1. The Green Factor of a property is measured as a ratio of the weighted value of all landscape elements in
relation to the total land area (in square feet) of a lot.
2. Calculation of the Green Factor uses a value based system to prioritize landscape elements and site design
that contributes to the reduction of storm water runoff, the improvement of urban air quality, mitigation of
the urban heat island effect, and improved well-being of residents and visitors.
3. The result of the Green Factor calculation relates to an increase in the environmental performance and quality of urban landscape features.
For all applications for new construction or substantial improvement requiring a Project Review Special Permit
under Section 19.23 – Special Permit Threshold, applicants shall submit certification of the project’s Green
Factor score, certified by a Certified Landscape Expert as defined in Section 22.86, to the Planning Board and
Cambridge Conservation Commission.
22.83 Calculation of Score
The Green Factor score is calculated as follows:
1. Determine total lot area.
2. Calculate the area of each proposed landscape element for each category identified in the first column of
Table 1. Certain types of plantings use the number of individual plants multiplied by an equivalent square
footage when indicated.
3. Multiply the area in square feet, or the equivalent square footage, of each landscape element by the
assigned multiplier identified in the second column of Table 1 to determine its weighted square footage.
4. Add the weighted square footage of all landscape elements together.
5. Divide the resulting sum by the area of the lot to determine the Green Factor score.
22.84 Plant Eligibility
All landscape elements must meet eligibility and quality standards established by the City to ensure the long-
term health, viability, and coverage of plantings.
1. If multiple landscape elements identified in the first column of Table 1 occupy the same area, for example
groundcover under a tree, the full square footage or equivalent square footage of each element is counted.
2. For trees, large shrubs, and large perennials, use the equivalent square footage indicated inTable 1.
3. For vegetated walls, the area calculated is the height times the width of the area to be covered by vegetation.
4. For all elements other than trees, large shrubs, large perennials, and vegetated walls, square footage is
calculated as the area of a horizontal plane that is over the landscape element.
5. Landscape elements may qualify for bonus credits in addition to the standard Green Factor categories
used to determine the Green Factor score.
22.86 Certified Landscape Expert
The project applicant shall secure a Certified Landscape Expert (Landscape Expert) for plan submittal and
verification of installation to confirm Green Factor compliance. The Landscape Expert who signs the Green
Factor plans may be different from the individual who signs the Landscape Checklist. The applicant should
select a Landscape Expert with expertise and specialization appropriate to the type(s) of landscape elements
used in the project.
1. A Certified Landscape Expert is defined as any of the following:
a. Massachusetts Licensed Landscape Architect
b. International Society of Arboriculture (ISA) Certified Arborist
c. Massachusetts Professional Horticulturist
d. Landscape Industry Certified Technician
22.87 Filing Requirements
The Landscape Expert shall do the following:
1. Prepare, sign, and submit plans to indicate that plans conform to all Green Factor criteria. Plan submittals must have the following elements to be considered for review and approval:
a. Green Factor score sheet
b. Green Factor score elements called out by category and square footage
c. Lot dimension and size
d. Location and area of all landscape elements with associated dimensions
e. Other drawings, including details, that enable interpretation of Green Factor plan documents
f. Schematic irrigation and drainage plan for rooftop and container landscaping or areas requiring harvested rainwater irrigation
g. Signed landscape maintenance plan within the submitted drawings or as separate document with notation in the plans that the landscape maintenance plan is a separate document within the submittal.
h. Landscape Expert’s signature, printed name, name of certifying organization, and certification number.
i. Location, installed size, and species of all new and existing plants used to meet Green Factor requirements
j. Common and botanical names of all plant materials
k. Location, trunk diameter at breast height, estimated canopy radius, and species of each preserved tree
l. Tree preservation plans for the demolition and construction phases
m. Location and dimensions of all measures used to protect landscape areas from vehicular traffic
n. Location and size of all tree removals
o. Soil and amendment specifications
2. Confirm that the landscape elements are installed according to the approved plan and sign off on the Landscape Checklist
3. Prepare and sign a landscape maintenance plan for the property owner to cover the initial three (3) years
following issuance of a Certificate of Occupancy.
TABLE 1 Green Factor Calculation
|Green space with new & uncompacted topsoil of less than 24”||0.3|
|Green space with new & uncompacted topsoil of 24” or more||0.6|
|Pervious Paving (more than 6” but less than 24” of soil or gravel)||0.2|
|Pervious Paving (more than 24” of soil or gravel)||0.5|
|Bio-swale / Bio-retention / Rain garden||0.8|
|Grass, mulch, and other organic and inorganic plant or earthen material ground covers; plants less than 2’ tall at maturity||0.1|
|Large shrubs or large perennials at least 2’ tall at maturity||0.3||Multiply by 9 square feet per plant|
|New Tree, Small (less than 40 foot canopy spread at maturity)||0.5||Multiply by 50 square feet per tree|
|New Tree, Large (greater than 40 foot canopy spread at maturity)||0.6||Multiply by 250 square feet per tree|
|Preserved Tree (must be greater than 6” Diameter at Breast Height (DBH) to qualify)||0.8||Multiply as follows based on current Diameter at Breast Height (DBH):
6-12” DBH: 250 square feet per tree
12-18” DBH: 600 square feet per tree
18-24” DBH: 1300 square feet per tree
>24” DBH: 2000 square feet per tree
|Vegetated Wall||0.7||Multiply by width x height|
|Green Roof (depth greater than 2” but less than 8”)||0.4|
|Green Roof (depth greater than 8”)||0.5|
|Landscape visible and open to public||0.1|
|Harvested storm water irrigation (>50% of annual irrigation met with harvested storm water)||0.1|