ADU rules in Lower Merion

Lower Merion has no general accessory dwelling unit use: Table 5.1, Uses, has no ADU line for the LDR or MDR residential districts, so a market-rate backyard cottage for an unrelated tenant is not available on an ordinary Main Line lot. Two narrow paths exist. Under § 155-10.2C, Restricted accessory dwelling units, a single-family dwelling in the LDR, MDR, IC and IH Districts may be converted into two units, and Subsection C(6) expressly contemplates the unit sitting in an accessory structure, which must then meet the principal building setbacks of the underlying district; the price is that every occupant of both units must be related by blood, marriage or legal adoption or be domestic partners, and the accessory unit is limited to two people, one of whom is 62 or older. The second path is preservation-based: for a property carried on the township's Historic Resource Inventory as a Class 1 or Class 2 Historic Resource, Table 7.1.1 lists 'Accessory dwelling unit' as a regulated (R) use, and § 155-2.1 defines an ADU as a dwelling unit sharing a lot with a principal building 'that may or may not be in a separate structure.' A detached unit is therefore reachable only through the elder-family special exception or through historic designation.

The attached or internal case is what § 155-10.2C is written around: in the LDR, MDR, IC and IH Districts 'a single-family dwelling or an existing institutional building may be converted into two dwelling units, each with its own cooking facilities,' subject to ten conditions including the family-relationship rule, the age-62 occupancy limit, a recorded agreement to remove the second kitchen when the qualifying use ends, and an annual township permit. Table 5.1 makes the parent use, Alternative housing for the elderly, a special exception in LDR and MDR (Table 5.2 makes it permitted by right only in the IC and IH institutional districts), so a basement or addition unit rented to an unrelated tenant has no approval path. For a Class 1 or Class 2 Historic Resource, Table 7.1.2 allows an accessory dwelling unit as a regulated use with just two conditions: it must be the only dwelling unit besides the principal dwelling, and it must satisfy Table 8.1 parking. § 155-7.1B(4)(a) also requires an added historic-resource use to be 'contained within the historic buildings or structures unless otherwise specifically permitted,' which favors conversions inside the historic house or an existing carriage house over new construction.

The zoning code sets no floor-area ceiling in square feet for an accessory dwelling unit. In the § 155-10.2C elder conversion the split is proportional: 'One dwelling unit shall have no less than two times the square footage of occupied space than the other,' so the accessory unit can be at most half the size of the main unit, roughly a third of the two units combined. Height and placement carry the rest of the load: § 155-3.4F requires accessory buildings to be erected to the rear of the principal building and limits them to two stories or 20 feet, dropping to one story or 15 feet if built into the reduced side or rear setback, and the LDR and MDR dimensional tables in Article IV repeat the 2 stories and 20 feet accessory-building height cap in every residential district. § 155-5.2F(3) separately provides that the area occupied by an accessory use may not exceed 50% of the area occupied by the principal use. In practice the binding constraints on most Lower Merion lots are lot area, impervious surface and setbacks: LDR1 alone requires 90,000 square feet of lot area with a 20% impervious surface maximum.

There is no flat owner-occupancy mandate, but the elder-conversion path effectively requires the owner or a sponsoring nonprofit on site. § 155-10.2C(1) requires that all individuals living in the two dwelling units be related by blood, marriage or legal adoption or be domestic partners, and C(10) adds that if the facility is not owner-occupied its use must be sponsored by a nonprofit organization whose purpose includes housing the elderly and overseeing residents' care, with a designated agent or offices in Pennsylvania. The historic-resource accessory dwelling unit in Table 7.1.2 carries no owner-occupancy condition at all. Pennsylvania preempts nothing here: the Municipalities Planning Code leaves owner-occupancy conditions entirely to the municipality, and no statewide ADU act has been enacted.

Table 8.1, Minimum Parking Requirements, sets LDR and MDR parking for single-family detached housing at '2/unit + 1 space/ADU,' and the table's notes gloss ADU as accessory dwelling unit; § 155-8.1B(3) confirms that residential required parking is calculated by the total number of dwelling units and/or accessory dwelling units on the lot. A house with an accessory unit therefore needs three off-street spaces. Where the unit is approved as an elder conversion, the Table 8.1 row for Alternative housing for the elderly instead requires one space per unit, and § 155-10.2C(5) makes Article VIII applicable; Table 7.1.2 requires a Class 1 or Class 2 Historic Resource ADU to comply with Table 8.1. No transit-proximity relief exists: § 155-8.2C, Transit, is reserved, and § 155-8.2A(2) bars reducing LDR or MDR parking below one space per dwelling unit. Special exception applicants in residential districts must also show that all required parking sits outside the front yard.

Approval depends entirely on which path the unit uses. In LDR and MDR, Alternative housing for the elderly, the use that carries the § 155-10.2C restricted accessory dwelling unit, is an 'S' use: a special exception decided by the Zoning Hearing Board after a public hearing (Table 5.1; § 155-5.1E(4)), and Table 5.3 adds that in a Class 1 Historic Resource the same use requires conditional-use approval from the Board of Commissioners instead. Approved units then need an annual township permit under § 155-10.2C(8), and the zoning permit expires six months after the building stops being occupied by the qualifying elderly resident. By contrast, on a Class 1 or Class 2 Historic Resource an accessory dwelling unit is a regulated 'R' use, which § 155-7.1D(2) makes 'subject to administrative approval by the issuance of a zoning permit by the Zoning Officer.' In the IC and IH institutional districts the elderly-housing use is permitted by right (Table 5.2). Budget for a hearing unless the property is a designated historic resource.

The § 155-10.2C restricted accessory dwelling unit is not a rental product: C(1) requires every occupant of both units to be related by blood, marriage or legal adoption or be domestic partners, C(2) caps the accessory unit at two people with one aged 62 or older, C(3) requires an agreement recorded with the Montgomery County Recorder of Deeds providing for immediate removal of the separate cooking facilities once they are no longer used as specified, and C(7) expires the zoning permit six months after the building ceases to be occupied by elderly persons. An accessory dwelling unit on a Class 1 or Class 2 Historic Resource carries no occupancy limit, so it can be leased long term, but Chapter 75, Article IV, makes it unlawful to rent a residential rental unit without a license for each unit, exempting only dwelling units occupied by the owner as a primary residence; licenses run January through December and are conditioned on inspection. The township has no short-term rental regime: no STR ordinance appears in the code or in the Chapter DL disposition list, and Table 5.1 permits the two lodging categories, bed-and-breakfast and hotel, only in the NC, VC, TC, BMV and CAD Districts, never in LDR or MDR.