, and inspections

Typical ranges and cost drivers

• Egress window plus well: about 2,500 to 7,000 dollars per opening, depending on excavation and drainage needs.
• Radon mitigation: about 1,000 to 3,000 dollars for a standard system in Colorado. Plan the route early and keep the post‑mitigation test report. Guidance here: CDPHE radon mitigation.
• Full basement finish: widely variable. Rough guideposts range from about 30 to 100 plus dollars per square foot based on scope, with midrange projects often 20,000 to 70,000 dollars. See national and local ranges here.

Levers to protect ROI

• Keep layout simple. Fewer walls reduce costs and keep light flowing.
• Add a bathroom if plumbing runs are reasonable. It usually helps daily use and resale.
• Choose finishes based on use. Durable, low‑maintenance for rentals. Well‑chosen midrange finishes for resale.
• Set a 10 to 15 percent contingency for surprises like moisture, sub‑floor fixes, or panel upgrades.
• Consider phasing. Do egress, radon, waterproofing, and rough‑ins first, then finish surfaces.

Resale and ROI: How Finished Basements Perform in Denver Markets

A well‑executed, permitted basement usually boosts marketability. Appraisers often value finished below‑grade space at a lower rate per square foot than above‑grade space, and a bedroom must meet habitability rules like egress to count as a legal bedroom. Industry benchmarks suggest a midrange basement finish often recovers about 60 to 80 percent of its cost at resale, depending on neighborhood, size, and quality. See Cost vs. Value context in Remodeling Magazine's regional report.

What helps value

• Legal bedrooms with compliant egress
• A bathroom and good storage
• Dry, clean, well‑lit space with documentation of permits and final inspections
• Radon mitigation with a clear post‑mitigation test report

What hurts value

• Unpermitted work or missing final inspection records
• Moisture or prior flooding without remediation
• Elevated radon with no mitigation or paperwork. See guidance here and a practical overview of resale risks from moisture here.

Design, Use Cases, and Market Positioning

Tie design to your plan for the space.

Family living

• Comfortable ceiling height, warm lighting, and a clear egress plan
• Open rec area plus a guest room and bath
• Built‑ins, laundry upgrades, and a mud zone if your stairs allow

Long‑term rental

• Durable flooring like LVP, simple bath finishes, and easy‑clean surfaces
• Sound control at the ceiling and door sweeps at the stairwell
• Separate thermostat if your HVAC allows

Short‑term rental

• Clear sleeping zones, an ensuite bath, and a snack bar or small kitchenette where legal
• Smart locks, labeled switches, and simple storage
• Safety first: egress, smoke and CO alarms, and a posted radon note if mitigated

Good photos and staging start with layout. Frame shots to show light, ceiling height, and flow to the stairs.

Choosing Contractors and Managing the Project Timeline

Who you may need

• General contractor to run the schedule and trades
• Electrician, plumber, and HVAC contractor
• Egress window and concrete cutting specialist
• Licensed radon measurement and mitigation pro

How to compare bids

• Scope match, materials and finishes, and a written schedule
• Who handles permits and plan submittals
• Warranty terms, radon system guarantees, and references with photos

Scheduling

• Build a calendar with permit lead time, rough‑in dates, and inspection milestones
• Add contingency days for material delays, inspections, and any foundation or drainage surprises

Red flags

• Vague scopes, cash‑only demands, no permits, or no references

Practical Checklist & Next Steps

1. Define your goal and budget. Family space, rental, or resale timeline.
2. Test for radon early. If at or above 4.0 pCi/L, plan mitigation and keep reports. Start here: CDPHE testing.
3. Confirm egress options for any planned bedroom. Review basics: egress overview.
4. Get ballpark numbers for egress and radon. Align scope to your budget.
5. Gather 2 to 3 contractor bids. Ask who handles permits, timelines, and warranties.
6. Submit clear plans to Denver e‑permits. Show room use, window sizes, and well details. Start here: Denver permits.
7. Schedule mitigation and egress work before drywall.
8. Complete rough‑ins, pass inspections, insulate, then finish.
9. Keep all permits, inspection sign‑offs, radon test results, and invoices for resale disclosure.

Conclusion

A smart Denver basement finish comes down to three things: safety with compliant egress, health with tested and mitigated radon, and a permitted build that buyers and appraisers will embrace. Start with a radon test and an egress check, then align scope and finishes with your goals. If you want local comps, contractor intros, or a reality check on ROI, reach out to Chad Goodale. He can help you price the impact in your neighborhood and connect you with the right team to get it done.

FAQs

What counts as a legal basement bedroom in Denver?

• It must meet habitability standards like ceiling height, heating, and a code‑compliant egress opening. Egress rules are set by the IRC and enforced at permitting. See summaries here.

Do I need egress if I am not adding a bedroom?

• If you are only creating open living space, you may not need a new egress window. But if you add any sleeping room, that room needs its own egress. Always confirm with Denver plan review at permit time.

How much does an egress window usually cost?

• Often 2,500 to 7,000 dollars per opening, depending on excavation, well type, and drainage. See a breakdown here.

How common is radon in Denver?

• Very common. Roughly half of Colorado homes test at or above the EPA action level. Learn more from the state and city: CDPHE and Denver.

What does radon mitigation involve and how long does it take?

• A pro installs piping and a fan to vent soil gases outside. Many systems finish in a day and cost about 1,000 to 3,000 dollars in Colorado. Get a written guarantee and post‑mitigation test results.

Will my finished basement square footage count at appraisal?

• Finished below‑grade space is usually valued, but often at a lower rate per square foot than above‑grade space. Work should be permitted, inspected, and bedrooms must meet egress rules to be counted as legal living area.

What paperwork should I keep for resale?

• Permit applications, approved plans, inspection sign‑offs, contractor invoices, radon test reports, and mitigation warranties. Colorado law requires seller disclosure of known radon test results and mitigation history. Read the statute here.