Town of Sherborn, MA Design Standards

Design features and construction practices shall avoid groundwater impacts and shall maximize environmental sustainability by adhering to these directives:

Avoid any encroachment within any wetland, wetland buffer area, or floodplain;

Avoid any alteration of waterways or existing natural drainage;

Avoid fragmentation of wildlife habitat or wildlife corridors;

Minimize disruption of existing bedrock or ledge;

(e)

Minimize dimensions of paved areas;

(f)

Minimize the volume of cut and fill;

(g)

Minimize the area over which vegetation will be disturbed;

(h)

Landscape in a manner not requiring irrigation or the use of pesticides.

The proposed subdivision design, in particular the placement of housing and infrastructure in relation to wetland resources, will be evaluated based on the groundwater impact assessment analyses (see § 380-2.10F). This assessment will include a hydrogeological evaluation undertaken in accordance with BOH regulations for an environmental health impact report or an equivalent, preapproved evaluation approach, as well as technical evidence that the proposed designs will avoid adverse cumulative impacts to groundwater and wetland resources.

Pollution of groundwater during and after construction shall be prevented by control devices, including provisions for contaminant removal employing detention basins, subsurface drains or perforated risers, oil and grit separator catch basins, and other appropriate devices.

Measures to restrict nutrient loading in down-gradient groundwater to a maximum of five milligrams per liter (mgl) nitrate-nitrogen.

Measures shall be taken to restrict projected nutrient and contaminant levels (resulting from septic effluent subdivision-wide) in groundwater reaching sensitive receptors to a maximum of five milligrams per liter (mgl) nitrate-nitrogen (prior to the application of any nitrogen-reducing technologies).

For septic systems with a design capacity of 2,000 gallons per day or greater and for subdivisions with aggregate septic design capacity of 5,000 gallons per day or greater, the Planning Board will support determinations of the Board of Health and/or Conservation Commission to require monitoring wells at selected sensitive receptors (e.g., drinking water wells, potential sources of drinking water, wetland resources, property lines) with periodic testing (at least once every three years) to detect nutrient and contaminant loadings from subdivision septic systems.

Measures shall be taken to control erosion and sedimentation, as specified in an erosion and sedimentation control plan to be submitted with the definitive plan, and the use of construction site best management practices (BMPs). The erosion and sedimentation control plan should emphasize phased construction, temporary and permanent ground cover, and sedimentation control devices.

§ 380-2.13 Grading.

Minimum disturbance. All excavation, filling, sloping and grading outside the right-of-way of each subdivision street shall be designed and completed to minimize disturbance to the existing natural conditions encountered.

Stabilization. All new slopes and areas disturbed by grading operations shall be topsoiled, seeded or sodded and planted to stabilize the finished ground forms and surfaces. Seeding and planting shall take place as soon as possible following the completion of grading. A temporary cover crop of winter rye shall be planted within 30 days on all soils disturbed during months not suitable for seeding, sodding or planting or surfaces shall be stabilized by mulch or an erosion control fabric.

Landscape plan. A landscape plan, prepared by a registered landscape architect, shall be required where site clearing for a street may affect watersheds, affects more than one-half acre, is visible from an existing public way, or where significant changes in grades or topography are involved.

Slope easements. The Board may require that defined slope easements be shown on the definitive plan and that such easements be reserved by the applicant for future conveyance to the Town for maintenance purposes.

§ 380-2.14 Streets and driveways.

Location.

All streets and driveways in the subdivision shall be designed so that, in the opinion of the Planning Board, they will provide safe vehicular and pedestrian travel and an attractive street layout to obtain the maximum safety and amenity for future residents of the subdivision and the Town. Ways should run along rather than across a slope to the extent possible.

The proposed streets shall conform in location, so far as practicable, to any existing plans of the Planning Board and, where required by the Planning Board, to the existing street system and include only a minimum number of intersections with streets classified as major arterials.

