Aggressive action is necessary to mitigate climate change by significantly reducing the carbon impact of our built environment. While the Commonwealth and many communities have made commitments to achieve carbon neutrality by 2050, Boston and Cambridge specifically are on the leading edge of implementing requirements around existing building carbon emission reductions. It is expected that the number of communities with these types of requirements will increase. Carbon emissions tracking has started to move building owners toward benchmarking their existing buildings’ carbon impact and developing long-term plans for compliance, with an eye on minimizing the capital and operating costs of compliance. We will review a new “Zero Over Time” evaluation and planning process we have recently implemented for two affordable housing developments, on an elderly building in Newton, and a scattered site development in Boston. We will discuss how we have adapted the standard energy auditing process and deliverables and integrated it with each development’s unique physical and financial circumstance to create a Zero Over Time Plan.