BOULDER COUNTY - Homeowners and prospective buyers in unincorporated Boulder County should be aware of new regulations that went into effect on May 13, 2025, limiting the size of new and expanded homes.

The changes mark a major shift in how Boulder County manages residential development, aiming to preserve neighborhood character, promote sustainability, and address affordability concerns.

Under the new rules, the maximum allowable size for a home is now based on the median residential floor area of the surrounding neighborhood. This replaces the previous policy, which allowed homes to be built up to 125% of the neighborhood median size.

There is some ability to expand existing home size, but there are limits – for instance, homes of 1,500 square feet or fewer may grow by up to 1,000 square feet or to the median size of the neighborhood, whichever is greater.

Similar rules apply to homes of 1,501 – 3,000 square feet (an additional 750 sq. ft. may be added), and 3,001 – 3500 square feet (an additional 675 sq. ft. may be added).

The updated regulations also eliminate several exceptions that previously allowed homeowners to exceed the 125% threshold. These changes were made through amendments to the County’s site plan review process and reflect Boulder County’s long-term efforts to manage growth in a way that protects the rural and scenic character of its unincorporated areas.

The changes only apply to properties within the unincorporated areas of the county. They do not apply to incorporated cities or towns (i.e. Boulder, Nederland, etc.). Projects with a valid approval prior to the effective date of the new regulations are not impacted by the changes.

For some homeowners, these changes may come as a surprise, especially those considering major renovations or building a new home. Anyone planning to build or expand should consult with the County's Land Use Department early in the process to understand what’s permitted under the new rules. 

For anyone looking for a bit more flexible alternative in the mountains, Gilpin County might be the place for you. Gilpin does not currently impose size restrictions tied to neighborhood medians, and it also allows accessory dwelling units (ADUs), making it an attractive option for those looking to accommodate additional guests, or even generate some rental income.

As housing needs and land use policies continue to evolve along the Front Range, understanding these differences between counties can be an important part of making an informed real estate decision. Whether you’re dreaming of a mountain getaway or planning a permanent move, it pays to know the rules before you break ground.

Josh Harrod is a long-time Nederland resident and Realtor® at 8z Real Estate. He can be reached at Josh.Harrod@8z.com. Through his columns, Josh Harrod will share insightful tips and advice about living in the Peak to Peak region.