Roofing Building Codes: What the IRC Requires When You Re-Roof

The International Residential Code (IRC) sets the model rules for residential roofs, but the version that binds your re-roof is the edition your state or city adopted plus whatever it changed. For an asphalt shingle re-roof, the items to check are tear-off layers, minimum slope and low-slope underlayment, the ice barrier, drip edge, flashing, chimney crickets and the shingles’ wind classification.

The same item can have different answers two states apart. Drip edge is the standard example: one city’s re-roof policy requires it on every eave and gable, while another state’s amended code drops the mandate unless the shingle maker requires it.

The IRC Is a Model: Find the Edition Your City Adopted

The IRC is written by the International Code Council as a model. It has no force until a state or city adopts it, and adopting governments choose an edition and amend it.

Three local documents show how that works in practice:

• Seattle publishes the 2021 Seattle Residential Code, Chapter 9: Roof Assemblies, the 2021 IRC with Seattle and Washington amendments.
• Bloomington, Minnesota’s Reroofing information sheet applies the 2020 Minnesota Residential Code, which is based on the 2018 IRC.
• Lincoln, Nebraska’s Re-Roof Policy is based on the 2018 IRC.

That is two editions across three cities, with at least two different sets of state or local amendments. Section numbers can also shift between editions, so a section cited in one city’s handout may carry a different number in another’s.

Ask your building department three questions: which IRC edition it enforces, which state and local amendments apply to roofs, and whether it publishes a re-roof handout. Whether the job needs a permit is a separate question, covered in when a re-roof needs a permit and who applies.

The Re-Roof Code Checklist

The table below lists the provisions that come up on an asphalt shingle re-roof. The wording comes from local governments’ adopted codes and handouts, because those are the documents that bind; your edition may word or number them differently.

Three of these items have their own pages. Whether a new roof may go over the old one, and the recover conditions beyond the layer count, are explained in when an overlay is allowed instead of a tear-off. Where the code calls for an ice barrier and where it helps anyway is in ice and water shield. When a chimney needs a cricket and how it is flashed is in chimney crickets.

The code ties the required shingle classification to the design wind speed for your location, so ask the department for that speed and check that the shingle’s packaging or product data shows a class that meets it.

Where State and Local Amendments Change the Answer

Drip edge shows how far amendments can move a requirement. Lincoln’s policy states that “Drip edge flashing is required on all eaves and gables.” Bloomington’s sheet, applying Minnesota’s amended code, says drip edge “Is not required by the MN Residential Building Code unless required by shingle manufacture.” A shingle maker’s instructions can still require it where the code does not, which is why the manufacturer’s installation sheet belongs in your quote file. What drip edge does is covered in the drip edge guide.

Florida shows a different kind of amendment: one that changes how much of the roof must meet current code. Section 553.844(5) of the 2026 Florida Statutes provides that if an existing roof was built, repaired or replaced under the 2007 Florida Building Code or later, and 25 percent or more of it is repaired, replaced or recovered, only the repaired, replaced or recovered portion must be built to current code. The statute also bars local governments from amending that exception by ordinance.

Read the Florida rule carefully. It turns on the roof’s code history, not just its age, so a roof that was not built, repaired or replaced under the 2007 code or a later edition is outside the exception. If you are in Florida, ask the department or your contractor which code the existing roof was permitted under.

Other states and cities have their own amendments. The only reliable list is the one your building department enforces.

State Energy Codes Can Add Roof Requirements

Energy codes can reach a re-roof even though they are not part of the IRC’s roofing chapter. California is the clearest case. The Cool Roof Rating Council’s California Title 24 summary covers the 2025 Energy Code, effective January 1, 2026, and states that “Any roofing product used for compliance must be rated by the CRRC.”

For alterations, CRRC summarizes the steep-slope minimums this way: “Steep-sloped roofs shall have a minimum aged SR of 0.20 and minimum TE of 0.75.” SR is solar reflectance and TE is thermal emittance. Those minimums are conditional. CRRC’s chart of the 2025 requirements applies the single-family steep-slope values only in Climate Zones 4 and 8 through 15, sets separate low-slope values, accepts equivalents such as R-38 ceiling insulation or a qualifying radiant barrier, and exempts roofs weighing at least 25 pounds per square foot; the cool roofs guide walks through each condition. Confirm with your building department whether your re-roof triggers the requirement, and which condition applies, before you choose a color.

Outside California, ask the department whether the state energy code applies to roof replacements and, if so, what it requires.

Exhaust Problems a Re-Roof Can Expose

One code item tends to surface only once the old roof is off. Tear-off opens the roof deck, and with it a view of what vents through the attic. One possible find is a bathroom or kitchen fan duct that ends in the attic or blows toward a soffit vent.

Codes based on the IRC send that air outside. Ohio’s residential code, an IRC-based text published as Ohio Admin. Code 4101:8-15-01, states: “Air shall not be exhausted into an attic, soffit, ridge vent or crawl space.” Seattle’s 2015 residential code carries the same outdoor-discharge rule under a different section number, so ask for the section in your edition rather than relying on a number from another city.

Warm, wet air dumped into a cold attic condenses on the underside of the deck, and a new roof does not stop it. If the crew finds a fan venting into the attic, ask for a price to run it to a roof or wall cap while the roof is open, and list it in the quote like any other code item; how attic-vented fans damage the deck and how the duct is rerouted covers the fix.

Which Code Items Should Your Quote List?

Use this rule: every item in the checklist should appear in your quote either as included work or as ruled out with a reason. “Drip edge: not required by our code and not required by the shingle maker” is an answer. Silence is not.

Before you compare quotes, call the building department and confirm the edition and amendments. Then check each quote for:

1. The number of existing layers and a full tear-off where the code requires it.
2. Underlayment type, and a double layer on any section between 2:12 and 4:12.
3. Ice barrier extent, measured from the eave to the point inside the exterior wall line your code sets.
4. Drip edge at eaves and rakes, or the reason it is omitted.
5. Flashing at walls, chimneys and openings: replaced or reused, and a diverter where an eave meets a wall.
6. A cricket on any chimney that meets your code’s width trigger.
7. Exhaust ducts ending outdoors.
8. The shingle’s wind classification against your local design wind speed.
9. Energy code compliance, where your state requires it.

Write the edition and amendments the department confirms at the top of your quote comparison, and check each bid against them before you sign. The code items then slot into the stages of a re-roof, from tear-off to final inspection.

This guide is general information for U.S. homeowners, not legal, insurance, tax, or engineering advice. Codes, laws, and policy terms vary by location and change over time; confirm details with your local building department, your insurer, or a licensed professional.

Sources

• 2021 Seattle Residential Code, Chapter 9: Roof Assemblies, City of Seattle, Seattle Department of Construction and Inspections
• Reroofing (information sheet), City of Bloomington, Minnesota
• Re-Roof Policy, City of Lincoln, Nebraska, Building and Safety
• 2026 Florida Statutes, s. 553.844 Windstorm loss mitigation; requirements for roofs and opening protection, The Florida Senate
• Ohio Admin. Code 4101:8-15-01 Exhaust systems, Ohio Board of Building Standards (text via Cornell LII)
• California Title 24, Cool Roof Rating Council