Allegheny County

ADU Pass helps homeowners in Allegheny County, Pennsylvania navigate the permit paperwork for building an accessory dwelling unit. We cover 60 cities and 141 ZIP codes in this county.

141 ZIP codes
60 Cities

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County ADU details

County assessor

The Allegheny County Office of Property Assessments (part of the Department of Administrative Services) maintains parcel-level assessment records for all real property in the county, including parcels inside the City of Pittsburgh and the 129 other municipalities. Allegheny County is on a 2012 base-year assessment; no general reassessment has occurred since, and the county has actively resisted countywide reassessment despite ongoing litigation demanding one. The 2024 Common Level Ratio (CLR) published by the State Tax Equalization Board (STEB) was 50.14 (reflecting that 2012 assessed values average about 50% of 2024 market value) and was revised downward again for 2025 to 52.7% (applying to appeals filed for tax year 2026). An ADU addition to a parcel triggers a discretionary mid-cycle interim assessment under Allegheny County Code Chapter 210 when the municipality reports the building permit to the Office of Property Assessments; the interim assessment captures only the incremental value of the new improvement and does not reset the base-year assessment on the pre-existing primary dwelling.

NameAllegheny County Office of Property Assessments
Address542 Forbes Avenue, Room 347, Pittsburgh, PA 15219
Phone412-350-4600
Parcel lookupOnline lookup

Assessment policy: An ADU is captured as an interim assessment under 72 P.S. ss 5020-602.2 and Allegheny County Code Chapter 210 when the municipality transmits the building-permit record (Form BP-2) to the Office of Property Assessments. The interim assessment adds the 2012-base-year-equivalent value of the new structure to the parcel's existing assessed value; it does not re-value the primary dwelling or the land. For ADU construction cost conversion, assessors apply Marshall & Swift residential cost multipliers adjusted backwards to the 2012 base year using STEB's published CLR (effectively a 50% discount on 2024 construction cost). There is no Pennsylvania or Allegheny County ADU-specific assessment exemption; the 2022 Homestead/Farmstead exemption (up to $18,000 off assessed value for owner-occupied primary dwellings) applies to the primary dwelling only and does not extend to an accessory dwelling unit. Pittsburgh residents additionally face City and School District Homestead exemptions under separate rate structures.

checked 2026-04-20

County overlays (6)

Allegheny County administers three county-wide overlay regimes that bear on ADU development across multiple municipalities: (1) FEMA floodplain / Special Flood Hazard Area enforcement along the Ohio, Allegheny, and Monongahela Rivers and their tributaries; (2) the Allegheny County Act 167 Stormwater Management Plan (Phase 2, 2018 update) which sets release-rate and volume-control standards municipalities must incorporate; and (3) Allegheny County Health Department air-quality oversight including the Liberty-Clairton SO2 / PM2.5 non-attainment area in the Mon Valley that can add indoor-air-quality construction requirements. Pennsylvania has no CalFire-equivalent statewide WUI wildfire regime and no seismic retrofit zone; USGS hazard maps place the county in a moderate seismic-hazard band (roughly NEHRP Site Class equivalents; no statewide ASCE 7 seismic retrofit overlay applies). County-wide historic preservation is minimal - Pittsburgh History & Landmarks Foundation operates advisory plaques and several boroughs (Sewickley, Edgeworth, Mount Lebanon's Washington Road corridor) maintain local historic districts, but there is no county-wide historic overlay.

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Known county issues (5)

  • pending-litigation — Pittsburgh Public Schools filed suit in May 2022 seeking a court-ordered countywide reassessment on PA Constitution Art. VIII ss 1 uniformity-clause grounds. A taxpayer-led companion action was filed 2023. Both are pending at the Allegheny County Court of Common Pleas / Commonwealth Court. A ruling compelling reassessment during 2026-2028 would materially change ADU-related interim-assessment math: a post-reassessment ADU addition would be added at full market-value increment rather than at the ~50% CLR-discounted 2012 base year. Owners planning ADU construction should model both scenarios.
  • policy-review — FEMA is actively studying the full length of the Ohio River for an updated Flood Insurance Study. Preliminary First Street Foundation / Penn State PA Flood Risk Tool modelling suggests the mapped Special Flood Hazard Area will expand materially - from ~1,750 structures currently identified to a potential ~86,000 parcels in the broader 100-year pluvial+fluvial risk band. ADU projects in river-town municipalities (Millvale, Sharpsburg, Etna, McKees Rocks, Carnegie, Ingram, Oakmont) planned for 2027-2030 may face NFIP elevation-certificate requirements they would not face under today's maps.
  • other — Every acre of Allegheny County sits inside one of 130 municipalities, each with its own zoning ordinance and ADU policy (or silence). ADU legality ranges from explicit permission (Pittsburgh, Mount Lebanon, Wilkinsburg post-2023) through discretionary conditional-use (most boroughs) to de facto prohibition via silence + single-family-detached-only zoning (many exurban boroughs and townships). There is no county-level cure; consumers must consult the specific municipality. ADU Pass's per-city research is the primary usable resource.
  • other — The 2024 STEB CLR of 50.14 and the 2025 revision to 52.7% reflect ongoing appeal-driven non-uniformity. Owners of parcels appealed within the last three years may hold assessments materially below the 50% average; owners who have not appealed may hold assessments at or near 2012 market value (effectively 100% of base-year value, or ~50% of current market). An ADU interim assessment inherits the parcel's existing appeal posture; the interim notice is separately appealable within 30 days.
  • other — Several SEO-driven content sites (steadily.com, zookcabins.com, and others) describe Pennsylvania as if it had a statewide ADU preemption statute and sometimes describe Allegheny County as having a county-level ADU ordinance. Neither is true as of 2026-04-20. PA ADU law is governed exclusively by each municipality's zoning ordinance; no Pennsylvania statewide ADU statute has been enacted; Allegheny County issues no ADU building permits and has no ADU ordinance. Consumers should verify against the specific municipality's code, not against generic Pennsylvania or Allegheny County sources.
Pennsylvania state — ADU law and programs

