Cover photo: Olerra detached unit installed on a Denver bungalow lot, daylight, alley access visible. Avoid renders.
At a Glance
A quick scan if you don’t have time for the full guide:
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A typical 490 sq ft detached Olerra unit in Denver lands at $245K to $285K all-in.
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Across three Olerra sizes: $175K to $215K (245 sq ft studio), $245K to $285K (490 sq ft one-bedroom), $335K to $395K (735 sq ft two-bedroom).
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HB24-1152 made administrative approval mandatory in June 2025. Denver’s CPD pipeline still runs 3 to 6 months in practice due to throughput backlog.
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Denver Water charges ADUs a separate System Development Charge in the $2K to $3K range in 2026, much smaller than the single-family base SDC. The schedule steps up slightly on July 1.
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Bulk-plane regulations limit ADU height to 24 ft and require the unit to sit in the rear 35% of your lot. These rules drive structural engineering complexity, not size-cap math.
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Parking compensation is still required when a garage conversion eliminates off-street parking. That add-back typically costs $10K to $30K.
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Owner-occupancy is not required for long-term rental. Owner-occupancy IS required for short-term rental licensing.
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Also in this series: Boulder, Fort Collins, and Colorado Springs ADU cost guides.
Why Denver ADU Costs Are Different
Most cost articles treat Denver as generic Front Range. The reality is more specific. Three Denver-shaped forces drive the cost curve.
First, bulk-plane. Denver caps ADU size by geometry, not square footage. Max height 24 ft, unit in the rear 35% of your lot, volume tighter as you approach property lines. Stick-built designs face more iteration than modular floor plans pre-engineered around the rules.
Second, the CPD permit calendar. HB24-1152 made administrative approval mandatory in June 2025. No discretionary hearings, no neighbor votes. The practical Denver timeline still runs 3 to 6 months because of CPD throughput. “Ministerial” on paper does not equal fast on the calendar.
Third, parking compensation. Garage conversions that eliminate off-street parking must replace it elsewhere on the lot. That adds $10K to $30K. Most of the rest of the Front Range dropped this requirement after HB24-1152. Denver kept it.
The trade-off worth absorbing: Denver is the largest rental market in the state, with the deepest tenant pool and the most consistent year-over-year rent growth on the Front Range.
What HB24-1152 and Denver’s Rules Allow
Yes, you can build an ADU on your Denver single-family lot. The rules just shifted in your favor.
HB24-1152 baseline. Since June 30, 2025, Denver must allow at least one ADU on every single-family lot, must process code-compliant applications administratively, and cannot impose owner-occupancy mandates. HOAs lost the power to ban ADUs outright. Our HB24-1152 explainer walks the full text.
Bulk-plane in plain English. Denver’s bulk-plane rule limits the volume you can build above a certain distance from your side and rear property lines. For ADUs: 24 ft max height, unit in the rear 35% of your zone lot, 12 ft bulk plane on lots 40 ft wide or narrower. A single-story modular unit fits cleanly almost everywhere. Two-story units require careful siting, especially on narrower lots.
Owner-occupancy. Not required for long-term rental. Required to hold a short-term rental license: you can live in your primary and STR your ADU, but not the reverse.
Short-term rental rules. STR license application capped at $150, with $100 annual renewal. The owner-occupancy requirement is the binding constraint for most ADU owners considering STR. If pure-investment STR is your goal, Denver isn’t the city for it.
Parking. Still required. Garage conversions that remove off-street parking must compensate elsewhere on the lot. New detached ADUs without garage removal are typically fine.
Affordable ADU pathway. Denver doesn’t have a Boulder-style fee-waiver ordinance. The closest equivalent is the West Denver SF+ ADU Pilot Program, run with Denver Housing Authority and Habitat for Humanity of Metro Denver, which offers pre-approved plans and financing assistance in exchange for long-term affordable rental terms. The city has also allocated roughly $8M in low-and-moderate-income ADU loans and down-payment assistance. At the state level, the Colorado ADU Grant Program opens its next window February 2 to March 18, 2026.
The Denver Cost Stack
Break a typical Denver detached modular ADU project apart and the cost stack looks like this for a 490 sq ft unit on a clean suburban lot.
Structure (the unit itself): roughly 50% of total. A modular detached unit at 490 sq ft runs $130K to $160K for the structure. Stick-built at the same size runs $180K to $220K. Includes framing, roofing, exterior finish, interior finish, plumbing rough-in, electrical rough-in, and HVAC. Does not include foundation or anything that connects the unit to your lot.
