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ADU Guide for Castle Rock Homeowners

Castle Rock has some of the largest single-family lots in the Denver metro and HOA-governed communities that now must allow ADUs under Colorado law. Here’s what that means for your property.

ADU Rules at a Glance

ADUs Allowed?	✅ Yes — subject jurisdiction under HB 24-1152
Maximum Size	1,000 sq ft or 50% of primary home area
ADU Types Permitted	Detached, attached, basement, garage conversion
Owner-Occupancy Required?	Not required under HB 24-1152
Parking Requirement	1 space per ADU
HOA Override?	HOAs cannot prohibit ADUs per HB 24-1152; design review still applies
Short-Term Rental (STR)?	Douglas County STR rules apply; Castle Rock has its own STR ordinance
Permit Path	Administrative approval through Town of Castle Rock
Estimated Permit Timeline	10–16 weeks
Official Source	Town of Castle Rock Development Services

⟳ Last reviewed: October 2026. ADU rules change. Always verify current code with Castle Rock before starting a project. View official source →

What This Means for Homeowners

Castle Rock is one of Colorado’s fastest-growing communities, with rolling terrain and newer homes that often feature walk-out basements — making basement ADUs the most practical first option for many homeowners. The town is at the southern end of the Denver metro and handles its own permit process independently from Douglas County. Average home values are high and the multigenerational housing market is strong, particularly for families relocating from higher-cost metros.

Key Considerations

Rolling terrain means walk-out basements are common and often the lowest-cost ADU path
Castle Rock processes its own permits independently of Douglas County — submit to the Town, not the County
Newer subdivision lots may have HOA design standards that require material and color matching
Castle Rock’s STR ordinance has specific requirements — verify if short-term rental is your intended use
Castle Rock is one of the few suburban towns still actively managing rapid growth; permit timelines can stretch
The town’s newer housing stock means fewer aging systems to replace compared to older Denver suburbs

Not sure if your lot qualifies? The ADU quiz takes 3 minutes and gives you a personalized eligibility summary based on your property type, location, and goals. Take the free ADU quiz →

ADU Cost Snapshot: Castle Rock

Detached Backyard Cottage	$215,000–$400,000
Garage Conversion	$55,000–$142,000
Basement ADU Conversion	$42,000–$115,000
Permit Fees (estimate)	$3,200–$10,000 (Town of Castle Rock — separate from Douglas County)
Utility Tap Fees (detached)	$6,000–$17,000 (Castle Rock Water)
Estimated Monthly Rent	$1,750–$2,950/month
Estimated Break-Even	7–12 years for detached; 3–5 years for walk-out basement

Local note: Castle Rock Water has its own tap fee schedule — confirm current rates before budgeting, as fees have increased with the town’s rapid growth. Walk-out basements on sloped lots are the most cost-effective ADU path for most Castle Rock properties.

Cost ranges reflect 2026 Denver metro construction pricing. Individual project costs depend on site conditions, finishes, utility distances, and contractor selection. Get multiple bids before committing to a budget.

Sources & Official References

Official Sources

Rules and fees change. Always verify current requirements directly with your local jurisdiction and utility provider before starting a project.

Check Your Property

Answer 7 questions to see your estimated cost range, likely ADU type, and local eligibility — free, no sign-up required.