NYC Struggles to Enforce LL97 as Climate Goals Loom

Image Credit: Urban Green Council

By Katie MacDougall

New York City passed Local Law 97 (LL97) in 2019 as the centerpiece of the Climate Mobilization Act. The law set emissions caps for buildings over 25,000 square feet, targeting a ten-percent reduction in citywide emissions by 2030. Seven years later, the city’s struggle to enforce it continues. Officials rarely issue penalties for noncompliance, and unclear timelines exacerbate uncertainty about implementation. LL97 illustrates a broader problem: Ambitious legislation without sustained enforcement confuses residents and fails to achieve its goals. 

Under former Mayor Eric Adams, the city expanded compliance extensions and alternative pathways, delaying penalties for many large office and commercial buildings. Some buildings have circumvented the policy altogether through Renewable Energy Credits introduced under Mayor Adams, which enable building owners to buy their way out of compliance by purchasing credits rather than reducing their building’s emissions. 

Now, newly elected Mayor Zohran Mamdani faces the challenge of catching up. He must meet the law’s climate targets while managing the enormous financial and labor costs of retrofitting thousands of existing residential buildings in NYC. Retrofitting involves a series of physical and mechanical upgrades that reduce fossil fuel dependence, such as upgrading insulation or modernizing electrical panels. Costs widely vary for building size and scope; for large buildings, full system overhauls such as replacing gas boilers with electric heat pumps can cost millions of dollars. 

Mamdani faces a political balancing act: NYC must reduce emissions without worsening its housing affordability crisis. Mamdani campaigned explicitly on addressing affordability, positioning himself as the candidate best equipped to protect middle- and working-class New Yorkers. If LL97 drives up housing costs, Mamdani’s credibility could erode. 

LL97 applies to buildings over 25,000 square feet, including many multi-family buildings and co-ops. As building owners undertake retrofits, costs are often passed to the tenants through rising maintenance costs, rents, or special assessments. 

Mamdani’s Homeowner Policy Memo explicitly acknowledges that LL97 implementation has lagged, particularly for co-ops in outer boroughs and Naturally-Occurring Retirement Communities. Oftentimes, these housing boards do not have access to capital to support the required renovations. Without government support, building owners face “expensive renovations or fines, all while failing to deliver on the important climate objectives of LL97,” per Mamdani’s Homeowner Policy Memo. The law includes a $268 fine per metric ton of CO2 equivalent over the limit each year. For large multi-family buildings, exceeding emissions caps by several hundred tons could result in annual six-figure penalties. As a result, the affordability of retrofitting large residential properties—especially co-ops, where residents effectively own shares in the building owner—has become a central point of contention. Effective, measurable enforcement will require closing that financing gap. The city has several options to strengthen compliance with LL97 without imposing excessive fines. 

One proposal builds on the state’s existing J-51 Exemption and Abatement Tax, which allows property owners to deduct up to 70 percent of renovation costs from property taxes over twenty years. Mayor Mamdani’s administration has signaled support for extending the program through 2035 to facilitate the LL97 retrofits. Officials also proposed reducing per-unit fees required to qualify for the abatement. At $85 per unit, Mayor Mamdani’s Homeowner Policy Memo estimates that a large affordable housing development like Penn South, with 2,800 units, would owe more than $230,000 simply to file.

More critically, Mayor Mamdani’s administration aims to strengthen the NYC Accelerator, an understaffed and underfunded agency designed to support LL97 compliance. The program provides advisory services, retrofit planning guidance, and financing support to building owners navigating complex decarbonization requirements. Expanding the agency’s capacity could lower retrofitting costs through bulk purchasing initiatives. For example, the city could procure and resell heat pumps to New Yorkers in bulk, reducing upfront costs. By reducing compliance costs rather than delaying enforcement, such an approach would address the affordability challenge at its source while preserving the integrity of LL97. 

Ultimately, lax enforcement and flexible compliance pathways have diluted LL97’s impact by delaying the first rounds of implementation and offering larger commercial buildings Renewable Energy Credits that allow them to avoid meeting sustainability goals. Residential retrofits remain the central challenge. 

With less than four years to meet the first set of climate emissions goals in 2030, Mamdani’s team must pair consistent enforcement with targeted financial and technical support to ensure that compliance is feasible. If New York succeeds, LL97 could become a national model for urban building decarbonization. If it fails, it will reinforce skepticism about whether cities can pursue ambitious climate mandates without undermining economic stability and housing affordability.