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Permitting Authorities / Missouri / City of O'Fallon, Missouri - Building Division

Do you need a permit to replace a roof in O'Fallon, MO?

Adopted code

City of O'Fallon, Missouri - Building Division

No, O'Fallon, MO does not require a permit for like-for-like roof replacement (City of O'Fallon, Missouri - Building Division). Currently codified Section 500.340 (Article X, adopting the 2021 IRC via Ord. No. 7133, 9-12-2024), amending IRC R105.2 Work exempt from permit, lists under "Building": item 12, "Reroofing of asphalt shingle roofs" -- exempt from permit. This confirms and supersedes the city's older "Residential Re-Roofing Requirements" guideline (Building Department, dated 5/16/2017, still linked from the current Building and Permits page as of 2026-07-25), which separately states: "Permit Requirement: A permit for re-covering or replacing roofing is not required; however, all work must meet the requirements of the adopted code." No repair-size threshold is stated in either source -- the no-permit policy for asphalt-shingle reroofing applies regardless of repair extent. Non-asphalt-shingle roof coverings (e.g., tile, metal, slate) are not covered by the R105.2 exemption language and may require a permit; check with the Building Department before assuming otherwise.

Roof code checklist: O'Fallon, MO

ItemAnswerCode citeSourceVerified
Permit to replace a roofNoecode360.com2026-07-25
Repair permit thresholdNot published
Layer limit / roof-overNot published
Deck & sheathingNot published
Drip edgeNot published
Ice & water shieldNoR905.2.7ecode360.com2026-07-25
Mid-roof inspectionNot published
Impact-resistant (Class 4) roofingNo17491_Bill_No._7671_Building_Code...2026-07-31
Wind design criteriaPublishedecode360.com2026-07-25
Adopted codePublishedSec. 500.330ecode360.com2026-07-25
Contractor license / registrationYesecode360.com2026-07-25
Sales & use taxPublisheddor.mo.gov2026-07-25

Each row comes from the sourced record on this page; full wording is in the table below. "Not published" means no official source for that item was found when the record was last verified.