Foundation: $15K to $25K typical on Denver suburban lots. Stable, well-drained lots near the lower end. Expansive clay soil across the Denver metro bumps to $25K to $40K and often requires engineered solutions. Helical piles run at the lower end; poured concrete foundations at the higher end.
Site prep and grading: $5K to $15K typical. Denver’s flat-lot patterns help. Alley access in older grid neighborhoods like Park Hill or Berkeley saves on crane staging and material delivery. Lots with limited rear access run higher.
Utility connections: $5K to $15K combined. Covers water, sewer, electric, and gas on a typical Denver lot. The Denver Water ADU SDC sits inside this line at $2K to $3K, covered in detail below. Sewer connection, new electric service, and gas tie-in add the rest.
Permits and inspections: $5K to $8K. Building permit for a new dwelling structure runs $5K to $6K, paid at application. Plan review surcharges add roughly 50% over base for valuations above $2K. Re-inspections run $100/hr. Combined, the Denver permit fee category typically lands at $5K to $8K, occasionally climbing to $10K on complex projects.
Contingency: 10 to 15% of total, or $25K to $40K on a $250K project. Not optional. Every Denver ADU project surfaces something during construction the original quote didn’t show: soil surprises, alley utility congestion, plan-review change requests. The owners who finish on budget all carried real contingency.
Total typical Denver 490 sq ft modular detached: $245K to $285K all-in. Lower end for a clean suburban lot with stable soil. Upper end for lots with expansive clay, alley access constraints, or bulk-plane complications.
The Denver Water SDC + Permit Fees Deep Dive
Most of what people read about Denver Water fees in ADU contexts is wrong or out of date, and the misconception is consequential. Two things to know.
The ADU-specific SDC is much smaller than the single-family base SDC. Denver Water assesses System Development Charges based on the expected water demand a new tap will create. A new single-family home gets the base SDC, which exceeds $10K inside Denver in 2026 plus a per-square-foot surcharge. An ADU gets a smaller, separate ADU SDC because the expected demand is lower.
The 2026 ADU SDC schedule: $2,055 inside Denver and $2,870 outside Denver through June 30, 2026. Starting July 1, 2026, the rates step up to $2,170 inside and $3,030 outside. A 20% Water Efficiency Credit is available for qualifying installations. The schedule is reviewed every two years; the next revision lands in 2028.
Combined with building permit and inspection fees of $5K to $8K, the “permits + tap” line on a typical Denver ADU project lands at $8K to $12K, not the $30K some out-of-date guides cite. The bigger Denver cost drivers are bulk-plane engineering complexity, the CPD permit calendar, and parking compensation for garage conversions, not the water SDC itself.
Parking Compensation: The Denver-Specific Garage Conversion Cost
Denver kept its parking mandate after HB24-1152 took effect. Most of the rest of the Front Range removed it. The result: garage conversions in Denver carry a cost most other Front Range markets don’t.
If your garage conversion eliminates required off-street parking, and most do, you have to add equivalent parking back somewhere on your lot. That typically means a new dedicated pad on the side or rear, sometimes with driveway extension or grading work. The compensation cost runs $10K to $30K on most lots, more on tight or sloped sites where the rebuild geometry is constrained.
On small historic-neighborhood lots in places like Five Points or West Highland, the compensation requirement is often the deal-breaker that pushes the project from garage conversion to detached new build instead. If you’re weighing the two, our ADU type comparison walks the trade-offs.
Where ADUs Get Built in Denver
Lot patterns shape what’s buildable and what’s affordable. Four Denver neighborhood archetypes worth knowing about your own lot.
Berkeley, Park Hill, Sunnyside, Sloan’s Lake. Older grid lots with alley access. The most ADU-friendly geometry in Denver. Detached units sit in the rear 35% with crane staging from the alley. Bulk-plane rarely binds because lots are 40 to 50 ft wide and the unit sits well back. Foundation and utility costs run at the lower end of typical ranges.
Highland, West Highland, and Central Park. Highland mixes older grid lots with historic overlays that add a design review layer: administrative, but with style and material constraints, plus $5K to $15K in design adjustments. Central Park is the newer-subdivision counterpoint: easier geometry, fewer historic constraints, but HOA design review still slows the calendar. In both cases the ADU itself fits the same cost stack; the wrapper around it is heavier.
Bulk-plane-tight lots. Ranch homes on lots 40 ft wide or narrower, with primary structures already near the front setback. The rear-35% envelope is small, the bulk-plane geometry binds, and modular floor plans pre-engineered for tight envelopes are usually the only practical path. Stick-built on these lots requires custom engineering that adds $10K to $25K to design cost.
