ADU rules in Montgomery County, PA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Montgomery County does not regulate accessory dwelling units. Under the Pennsylvania Municipalities Planning Code (Act 247 of 1968), zoning authority is vested in townships, boroughs, and cities — not counties. Each of Montgomery County's 62 municipalities (Norristown, Pottstown, Lower Merion, Upper Merion/King of Prussia, Abington, Cheltenham, etc.) sets its own ADU rules.
Pennsylvania is a 'Dillon's Rule' state where land use and zoning authority is delegated to municipalities under the PA Municipalities Planning Code, Act 247 of 1968 (53 P.S. §10101 et seq.). Section 603 of the MPC (53 P.S. §10603) authorizes townships, boroughs, and cities — but not counties — to enact zoning ordinances. Montgomery County's role is advisory through the Montgomery County Planning Commission, which publishes model ordinances and provides technical assistance, but has no enforcement power over residential land use. Whether an ADU is permitted by right, by special exception, by conditional use, or prohibited entirely depends entirely on the host municipality. Any approved ADU must still comply with the Pennsylvania Uniform Construction Code (Act 45 of 1999, 35 P.S. §7210.101 et seq.), which adopts the International Residential Code with PA amendments. Property owners must contact their specific township or borough zoning officer to determine local rules.
Penalties for unpermitted accessory dwellings are set by the municipality where the property is located. Under PA MPC §617.2 (53 P.S. §10617.2), municipalities may impose fines up to $500 per violation per day plus court costs and attorney fees. Building Code violations under PA UCC §903 (35 P.S. §7210.903) carry separate fines up to $1,000 plus stop-work orders.
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See how Montgomery County's adu rules rules stack up against other locations.
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