Illinois Building Permit Guides

Illinois leaves building codes to local government: each municipality or county decides whether to adopt a building code and which edition, with its own amendments. Public Act 103-0510 (effective 1 January 2024) added a statewide floor. From 1 January 2025, any municipal or county building code must regulate the structural design of buildings at least as strictly as a baseline edition of the International Building Code (with Appendix G), the International Existing Building Code and the International Residential Code (20 ILCS 3105/10.18(e)).

Where a jurisdiction has adopted no building code, the statute sets the minimum instead. A new or substantially improved commercial building may not be occupied until a qualified inspector certifies that it complies with the current or preceding International Building Code (excluding Chapters 11, 13 and 29) and International Existing Building Code, the National Electrical Code, the Illinois energy code, the Illinois Accessibility Code, the Illinois Plumbing Code and the state fire rules (20 ILCS 3105/10.09-1). For a new one- or two-family home, a residential code becomes part of the construction contract by law, by default the International Residential Code (815 ILCS 670/15). The Capital Development Board does no permitting or inspection for private projects.

The Illinois Energy Conservation Code applies statewide (20 ILCS 3125), and plumbing follows the Illinois Plumbing Code. So the first question on any Illinois project is which local code and amendments apply to the parcel — or, where none were adopted, which statutory minimums — and whether the parcel is in a municipality or the unincorporated county.

Illinois splits contractor credentials between the state and the local jurisdiction. The state licenses plumbers through the Department of Public Health and roofing contractors through the Department of Financial and Professional Regulation. General contractors and electricians, by contrast, are licensed or registered locally — many municipalities and counties require contractors to register before they can pull a permit.

Trade permits are separate from the building permit and, on projects that require one, generally cannot be issued until the building permit is in place. Plumbing is the clearest statewide case: it follows the Illinois Plumbing Code and must be performed under a state-licensed plumber, wherever the project sits. Electrical work follows the locally adopted electrical code and is tied to a locally licensed or registered electrician.

• Electrical work follows the locally adopted code and a locally licensed or registered electrician.
• Plumbing work follows the statewide Illinois Plumbing Code and a state-licensed plumber.
• Mechanical work follows the adopted mechanical and energy codes; the contractor registers locally.