Five Points and historic-district lots. Tight lots, mature trees, alley patterns that pre-date current utility codes. Detached ADUs are buildable but need careful site planning. Garage conversions are common here, which makes the parking compensation cost especially material.
Denver pulled more ADU permits in 2024 than it had pulled across the previous five years combined. The 2025 and 2026 trajectories are steeper still. Most of the growth concentrates in the neighborhoods above.
Worked Examples by Size
Three Olerra Flex Flat sizes, with typical Denver all-in pricing on a clean suburban lot. Sloped lots, expansive clay, alley access constraints, or historic overlays shift these upward.
245 sq ft Flex Flat: $175K to $215K all-in. Studio or one-room unit. Best fit for a home office, gym, guest space, or compact rental. Structure cost is roughly half the total.
490 sq ft Flex Flat: $245K to $285K all-in. True one-bedroom rental with full bathroom and full kitchen. Front Range rental comparables suggest $1,650 to $1,900 per month long-term in Denver. Berkeley, Park Hill, and Sloan’s Lake lean toward the upper end.
735 sq ft Flex Flat: $335K to $395K all-in. Two-bedroom or family use. Big enough for a long-term tenant family or a multigenerational household. Per-square-foot economics improve at this size because fixed costs spread across more area.
Stick-built premium. Add roughly 15 to 25% to each modular figure.
Site-specific shifts. Expansive clay adds $10K to $20K to foundation. Bulk-plane-tight lots add $10K to $25K to design cost if stick-built. Historic overlay lots add $5K to $15K in design adjustments plus a few weeks of calendar.
How Denver Compares to the Rest of Colorado
Same project, four Colorado cities. Boulder and Fort Collins are the closest peers; Colorado Springs runs noticeably cheaper but trades wildfire-zone restrictions and a parking mandate of its own.
| Parameter | Denver (this guide) | Boulder | Fort Collins | Colorado Springs |
|---|---|---|---|---|
| Typical 490 sq ft all-in | $245K to $285K | $260K to $300K | $240K to $280K | $220K to $260K |
| Size cap | Bulk-plane volume (no flat sq ft) | 800 sq ft (1,000 affordable detached) | ≤1,000 sq ft or proportional | 1,250 sq ft or 50% of primary (whichever is less) |
| Water tap / SDC | $2K to $3K ADU SDC | Shared with primary; small PIFs | Shared, but PIFs assessed; $5K to $15K typical | Case-by-case; sharing common |
| Permit + inspection | $5K to $8K | $1,900 to $3,200 | $10K to $18K with utility hookups | $1K to $5K |
| Parking | Compensation required (garage conversions) | Eliminated March 2025 | Eliminated citywide | 1 off-street space required |
| Short-term rental | Owner-occupancy required for license | Effectively closed (pre-2019 license carve-out) | Allowed without owner-occupancy | Prohibited on properties with ADUs (June 30, 2025) |
| Owner-occupancy | Not required | Eliminated March 2025 (Ord 8650) | Not required | Eliminated April 2025 (Ord #25-45) |
| Typical permit timeline | 3 to 6 months | ~6 weeks | 2-3 months + 6-8 weeks | ~6 weeks + 14-day public posting |
What the table shows. Denver is mid-pack on price (cheaper than Boulder, comparable to Fort Collins, more than Colorado Springs) but the slowest on permit calendar. The Denver-unique cost driver is parking compensation for garage conversions, which the rest of the Front Range eliminated. The Denver-unique advantage is rental depth: the largest tenant market in the state.
For the broader US framing including Los Angeles and Portland, the ADU Construction Cost national guide sets the national context.
Reading a Denver ADU Cost Quote
Most homeowners receive a quote and don’t know what to check. Five things specific to Denver projects.
Is the Denver Water ADU SDC named specifically? A real Denver quote will name it. A vague “permits and fees: $5,000” line is hiding variance you’ll discover later. The accurate breakdown looks like: “Denver Water ADU SDC: $2.2K, City of Denver building permit: $4.5K, electric tap: $1.5K, contingency for additional municipal fees: $2K.”
Is the bulk-plane analysis done? Before you sign a contract, the builder should have confirmed the unit fits Denver’s bulk-plane envelope. On bulk-plane-tight lots, a builder who hasn’t done the analysis is hiding a redesign in your future.
