Building code requirements creating obstacles for building “missing middle” residential housing, suggests new report

Permitting, fire, and accessibility codes designed for larger buildings raise costs and complications for small (3-24 unit) developments in transit corridors

July 14, 2026

Boston – The system of building codes in Massachusetts is driving up costs and complicating requirements for building the smaller multifamily housing near transit that could have the greatest impact on Massachusetts’ housing shortage, says a new report released today by Boston Indicators, the Joint Center for Housing Studies at Harvard and the design firm Nominal.

The report, Unlocking Small Multifamily Housing Through Building Code Reform, compared the two international codes that form the model for nearly all residential construction in Massachusetts: the International Residential Code (IRC), which applies to single-family homes, duplexes, and townhomes, and the International Building Code (IBC), which governs everything else, from triple-deckers to soccer stadiums. In interviews and research, report lead author Sam Naylor from Nominal found that moving from a two-unit building subject to the IRC to a three-unit building subject to the IBC requires substantial design and permitting changes often costing $100,000 or more – making 3-10 unit developments less suitable for affordable housing development.

The report then recommends following examples from other cities and states that have revised their building codes to better support small multifamily developments, and that have given greater authority and support to local bodies in charge of crafting and revising codes in their jurisdictions.

Multifamily Buildings Read the brief and download the report

“Our two-tiered building code system is well-intended, but too often results in unnecessary regulations that don’t improve safety, accessibility or design for smaller buildings,” said Naylor. “In Massachusetts, we could make an immediate impact by developing code requirements that specifically apply to small multifamily developments, and by better equipping the Board of Building Regulations and Standards (BBRS) to review and improve state codes applying to these buildings. Doing so would ensure we can fully take advantage of the state’s zoning reform efforts and build much-needed homes for Massachusetts families.”

The report specifically notes a number of areas where requirements that are sensible for large, 100 or more-unit buildings are less appropriate for buildings like triple-deckers or small apartment buildings. Commercial-grade sprinkler systems, elevator requirements and review processes befitting large-scale developments are often applied to much smaller buildings, with predictable results.

“When the requirements, timeline and review processes are the same for a three-unit and a 100-unit building, it’s not surprising that developers will forgo the smaller projects,” said Luc Schuster, Executive Director of Boston Indicators. “As a result, while we have removed zoning restrictions that discourage building on smaller lots near transit, the code requirements make projects less desirable for developers and less affordable for families.”

The report recommends several changes based on reforms undertaken in several other U.S. cities and states that have sparked production. Among them:

  • Develop a dedicated section of the building code for small multifamily housing (up to 24 units, no more than 3 stories), likely as an appendix to the Residential Code/IRC. This approach would keep the less burdensome residential code as the baseline and facilitate the addition of requirements that are necessary for small multifamily housing, but nothing more.
  • Strengthen the BBRS’s capacity and responsibility to revise model codes, by updating its mission to more explicitly evaluate how building code provisions affect housing production, affordability, and design quality, while maintaining appropriate safety standards.
  • Provide the board with added research and evaluation capacity and a broader representation of perspectives, including a dedicated multifamily housing technical advisory committee focused on the affordability, feasibility, and design of multi-unit housing.
  • Reform fire protection standards to provide multiple compliance pathways that better balance  automatic sprinkler protection with other passive systems such as fire-rated assemblies and compartmentalization..
  • Amend the code to allow for low-rise single-stair construction in buildings of up to eight units per floor, and modernize codes and standards related to elevators and other accessibility requirements to align with current technologies and best practices.
  • Streamline engineering and permitting requirements and processes for smaller wood-framed buildings, and review other places where the costs and complexity of code requirements may work against broader goals – for example, where energy code requirements for new buildings are so stringent they result in people being forced to remain in older, less efficient homes.

The full report and accompanying brief are both available now on bostonindicators.org.