If deemed appropriate for the site and consistent with the goals of the Sherborn Master Plan, the Planning Board may require that provision be made for the future projection of pedestrian walkways or trails, bicycle paths or streets to, or for access to, adjoining property, whether or not subdivided.

No subdivision shall be approved unless the streets therein connect to, and are accessible from, a public way in which the applicant has the necessary access rights.

Reserve strips prohibiting access to streets or adjoining property shall not be permitted, except where the Board finds them to be in the public interest.

Driveway cuts into streets shall be prohibited until the Planning Board finds that the location, width, length, line of sight, proximity to other driveways and streets, grade and elevation will provide adequate provisions for the public safety.

Existing streets that will be used to access the proposed subdivision shall be of a pavement width and condition adequate for the projected traffic. The Board may require the applicant to fund or conduct off-site improvements if the existing streets are not adequate.

Alignment.

Subdivision streets shall be continuous and of uniform width.

Subdivision streets intersecting existing streets or other existing or proposed subdivision streets shall do so:

As nearly as possible at right angles, and no less than 60° or more than 120°;

Either directly opposite or with at least 150 feet center-line offset from existing or proposed street intersections.

The minimum center-line radii of curved streets shall be 150 feet with greater radii on arterial streets.

A tangent at least 150 feet in length shall separate all reverse curves except where the center line radius of one curve is 500 feet or more.

Street lines at intersections shall be rounded or cut back to provide for a curb radius of not less than 30 feet.

Width (See Appendix, Schedule A, Typical Street Cross-Sections,[1] for each of the above categories.)

The minimum width of street rights of way shall be 60 feet. The street pavement shall be 22 feet or as approved by the Planning Board based on specific conditions of the site or proposed subdivision. Where a subdivision street intersects an existing street, the minimum subdivision street right of way (ROW) line shall follow a thirty-foot radius drawn between the subdivision street ROW line and the existing street ROW line. The curved, widened subdivision street ROW lines at such intersections shall be entirely within the subdivision property line.

[1]

Editor's Note: Schedule A is included as an attachment to this chapter.

Grade.

The minimum center-line grade for any street shall not be less than .5%.

The maximum center line grade for streets shall not be more than 8%.

Where changes in grade exceed 1%, vertical curves as required by the Board shall be provided. The length of vertical curve shall be designed to provide a minimum sight distance of 200 feet to an object 4.5 feet above the roadway surface from an eye height of three feet six inches. The sight distance shall be shown on the proposed street profiles.

Where a grade is 5% or greater within 150 feet of the intersection of street right-of-way lines, a relatively level area at least 75 feet long, with a maximum grade of 3%, shall be provided.

Street trees and planted shrubs.

Wherever feasible, shade trees 12 inches in diameter or larger shall not be removed from within street rights-of-way, unless approved by the Planning Board.

Where the distance between twelve-inch-plus-diameter trees is such that the roadway is not shaded, the Planning Board may select existing healthy trees of lesser diameter to be retained and protected during construction.

The Planning Board may require that street trees not less than six feet in height and with caliper of at least two and one-half inches shall be planted at varying distances along both sides of every street and spaced on average not more than 40 feet on center.

Roadside rights-of-way shall be graded and planted to maximize retention of road runoff and groundwater recharge.

Curbs shall not be continuous but shall be designed to allow road runoff to drain to roadside plantings and/or swales.

Street trees, shrubs and plant materials shall be selected from an approved list supplied by the Tree Warden.

A continuous healthy growth for all planted trees, shrubs, plants and seeded areas shall be maintained for one year from the date of completion of all work on the street or until the street is accepted by the Town of Sherborn, whichever is later.

Curb cuts.

Driveways shall be at least 10 feet wide, but no more than 20 feet wide, and have a curb return at the street of three feet in radius.

Where no curbs exist, the driveway flare should have a three-foot radius.

Unless otherwise allowed by the Planning Board, driveway cuts shall be permitted only at the street where the frontage requirement has been met.

Shared, or common, driveways serving two dwellings shall be allowed by right. Common driveways serving three or more dwelling units are permitted with a special permit from the Planning Board.

