ADU Zoning Explained for Denver Buyers

Thinking about buying a Denver home and adding an accessory dwelling unit to help with the mortgage? You are not alone. ADUs can add flexibility and potential rental income, but the rules are specific to your lot and zoning. In this guide, you will learn how ADU zoning works in Denver, what to check on a property, timelines for permits, and the key cost drivers so you can plan with confidence. Let’s dive in.

ADU basics in Denver

An accessory dwelling unit is a secondary home on the same lot as your main house or duplex. It can be inside the existing structure, like a basement apartment, attached to the house, or a new detached unit in the yard.

Why buyers care in Denver:

• Potential rental income that may improve affordability if you plan to live on the property.
• Flexibility for multigenerational living, a caretaker, or a home office.
• Possible impact on resale value, property taxes, insurance, and utilities.

The rules come from the City and County of Denver’s zoning and building codes. Overlay districts, floodplain rules, and HOA covenants can add more limits. Always verify current city rules and any private restrictions before you assume an ADU is allowed.

Zoning basics to check

The single most important step is to confirm the property’s zoning designation and what it allows. Every parcel is different, so start here.

Confirm base zoning

• Look up the property’s official zoning with the City and County of Denver.
• Check if your zone allows an ADU for the lot type, such as single family or duplex.
• Review dimensional standards like unit size, height, setbacks, and lot coverage. These vary by zone.

Review lot size and access

• Small, narrow, or irregular lots can make it hard to meet setback or coverage rules for a detached unit.
• Alley access often makes placement and parking simpler. Frontage-only access can be more constrained.
• Sloped or uneven yards can add cost for grading, drainage, or foundations.

Understand setbacks, height, and coverage

• Setbacks define how close the ADU can be to property lines.
• Height limits control rooflines and the number of stories.
• Maximum lot coverage or floor area rules cap how much you can build. Compare the home’s current built area to what is allowed to see what space remains.

Check parking rules

• Some zones or overlays require on-site parking for an added unit. Others reduce or waive the requirement.
• If parking is required and there is no room to add it, that can block the project or increase costs.

Factor in overlays and special districts

• Historic districts or landmarked properties may have strict design review and limits on new detached structures.
• Floodplain, steep-slope, or environmental overlays can require mitigation or restrict building.
• Neighborhood conservation areas and airport influence zones can add extra rules.

Overlay reviews can add design requirements and time. Plan for that early.

Map utilities and easements

• Confirm connections to Denver Water and sewer. If you need new taps or upgrades, impact fees may apply.
• Identify recorded utility easements, often at the rear or side property lines, that can limit where you build.
• Verify utility capacity and meter plans up front to avoid delays.

Read HOA and CC&Rs

• Private covenants can restrict additional units, exterior changes, or rentals even when the city allows an ADU.
• Ask for the recorded CC&Rs and read them before you rely on city approvals.

Denver permitting timeline

Every project is unique, but most ADUs follow a predictable path. Plan your schedule using these typical ranges.

Pre-application and feasibility: 1–4 weeks

• Verify zoning, overlays, and utility service.
• Review the survey or plat and check for easements.
• Consider a pre-application call or meeting with city staff to confirm constraints and next steps.

Outcome: a simple go or no-go decision before you spend on design.

Design and documentation: 4–12 weeks

• Hire an architect or ADU-focused designer, and a structural engineer as needed.
• Produce site plan, floor plans, elevations, and a utility plan. Include drainage or grading sketches if required.
• Complete historic or overlay design reviews if your property is in a special district.

Timeline depends on scope and whether it is a conversion or a new detached unit.

Plan submittal and city review: 4–12+ weeks

• Submit your building permit package to Development Services.
• Your plans will be reviewed for building, zoning, civil, fire, and utilities.
• Expect comment rounds and resubmittals.

Historic or overlay reviews can add weeks to months.

Permit issuance: 1–4 weeks

• Once reviews are approved and fees are paid, you receive the permit.

Construction and inspections: 8–24+ weeks

• Interior conversions often finish in 2–4 months.
• New detached ADUs often take 4–9 months, depending on site work and utility connections.
• City inspections occur throughout construction, with a final certificate of completion at the end.

Overall timeline guide

• Simple conversion: about 3–6 months from feasibility to occupancy.
• New detached unit with utility work: about 6–12+ months.
• Historic or complex sites can take longer.

Common delays to avoid

• Submitting incomplete plans or ignoring setbacks, drainage, or utility constraints.
• Underestimating historic or overlay design review timelines.
• Waiting on water or sewer tap approvals and fee coordination.
• Public notice or neighbor concerns where design review triggers outreach.

