Replacing Siding in Austin’s Wildfire (WUI) Code Area: What the Code Actually Requires
Austin Uses Proximity Zones, Not Classes
The City of Austin adopted the 2024 International Wildland-Urban Interface Code (IWUIC) with local amendments in Ordinance No. 20250410-041, effective for work starting on or after July 10, 2025. The model code sorts homes into Class 1, 2 and 3 "ignition-resistant construction" using a hazard table. Austin deleted that table and those class definitions. In their place, the ordinance assigns every structure in the WUI area to a Proximity Zone based on its distance from the wildland:
- Zone A: structures "50 feet or closer to 40 acres of wildland."
- Zone B: structures more than 50 feet and up to 150 feet from 40 acres of wildland.
- Zone C: structures more than 150 feet and up to 0.5 miles from 40 acres of wildland, or up to 1.5 miles from 750 acres of wildland.
The ordinance measures that distance "from the structure to the actual wildland, regardless of the location of the property line," and where a lot falls in more than one zone, "the most restrictive Proximity Zone shall be used for the entire structure." Zones A, B and C use the model code's sections 504, 505 and 506, and the exterior wall sections in them were not rewritten by the City.
What Zones A and B Require for Exterior Walls
The ordinance lists every IWUIC section Austin deleted or amended. Sections 504.5 and 505.5, the exterior wall sections, are on neither list, so the 2024 IWUIC text applies as published. For Zone A (504.5), exterior walls "shall be constructed with one of the following methods":
- Materials approved for not less than 1-hour fire-resistance-rated construction on the exterior side.
- Approved noncombustible materials.
- Heavy timber or log wall construction.
- Fire-retardant-treated wood on the exterior side, labeled for exterior use.
- Ignition-resistant materials complying with Section 503.2 on the exterior side.
The code adds: "Such material shall extend from the top of the foundation to the underside of the roof sheathing." Zone B (505.5) lists the same five methods with the same foundation-to-roof-sheathing rule. Zone A has one more wall requirement, 504.5.1: "A minimum of 6 inches (152 mm) of metal flashing or noncombustible material applied vertically on the exterior of the wall shall be installed at the ground, decking and roof intersections."
What counts as ignition-resistant is set by Section 503.2. A material qualifies if it is noncombustible (the IWUIC definition treats a material conforming to ASTM E136 as noncombustible), fire-retardant-treated wood, or a material tested on both faces to the extended 30-minute ASTM E84 or UL 723 test, or to ASTM E2768. Austin added an exception: in Zones B and C, a Class A rated exterior material tested to the standard 10-minute ASTM E84 test is allowed. The City's own summary puts it simply: Zone A is "30-minute test" and Zones B and C allow a "reduced 10-minute test."
Zone C and the Rest of the House
Austin's Zone C section covers the roof assembly, eaves, fascia, vents, gutters, decks and other appendages, fences, skylights and detached structures. It does not contain an exterior wall section, and the City's Zone C summary lists no exterior wall line, while its Zone A and B summaries do. If your home is in Zone C, the siding itself is not covered by a wall requirement in the text we read, but much of what surrounds it is.
In all three zones, the ordinance requires ignition-resistant fasciae, built from 3/4-inch solid ignition-resistant material, or a 1-hour assembly or 2x lumber protected on the exterior by ignition-resistant material. Gutters and downspouts must be noncombustible with a means to keep leaves out. The City's construction guide gives a simple option that works in every zone: "Fascia: Use fiber cement, stucco, or metal. Back up fascia with continuous 2x lumber." Re-siding jobs often include trim, soffit and fascia, so this is where Zone C projects meet the wildfire code. Our page on soffit and fascia repair explains what that work involves, and gutter installation covers gutter options.
When a Siding Replacement Has to Meet the Code
The City's FAQ is clear that existing homes are not forced to upgrade: "Existing buildings do not need to be changed," except when a code official decides they are a serious safety hazard. Replacing siding is different, because it is new work on the house.
- Alterations must meet new-construction rules. Austin's Section 101.5 allows alterations "without requiring the unaltered portion of the existing building or structure to comply," provided "the entire addition or alteration to the existing structure conforms to that required for a new building or structure."
- No permit does not mean no code. The City states: "Even if a permit is not needed, the work still must follow WUI Code requirements." Its WUI page adds that compliance covers "construction, alteration, movement, repair, maintenance, and use of the structure."
- Roofs have their own 50% rule; siding does not. Austin's Section 507.1 says a roof covering that is replaced, or has 50 percent or more replaced, must be entirely replaced with a covering that meets new-construction rules. We found no matching percentage rule for walls. The rule for siding is the general one above: the part you replace has to comply.
One question the code text does not answer directly is how the City applies the "top of the foundation to the underside of the roof sheathing" language when only one wall or one section is re-sided. If you are replacing part of the siding in Zone A or B, ask the City's WUI staff before you choose materials. The roof-side version of these rules is in our guide to roof replacement permits and the wildfire code.