State ADU law

Pennsylvania has NOT enacted a statewide ADU preemption law. Under the Pennsylvania Municipalities Planning Code (Act 247 of 1968, 53 P.S. §§10101 et seq.), local governments retain broad authority over zoning, including ADU permission, setbacks, parking, size limits, and owner-occupancy. ADU rules vary widely by township, borough, city, and county. One active bill in the 2025-2026 session, HB 2186 (chief sponsor Rep. John Inglis), would amend Title 53 of the Consolidated Statutes to provide for ADUs, but was laid on the table on 2026-04-13 after a Housing and Community Development Committee vote (reported as 19 yes, 7 no during committee action) and has not advanced to third consideration.

checked 2026-04-20

State financing programs

Pennsylvania does not operate an ADU-specific statewide loan, grant, or forgivable-loan program. The Pennsylvania Housing Finance Agency (PHFA) administers general first-time-homebuyer, down-payment-assistance, and purchase-plus-improvement programs that can apply to properties with ADUs when eligibility criteria are met, but none target ADU construction as a distinct product. Notably, PHFA's HFA Preferred conventional product explicitly excludes two-unit properties, which can complicate financing an owner-occupied primary home that has (or plans to add) an attached ADU depending on how the appraiser and investor classify the unit.

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State housing programs

Pennsylvania does not run a state-level pre-approved-ADU-plan catalog, statewide impact-fee-waiver statute for ADUs, or streamlined-review mandate. State-level programs that touch ADU-adjacent policy are primarily coordinated through the Department of Community and Economic Development (DCED) and PHFA, and act by funding or assisting local jurisdictions rather than by preemption. Local ADU momentum — Pittsburgh's by-right ADU ordinance in designated zones and Philadelphia's 2020 zoning-code ADU provisions — is authorized under municipal authority granted by the Municipalities Planning Code (Act 247 of 1968), not by state mandate.

  • Keystone Communities Program — DCED program that provides planning, design, and construction funding to municipalities for downtown revitalization, elm-street neighborhood improvement, facade grants, and blight remediation. Not ADU-specific. Participating municipalities can direct Keystone Communities funds toward housing-rehab and missing-middle projects where local policy supports ADUs.
  • Pennsylvania Land Use Planning Assistance (PALUPA) / DCED Land Use Planning Technical Assistance — DCED and associated local-government-services staff provide model-ordinance drafting, zoning-code review, and planning technical assistance to municipalities interested in modernizing zoning (including ADU permission). Acts through local adoption rather than state preemption.
  • Pennsylvania Municipalities Planning Code (Act 247 of 1968) Model-Ordinance Guidance — The DCED-published Pennsylvania Municipalities Planning Code PDF and companion Planning Series documents include model language municipalities can adopt, including for accessory uses, home occupations, and mixed-use areas. Not a statewide ADU mandate; a guidance and boilerplate library that municipalities may or may not adopt.
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Federal (United States) — ADU-relevant rules and programs

Federal ADU law

The United States has no federal statute that directly regulates accessory dwelling unit entitlement or design. Land-use authority over ADUs resides with states and local governments under the traditional police power. Federal engagement is limited to financing (Fannie/Freddie/FHA/VA/USDA), flood insurance (FEMA/NFIP), and discretionary housing programs (HUD), which are recorded in sibling sections of this file.

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Federal financing programs

Federal housing-finance agencies and GSEs set nationwide underwriting rules that govern whether an ADU can be financed, appraised, and counted toward mortgage qualifying income. The relevant actors are Fannie Mae, Freddie Mac, FHA (HUD), VA, and USDA Rural Development.

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Federal tax credits

There is no ADU-specific federal tax credit. ADUs may incidentally qualify for existing federal energy-efficiency and clean-energy tax credits when the ADU construction includes qualifying measures.

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Federal housing programs

HUD administers several discretionary programs that can fund ADU-related activity at the grantee's election, but none is an ADU-specific program.

checked 2026-04-20

Cities

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