Article 22 Green Roofs Requirement


Under the Green Roofs Requirement, most new buildings or structures over 25,000 square feet must have a green roof and/or solar energy system. (See Section 22.30 of the Zoning Ordinance). These systems are not included in the Gross Floor Area. Submit the operation and maintenance plan for the Green Roofs to the Department of Public Works (DPW) for approval before applying for a building permit for any building containing Green Roof area. 

Developers can apply for a special permit from the Planning Board to reduce the amount of green roof they are required to build. The project team must make a “unit contribution” to the Cambridge Affordable Housing Trust for every square foot of reduction that the Planning Board grants.

Calculating a Cash Contribution

  1. Identify Total Roof Area
  2. Identify Exempt Roof Area:
    1. Areas with a slope greater than 25%;
    2. Areas that are usable by building occupants or the general public;
    3. Vehicular parking decks; and
    4. Mechanical equipment and appurtenances carried above the roof and not intended for human occupancy.
  3. Calculate the Required Green Roof Area
    1. Required Green Roof Area = 80% * (Total Roof Area from Item 1 - Roof Area Exempt from Item 2)
  4. Identify Built Green Roof Area in the project
  5. Calculate the Required Green Roof Area Not Installed
    1. Required Green Roof Area Not Installed = Required Green Roof Area from Item 3 – Built Green Roof Area from Item 4

The amount of the cash contribution is finally calculated by multiplying the Required Green Roof Area Not Installed by the “Unit Price Contribution” according to the below chart:

Calendar Year

Unit Price Contribution
(Per Square Foot of Required Green Roof Area Not Installed)

2022 (and before)






Note:  Figures subject to recalculation every three (3) years. Cash contributions shall be calculated and provided at the time of issuance of a building permit for a project.

For more information or to make a payment under the special permit