Driveway cuts shall not be permitted within 100 feet of the sideline of intersecting streets or railroad crossings.

No more than one driveway cut shall be permitted per lot unless allowed by the Planning Board.

Dead-end streets.

Any proposed street which connects only with a dead-end street shall be deemed to be an extension of the dead-end street.

Dead-end streets and their extensions, if allowed, shall not exceed 600 feet in length, measured from the center line of the nearest through street with which it intersects to the center line of the circle or ellipse.

Dead-end streets shall be provided with a turnaround [see Subsection G(6) below] at the closed end.

If the Planning Board determines that future extension of a dead-end street to an adjacent property is in the best long-term interest of the Town, the definitive plan shall show the right-of-way lines of each dead-end street projected through the turnaround to the subdivision property line. In this case, street easements in the segments of a turnaround lying outside of such projected lines (including sufficient land beyond the pavement for snow storage or other street maintenance needs) shall be temporary and shall terminate pursuant to MGL c. 41, § 81M, when the street is extended beyond the turnaround. The land between such right-of-way lines between the edge of the paved turnaround and the subdivision property line shall be designated as a separate parcel and shall be conveyed to the Town of Sherborn along with the constructed portion of the street right-of-way at the time of street acceptance. The purpose of the parcel shall be designated on the plan as future street right-of-way.

An applicant who extends a dead-end street at a later date shall remove the pavement, relocate any sidewalks, extend any driveway entrance and properly grade, loam and seed the areas included within the temporary easements. All such work shall be deemed to be a part of the required improvements of the connecting subdivision.

If, by reason of topography or other physical characteristics of land within or adjoining the subdivision, or by reason of the present use or development of the adjoining land, the Board is of the opinion that a particular dead-end street will not be extended beyond the turnaround, the Board may require that the outside right-of-way line of the turnaround be laid out with a radius of 60 feet. A paved circle with a radius of 45 feet and a circular landscaped island having a radius of 22 feet less than the designed radius of the turnaround shall be provided at the center of the turnaround. The circumference of such island shall coincide with the inside edge of the circular paved street.

The center-line profile grade of a turnaround from its beginning to its terminus shall not exceed 3% unless otherwise approved by the Board.

§ 380-2.15 Drainage design.

General. The definitive plan shall provide adequate drainage facilities within the subdivision for collecting, conveying and disposing of stormwater in a manner which will ensure proper protection of the streets and the areas adjacent thereto. Drainage design shall provide for groundwater recharge to the maximum extent practicable. All drainage facilities shall be designed in compliance with these rules and regulations. Low-impact development site design, including best management practices, and other more natural drainage design techniques such as are outlined in the Metropolitan Area Planning Council's "Low Impact Development Toolkit" are required. Those techniques may include but are not limited to bioretention areas, cisterns and rain barrels, grass filter strips, green roofs, permeable pavement, rain gardens, vegetated swales, and infiltration trenches and dry wells. In cases where soil conditions or other factors do not allow such techniques to be used, those techniques shall be used to the maximum extent practicable in combination with conventional structural drainage systems.

All drainage systems must comply with the Massachusetts Department of Environmental Protection Ten Stormwater Management Standards and with the EPA 2016 Massachusetts MS4 general permit (as it may be amended from time to time by EPA). Waivers from these regulations will be favorably considered if needed to accommodate designs that, in the opinion of the Planning Board, provide environmental benefits while adequately managing storm water and preventing negative impacts on surrounding properties.

Lot drainage. Lots shall be laid out and graded in a manner that ensures development of one shall not result in an increase in drainage runoff onto property outside the subdivision and with the intent that such drainage shall maximize local groundwater recharge. Within the subdivision, if it is necessary to carry drainage from one lot to or across another lot, the definitive plan shall show a drainage easement of adequate width. A copy of the instrument creating such easement shall be made a part of the definitive plan submission as provided in § 380-2.10B. To the extent possible, the subdivision plan shall retain natural patterns of drainage and stormwater recharge.

