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HomeMy WebLinkAbout2026/04/10 - Alternative Analysis - 200 Bridle Path ALTERNATIVES ANALYSIS Proposed ADU Stairway and Second-Story Porch Structure 200 Bridle Path, North Andover, MA Chapter 190 Wetland Protection Bylaw/Watershed Protection District 1. Project Purpose The project proposes extending the existing garage by approximately 13 feet toward the driveway to create a footprint large enough to support a second story ADU for my mother to age in place. The proposed build meets the ADU bylaw requirement of remaining under the 900 sq ft maximum. The garage extension would also provide space for two tandem parking spaces for the primary residence on the left side of the garage, one required ADU parking space in the right-front bay, and uses the right-rear bay for the interior stairs to the shared mudroom, entrance to the primary residence, and elevator to the garage, mudroom and ADU. An exterior stairway behind the garage and connecting to the mudroom provides the ADU's independent entrance. A second- story porch structure is constructed on the left side of the ADU stairway (supported by helical piles), and a single continuous roof plane minimizes structural footprint and improves runoff control. 2. Regulatory Context The alternatives analysis requires demonstration that no practicable alternative exists with less environmental impact, that disturbance to natural soils is minimized, and that existing disturbed areas are used whenever possible. Impervious area and excavation must be minimized. 3. Existing Conditions and Disturbance Minimization With the ADU stairway structure and second story porch located behind the garage, the actual ground disturbance is extremely limited: only three helical piles fall within the 25- foot zone, each comprising approximately 1 square foot or less. One pile replaces the existing AC unit structure, and another replaces an existing privacy fence. No excavation, trenching, or foundation work occurs in the 25-foot zone. The area behind the garage is already disturbed (gravel/mowed). The continuous roof plane allows controlled runoff management. 4. Egress Requirements and ADU Footprint Constraints The ADU must have two independent means of egress: (1) the exterior stairs to the mudroom and garage side door, and (2) the elevator to the garage side door. A rear exit from the stair structure is not feasible due to required landings, additional stairs, and increased disturbance. The ADU footprint is capped at 900 sq ft; extending the garage further down the driveway to fit interior stairs would increase the ADU footprint beyond the bylaw limit. 5. Alternatives Considered A. No-Build Alternative: Not practicable. The ADU requires two independent means of egress, a dedicated parking space, and accessible circulation for an aging-in-place occupant. Without the back stairs and garage expansion, the ADU cannot meet building code, zoning, or accessibility requirements. The no-build option fails to achieve the project purpose and is therefore not a viable alternative. B. Interior Garage Stair Alternative: Not practicable due to loss of required parking, ADU footprint limits, and circulation constraints. The interior of the expanded garage is fully allocated to meet zoning and ADU bylaw requirements. The layout includes: • Two tandem parking spaces on the left side serving the primary-residence parking spaces (required by zoning and cannot be eliminated). • One dedicated ADU parking space in the right-front bay (required by the ADU bylaw) • Designating part of the driveway as the ADU parking space would block circulation and violate the intended use of the driveway under zoning. • A shared mudroom and elevator area in the right-rear bay, which provides accessible circulation for the ADU occupant and entrance into the primary residence. There is no remaining area within the garage footprint that can accommodate a full-width, code-compliant interior stair without displacing one of these required elements. Any interior stair configuration would necessarily: • Eliminating the ADU parking space (violates ADU bylaw) • Designating part of the driveway as the ADU parking space would block circulation and violate the intended use of the driveway under zoning. • Eliminating the two primary residence parking spaces (violates zoning) • Eliminating the mudroom/elevator bay (eliminates accessibility and a second means of egress) • Extending the garage further down the driveway to make room for interior stairs would increase the ADU footprint beyond the 900 sq ft limit, violating the ADU bylaw, and increase the overall structure size and require more excavation than the helical piles. For these reasons, interior stairs are not a practicable alternative. C. Front-of-Garage Stair A Item ative: Not practicable due to safety, zoning, and environmental impacts. • A front stair would sit directly in front of the garage doors, blocking access to required parking and preventing the garage from functioning as intended. • This location requires a full foundation or frost wall, resulting in: • Substantial excavation • Greater disturbance within the watershed district • The ADU bylaw strongly prefers that exterior stairs not be visible from the street; a front stair violates this design intent. • The front yard is less disturbed than the rear, so placing stairs here increases environmental impact. This alternative is not practicable. D. Left-Side Stair Alternative: Not practicable due to topography, proximity to the 25-foot zone, and structural inefficiency. • The left side of the property slopes toward the resource area, requiring: • Grading • Cut-and-fill • Potential retaining walls • Full foundation • This side is close to the 25-foot no-disturb zone, increasing environmental impact • A left-side stair cannot connect efficiently to the mudroom without: • A long elevated walkway or stairs down (removing a required parking space and an unsafe passage across the entire garage to reach the egress door or needing to create an egress from the left side stair which would require additional ground disturbance in the 25-50 ft zone with a landing/sidewalk to the driveway. • Additional structural supports These additions increase disturbance and structural footprint compared to the compact rear stair. For those reasons, this alternative is not practicable. E. Stair in Place of the Right Screened-in-Porch (Primary Residence Porch): Not practicable due to zoning, circulation, and loss of primary residence functionality. • The right porch is part of the primary residence, not the ADU. Replacing it with a stair: • Eliminates essential living space • Blocks access to the backyard • Disrupts the home's circulation • Even if replaced with a stair, it cannot connect to the ADU without: • Cutting through the primary residence, or • Constructing a long elevated walkway • Either option violates the ADU bylaw requirement for an independent entrance and would compromise the primary residence. This alternative is not practicable. 6. Preferred Alternative (Proposed Design) The proposed stair location behind the garage is the only practicable alternative because it uses an already disturbed area, requires only three helical piles within the border of the 25 foot zone, avoids excavation, aligns with the current back-right entrance to the primary residence, maintains required parking, preserves primary residence space, complies with the ADU bylaw, fits within the 900 sq ft ADU footprint, and minimizes environmental impact. The second-story porch structure behind the garage is not merely an amenity; it is a critical structural component of the overall design. The porch provides one of the primary support points for the stair structure and the continuous roof plane that spans the garage, and the porch itself. Without this porch, the roof would require additional load-bearing walls, or a full foundation or frost wall to carry the same loads. Each of those alternatives would introduce substantially more excavation, soil disturbance, and impervious surface within the 25-foot buffer zone. By supporting the roof on helical piles beneath the porch, the design avoids excavation entirely and limits disturbance to approximately one square foot per pile. This structural configuration is also essential for runoff control. A single, continuous roof plane allows stormwater to be collected and directed in a predictable, controlled manner toward existing drainage patterns. Multiple roof sections or disjointed rooflines—such as those required if the porch were removed—would create additional drip edges, increase uncontrolled sheet flow, and disperse runoff into sensitive areas of the buffer zone. The continuous roof plane therefore minimizes hydrologic impact by reducing the number of discharge points and concentrating runoff where it can be safely managed. The second-story porch is thus a key element in both structural efficiency and environmental protection, and removing it would increase—not decrease—disturbance under the wetland protection bylaw. Although the stairway and porch are for the ADU, they are not considered dwelling space, they are separate accessory structures. 7. Conclusion The proposed design is the least environmentally impactful practicable alternative and should be approved under Chapter 190 Wetland Protection Bylaw.