Feasibility and cost factors

Before you write an offer, use this checklist to size up ADU potential and budget drivers.

Buyer feasibility checklist

Ask the seller for:

• Current survey or plat and any boundary evidence.
• As-built floor plans and proof of permits for major work on the main home.
• Any open permits or code violations.
• Title report and recorded easements.
• HOA covenants or CC&Rs, if applicable.
• Utility bills and contacts for Denver Water and Wastewater to discuss capacity and taps.

On-site items to review:

• Alley access and driveway location.
• Topography, drainage, and any retaining walls.
• Existing garage placement and condition, if you plan a conversion.
• Space for setbacks, parking, and utility runs.
• Any overlay flags like historic districts or floodplain.

Typical cost components

Every site is different. Use these ranges as a planning framework and get local quotes.

Design and permitting:

• Architect, designer, and engineering can range from several thousand to tens of thousands of dollars based on scope.
• City permit and plan review fees are typically hundreds to a few thousand dollars, tied to project valuation and fee schedules.
• Water and sewer impact or tap fees can be a few thousand dollars or more. Verify current fees with the utilities.

Construction:

• Interior conversions often cost less, ranging from tens of thousands into the low six figures, depending on finishes and system upgrades.
• New detached ADUs commonly land in the mid six figures for a complete build in the Denver market, though smaller or prefab options can reduce costs.
• Site work like grading, foundation, and utility trenching can add significant expense.

Soft costs and operations:

• Surveying, permit fees, inspections, construction financing, and insurance.
• Property taxes may rise as assessed value changes. Utilities and insurance can increase.
• Rental income depends on unit size and neighborhood demand. Research current local rents before relying on projections.

Pitfalls to avoid

• Relying on an unpermitted ADU or short-term rental without proper licensing. This can lead to fines and forced changes.
• Ignoring utility capacity or recorded easements that limit placement.
• Assuming HOA approval is automatic. CC&Rs can be stricter than city rules.
• Underestimating drainage, grading, or retaining wall costs on sloped lots.

Verify rules and contacts

Use these steps to confirm what is possible on a specific Denver property:

• Look up the parcel on the City and County of Denver zoning and property map to confirm zoning and any overlays.
• Read the relevant sections of the Denver Zoning Code for ADU standards tied to your zone.
• Call or meet with Denver Development Services to confirm submittal requirements and current review timelines.
• Contact Denver Water and Denver Wastewater about tap fees and capacity for an added dwelling.
• If the home is in a historic district, consult the Historic Preservation Office early for design review procedures.
• Ask your title company, real estate attorney, or HOA manager for CC&Rs and recorded easements.

Pro tip: Schedule a brief pre-application meeting with the city or use any published ADU intake checklist to surface issues early.

Make a smarter ADU move

Adding an ADU can be a smart way to improve flexibility and long-term value, but the details live at the parcel level. A clear plan starts with zoning, utilities, and a realistic budget, then moves through a tight design and permit process.

If you want expert help evaluating ADU potential while you shop, or you need introductions to Denver designers, engineers, or contractors who know the process, reach out to Nick Crothers. You will get practical guidance, local intel, and an efficient path from idea to action.

FAQs

What is an ADU in Denver?

• An accessory dwelling unit is a secondary home on the same lot as your main house or duplex. It can be internal, attached, or a detached backyard unit, subject to zoning and building rules.

How do I know if my Denver lot allows an ADU?

• Start by confirming your parcel’s zoning with the City and County of Denver, then review any overlays, setbacks, height limits, and lot coverage that apply to your specific zone.

How long does the Denver ADU permit process take?

• Simple conversions often take about 3–6 months from feasibility to occupancy, while new detached units with utility work often take about 6–12+ months depending on reviews and site conditions.

What are the biggest cost drivers for a Denver ADU?

• Design and engineering, permit and tap fees, site work like grading and utilities, and construction scope and finishes are the main drivers, with detached builds typically costing more than conversions.

Can my HOA block an ADU in Denver even if zoning allows it?

• Yes, private covenants can restrict additional units, exterior changes, or rentals, so you need to read the recorded CC&Rs and confirm HOA rules before you rely on city allowances.

Do I need extra parking for an ADU in Denver?

• Some zones or overlays require on-site parking for a new dwelling. Others reduce or waive the requirement, so verify the rule for your specific parcel before you design.

Will an ADU change my property taxes and insurance?

• Likely yes. An ADU can raise assessed value, increase utilities, and may require insurance updates, so plan for higher carrying costs as part of your budget.