Jurisdiction
City of O'Fallon, Missouri
Jurisdiction type
city
Address
100 North Main Street, O'Fallon, MO 63366
Contact
  • url: https://www.ofallon.mo.us/building-permits
  • phone: 636-379-5660
  • email: permits@ofallonmo.gov
Roofing permit required
Not required
Contractor registration required
Required
Registration details
  • license: City of O'Fallon Code Section 605.020 (Business License Required): "All merchants doing business within the City of O'Fallon shall be required to purchase and keep on display at their usual place of business a City of O'Fallon business license." Section 605.010 defines "MERCHANT" as "A person, business or other legal entity doing business within the City of O'Fallon, except those exempted in Section 605.015." Section 605.015's exemptions are limited to specific professions (clergy, Christian Science practitioners, teachers/college professors, lawyers, CPAs, dentists, chiropractors, optometrists, chiropodists, physicians/surgeons; and, only if the person maintains no business office in the City, insurance agents/brokers, veterinarians, architects, professional engineers, land surveyors, auctioneers, real estate brokers/salespersons) -- roofing/general contractors are not among the exempted categories, so a roofing contractor doing business in O'Fallon is a "merchant" required to hold a City business license. This is a general business license, NOT a roofing- or construction-trade-specific license. Fee (Section 605.030): $50/year for up to 5,000 sq ft occupied at the licensed location (2025-2026 and subsequent years), plus $0.03/sq ft beyond that, capped at $1,000/year per location. NOTE: Section R103.90 of the currently adopted 2021 IRC (Article X) separately requires county/state licensing specifically for MECHANICAL, ELECTRICAL, PLUMBING, and DRAINLAYING contractors (via St. Charles County or State of Missouri) -- roofing/general contractors are not named in that trade-licensing section, so no roofing-specific trade license requirement was found; only the general merchant's business license applies.
Permit process note
Currently codified Section 500.340 (Article X, adopting the 2021 IRC via Ord. No. 7133, 9-12-2024), amending IRC R105.2 Work exempt from permit, lists under "Building": item 12, "Reroofing of asphalt shingle roofs" -- exempt from permit. This confirms and supersedes the city's older "Residential Re-Roofing Requirements" guideline (Building Department, dated 5/16/2017, still linked from the current Building and Permits page as of 2026-07-25), which separately states: "Permit Requirement: A permit for re-covering or replacing roofing is not required; however, all work must meet the requirements of the adopted code." No repair-size threshold is stated in either source -- the no-permit policy for asphalt-shingle reroofing applies regardless of repair extent. Non-asphalt-shingle roof coverings (e.g., tile, metal, slate) are not covered by the R105.2 exemption language and may require a permit; check with the Building Department before assuming otherwise.
Adopted code
International Residential Code (IRC), 2021 Edition, including Appendices AE, AF, AG, AH, AI, AJ, AK, and AP, adopted by Section 500.330 (most recently amended by Ord. No. 7133, 9-12-2024). EDITION MISMATCH: the city's own "Residential Re-Roofing Requirements" guideline (dated 5/16/2017, still linked live from the current Building and Permits page) states "Applicable Code: 2015 International Residential Code (IRC) with amendments" -- that document has not been updated to reflect the city's 2021 IRC adoption. The 2021 edition, as currently codified by ordinance, is the authoritative one; section numbers and table content here follow the 2021 edition, and the 2017 guide should not be relied on for code-specific detail.
Ice & water shield
Not required — Table R301.2(1) Climatic and Geographic Design Criteria, as currently codified (Article X, 2021 IRC as amended by Ord. No. 7133, 9-12-2024): row "ICE BARRIER UNDERLAYMENT REQUIRED" = "No." This directly corroborates the city's separate 2017 re-roofing guide, which states: "Ice and Water Shield: Ice and water shield (R905.2.7) is not required per Table R301.2(1) as completed and adopted by the City." Confirmed from the current (2021 IRC) table itself, not just the older guide. About ice & water barrier
Impact-resistant roofing
Not required — Read Bill No. 7671.1 (enacted as Ordinance No. 7133, adopted 9-12-2024), "An Ordinance Amending Chapter 500 of the City of O'Fallon City Code and Adopting the 2021 Edition of the International Building Code... International Residential Code..." Section 500.330 (Adoption of International Residential Code) adopts the 2021 IRC, including Appendices AE, AF, AG, AH, AI, AJ, AK, and AP. Section 500.340 (Additions, Insertions and Changes) is the full local amendment list, running Chapter 1 (Administration) through the AE-series appendices. Within IRC Chapter 9 (Roof Assemblies), only one item is amended: Section 905, R905.2.8.2 Valleys, which sets the permitted valley-lining materials. No other Chapter 9 section, including R902 Roof Classification or R908 Reroofing, is added, deleted, or amended; it stands adopted as base 2021 IRC text. No UL 2218, Class 4, or impact-resistance provision appears anywhere in Section 500.340. The city's separate "Residential Re-Roofing Requirements" guideline (Building Department handout dated 5/16/2017, still linked from the city's Building Permits page) likewise contains no impact-resistance provision in its 16 numbered items, though that handout cites the 2015 IRC and has not been updated to the city's 2021 IRC adoption.
Wind design criteria
115 mph wind speed, topographic effects No, special wind region No, windborne debris zone No, Seismic Design Category C (Table R301.2(1) Climatic and Geographic Design Criteria, currently codified Article X, 2021 IRC as amended by Ord. No. 7133, 9-12-2024): "Speed (mph) 115 MPH. Topographic effects: No. Special wind region: No. Windborne debris zone: No. SDC: C."
Sales & use tax
Base combined sales tax rate for O'Fallon, Missouri (St. Charles County) is 7.9500% (Missouri DOR jurisdiction code 54074-183-000), per the DOR's statewide Sales/Use Tax Rate Table for July/August/September 2026 (updated 5/22/2026). Numerous stacked CIDs and TDDs push the combined rate higher on specific parcels: e.g. Belleau CID (54074-183-001), O'Fallon Retail Walk CID (54074-183-009), South Ridge CID (54074-183-010), and White Magnolia CID (54074-183-012) each raise it to 8.9500%; the most heavily stacked parcel found, Mexico Road TDD + 1421 Mexico Road CID (54074-183-013), reaches 9.9500%. Missouri's own Contractors Tax Matrix (DOR Audit Services, Industry Guidance, eff. 10-24-2022, https://dor.mo.gov/taxation/business/documents/Contractors_000.pdf) treats a roofing contractor as the final consumer of materials incorporated into real property: "Contractor sales of tangible personal property where title passed to the customer after installation" is listed Exempt, while "Tangible personal property to be sold as an attachment to real property" is listed Taxable -- meaning the contractor owes sales/use tax on shingles, underlayment, etc. at the point of purchase from the supplier, and does not separately charge the homeowner sales tax on the installed roof or on labor. The DOR's own Sales/Use Tax page (https://dor.mo.gov/taxation/business/tax-types/sales-use/) describes local use tax as a self-reported obligation, not a sum collected at the permit counter (and O'Fallon does not require a permit for asphalt-shingle re-roofing in any case).

