Replace 25% or more of your home’s total exterior wall surface, and the code no longer asks you to bring just that section up to standard. It requires the entire exterior wall surface, including attachments, to be replaced with materials meeting new-construction hardening requirements. A project that started as one elevation can become a whole-house project by operation of law.

Most homeowners find this out from a plan reviewer, after they have already signed a contract. This page exists so you find out first.

Not sure whether you’re in the WUI? Call us at (719)-445-7888 and we’ll check your address before you spend a dollar.

First: is your address in the WUI, and in which risk class?

The Wildland Urban Interface is a mapped boundary, not a vibe. Plenty of homes that feel suburban are inside it, and some that back to open space are not. Being near trees does not put you in; being on the map does.

There are really two questions. Appendix K requires that WUI risk areas be recorded on official maps, and it divides them into Class I and Class II risk areas. The classification is assigned by the fire code official based on vegetation fuels, topography, weather patterns and expected fire behavior — broadly, Class I covers lighter surface fuels and shorter expected flame lengths, Class II covers moderate to heavy fuel loads.

That second question drives almost everything downstream. Class II carries the heavier construction and defensible-space requirements, including the exterior wall provisions below. Class I is a lighter regime. Anyone quoting you WUI requirements without first establishing your classification is quoting you a guess.

We check both as part of the free estimate, before we quote materials — and you can look your address up yourself on the City’s official WUI map. The Colorado Springs Fire Department publishes the requirements on its wildfire risk reduction page, and its Wildfire Mitigation office offers free on-site consultations to homeowners.

What triggers Appendix K on a siding job

This is the provision that governs, quoted in full from the current Appendix K:

K101.9 — “The exterior walls of buildings or structures in existence prior to adoption of this Appendix where 25 percent (25%) or more of the total exterior wall surface area is replaced, or where work to reconstruct, alter or repair the exterior walls effectively replaces the exterior wall material, shall require the entirety of the exterior wall surface area, including attachments, to be replaced with materials required for new construction specified for class II structure hardening requirements based on the property’s risk classification and the fuels and site management requirements shall apply to all portions within a 30-foot radius from the perimeter of the scope of work, or to the property line if less, as appropriate to the parcel’s wildland urban interface risk classification.

Exception: Existing exterior walls that are compliant with requirements of the parcel’s wildland urban interface risk classification.”

Four things in there deserve attention.
“25 percent of the total exterior wall surface area.” Not 25% of one wall, and not 25% of your floor area — 25% of the whole envelope. The code text itself publishes no measuring method, but the Fire Department’s current homeowner guidance — its 2026 WUI acknowledgement materials — states the trigger as 25% net or more, meaning window and door openings are subtracted before the percentage is figured. We measure the envelope that way, and still confirm the method with the fire code official on your project rather than assuming it. On some two-story homes a single large elevation gets close on its own.

“Or where work to reconstruct, alter or repair the exterior walls effectively replaces the exterior wall material.” The percentage is not the only trigger. Work that functionally replaces the cladding counts even if the arithmetic lands under 25%.

“The entirety of the exterior wall surface area, including attachments.” Cross the threshold and the obligation is not limited to the area you were replacing. This is the expensive surprise, and it is the reason to measure before you sign.

The Exception matters. Exterior walls already compliant with your parcel’s risk classification are not pulled back in. If part of your home was re-sided to standard at some point, that section may already be satisfied. It is worth establishing before anyone prices a whole envelope.

Note also the last clause of the main paragraph: crossing the threshold pulls in fuels and site management within a 30-foot radius of the scope of work, or to the property line if that is closer. More on that below, because it is the part that costs homeowners money outside the siding contract.

If you have an older estimate, an older permit form, or a contractor quoting you a 50% trigger: that was Ordinance 23-14, in force from June 30, 2023, and it has been replaced. The current requirements apply to exterior work on or after June 30, 2026 — the date both the code text and the Fire Department’s own homeowner materials key to.

What “ignition-resistant” means under the current code

The superseded Appendix K published a list. Fiber cement, stucco, masonry, brick and manufactured stone were approved; natural wood and cedar, hardboard and vinyl were expressly not allowed. The current code took a different approach: it stopped naming products and set a performance test instead.

K106.2.1 — “Material shall be tested on the front and back faces in accordance with the extended ASTM E84 or UL 723 test, for a total test period of 30 minutes, or with the ASTM E2768 test. The materials shall bear identification showing the fire test results. The materials, when tested shall comply with Sections K106.2.2 through K106.2.6. Materials shall have a minimum of a class A rating.”

