Beta — site is under development, information may contain errors. Read disclaimer
Zoning Guide

ADU Rules in Johnstown, Pennsylvania

Last updated: Verified:

ADU Rules in Johnstown, Pennsylvania

Johnstown is the seat of Cambria County in the Allegheny Mountains of southwestern Pennsylvania, situated at the confluence of the Conemaugh River and Stonycreek. With a population that has fallen from over 67,000 in 1920 to approximately 18,000 today, Johnstown is one of the most dramatic examples of deindustrialization in the United States — a shrinking city with a rich and at times tragic history.

The Johnstown Flood Legacy

No discussion of Johnstown can begin without acknowledging the 1889 Johnstown Flood. On May 31, 1889, the privately owned South Fork Dam failed after heavy rains, releasing a wave of 20 million tons of water down the Conemaugh Valley. The flood killed 2,209 people — the worst flood disaster in American history at the time — and destroyed much of the city. Johnstown was rebuilt, but flooding remained a recurring tragedy:

  • 1936 Flood: The St. Patrick's Day flood killed 25 people and caused major destruction.
  • 1977 Flood: Tropical storm-driven rains caused catastrophic flooding that killed 84 people and caused approximately $200 million in damage.

Today, the US Army Corps of Engineers has constructed flood control infrastructure including channel improvements and levees in the Johnstown area. However, flood risk has not been eliminated, and portions of Johnstown remain in FEMA flood zones.

No Pennsylvania Statewide ADU Law

Pennsylvania has not enacted statewide ADU preemption legislation. Under the Pennsylvania Municipalities Planning Code (MPC), all zoning authority is local. Johnstown's ADU rules are governed entirely by the Johnstown Zoning Ordinance.

Flood Zones: A Critical ADU Consideration

Flooding is the defining environmental constraint on development in Johnstown. Before planning any ADU project:

  • Check FEMA flood maps: Determine whether your property is in a Special Flood Hazard Area (SFHA) using FEMA's Flood Map Service Center (msc.fema.gov).
  • Base Flood Elevation compliance: New construction and substantial improvements in FEMA flood zones must be elevated to or above the Base Flood Elevation (BFE).
  • Substantial improvement trigger: If ADU renovation costs exceed 50% of the structure's pre-improvement market value, the entire structure must be brought into floodplain compliance — this can be a major cost consideration in Johnstown's lower-value housing market.
  • Flood insurance: NFIP flood insurance is strongly recommended for all Johnstown properties, even those outside current mapped flood zones.
  • Levee-protected areas: Check the accreditation and certification status of any local flood control structures with the city and US Army Corps.

Zoning Districts and ADU Rules

Johnstown's zoning ordinance divides the city into residential, commercial, and industrial districts. In residential zones:

  • Single-family residential districts: Accessory structures generally permitted; conversion to a separate accessory dwelling unit may require special exception or variance.
  • Two-family and multi-family districts: More permissive of additional units.
  • Setbacks and lot coverage: Accessory structures must maintain minimum setbacks and comply with maximum lot coverage.
  • Height limits: Accessory structures limited relative to the principal building.

Contact the Department of Community and Economic Development to confirm your specific district designation.

Shrinking City Context

Johnstown's dramatic population loss has created an abundance of vacant and abandoned properties. This context affects ADU planning in several ways:

  • Low property values: Construction costs may exceed market value in some areas, challenging ADU investment economics.
  • Blight: Adjacent properties may be vacant or poorly maintained; structural conditions in older housing stock vary widely.
  • Rehabilitation programs: Johnstown and Cambria County have pursued various housing rehabilitation and stabilization programs. Contact the Department of Community and Economic Development and the Johnstown Area Regional Industries (JARI) for information on current programs.

Allegheny Mountain Topography

Johnstown's valley location surrounded by steep hillsides adds topographic complexity. Hillside properties may face slope stability and stormwater requirements. The city's steep-slope neighborhoods require careful site assessment before construction.

Permit Process

  1. Zoning determination: Contact the Department of Community and Economic Development for your district and ADU rules.
  2. Flood zone check: Critically important — verify via FEMA maps and consult with the city.
  3. Building permit: Apply to the Code Enforcement Division for all structural work.
  4. Zoning Hearing Board: Required for variances or special exceptions.

Contact

  • City of Johnstown: (814) 533-2009, johnstownpa.com
  • City Hall: 401 Washington Street, Johnstown, PA 15901
  • JARI (regional economic development): (814) 535-8675, jari.com

Disclaimer: Zoning regulations and FEMA flood maps change frequently. Flood risk in Johnstown is significant and historically documented. Verify all information directly with the City of Johnstown and FEMA before making any development decisions. Consulting a licensed floodplain manager is strongly recommended for properties in or near flood zones.

More about Johnstown Zoning

Sources

  1. City of Johnstown Ordinances·johnstownpa.gov·Accessed 2026-05-25·Direct link
  2. City of Johnstown Economic Development·johnstownpa.gov·Accessed 2026-05-25·Direct link

FAQ

Are ADUs allowed in Johnstown, Pennsylvania?
ADUs in Johnstown are regulated by the Johnstown Zoning Ordinance. Pennsylvania has no statewide ADU preemption law, so local rules govern. Whether an accessory dwelling unit is permitted depends on your specific zoning district and property configuration. Given Johnstown's history of flooding, flood zone status is a critical consideration for any construction. Contact the Johnstown Department of Community and Economic Development for a zoning determination.
What is the Johnstown Flood and why does flooding matter for ADU development?
The 1889 Johnstown Flood was caused by the failure of the South Fork Dam upstream, releasing a wall of water that killed 2,209 people — the deadliest flood in US history at the time. But Johnstown has flooded many times since: catastrophic floods struck again in 1936 (killing 25) and in 1977 (killing 84 and causing $200 million in damage from heavy rain alone). Today, Johnstown has flood control infrastructure, but portions of the city remain in FEMA flood zones. Any ADU construction requires careful flood zone review: new construction in Special Flood Hazard Areas must meet elevation and other floodplain requirements.
Where do I apply for a building permit for an ADU in Johnstown?
Building permits in Johnstown are issued by the Code Enforcement Division. Contact the City of Johnstown at (814) 533-2009 or visit City Hall at 401 Washington Street, Johnstown, PA 15901. Zoning review is handled by the Department of Community and Economic Development.