760 C.M.R. 72.06 – Minimum Gross Density

(1) M.G.L. c. 40A, § 3A expressly requires that a Multi-family zoning district-not just the individual lots of land within the district-must have a minimum Gross density of 15 units per acre, subject to any further limitations imposed by M.G.L. c. 131 and 310 CMR 15.000: The State Environmental Code, Title 5: Standard Requirements for the Siting, Construction, Inspection, Upgrade and Expansion of On-site Sewage Treatment and Disposal Systems and for the Transport and Disposal of Septage established pursuant to M.G.L. c. 21A. M.G.L. c. 40A, § 1A defines "Gross density" as "a units-per-acre density measurement that includes land occupied by public rights-of-way and any recreational, civic, commercial and other nonresidential uses."
(2) District-wide Gross Density.
1. (a) To meet the district-wide Gross density requirement, the dimensional restrictions and parking requirements for the Multi-family zoning district must allow for a Gross density of 15 units per acre of land within the district. By way of example, to meet that requirement for a 40-acre Multi-family zoning district, the zoning must allow for at least 15 multi-family units per acre, or a total of at least 600 Multi-family housing units.
2. (b) For purposes of determining compliance with M.G.L. c. 40A, § 3A's Gross density requirement, the EOHLC Compliance model will not count in the denominator any excluded land located within the Multi-family zoning district, except public rights-of-way, private rights-of-way, and publicly-owned land used for recreational, civic, commercial, and other nonresidential uses. This method of calculating minimum Gross density respects M.G.L. c. 40A, § 1A's definition of Gross density — "a units-per-acre density measurement that includes land occupied by public rights-of-way and any recreational, civic, commercial and other nonresidential uses" — while making it unnecessary to draw patchwork Multi-family zoning districts that carve out wetlands and other types of excluded land that are not developed or developable.
(3) Achieving District-wide Gross Density by Sub-districts. Zoning ordinances and by-laws typically limit the unit density on individual lots. To comply with M.G.L. c. 40A, § 3A's Gross density requirement, an MBTA community may establish reasonable sub-districts within a Multi-family zoning district, with different density limits for each sub-district, provided that the Gross density for the district as a whole meets the statutory requirement of not less than 15 Multi-family units per acre. EOHLC will review sub-districts to ensure that the density allowed As of right in each sub-district is reasonable and not intended to frustrate the purpose of M.G.L. c. 40A, § 3A by allowing projects of a such high density that they are not likely to be constructed.
(4) Wetland and Septic Considerations Relating to Density. M.G.L. c. 40A, § 3A provides that a district of reasonable size shall have a minimum Gross density of 15 units per acre, "subject to any further limitations imposed by M.G.L. c. 131, § 40 and 310 CMR 15.000: The State Environmental Code, Title 5: Standard Requirements for the Siting, Construction, Inspection, Upgrade and Expansion of On-site Sewage Treatment and Disposal Systems and for the Transport and Disposal of Septage pursuant to M.G.L. c. 21A, § 13." This directive means that even though the zoning district must permit 15 units per acre As of right, Multi-family housing produced within the district is subject to, and must comply with, 310 CMR 10.00: Wetlands Protection and 310 CMR 15.000 even if such compliance means a proposed project will be less dense than 15 units per acre.