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Related guides

Hail-Belt Rules by State Denver-Metro Roofing Permits Filing a Hail Insurance Claim Colorado Hail Season Prep Hiring a Contractor

The permitting authority for the City of O'Fallon, Missouri (St. Charles County). NOTE: this is O'Fallon, MISSOURI, distinct from the similarly-named and similarly-sized O'Fallon, Illinois (St. Clair County) ~20 miles east. The Building Division, within Community Development, publishes residential re-roofing guidance stating ordinary asphalt-shingle re-covering/replacement does not require a permit, though all work must meet the adopted code.

Hail reports near O'Fallon, MO

Reports, last 24 months
52
Largest, last 24 months
2.50 in May 16, 2025
Most recent
Sep 17, 2026 1.00 in
Reports, last 5 years
59
5 most recent reports, last 5 years
DateHail sizeDistance
Sep 17, 20261.00 in4 mi NNW
Apr 27, 20261.25 in2 mi NE
Apr 27, 20261.25 in3 mi ENE
Apr 27, 20261.25 in2 mi NNE
Apr 27, 20261.00 in8 mi ESE

Source: NOAA Storm Prediction Center severe weather database and daily storm reports (reports since the start of the current year are preliminary), within 10 miles of O'Fallon, MO (Census point). Data through Oct 7, 2026, not updated since. A report is an observation, not a damage record.

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Sources

Roofing questions: O'Fallon, MO

Do you need a permit to replace a roof in O'Fallon, MO?

No, O'Fallon, MO does not require a permit to replace a roof.

Is ice & water shield required in O'Fallon, MO?

No. Table R301.2(1) Climatic and Geographic Design Criteria, as currently codified (Article X, 2021 IRC as amended by Ord. No. 7133, 9-12-2024): row "ICE BARRIER UNDERLAYMENT REQUIRED" = "No." This directly corroborates the city's separate 2017 re-roofing guide, which states: "Ice and Water Shield: Ice and water shield (R905.2.7) is not required per Table R301.2(1) as completed and adopted by the City." Confirmed from the current (2021 IRC) table itself, not just the older guide.

Do roofing contractors need a license or registration in O'Fallon, MO?

Yes. City of O'Fallon Code Section 605.020 (Business License Required): "All merchants doing business within the City of O'Fallon shall be required to purchase and keep on display at their usual place of business a City of O'Fallon business license." Section 605.010 defines "MERCHANT" as "A person, business or other legal entity doing business within the City of O'Fallon, except those exempted in Section 605.015." Section 605.015's exemptions are limited to specific professions (clergy, Christian Science practitioners, teachers/college professors, lawyers, CPAs, dentists, chiropractors, optometrists, chiropodists, physicians/surgeons; and, only if the person maintains no business office in the City, insurance agents/brokers, veterinarians, architects, professional engineers, land surveyors, auctioneers, real estate brokers/salespersons) -- roofing/general contractors are not among the exempted categories, so a roofing contractor doing business in O'Fallon is a "merchant" required to hold a City business license. This is a general business license, NOT a roofing- or construction-trade-specific license. Fee (Section 605.030): $50/year for up to 5,000 sq ft occupied at the licensed location (2025-2026 and subsequent years), plus $0.03/sq ft beyond that, capped at $1,000/year per location. NOTE: Section R103.90 of the currently adopted 2021 IRC (Article X) separately requires county/state licensing specifically for MECHANICAL, ELECTRICAL, PLUMBING, and DRAINLAYING contractors (via St. Charles County or State of Missouri) -- roofing/general contractors are not named in that trade-licensing section, so no roofing-specific trade license requirement was found; only the general merchant's business license applies.

What building code does O'Fallon, MO use?

International Residential Code (IRC), 2021 Edition, including Appendices AE, AF, AG, AH, AI, AJ, AK, and AP, adopted by Section 500.330 (most recently amended by Ord. No. 7133, 9-12-2024). EDITION MISMATCH: the city's own "Residential Re-Roofing Requirements" guideline (dated 5/16/2017, still linked live from the current Building and Permits page) states "Applicable Code: 2015 International Residential Code (IRC) with amendments" -- that document has not been updated to reflect the city's 2021 IRC adoption. The 2021 edition, as currently codified by ordinance, is the authoritative one; section numbers and table content here follow the 2021 edition, and the 2017 guide should not be relied on for code-specific detail.