Building an ADU in Pennsylvania

Pennsylvania has no statewide ADU law (yet)

No Pennsylvania law in effect today makes municipalities allow ADUs. The Municipalities Planning Code (MPC), the main state law that gives municipalities their zoning powers, does not mention accessory dwelling units. Your municipality's zoning ordinance decides whether you can add a backyard cottage, garage apartment, basement unit or in-law suite, and on what terms.

Under the MPC, a municipality's governing body "may enact, amend and repeal zoning ordinances." Those ordinances may "permit, prohibit, regulate, restrict and determine" the uses of land and the "size, height, bulk, location, erection, construction, repair, maintenance, alteration, razing, removal and use of structures," as well as yards, open space and population density. Those general zoning powers are where local ADU rules come from.

Two ADU bills were moving in the 2025-2026 session as of October 10, 2026; neither has become law. They are described below. [1][2][3]

HB 2186: one ADU per lot by right (passed the House)

HB 2186, by Rep. John Inglis III, is titled "providing for accessory dwelling units." It would add a new chapter to Title 53 of the Pennsylvania Consolidated Statutes. The House passed it 139-62 on June 1, 2026. It was referred to the Senate Urban Affairs and Housing Committee on June 5, 2026, and the Senate had not acted on it as of October 10, 2026. It is not law.

As passed by the House, it would make "one accessory dwelling unit per lot or parcel" a permitted use by right in every municipality with zoning where a residential building is a permitted use. It would also, among other things:

• allow attached, interior and detached ADUs;
• bar a minimum ADU size above 200 sq ft, and let a municipality cap ADU size at no less than 50% of the home or 850 sq ft (whichever is less), or the entire floor plate of a basement or attic;
• let a municipality cap ADU height at no less than 25 feet or the height of the home, whichever is less;
• bar setbacks for ADUs in existing structures, and allow side and rear setbacks of no more than four feet for new ones;
• bar owner-occupancy rules, family-relationship rules and extra off-street parking, including replacing parking lost when a garage is converted;
• require municipalities to let you rent the ADU, while letting them ban selling it separately and ban rentals of less than 30 consecutive days;
• take effect 60 days after enactment.

It would not override deed restrictions, covenants or the documents of a planned community (such as an HOA). The Senate could still change the bill; if it becomes law, check the final text. [1][4]

SB 1346: the Senate ADU bill

SB 1346, by Sen. Greg Rothman, would amend the Municipalities Planning Code instead. It was referred to the Senate Urban Affairs and Housing Committee on May 26, 2026, reported as committed on July 12, 2026, and given first consideration the same day. It had no further action as of October 10, 2026. It is not law.

Because SB 1346 amends the MPC, it would reach only the municipalities the MPC covers. HB 2186 instead defines "municipality" as any city, borough, incorporated town, township or home rule municipality.

As introduced, it would require each municipality to "adopt an ordinance to permit the development of at least one accessory dwelling unit for each single-family detached dwelling unit, subject to reasonable regulation." Among other things, it would:

• make ADU applications ministerial (no hearing), with approval or denial within 14 days when a home already exists on the lot, or the application is deemed approved;
• let a municipality cap ADU size at no less than 50% of the home or 1,250 sq ft, whichever is less;
• bar owner-occupancy rules and extra off-street parking;
• bar treating an ADU as a new residential use for utility connection fees, in most cases;
• allow renting the ADU but not selling it separately.

The two bills differ (for example, 850 vs. 1,250 sq ft), so the final rules, if any, are not known yet. [2][5]

How your municipality decides on an ADU today

Under the MPC, a zoning ordinance can let a use happen in several ways. It may list special exceptions, decided by the zoning hearing board under "express standards and criteria," and conditional uses, decided by the governing body after a hearing. In both cases the decision-maker may attach "reasonable conditions and safeguards."

If your ordinance doesn't allow an ADU on your lot, a variance is the remaining route. The zoning hearing board may grant one only where the ordinance would "inflict unnecessary hardship," based on findings such as unique physical conditions of the property that the owner did not create.

Where the wording of an ordinance is unclear, the MPC says it is to be interpreted "in favor of the property owner and against any implied extension of the restriction." [3]

Building permits: the Uniform Construction Code

Pennsylvania's statewide building code is the Uniform Construction Code (UCC). Municipalities adopt it by ordinance and enforce it with their own code officials or certified third-party agencies. The Department of Labor & Industry says over 90% of the state's 2,562 municipalities enforce the UCC locally. In municipalities that have "opted out," certified third-party agencies hired by the owner or contractor enforce the residential requirements.

State law sets deadlines for building permits. An application for a one-family or two-family dwelling must be granted or denied within 15 business days of filing, or within five business days if a Pennsylvania-licensed design professional certifies that the plans meet the UCC. If the code official doesn't act in time on a one- or two-family application, it is "deemed approved." A denial must give the reasons in writing, with citations to the code.

These deadlines cover the building code review. The municipality must also give you a list of other permits you need, and the building permit is issued once all other required permits or approvals are in. Zoning approval has its own process; ask your municipality which approvals apply. [6][7]

State housing plan

Governor Shapiro announced Pennsylvania's first Housing Action Plan on February 12, 2026. Led by an executive committee that included the Department of Community and Economic Development (DCED), it says Pennsylvania "should explore updating the MPC," including to "expand housing options by enabling homeowners to build new structures and renovate underutilized structures into accessory dwelling units (ADUs)."

The plan is a set of recommendations, not a law or a grant program. It does not change what your municipality allows today. [8][9]

HOAs and deed restrictions

Both pending bills say an ADU permission would not override deed restrictions, covenants or the documents of a planned community. Even if your municipality allows an ADU, your HOA rules or deed may not. Read them before you design anything. [4][5]

What to check with your municipality

Pennsylvania's rules are set by each city, borough or township, so ask your zoning officer or planning office:

• Whether your zoning district allows an ADU, in-law unit or second dwelling unit, and whether it's by right, a special exception or a conditional use.
• The maximum ADU size, height and setbacks, and any minimum lot size.
• Whether the owner must live on the property, or the occupant must be a relative.
• How many parking spaces you need.
• Whether you can rent the ADU, including short term.
• Who enforces the building code in your municipality, and the zoning, building permit and sewer or water connection fees.

Our ADU permit process guide, garage conversion guide, basement apartment guide and ADU cost guide cover the general steps. [3][6]

Pennsylvania laws to know

• Pennsylvania Municipalities Planning Code (Act 247 of 1968), Article VI

  Lets a municipality's governing body enact zoning that regulates the uses of land and the size, height, location and use of structures, which is where local ADU rules come from. [3]

• Pennsylvania Construction Code Act (Act 45 of 1999), Section 502

  Sets the time limits for deciding building permit applications, including 15 business days for one- and two-family dwellings. [6]

• HB 2186 (2026), proposed ADU law (pending in the Senate)

  Would make one ADU per lot a permitted use by right wherever zoning allows a residential building, with limits on size caps, setbacks, parking and owner occupancy. [1][4]

• SB 1346 (2026), proposed ADU law (pending in the Senate)

  Would amend the Municipalities Planning Code to require at least one ADU per single-family home, decided within 14 days without a hearing when a home already exists on the lot. [2][5]

Questions people ask