And for the walls themselves:

K109.2.5 — “Exterior wall coverings of buildings or structures shall be constructed with one of the following methods: 1. Heavy timber or log wall construction as defined by the International Building Code. 2. Ignition-resistant materials complying with Section K106.2.1 on the exterior side. Such material shall extend from the top of the foundation to the underside of the eave or the underside of the roof sheathing.”

(K109.2.5 carries two exceptions worth knowing about: architectural trim and embellishments up to 5% of gross exterior wall square footage, when painted or as otherwise approved; and solid wood rafter tails and blocking of minimum 2-inch nominal dimension.)

Three practical consequences.

The 30-minute extended test is the hard part. A standard ASTM E84 test runs ten minutes. The version this code requires runs thirty, on both faces of the material. Products that pass a conventional flame-spread test do not automatically pass this one, and a Class A result from the standard test is not the same claim.

Documentation is part of the specification. “The materials shall bear identification showing the fire test results” means the product has to carry the paperwork, and that paperwork is what a plan reviewer wants to see. When you compare bids, ask each contractor for the listing showing the extended ASTM E84, UL 723 or ASTM E2768 result for the exact product they intend to install.

The wall covering has to run foundation to eave. Not to the top of the visible field — to the underside of the eave or roof sheathing.

There is also a detail behind the cladding that gets inspected:

K109.2.5.1 — “A minimum of six inches of metal flashing or fire-resistant material applied between the wall sheathing and the exterior cladding. The material shall be installed to span the joint at the intersections of the wall and the foundation, decking, and the roof intersections.”

Three intersections, not one. That is an installation requirement, not a product requirement — it gets built in during the job or it does not get built at all.

Which materials we specify for WUI work

Fiber cement — James Hardie. This is what we install on the large majority of WUI jobs, and it is the line we are authorized for.

One distinction worth being precise about, because it gets blurred in sales conversations. Fiber cement’s well-known ratings — noncombustible under ASTM E136, Class A flame spread under the standard ASTM E84 — are real, and they are not the compliance path K109.2.5 describes. That section recognizes two methods: heavy timber or log construction, or ignition-resistant material meeting K106.2.1. What satisfies a plan reviewer is the fire test identification the product carries under that section. We obtain that documentation for the specific product going on your house and submit it with the review. If a contractor answers the compliance question by reciting “Class A,” they have answered a different question than the one the code asks.

Masonry, brick, manufactured stone and stucco. Named as approved under the prior code and conventional choices for hardened walls. Under the current code they face the same K106.2.1 documentation requirement as anything else. We work alongside masonry trades where a job calls for it.

Heavy timber and log. Explicitly permitted by K109.2.5 as its own method. Relevant to a handful of properties in the mountain parts of our service area.

Vinyl and engineered wood. Be careful here, and be careful with anyone who is not. The current code does not print a prohibited-materials list — it prints the test. Standard vinyl siding, natural cedar and hardboard were all expressly disallowed under the previous Appendix K, and we will not specify them for a WUI job without written confirmation from the fire code official for that specific product and address. If a contractor tells you vinyl is fine inside the WUI, ask for that confirmation in writing before you sign anything.

Defensible space is part of the job — and it is your cost, not ours

This is what catches homeowners hardest, so we would rather say it plainly than let you discover it mid-project.

Crossing the 25% threshold pulls in fuels and site management around the work — and how far it extends is a point we pin down in writing before you sign. The code text keys it to a 30-foot radius from the perimeter of the scope of work (or the property line if closer), while the Fire Department’s current homeowner materials describe fuels management across the full 100-foot structural ignition zone. We confirm the extent the Fire Department will require for your project, so the mitigation scope is a known number rather than a mid-project surprise. The code organizes the work into zones. How much of this applies to you depends on your risk classification — the requirements below are the Class II regime, which is the heavier one. Class I properties have a lighter set, primarily tree pruning plus fencing and retaining wall provisions.

• Immediate Zone, 0–5 feet. Noncombustible, hard-surface materials — rock, gravel, sand, concrete, bare earth, stone or concrete pavers. Vegetation removed, no combustible mulch or woody debris, no new planting. This applies under and immediately around decks. The code does allow exceptions: low-flammability vegetation from an approved list, and existing character trees predating the appendix, maintained with clearance from other combustibles.
• Intermediate Zone, 5–30 feet. Dead plant material removed from live vegetation. Brush patches may remain but separated by at least ten feet of noncombustible material or grass mowed to no more than four inches. No hazardous vegetation within fifteen feet of a structure, measured from the drip line. Dead limbs pruned to a height of up to ten feet or no more than one-third of tree height; branches generally pruned to six to ten feet or a third of total height. Evergreens within fifteen feet of a structure pruned back to that clearance.
• Expanded Zone, 30–100 feet. Trees spaced a minimum of six feet dripline to dripline. This zone exists only in the Class II regime.

