Williamson County, Illinois Roofing Permit Regulations and County Ordinances for Unincorporated Areas

Williamson County, Illinois Roofing Permit Requirements

Williamson County, Illinois, has specific regulations for building permits, particularly in unincorporated areas. The county has adopted the 2021 International Residential Code (IRC) for enforcement in unincorporated areas.

Jurisdiction: Williamson County's Building Codes Division is responsible for overseeing construction and permit requirements.
Unincorporated Areas: For properties in unincorporated areas of Williamson County, Illinois, a building permit and inspection are generally not required for ordinary repairs or replacements to residential roofs. This is in accordance with Section R105.2.2 of the 2021 IRC.
Code Compliance: Even though a permit may not be required for roof repairs or replacements, all construction must still comply with the adopted codes and ordinances, including Chapter 9 of the 2021 IRC concerning roof assemblies. Additionally, roof assemblies and materials must be installed according to the manufacturer's instructions.
Ordinance Applicability: Williamson County Ordinance # 20-01-22-03, "The Building Permit Ordinance," applies to the construction, alteration, and demolition of buildings and structures in unincorporated areas that are 100 square feet or greater. This includes manufactured homes, mobile homes, and prefabricated/portable storage sheds and buildings.
Permit Application Process: Building permit applications are obtained from and submitted to the Williamson County Supervisor of Assessments. A filing fee is required for all permit applications.

Resources to Learn More

Note: The following state-wide building codes and regulations apply universally to all jurisdictions within Illinois, including Williamson County.

Illinois Roofing Legislation, Codes, and Guidelines

State-Level Building Codes and Legislation for Roofing in Illinois

As of January 1, 2025, Illinois has implemented a statewide baseline building code requirement pursuant to Public Act 103-0510, which amended the Capital Development Board Act. This legislation mandates that all municipalities and counties in Illinois must adopt and enforce building codes that meet or exceed the minimum structural requirements of the International Code Council (ICC) standards, specifically the International Building Code (IBC) and the International Residential Code (IRC). Prior to this, Illinois did not have a unified statewide building code, and regulations were determined entirely at the local municipal or county level.

While the state now requires a baseline, local jurisdictions retain the authority to adopt their own specific editions (such as the 2018, 2021, or 2024 editions) and implement local amendments, provided those amendments do not reduce the structural requirements below the state-mandated baseline. Consequently, specific roofing requirements—such as those for ice and water shields, ventilation, and shingle layering—can still vary significantly between different cities, villages, and counties. Property owners and contractors must consult their local Authority Having Jurisdiction (AHJ) to confirm the specific code edition and local amendments applicable to their project.

Primary State Agency

The Illinois Capital Development Board (CDB) is the primary state agency responsible for the administration of the state's building code framework. Under the Capital Development Board Act (20 ILCS 3105), the CDB is tasked with identifying and publishing local building codes and ensuring that municipalities and counties comply with the requirement to report their adopted codes and amendments to the state.

Resources to Learn More

Select a City in Williamson County

If your project is located within incorporated city limits, you will likely need to follow municipal ordinances rather than county rules. Select your city below to view local regulations.

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