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, Slippery Rock Township, Butler County, has its office at 155 Branchton Road, Slippery Rock, and Section 201 of Chapter 5 of the Township Code (Ord. 2004-1) says the Township "hereby elects to administer and enforce the provision of the Pennsylvania Construction Code Act"; the Township's Directory lists Construction Code Inspectors, Inc., of Seneca, as its "Building Code Inspector (Commercial & Residential)" for general and permit information, at 814-432-2630. Section 202 adopts "The Uniform Construction Code, contained in 34 PA Code, Chapters 401-405, as amended from time to time" as the municipal building code. Part 1 of Chapter 5 of the Township Code still adopts the 2000 edition of the International Residential Code, the chapter's revision page records that the Supervisors adopted the updated Uniform Construction Code including "the 2015 International Code Council Codes" on February 25, 2019, and the Township's pages name no current edition; this record has not read the 2000 or 2015 editions' text and does not decide which edition the Township applies.
Permit process
No Slippery Rock Township text read names reroofing as permit work or as exempt. Section 101 of Chapter 4 of the Township Code (Ord. 6, 1973, as amended in 2002) says "It shall be unlawful for any person, firm or corporation to proceed with the erection, alteration or improvement of any building in Slippery Rock Township, unless application for a permit shall have been made by the owner to the Permit Officer"; it names no roof work and does not name repairs. Part 1 of Chapter 5 (Ord. 2002-1) adopts the 2000 International Residential Code for the "alteration, repair, location, relocation, replacement" of one- and two-family dwellings "and providing for the issuance of permits," and Part 2 (Ord. 2004-1) adopts the Uniform Construction Code by reference; neither names roof work. The Township's 2026 fee schedule (Resolution 26-1-1) prices residential building permits for new homes, additions, garages, decks, "Roof over existing porch/deck" and "Roof Mount Solar Panels" and has no line for reroofing, and no Township page read names reroofing as permit work or as exempt. 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." No Township text read names reroofing as permit work or as exempt, and whether the Township's general permit clause reaches an ordinary reroof turns on whether that work is an alteration or improvement of a building, which this record does not decide; so this record does not decide whether the Township requires a permit for an ordinary reroof. Ask the Township office at 724-794-2369 or Construction Code Inspectors, Inc. at 814-432-2630 before work starts. The fee schedule lists a penalty for construction without a building permit of $100 for a first offense and $1,000 for a second, and Section 106 of Chapter 4 sets a fine of not more than $1,000 plus costs. The Township office is open Monday to Friday, 8:00am to 3:00pm. Read for this answer: Chapters 4 (Buildings) and 5 (Code Enforcement) of the Township Code in full; Chapter 27 (Zoning) and Chapter 13 (Licenses, Permits and General Business Regulations), searched for roofing and read in their permit sections; the Township's Directory, Ordinances and Documents and Forms pages; and the 2026 fee schedule.