Drainage calculations. To substantiate the proposed subdivision drainage mitigation system, drainage calculations prepared and certified by a registered professional engineer shall be filed as a part of the definitive plan (§ 380-2.10E) and shall include the following:

Drainage runoff plans, prepared at an adequate scale to show the full extent of both existing and proposed contributing watershed areas, including existing and proposed contours at two-foot intervals, and existing and proposed drainage systems (shown schematically) with tributary areas to each inlet.

Backup calculations for the approved methodology as stated in Subsection D(1), which include a narrative and overall drainage design philosophy with data supporting the following:

Existing site conditions and drainage computations;

Proposed site conditions and drainage computations;

Impacts to adjacent properties. If surface water drains onto adjacent existing street right-of-way or onto adjacent properties not owned by the applicant, the applicant shall clearly indicate what course the discharge will take, and shall present to the Board and to the owner of adjacent property evidence that such discharge is satisfactory and permitted by public or private ownership of adjacent street or property.

Backup calculations shall reference all sources of information, supporting data and assumptions used.

Drainage criteria.

Drainage design computations shall be based on currently accepted methods (including but not necessarily limited to the Rational, NRCS TR-55, NRCS TR-20 methods), as appropriate for the size, characteristics, and complexity of the existing/proposed drainage system.

Rainfall rates shall be the National Oceanic and Atmospheric Administration (NOAA) Atlas 14, as amended, the Northeast Regional Climate Center (NRCC) "Atlas of Precipitation Extremes for the Northeastern United States and Southeastern Canada," or another currently accepted industry standard that anticipates increased rainfall rates due to the impacts of climate change, as approved by the Planning Board. The specified "design storm" shall be defined as a twenty-four-hour storm using one of the preceding rainfall distribution calculations.

A twenty-five-year storm frequency shall be used for street drainage components and cross culverts.

To ensure that no properties shall be at risk in the event of a 100 year storm condition, the impact of a greater than 100-year storm shall be assessed at the applicant's expense, including:

Potential for damage to property inside and outside of the subdivision;

Potential for reduction in safety inside and outside of the subdivision;

Impact downstream; and

Changes to off-site runoff.

The proposed drainage system shall be shown to allow on-site recharge equal to or greater than the amount of recharge that existed prior to the development.

In no case shall a drainage line of less than 12 inches in diameter be used.

All drains shall be sloped to provide for a minimum velocity of 2 1/2 feet per second at design flow for self-cleaning purposes. The maximum culvert design velocity shall be 10 feet per second (flowing full).

(8)

Where it appears that any street may be extended to connect with an existing or proposed street on land adjoining the subdivision, the Board may require that provision be made for extension of the drainage system to a point at or near the subdivision property line.

Retention/detention basins.

Waiver required. The incorporation of retention/detention systems into the proposed drainage improvement program of the definitive plan shall require a waiver by the Board, which may be granted only after the applicant has exhausted all other studies of means of accommodating stormwater runoff by natural drainage strategies. The Board may require that an outside consultant be hired to confirm these studies at the applicant's expense (see Administration article of these Rules).

Design criteria. Design calculations and criteria shall meet the applicable requirements of Subsections D and E of this section and the following:

Where retention/detention facilities are deemed necessary by the Board, they shall be designed to contain the diverted site runoff generated from two-year, ten-year, and 100-year design storms. Runoff greater than that occurring from the 100-year, twenty-four-hour storm shall be passed over an emergency spillway.

Detention shall be provided such that after development, the peak rate of flow from the site shall not exceed that by similar storms prior to development.

Retention/detention basins shall maintain existing drainage patterns and flows and shall be located and discharged within the natural drainage area that they serve to control.

The design storage volume depth of basins shall not exceed four feet.

(e)

A crushed-stone berm at least twelve inches in height shall be placed across the basin perpendicular to the direction of flow. The berm shall be situated no more than 1/3 of the basin length from the inlet. The purpose of the berm is to promote sediment retention and prevent the discharge of sediments from the outlet.