Is parking compensation addressed? If the project is a garage conversion, the quote should explicitly include parking compensation construction or document why it isn’t required. A garage-conversion quote without that line is incomplete.
Is there a contingency line of 10 to 15%? Quotes without a contingency line are not finished quotes. Soil surprises and alley utility congestion are common Denver cost drivers that contingency exists for.
What’s not in the quote? Most exclude site survey, geotechnical report, landscaping after install, interior furnishings, and HOA or design review fees on historic overlay lots. Ask explicitly.
Financing a Denver ADU
Four common paths cover most Denver homeowners: cash (simplest, no interest), HELOC (flexible, floating rates), construction loan (most common ADU path, disburses in stages and converts to a permanent mortgage), and cash-out refinance (works when current rates are below your existing mortgage). The right one depends on your equity position, credit, and timeline.
Denver-specific incentives. The West Denver SF+ ADU Pilot Program offers pre-approved plans and financing assistance for owners committing to affordable rental terms. The Colorado ADU Grant Program opens a second 2026 funding window February 2 to March 18. Our Colorado ADU financing guide covers state-level programs in more depth.
How Olerra Builds in Denver
We build detached modular Flex Flat ADUs across the Front Range, Denver included, on a fixed-price contract. Once you sign, the unit price, foundation, site work, utility hookups, permits, and install are locked. No change orders unless excavation reveals something truly unforeseen, and even then we walk you through the change before it happens.
Our property check confirms what your specific Denver lot allows under bulk-plane, setback, and rear-35% rules before any contract gets written. Our process page walks the full five-step sequence from property check to keys, typically 3 to 6 months from contract signing.
→ Get your free Denver property check and quote.
FAQ
How much does an ADU cost to build in Denver?
A typical detached modular ADU in Denver runs $245K to $285K all-in for a 490 sq ft unit on a clean suburban lot. Smaller 245 sq ft units land at $175K to $215K; larger 735 sq ft units at $335K to $395K. Stick-built construction adds 15 to 25%.
What is the Denver Water tap fee for an ADU?
The ADU-specific SDC is $2,055 inside Denver and $2,870 outside through June 30, 2026, stepping up to $2,170 and $3,030 on July 1. Much smaller than the single-family base SDC, which can exceed $10K.
How long does a Denver ADU permit take?
Realistically 3 to 6 months from application to issued permit, despite HB24-1152 making administrative review mandatory. The bottleneck is Denver CPD throughput, not the underlying process.
Do I need owner-occupancy to rent out a Denver ADU?
Not for long-term rental. HB24-1152 preempts owner-occupancy mandates. Owner-occupancy IS required for a short-term rental license: you can live in your primary and STR your ADU, but not the reverse.
Can I Airbnb a Denver ADU?
Yes, with a short-term rental license, but only if you live on the property. STR license application fees are capped at $150, with $100 annual renewal.
What is the Denver bulk-plane rule?
It limits how much volume you can build above a certain distance from your side and rear property lines. For ADUs: 24 ft max height, unit in the rear 35% of your lot, 12 ft bulk plane on lots 40 ft wide or narrower. Single-story modular units fit cleanly almost everywhere; tight lots may constrain stick-built designs.
Can my HOA block my Denver ADU?
No. HB24-1152 stripped HOAs in Subject Jurisdictions (Denver included) of the power to ban ADUs. HOAs can still enforce reasonable aesthetic standards, but cannot use them as a back-door ban.
Are there grants or incentives for Denver ADUs?
Yes. The West Denver SF+ ADU Pilot Program offers pre-approved plans and financing assistance for affordable rental commitments. The Colorado ADU Grant Program (ADUG) provides separate state funding; the 2026 second round opens February 2 to March 18.
Price Your Denver Project
The fastest way to move from “general Denver ADU cost range” to “what mine will actually cost” is a property check on your specific lot. Bulk-plane, setbacks, alley access, soil conditions, and utility distance all shape the final number, and a good property check surfaces them before any contract gets signed.
No spec house. No long sales call. A real number based on your real Denver lot.
→ Get your free property check and quote.
Sources
1. Denver Water. System Development Charges, 2026 schedule.
2. City and County of Denver, Community Planning and Development. ADUs in Denver: Recommendations Summary.
3. Denver7. ADU permits increase as Front Range governments allow easier access to build them.
4. Colorado Newsline. A new Colorado law opens the doors wider for ADUs.
5. Habitat for Humanity of Metro Denver. West Denver SF+ ADU Pilot Program.
6. Colorado Department of Local Affairs. Accessory Dwelling Unit Grant Program.