Boulder County Home Size Limits: New Rules for Affordability and Environment

Boulder County, Colorado, has enacted new regulations capping the size of new and significantly expanded homes in its unincorporated areas. Effective May 13, 2025, the amendment limits homes to the neighborhood's median floor area, replacing a more lenient allowance of 125% of the median. The primary goals are to improve housing affordability, reduce environmental impact, and preserve community character by discouraging the construction of overly large houses, often called "McMansions."

Why Did Boulder County Implement Home Size Restrictions?

The Board of County Commissioners approved the change with a 2-1 vote, citing concerns that excessively large homes drive up property taxes for all residents and increase overall construction costs. Commissioner Ashley Stolzmann stated the rule will result in "smaller houses than you would have otherwise, which will have a lower impact on the environment and can have effects on affordability." The environmental argument is supported by organizations like Green America, which notes larger homes consume more energy, emit more carbon, use more resources, and generate more waste. This policy aligns with the commissioners' documented focus on climate action. The rule is a direct response to growing home sizes; Boulder County saw new home averages jump from about 3,500 square feet in 2010 to roughly 3,900 in 2023, with finished areas like basements pushing the average over 4,700 square feet.

What Do the New Rules Mean for Homeowners and Builders?

The new amendment to the site plan review process (the procedure for approving new development projects) establishes a hard cap based on the median home size in a specific neighborhood, eliminating several exceptions that previously allowed properties to exceed the old 125% limit. Key considerations include:

• Affordability: The commissioners believe that curbing the trend of large, expensive homes will help maintain a more diverse and attainable housing stock. This is particularly relevant as property taxes (levies on property that the owner is required to pay to the local government) rose by a national average of 2.7% in 2024.
• Exceptions: A significant exemption exists for properties destroyed in the 2021 Marshall Fire. These homes can be rebuilt without being subject to the new size caps.
• Industry Concerns: The building industry has expressed reservations. The Boulder Chamber president noted concern about policies that are "disruptive to the business climate." The county's volunteer Planning Commission had also unanimously voted to reject the proposal, feeling there might be better ways to achieve the stated goals.

The following table illustrates the high-value markets in unincorporated Boulder County that the amendment affects, based on recent data:

How Do Boulder County's Rules Compare to Other Cities?

Home size caps are not a novel concept. Several other municipalities have implemented similar measures, including cities in California, Oregon, Texas, and Rhode Island. These policies often aim to preserve neighborhood character and control density. Conversely, New York City recently repealed its long-standing 12 FAR (Floor Area Ratio), a zoning metric that capped a building's total floor area relative to its lot size. Critics of such restrictions argue they can stifle new housing construction and exacerbate housing shortages. Boulder County's approach focuses specifically on limiting the square footage of single-family homes in rural areas, a different context from urban zoning regulations.

Practical Advice for Navigating the New Regulations

For prospective homeowners and builders in Boulder County's unincorporated areas, understanding these rules is crucial. Based on our experience assessment, here are key takeaways:

• Check the Median: Before planning a new build or major expansion, research the specific median floor area for the neighborhood where the property is located.
• Understand Exemptions: If your property was affected by the Marshall Fire, you are exempt from these new limitations.
• Plan for Review: All projects must go through the county's site plan review process, where compliance with the new size cap will be strictly enforced.
• Consider Resale Value: While the goal is affordability, the long-term impact on property values in these exclusive markets remains to be seen.

The new regulation represents a significant shift in Boulder County's land use policy, emphasizing sustainability and affordability over unrestricted growth. The success of this initiative will depend on its implementation and the evolving response from the real estate market.