Castle Rock ADU rules
✓ Verified against code · August 20, 2026
Current rules under CRMC Ch. 17.61 (Accessory Dwelling Units), adopted by Ordinance 2025-023, in effect since July 1, 2025. Castle Rock is bound by HB24-1152 through DRCOG. Ordinance 2025-023 took effect July 1, 2025, one day after the statute's June 30 deadline — a timing note rather than evidence of anything, since the deadline governed filing rather than the effective date of local code. That ordinance made a real change: the original 2017 ADU ordinance imposed a genuinely ongoing occupancy obligation, and the current code checks residency only once, when you apply.
Common questions, answered from the code
Do I have to live on the property in Castle Rock?
You have to live there when you apply, but not afterwards. The code ties eligibility to the owner of an existing primary dwelling and the application includes an Affidavit of Residency attesting that you currently reside on the property. There is no ongoing obligation and no annual re-certification — which is what HB24-1152 permits. This is a change: the original 2017 ordinance imposed a genuinely ongoing occupancy requirement until Ordinance 2025-023 replaced it in July 2025.
CRMC §17.61.050(C)(2) · Permalink
How big can a Castle Rock ADU be?
For an interior or attached ADU, the greater of 50% of your home's floor area or 750 sq ft — note that it is the greater, so a small house still gets a 750 sq ft allowance rather than being scaled down. A detached ADU is capped at an 800 sq ft building footprint.
CRMC §17.61.050(C)(8) · Permalink
Do I need parking for a Castle Rock ADU?
This is genuinely unresolved and we would rather say so than guess. The ADU chapter itself contains no parking requirement. But that same chapter says all district zoning regulations apply to ADUs, and the town's general parking chapter requires two spaces per dwelling unit with no ADU exemption we could find. Whether the general standard reaches an ADU is a question for the town's planning staff before you rely on either answer.
CRMC Ch. 17.61; §17.61.050(B)(7); Ch. 17.54 · Permalink
Can I build an ADU on a Castle Rock townhome lot?
No. ADUs are barred on lots with an existing duplex, triplex, condominium, townhome or multifamily use, and in the MH district entirely. The rule is one ADU per lot or tract, accessory to a single-family home.
CRMC §17.61.040; §17.61.050(C)(1) · Permalink
Does my Castle Rock ADU have to match my house?
Yes, and the requirement is unusually specific. Roof pitch, materials, style, siding, eaves, and window treatment and colour all have to match the primary dwelling. Budget for that at design stage rather than discovering it at review. Separately, HOA approval is your responsibility — the town does not enforce covenants, so an HOA can block a unit the town would permit.
CRMC §17.61.050(C)(3) · Permalink
The rules at a glance
| ADUs allowed per lot | One per lot or tract — interior or attached, or detached, but not both. ADUs are barred entirely in the MH district and on lots with an existing duplex, triplex, condominium, townhome or multifamily use.CRMC §17.61.050(C)(1); §17.61.040 |
| Maximum size | For an interior or attached ADU, 50% of the primary dwelling's floor area or 750 sq ft, whichever is greater — a formula that protects small-home owners rather than penalising them. A detached ADU is capped at an 800 sq ft building footprint.CRMC §17.61.050(C)(8) |
| Detached ADU height | The ADU chapter sets no height limit; the base zone's accessory-building standard governs, which in the R-1 zone is 20 ft. We could not retrieve the zoning text directly from a primary source, so treat the 20 ft figure as sourced but unconfirmed, and note it has not been checked against the R-2, R-3 or PD zones.CRMC §17.61.050(B)(7), deferring to the base zone; §17.18.040(F) for R-1 |
| Detached ADU setbacks | The side setback equals the zone's accessory-structure side setback — unless that is greater than the primary dwelling's, in which case the primary dwelling's smaller setback governs. In R-1 that means 2 ft in the rear third of the lot and 7 ft elsewhere. The rear setback equals the zone's accessory rear setback, or 5 ft where the zone sets none; in R-1 the zone does set one, so 10 ft applies. No alley exception.CRMC §17.61.050(C)(9)–(10); §17.18.040 |
| Off-street parking | Chapter 17.61 sets no ADU parking requirement at all. But the chapter also states that all district zoning regulations apply to ADUs, and the town's general parking chapter sets two spaces per dwelling unit — with no ADU exemption we could find. Whether that general standard reaches an ADU is genuinely unresolved, so do not assume zero without asking the town.CRMC Ch. 17.61 (no parking provision); §17.61.050(B)(7); Ch. 17.54 Table 64-1 |
| Owner-occupancy | Required once, at the time of the building-permit application: the code ties eligibility to the owner of an existing primary dwelling, and the application includes an Affidavit of Residency attesting that the owner currently resides on the property. No ongoing obligation or annual re-certification exists — consistent with the application-time check the statute permits.CRMC §17.61.050(C)(2); Affidavit of ResidencyPreviously: An ongoing occupancy obligation applied under the original 2017 ordinance — changed by Ord 2025-023, effective Jul 1, 2025 |
| Lot coverage / floor area | We found no lot-coverage or floor-area standard for the R-1 zone; Castle Rock appears to control bulk through setbacks and height instead. The town's general site-development chapter was unreachable, so this is unconfirmed rather than established.CRMC §17.18 (searched, none found) |
| Permit path & timeline | Administrative review by the director plus a building permit, with no public hearing or notice requirement. No published review timeline.CRMC §17.61.040(C) |
Worth knowing
- A design-match requirement applies in detail: roof pitch, materials, style, siding, eaves, and window treatment and colour must match the primary dwelling.
- No separate water or sewer taps are needed — utilities are billed to the primary account holder.
- HOA approval is the owner's responsibility and the town does not enforce it, so a covenant can block an ADU the town would otherwise permit.
- The town reserves the right to regulate short-term rentals in ADUs separately, though we could not locate a standalone ordinance doing so.
- Violations carry fines of up to $1,000 per day.
- The size rule takes the greater of 50% of the house or 750 sq ft, which means a small home is not penalised — the opposite of the footprint-percentage formulas used in some neighbouring cities.
On our watchlist
Whether Castle Rock's general two-space-per-dwelling-unit parking standard applies to ADUs is unresolved — the ADU chapter is silent and no exemption was found.
The 20 ft accessory-building height for R-1 comes from a secondary source; the town's code host defeated every direct route. It has not been checked against the R-2, R-3 or PD zones.
No lot-coverage or floor-area standard was located; the general site-development chapter was unreachable.
The town reserves the right to regulate short-term rentals in ADUs but no standalone ordinance doing so was found.
Primary sources
- CRMC Ch. 17.61 (Accessory Dwelling Units)
- Castle Rock ADU application and Affidavit of Residency
- Colorado DOLA — Accessory Dwelling Units (HB24-1152)
Other Colorado cities
Arvada · Aurora · Boulder · Broomfield · Centennial · Colorado Springs · Denver · Fort Collins · Greeley · Lakewood · Longmont · Loveland · Pueblo · Thornton · Westminster
Not legal advice. Every fact above cites the code section it comes from — check the cite, or ask your city’s planning department to confirm your specific lot. Spotted an error or a new ordinance? See about to reach us; corrections are logged in the changelog.