Boulder County proposes home size limits

Boulder County Commissioners are proposing significant changes to residential building regulations that would curb the size of new homes and remodeled homes in unincorporated areas, citing mounting environmental concerns and affordability issues.

The proposed changes would mark the most substantial shift to the county's Site Plan Review (SPR) regulations since their introduction in 1993, reducing the maximum allowable home size from 125% of the neighborhood median to simply matching the median.

This change comes as the county's analysis reveals what the staff described as a troubling trend of ever-expanding residential footprints. In order to achieve the county's sustainability objectives, county staff stated that they must consider the size of homes in the unincorporated county and the resources consumed to construct or enlarge them.

The timing appears critical. Between 2019 and 2023, more than half of all residential modification applications sought to exceed neighborhood size compatibility standards, with a striking 90% approval rate. The environmental implications are significant, with residential energy use already accounting for 24% of Boulder County's greenhouse gas emissions.

County staff reported that even more concerning is the impact of embodied carbon – the emissions generated by construction materials and processes. Research presented at the recent community meeting highlighted that in Boulder County's cold climate, it takes 23 years for a typical home's operational emissions to equal its initial construction emissions.

The trend toward larger homes appears to be creating a self-reinforcing cycle of increased environmental impact. County staff, examining U.S. Census data and local building permit records, found that new homes in unincorporated Boulder County consistently exceed the national average in size. Research indicates that wealthier households tend to build larger homes, leading to higher per capita energy use and greenhouse gas emissions.

The impact extends beyond environmental concerns. As newer, larger homes replace more modest ones, housing costs are rising throughout unincorporated areas. Property owners who have not made any improvements to their homes may still see higher tax bills due to the changing character of their neighborhoods.

County staff indicated that the county's market-based property assessment system means that when larger homes are built, they can drive up property values and tax assessments for neighboring properties.

Under the proposed regulations, several changes would be made to size requirements while maintaining some existing standards. In mapped historic townsites, properties would continue to be limited to 1,500 square feet. However, in other areas, the maximum allowable size would be adjusted to match the neighborhood median, eliminating the current provision that permits exceeding this median by 25%. Meanwhile, the allowable maximum size would remain unchanged at 2,500 square feet, regardless of the neighborhood median.

Residential Floor Area calculations would continue to encompass all attached and detached floor area used for residential purposes, including accessory structures such as sheds and detached garages. The current rules provide a 400-square-foot exemption for certain structures, including gazebos and detached greenhouses.

The county plans to post draft regulations online for public comment before proceeding to Planning Commission review. Residents can follow the process and provide input through the county's website at boco.org/dc-24-0003.

As Boulder County grapples with these changes, the challenge lies in balancing property owners' rights with broader community interests in maintaining neighborhood character, environmental sustainability, and housing affordability. The data suggests that meaningful progress on climate goals may require more than just better building standards – it may demand a fundamental shift in how the community thinks about home size, luxury, and environmental responsibility.