(f)

The outlet shall be a minimum of twelve inches above the bottom of the detention basin and shall be located at an extreme distance from the basin inlet. Outlets shall be designed to minimize the potential for clogging by leaves or debris.

Basin landscaping.

Basins shall be provided generally within the landform and contours of undisturbed, naturally occurring topography and terrain. Basins shall not be regular geometric shapes but shall use an irregular or undulating shoreline.

Basin side slopes shall be as flat as possible and shall not exceed four feet horizontal to one foot vertical.

Side slopes shall be landscaped to provide a natural appearance, using native trees and shrubs. A twelve-foot-wide path shall be maintained to provide access to basins inlets and outlets.

Sides and bottoms of basins shall be stabilized with a perennial grass cover. One hundred percent cover by grasses shall be required within two years after planting. One hundred percent survival of trees and shrubs shall be demonstrated two years after planting.

Protection.

All drains and related systems shall be protected from erosion and siltation at all times. Prior to construction, all disturbed soils shall be temporarily stabilized, and after construction, all disturbed soils shall be immediately and permanently stabilized.

Any damage to these drainage systems, prior to acceptance by the Town, shall be repaired in a manner satisfactory to the Planning Board and the DPW Director, the full cost of which shall be borne by the applicant.

§ 380-2.16 Easements.

Layout of utility and drainage easements.

Easements shall be continuous from lot to lot and street to street, and their layout shall create as few irregularities as possible.

Center lines of easements shall follow lot lines so far as practicable and shall not be less than 20 feet in width.

Watercourse easements. Where a subdivision is traversed by a watercourse or stream, an emergency maintenance access easement shall be provided to encompass 25 feet on either side of the center line of the watercourse or stream or the mean annual high water line as defined by 310 CMR 10.00, whichever is greater.

Slope easements. Slope easements shall be provided where necessary to ensure lateral support and protection of streets and other construction features.

Pedestrianways and bridle paths.

Easements, or fee strips for pedestrian ways or footpaths, at least 20 feet in width will normally be required to provide convenient circulation and access to parks, schools, playgrounds and conservation areas.

Bridle path easements at least 20 feet in width may be required to connect with conservation areas, open spaces and existing trails.

Existing bridle paths and trails traversing the subdivision shall be preserved with as little relocation as practicable.

Green belt easements and conservation restrictions in conventional subdivision.

In cases where the Planning Board determines that a conventional subdivision design will fulfill the conservation goals of Zoning Bylaw § 240-4.5 better than an open space subdivision design, and a special permit application and preliminary plan for a conventional subdivision is submitted, the applicant is encouraged to set aside green belt sections within the conventional subdivision, consisting of wooded or other scenic areas to be preserved by mutual covenants and traversed by reciprocal trail easements for the benefit of each lot in the subdivision and to provide connections to trails on adjoining lands.

The applicant may grant to the Town or to any private, nonprofit corporation devoted to conservation purposes a conservation restriction or wildlife corridor over any portion of the subdivision in accordance with the procedure prescribed by MGL c. 184, §§ 31 and 32.

Before approval of a definitive conventional subdivision plan, the Planning Board may also require the plan to show a park or parks suitably located for playground or recreation purposes or for providing light and air for the residents of the subdivision. The Board may, by appropriate endorsement on the plan, require that such park or parks may not be converted to building lots without approval of the Board.

No stripping of topsoil shall be permitted in a reserved area. If required by the Board, the land shall be graded as necessary for surface drainage and left in a suitable condition for the intended use.

Open space subdivisions; protected open space. The legally protected open space within an open space subdivision shall consist of an area or connected areas that provide wildlife habitat and forest ecosystem continuity, recreational trail connections within the subdivision and on adjacent properties, agricultural lands, or a combination of the above as defined in Chapter 240, the Sherborn Zoning Bylaw. The minimum size, allowed uses, prohibited uses, monumentation, maintenance requirements and other features of the open space shall be as required by the Open Space Subdivision Bylaw, § 240-4.5.

§ 380-2.17 Sidewalks and trails.

