Adopted building code
The 2021 International Residential Code, as adopted by the State in the Pennsylvania Uniform Construction Code (UCC). 34 Pa. Code 403.21(a)(7) adopts "The 'International Residential Code of 2021,' except that:" followed by the State's list of exclusions and modifications, effective January 1, 2026 (55 Pa.B. 7701). None of the State's changes touches Chapter 9, Roof Assemblies, or Section R803, Roof Sheathing, so those apply as the International Code Council publishes them. Work on existing buildings is also pointed to the State's existing-building code: "The repair, alteration, change of occupancy, addition and relocation of existing buildings must comply with Chapter 34 of the 'International Building Code of 2021' or with the 'International Existing Building Code of 2021'" (34 Pa. Code 403.21(f)). The UCC is the minimum everywhere in the state: "no municipality may propose or enact any ordinance which is less than the minimum requirement of the Uniform Construction Code" (Pennsylvania Construction Code Act, Act 45 of 1999, section 503(b)). The Act also lists work it "shall not apply to", including "Alterations to residential buildings which do not make structural changes or changes to means of egress" or to "Repairs to residential buildings," in each case "except as might be required by ordinances" kept in force under section 303(b)(1) or adopted under section 503 (Act 45 section 104(b)(5) and (6); 34 Pa. Code 403.1(b)(8) and (9)). The Act defines a repair as "The reconstruction or renewal of any part of an existing building for the purpose of its maintenance." So whether the code's roofing rules reach a given house reroof depends on the municipality's own ordinances. Everything above is Pennsylvania state law, the same in every municipality. Locally, Shippensburg Borough takes building permit applications at its office and uses Pennsylvania Municipal Code Alliance, Inc. (PMCA) for inspections: Section 80-1 of the Borough Code (Ord. No. 777, 2004) says "The Borough of Shippensburg hereby elects to administer and enforce the provisions of the Pennsylvania Construction Code Act," Section 80-7 says applications for building permits "shall be made to the Borough," and the Borough's posted notice names "PA MUNICIPAL CODE ALLIANCE, INC." as the "APPROVED INSPECTION AGENCY FOR THE BOROUGH OF SHIPPENSBURG," at 380 Wayne Avenue, Chambersburg, 717-496-4996. Section 80-2 adopts the Uniform Construction Code "as amended from time to time" as "the municipal building code of the Borough of Shippensburg"; Chapter 80 changes nothing in the code's roofing provisions and names no edition of the International Residential Code, and neither do the Borough's pages.
Permit process
Section 80-7A of the Borough Code says "A building permit shall be required for all construction work done within the Borough, in accordance with the provisions of Chapter 78 of the Code of Ordinances of the Borough (hereinafter referred to as "Chapter 78") or as otherwise required under the Code," and Section 80-5A keeps in force earlier building code ordinances, "including but not limited to the provisions of Chapter 78," that exceed the Code. Chapter 78 (Building Permits, Fees and Inspections, Ord. No. 322 of 1961, as amended) defines ALTERATION as "Any enlargement of any building or any work of repair, remodeling or replacement of any exterior or interior wall, roof, floor or support or any part thereof of any building," excluding "repairs related to maintenance, health or safety having a cost, including labor and materials, of less than the sum of $1,500," but its permit section (Section 78-2) does not use that defined word: it requires a land use permit from the Zoning Officer before a building is "erected, constructed, moved, added to, structurally altered, extended, expanded, enlarged, demolished or razed," and says the owner of a property "upon which construction or remodeling or other activities requiring a permit take place shall make application for a building permit." This record does not decide whether a reroof is "construction work" under Section 80-7A or an alteration needing a permit under Chapter 78. In the Borough's Historic District, Section 78-36C says "the Zoning Officer may issue a building permit for the replacement of a shingle roof with the same or similar materials"; that section speaks only to work in the Historic District. PMCA's own Frequently Asked Questions page links, under a question on re-roofing a residential structure, a letter dated July 20, 2018 addressed "Dear Municipal Official" that says "a residential Re-roof still requires compliance with the provisions of the UCC but does not require a building permit" and "If structural work is required such as replacing studs, headers, rafters or trusses a permit would now be required"; the letter does not name Shippensburg and is not posted on the Borough's pages. PMCA's Residential Re-Roof application packet says "A Building Permit is required if there is a structural repair." The Borough's Fees page lists the Building Permit fee as "In accordance with current rate schedule of designated Borough inspection agency (In accordance with (PMCA) - PA Municipal Code Alliance)" and a Land Use Permit at $40.00; it has no roofing line. Under state law, Act 45 section 104(b)(5) and (6) list "Alterations to residential buildings which do not make structural changes or changes to means of egress" and "Repairs to residential buildings" among work the Act does not apply to, "except as might be required by ordinances in effect pursuant to section 303(b)(1) or adopted pursuant to section 503," and 34 Pa. Code 403.62(c) says "A permit is not required for the exceptions listed in § 403.1(b) (relating to scope) and the following, if the work does not violate a law or ordinance." This record does not state whether a permit is required for a house reroof in Shippensburg Borough; ask the Borough office at 717-532-2147 before starting. Section 78-2 makes a land use permit from the Zoning Officer "a prerequisite to making application for a building permit," and Section 80-11 says that where an owner "commences construction without first having obtained a permit as required hereunder, a penalty of 25% of the established fee for said permit shall be added thereto," with a fine of "not more than $1,000 and the costs of prosecution" for a violation of Chapter 80. The Borough office is open "Monday - Friday" "8:00am - 4:00pm." Read for this answer: Chapter 80 of the Borough Code (Construction Codes, Uniform, Sections 80-1 to 80-11) and Articles I and III of Chapter 78 (Building Construction), in full; every page of searches of the whole Borough Code for "roof" and for "reroofing," which found none; the Borough's Codes/Zoning, Fees and Forms/Applications pages, its approved inspection agency notice and its land use permit application; and PMCA's Frequently Asked Questions and Permit Applications pages, its 2018 re-roof letter and its Residential Re-Roof application packet. PMCA's rate schedule is not posted on the Borough's pages.