Last week, the Boston Zoning Commission adopted Net Zero Carbon (NZC) zoning. As addressed in our 2021 and 2023 advisories, this completes a three-part decarbonization strategy, along with the Specialized Energy Code and the Boston Emissions Reduction and Disclosure Ordinance (BERDO 2.0).

NZC requires carbon neutrality for new buildings of at least 20,000 square feet or 15 dwelling units, or additions of at least 50,000 square feet, that file for Large Project Review or Small Project Review on or after July 1, 2025. It will not apply to renovations or changes of use. It requires carbon neutrality once new buildings become operational, with exceptions for lab use (until 2035), and hospital and general manufacturing uses (until 2045).

Here is how NZC interrelates to the other prongs:

• The Specialized Energy Code, adopted by Boston in 2023, provides stricter energy efficiency requirements than the frequently iterated Stretch Energy Code, which in turn exceeds the Massachusetts Base Energy Code. The Boston Planning Department estimates that the 2023 Specialized Code may have halved greenhouse gas emissions from new buildings compared to the version of the Stretch Code in effect when Boston’s 2019 Climate Action Plan was adopted. NZC is intended to address the remaining half for new construction. 
   
• BERDO 2.0 also targets carbon neutrality, but for covered buildings that already exist (i.e., containing at least 20,000 square feet or 15 dwelling units), phased in to 2050. Emissions levels must decrease every 5 years following a prescribed schedule unless the Emissions Review Board approves an alternative compliance pathway. The Planning Department estimates that 70% of covered existing buildings will have to take steps to comply with emissions reduction requirements by the first milestone in 2030. 

NZC compliance will be assessed through Article 80B Large Project Review or Article 80E Small Project Review based on Planning Department review of a project’s already required Leadership in Energy and Environmental Design (LEED) scorecard, together with a new Greenhouse Gas Emissions checklist. Projects with at least 50,000 square feet will also submit a new structural life cycle analysis addressing embodied carbon emissions from fabrication, transportation, demolition disposal, construction materials, and the like. After becoming operational, the new building becomes an existing building subject to, but presumably already compliant with, BERDO 2.0.