General. Sidewalk and trail requirements will be flexible and shall be designed to fit subdivision layout and fulfill the anticipated needs of residents of all ages and abilities.

A sidewalk may be constructed on one side of some or all subdivision streets, or on frontage of existing public ways, if deemed necessary for the safety and conveninece of pedestrians and cyclists, and to facilitate nonvehicular travel within the subdivision.

Paved sidewalks and crosswalks will conform to ADA standards.

Unpaved paths and connections between existing trails or bridle paths may be laid out along subdivision streets within the street right of way instead of, or in addition to, the sidewalk.

Sidewalks and trails will be laid out to optimize connections to surrounding neighborhoods, Town center, and other amenities such as recreational trails and open space.

Sidewalk design.

Sidewalks shall be set back not less than six feet from the edge of the paved street but may be reduced to as little as three feet if a meandering sidewalk is proposed with a minimum of six feet in the area of street trees.

Open areas between the sidewalk and street shall be landscaped with swales and/or plantings for retention and absorption of street runoff and recharge of groundwater resources.

Sidewalks need not be parallel to the street and shall be laid out along a curvilinear course within the right-of-way with a minimum disturbance of the natural terrain. Sidewalks shall be laid out and constructed so as to preserve trees having a caliper of three inches or more, rock outcroppings, stone walls and other attractive features of the terrain. Prior to the start of clearing and grubbing, the applicant shall walk the proposed street locations with the Planning Board agent or a member or members of the Board and mark all trees to be preserved within the street rights-of-way.

Sidewalks shall be four feet in width, unless the Board shall specify a greater width.

Sidewalks shall be paved with bituminous concrete placed on a compacted foundation of gravel as detailed in Schedule A, Typical Section, Subdivision Street.

Sidewalks shall fully comply with the Massachusetts Architectural Access Board requirements, including handicapped access ramps at appropriate locations, as stated in 521 CMR 21.00 and 22.00. Also, temporary accessible routes shall be provided as applicable in accordance with 521 CMR 3.10.

§ 380-2.18 Utilities.

General. Choice of energy sources for residential heating, cooling and electric power shall be consistent with the green community goals of the Town of Sherborn and by the Town's commitment to minimizing greenhouse gas emissions and mitigating climate change. Installation of solar panels, renewable energy technologies and other energy-efficient utilities will be strongly encouraged. All utilities, including house connections, shall be placed underground at the time of initial construction. Complete location plans of each utility system shall be filed with and approved by the Board in compliance with § 380-2.11 prior to installation. All utility pipes and conduits and appurtenant facilities shall be located along the side of the streets, preferably between the street and the sidewalk, as described in Subsection B. If such facilities must be located under the sidewalk, they shall be installed before placement of the gravel base of the sidewalk. All manholes shall be placed along the side of the road outside the pavement area. See Appendix, Schedule B, Typical Sidewalk Cross-Section.[1]

[1]

Editor's Note: Appendix B is included as an attachment to this chapter.

Installation.

Electric, telephone and other telecommunication services.

Exposed, above-grade pull or distribution boxes are prohibited.

Electric power supply cables and telephone cables shall be placed in a trench centered two feet from the edge of the street pavement on the side of the street where the sidewalk is to be placed.

All electric and telephone service connections to be located underground shall be placed in conduit extending from the electric service transformers and telephone distribution box to the right-of-way lines on both sides of the street.

All service transformers shall be located in vaults below the finished grade unless otherwise specified by the Board and located as far from dwellings as practical given the nature of the site.

Gas service.

Distribution pipes for gas service, when provided in a subdivision, shall be placed in a trench centered two feet from the edge of the street pavement on the side of the street opposite from the sidewalk. Service stubs for all house lots shall be placed at the time of initial installation.

All pipes to be located under the street or sidewalk shall be installed prior to the placing of the gravel base and bituminous concrete pavement.

Protection.

The subdivider shall protect all utilities and appurtenances installed from any and all damage until the entire subdivision is completed and approved as a whole by the Planning Board.