Which Siding Materials Qualify
Austin Fire publishes a WUI Approved Materials List. The version dated March 31, 2026 says some materials "are already recognized as acceptable and do not require fire test data," and fiber cement is on that list along with metal, masonry, stucco and other cement-based materials. The list also names specific products. It lists James Hardie fiber cement siding, trim and soffit products, including HardiePlank, Hardie Artisan siding, HardiePanel, HardieShingle and HardieTrim, as approved for Zones A, B and C, with the fire rating noted as "Non-Combustible - ASTM E136" and ASTM E84 Class A with 0 flame spread.
The independent evaluation report for these products, ICC-ES ESR-2290, says they "are classified as noncombustible when tested in accordance with ASTM E136." Its IWUIC supplement states that HardiePlank, HardieShingle and Artisan products "comply as noncombustible materials in accordance with 2024 IWUIC Section 503.2.1" and may be used in "construction, alteration, or repair" under the IWUIC. Two limits to know:
- Paint is not the siding. James Hardie states that "fiber cement fire resistance does not extend to applied paints or coatings, which may be damaged or char when exposed to flames."
- What is behind the siding counts. Austin Fire's list notes that "siding installed as a rainscreen requires ignition-resistant material or a 1-hour rated wall assembly behind it," because of the ventilated cavity behind the siding.
Austin Fire warns that products labeled "WUI compliant" "may not meet City of Austin standards," so check the City's list or the test report. Driftwood installs James Hardie fiber cement siding and is a James Hardie Siding Contractor. For pricing, see our James Hardie siding cost guide.
Permits and How to Check Your Address
The City's permit-exempt list includes "siding that does not exceed 128 square feet and is not part of a fire-resistance-rated assembly," and replacing exterior trim, fascia and soffits. A whole-house re-side goes well past 128 square feet, so it needs a permit. For work that goes through WUI plan review, the City asks for the exact products, "manufacturer name, product model or number, and fire test data for each material," and says the installed materials must match the approved plans.
To find your zone, use the City's Interactive WUI Code Map, linked from the Wildland-Urban Interface Code page. The map shows Zones A and B together, and the City says it "cannot replace the process of verifying a site." If the map puts you in Zone A or B, the City says to confirm by measuring to the nearest wildland. The WUI code applies in Austin's full-purpose and limited-purpose areas, not to properties fully in the extraterritorial jurisdiction, and surrounding cities set their own rules.
Questions to ask before you sign a siding contract:
- Which Proximity Zone is the house in, and has someone measured to the wildland?
- Does the exact siding, trim and soffit product appear on Austin Fire's approved list, or is there a test report for it?
- In Zone A, how will the 6-inch noncombustible flashing be handled at the ground, deck and roof lines?
If you are planning siding work in the WUI area, we can check your address against the City map during a free estimate and walk through which rules apply. Start with our siding installation and repair page.
Sources: City of Austin Ordinance No. 20250410-041 (2024 Wildland-Urban Interface Code and local amendments, Sections 101.5, 202.1, 302.4, 503.2.4, 504 to 507); 2024 International Wildland-Urban Interface Code, Chapter 2 definitions and Chapter 5 (Sections 503.2, 504.5, 504.5.1, 505.5); City of Austin Fire Department, Wildland-Urban Interface Code page and FAQs; Austin Fire, 2024 WUIC Approved Materials List (March 31, 2026); City of Austin, Work Exempt from Building Permits; ICC-ES ESR-2290 and IWUIC Supplement (revised May 2026); James Hardie, fire-resistant siding page. Checked October 2026. Codes and lists change, so confirm with the City before starting work.
Frequently Asked Questions
Do I have to replace my siding because my house is in Austin’s WUI area?
No. The City says existing buildings do not need to be changed unless a code official finds a serious safety hazard. The rules apply when you build, alter or repair, including replacing siding.
What does Austin’s wildfire code require for siding in Zone A or B?
Exterior walls must use one of five methods in IWUIC 504.5 or 505.5, such as noncombustible or ignition-resistant materials on the exterior side, from the top of the foundation to the underside of the roof sheathing. Zone A also needs 6 inches of metal or noncombustible flashing at ground, deck and roof intersections.
Does Zone C have siding requirements?
Austin’s Zone C section does not include an exterior wall requirement, and the City’s Zone C summary lists none. Zone C still has rules for fascia, eaves, vents, gutters, decks and fences, which siding projects often touch.
Is James Hardie siding approved for Austin’s WUI zones?
Austin Fire’s WUI Approved Materials List dated March 31, 2026 lists James Hardie siding, trim and soffit products for Zones A, B and C as noncombustible per ASTM E136. ICC-ES ESR-2290 also finds them noncombustible under IWUIC 503.2.1. Painted finishes are not covered by that rating.
Do I need a permit to replace siding in Austin?
Siding up to 128 square feet that is not part of a fire-resistance-rated assembly is on the City’s permit-exempt list. Larger siding jobs need a permit. Either way, work in the WUI area must follow the WUI Code.
