If you buy an older Boulder house planning to scrape it or add on, the date you submit a complete building permit application decides whether you owe a new fee. Every complete application submitted on or after Jan. 31, 2026 falls under Ordinance 8712. That ordinance is a citywide affordable housing impact fee on replacement homes and substantial additions to single-unit homes, and City Council approved it on Nov. 6, 2025. A rebuild that adds enough floor area to qualify will owe it.
The fee is real, and you should budget for it. It also turns out to be one of the smaller numbers in the project. Boulder has spent the past two years making it easier to add space and units to a residential lot. Most of what's left between a listing's "potential" and actual new square footage is construction cost. Treat the fee as a line item in that budget. The construction estimate is what should set your offer.
The fee, run on real square footage
The 2026 fee schedule sets one rate for expanding an existing single-unit home or replacing one: $11 per square foot. The rate doesn't change with the size of the finished house. On a replacement home, the charge applies only to the floor area beyond what the old house had on that lot. The city's own summary describes this as a "credit" for the existing home's size.
| Project | Square feet charged | Fee at $11 |
|---|---|---|
| Replace a 2,000 sq ft home with 3,000 sq ft | 1,000 | $11,000 |
| Replace a 2,000 sq ft home with 4,000 sq ft | 2,000 | $22,000 |
| Add a new ADU of any permitted size, per the City of Boulder | 0 | $0 |
To put it in scale, the City of Boulder's single-family median sale price was $1,193,500 in August 2026, according to IRES data reported by BizWest. A $22,000 fee works out to a bit under 2% of that. The fee also ended up lower than first proposed. An Aug. 27, 2025 staff memo recommended $15 per square foot, and under that version 4,000 square feet of additions would have cost $52,500. Council passed the $11 rate on a 7–2 vote. The city projected about $1.2 million a year in revenue.
The credit pays off when the old house is bigger
The credit also changes which house is the better buy. Under it, a small ranch is the more expensive starting point for a large rebuild. Take a buyer who replaces a 1,200-square-foot house with a 3,500-square-foot one. A plain reading of the credit charges 2,300 square feet, or $25,300. If the old house was 2,000 square feet, the same new home is charged 1,500 square feet, or $16,500.
There's one detail to settle before you rely on that math. The ordinance text exempts "any floor area in a single-unit dwelling use that is 2,000 square feet in floor area or less." The city's project page says the fee "does not apply to homes under 2,000 square feet in total area." Those two wordings could produce different bills, especially on a small original house. Before adoption, Boulder Reporting Lab reported that staff were still working out how basement area would count. On a specific property, get the city's calculation in writing before you treat the fee as a known number. The same goes for a lower-level-heavy floor plan.
Adding units costs less in city fees than adding size
The fee doesn't apply to ADU floor area, whether you're replacing a home or adding on. That exemption builds on the ADU changes Council approved in February 2025, which removed the owner-occupancy requirement and the minimum lot size and waived off-street parking for market-rate ADUs. The city applies those rules to ADUs proposed on or after March 8, 2025.
Other rules point the same way. According to KUNC, a February 2025 zoning change made it easier to convert some single-family homes into duplexes, including homes within 350 feet of a bus line in lower-density areas. The updated Boulder Valley Comprehensive Plan is now in effect. It was approved by City Council, Planning Board, the Boulder County Commissioners and the County Planning Commission. The plan designates nearly all of the city's residential land "Neighborhood 1" for gentle infill: duplexes, triplexes, rowhomes, cottage courts and ADUs. Officials estimate 35% to 40% more housing capacity than the previous plan, but how much gets built depends on market conditions and on future zoning.
Put together, Boulder now charges a fee for a bigger single house and charges none for a second unit. That's the incentive at work. Whether the incentive leads to anything getting built is a different question.
What happens to ADU permits once they're issued
Boulder's open-data construction permits dataset was last updated October 4, 2026, so you can check this yourself. We filtered primary building permits for descriptions mentioning an ADU or accessory dwelling. That pulls 53 applications filed in 2024 and 70 in 2025. From March 8, 2025 through early October 2026, the filter finds 116 records, and 60 of them show an issue date. These are permit records, not finished cottages. The list includes applications to legalize existing basement units, plus void and replacement records.
The local builders who handle these projects described the gap at a BizWest roundtable in May 2025:
"Out of 20 ADU permits, only three or four get built," said Lance Cayko, co-owner of F9 Productions. Scott Rodwin, of Rodwin Architecture and Skycastle Construction, added: "Most people don't have $400,000 or $500,000 in cash lying around to build those."
Rodwin also pointed to high interest rates as what was holding projects back, more than any lack of interest. Those comments are more than a year old, so ask a builder for a current number. Compare the scales anyway. An ADU that skips an impact fee in the tens of thousands can still carry a construction bill several times that size. The city also doesn't pre-review building permit applications, so design and engineering costs come before you know whether the plan clears.
Why the August median doesn't tell you what potential is worth
A buyer looking at August 2026 might take the 14% year-over-year drop in the city's single-family median as a discount on everything. That month had 40 sales against 168 active listings. In July 2026, BizWest reported a median of $1.5 million on 54 sales and 165 listings. A swing of about $300,000 in one month on samples that small says more about which houses sold than about what any particular house is worth.
For a broader view, the Colorado Association of Realtors' August report found that Boulder County listings were down about 10% and prices had been flat since the start of the year. Correctly priced homes averaged about 62 days on market and sold for 98.5% of asking. At 98.5% of asking, a seller pricing in a future ADU or a bigger rebuild is asking you to pay up front for a project you would fund yourself. Unless a home's price reflects that build cost, the upside doesn't come at a discount.
Questions to settle before paying for potential
- What does the city calculate as the prior home's floor area, and how does it count the basement? That number is your credit.
- Under the ordinance's 2,000-square-foot language, does your planned home owe the fee on its full expansion or only on the area above 2,000 square feet?
- Do any deed restrictions or an HOA covenant block an ADU on this lot? City rules allowing one doesn't settle that.
- What does a builder quote today for the ADU or addition, and how would you finance it at current rates?
- If you'd rent the unit at a capped rent, would the City of Boulder's affordable-ADU option, with rents tied to 75% of area median income, give you the size allowance your plan needs?
None of this is tax or legal advice. The city's planning staff and your own advisors make the final call on any specific project.
If you're weighing a Boulder house mostly for what you could add to it, Arlene Burgess can help you get the floor-area history, the covenant check and a builder's number before you write the offer, so the price you pay matches what you can realistically build. Let's Connect — Schedule a Consultation.
