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, Mount Union Borough's Code and Zoning Enforcement page says "Borough building permit applications are available at the Borough Office located at 9 West Market Street, Mount Union Pennsylvania" and that "Any Electrical, Plumbing HVAC, or General Construction inside a property requires a permit to be filed through the Bureau Veritas in Huntingdon Pennsylvania." Section 130-13 of the Borough Code (Ord. No. 1065, adopted April 5, 2004, read October 12, 2026) says "The Borough of Mount Union hereby elects to administer and enforce the provisions of the Pennsylvania Construction Code Act," Section 130-14 adopts "The Uniform Construction Code, contained in 34 Pa. Code Chapters 401 to 405, as amended from time to time," naming no edition and no roof work, and Section 130-17 A keeps in force building code ordinances adopted on or before July 1, 1999 "which equal or exceed the requirements of the code."
Permit process
Mount Union Borough's pages and code read for this record do not say in terms whether a house reroof needs a permit. The Borough's own building permit is a separate local permit. Its Code and Zoning Enforcement page answers "What do I need a building permit for? And how do I get one?" with "Any work on the exterior of your home requires a building permit. Repairing and replacing also requires a building permit," and its resident sheet says "Building Permits are required for ALL PROJECTS that are visible from the street ie: decks, window/door replacement, new siding etc." Neither names roof work, and this record does not decide whether a house reroof is "work on the exterior" or a project "visible from the street." The Borough's building permit application lists the types of improvement "NEW BUILDING," "ADDITION," "ALTERATION," "REPAIR OR REPLACEMENT OF" and others and names no roof work. Section 130-11 F of the Borough Code, in Article II adopting the "BOCA Basic Building Code/1978, Seventh Edition," says "It shall be unlawful to construct, enlarge, alter or demolish a structure" without a permit, "except that ordinary repairs, as defined in Section 102.0, which do not involve any violation of this code and ordinary carpeting and painting shall be exempt from this provision"; this record has not read the BOCA code's definition of "ordinary repairs" and does not decide whether a house reroof is one, or whether Article II is still in effect after Section 130-17. Section 330-53 of the Zoning chapter says "Persons desiring to undertake any new construction, structural alteration, or change in the use of a building or lot shall apply to the Zoning Officer for a zoning permit," and Section 330-55 A says "no person shall erect, alter, or convert any structure, building, or part thereof" until a zoning permit is issued; neither names roof work, and this record does not decide whether a house reroof is either. A search of the whole Borough Code for "roof" found only definitions, sewer, sign and mobile-home provisions, and a search for "reroofing" found nothing. 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 the Borough requires a permit for a house reroof; ask the Borough Office (814-542-4051) before starting. Read for this answer: the Borough's home and Code and Zoning Enforcement pages; its Building Permit Application and resident sheet (scanned, read from the rendered page images); Chapter 130, Articles II and III, and Chapter 330, Article VIII, of the Borough Code on eCode360; and eCode360 searches of the whole Borough Code for "roof" and "reroofing." Chapter 173, Floodplain Management, was found only through those searches and was not read for a permit clause.