Southborough, MA Building Setbacks & Zoning: Lot Coverage Limits (2026)

Section 174-13.4, Water resource protection, lists the uses that shall be allowed only if granted a special permit from the special permit granting authority. One entry is "Rendering impervious more than 75% of lot area." Subsection B(2) adds that a change in activity resulting in crossing any of the thresholds of B(1)(a) through (d) constitutes a change of use requiring a special permit. Under § 174-13.4(C)(1) the special permit granting authority is the Board of Appeals.

The Board of Appeals sends one copy of the application each to the Planning Board, the Conservation Commission, the Board of Health and the Building Inspector for written recommendations, and failure to respond within 35 days of transmittal indicates approval by those agencies. A permit is granted only if the Board determines there is adequate assurance of no violation of the Massachusetts Surface Water Quality Standards (314 CMR 4.00) and that groundwater quality will not fall below federal or state standards for drinking water.

The same section ties drainage to impervious surfaces. Section 174-13.4(A)(3) says provision shall be made for on-site recharge of all stormwater runoff from impervious surfaces unless, following consultation with the Conservation Commission, the Building Inspector determines that recharge is infeasible because of site conditions or undesirable because of uncontrollable risks to water quality. Subsection A applies to all new nonresidential construction.

The Residence A and Residence B development standards in § 174-8.2(D) and § 174-8.3(D) list lot area, frontage, setbacks, height and a maximum floor area ratio, not a lot coverage percentage. Separately, the lower impact development bylaw in § 174-13.3 applies to activity that will result in soil disturbance of one acre or more, and presumes a redevelopment project meets its requirements if total impervious cover is reduced by 40% from existing conditions.