Mitigation is the homeowner’s responsibility and the homeowner’s expense. The Fire Department puts that in writing: its 2026 WUI Homeowner Acknowledgement Application — a short form you and a CSFD representative both sign, with scope checkboxes for siding, decking and accessory structures — records that you understand the responsibility. We bring the form to the estimate and walk through it with you, so nothing in it arrives as a surprise. The mitigation itself is not part of a siding contract, we are not licensed to perform tree work, and no honest siding bid includes it.

What we do instead: we identify what will be required before you sign, and before we order material. On WUI addresses we photograph the work area and its surroundings during the estimate and raise the mitigation question with the Fire Department up front, so what an inspector will ask for is a known quantity rather than a surprise that arrives with your walls open. Where tree work is needed we can refer you to arborists who have done mitigation to Fire Department standards.

We also encourage WUI homeowners to request the Fire Department’s free consultation early, and we attend it with you — so everyone hears the same requirements from the same person on the same day.

The reason we are insistent about sequence: once the siding is disturbed, the permit has to be closed. There is no version of this where the work starts and the mitigation gets sorted out later.

The parts of a siding job that pull other things into scope

Decks. Decks added, modified, altered or reconstructed in the WUI have had to comply since June 30, 2023 — a date the current code carries forward unchanged, and which it applies to siding work as well. On surfaces the code is direct: “Wood is not permitted to be used for the decking surface but can be used for all large structural components and railings.” If a crew removes and replaces deck boards to run cladding behind a ledger, that deck is arguably in scope, and rebuilding a deck in composite is not a small line item. Our crews are instructed not to disturb deck boards or standalone railings, and we detail our flashing to keep the separation between our work and your deck unambiguous.

Accessory buildings. Under K109.2.13, detached accessory structures less than 50 feet from a habitable or occupiable building must have exterior walls built to the same K109.2.5 standard — and the Fire Department’s 2026 homeowner materials apply this to accessory buildings constructed or reconstructed on or after January 15, 2013. A shed added in the last decade is not automatically outside the conversation.

Eaves, soffits and attachments. K101.9 attaches the obligation to the wall surface “including attachments,” and K109.2.5 runs the covering to the underside of the eave. Soffit and trim are part of the assembly, not an afterthought.

How the permit actually works

Siding replacement requires a building permit from Pikes Peak Regional Building Department, which lists exterior siding among the work requiring one. Inside the Colorado Springs WUI, fire review can sit in front of it:

K101.7 — “All requirements must be reviewed and approved by the fire code official prior to building department permit issuance and prior to final inspection.

Exception: Class 1 residential projects.”

Read both parts. For work that is not Class 1 residential, fire approval comes before the building permit is issued and is required again before final inspection — the Fire Department gates both ends. Class 1 residential projects are excepted from that review sequence. This is another reason establishing your risk classification early is not a formality: it determines how much process your project carries.

Class II work additionally contemplates a pre-construction fuels inspection, a framing inspection and a final, though those provisions are drafted primarily around new construction and map imperfectly onto a re-side.

CSFD Fire Construction Services handles the construction side at (719) 385-5982 or fireconstructionservices@coloradosprings.gov, and reviews are filed through the City’s Accela Citizen Access portal. We pull the permits, set up and file the submission, meet the inspectors and close the permit. You should not have to learn any of this — but if you are comparing bids, a contractor who has never mentioned fire review has probably never done a WUI job.

Outside Colorado Springs city limits

Appendix K is City of Colorado Springs fire code. It does not apply of its own force in Black Forest, Monument, Palmer Lake, Woodland Park, Cascade or unincorporated El Paso County — and anyone telling you otherwise is guessing.

What applies out there is the Colorado Wildfire Resiliency Code, created under SB 23-166 and adopted by the state Wildfire Resiliency Code Board. It sets minimum WUI construction standards that jurisdictions containing mapped WUI areas are required to adopt and may exceed. The adoption deadline was April 1, 2026 and compliance was required by July 1, 2026, so the state floor is now in force — but how each jurisdiction implements it, and what its local amendments require, still varies district by district. Pikes Peak Regional Building Department issues building permits across most of this area, including Woodland Park, Monument, Palmer Lake, Green Mountain Falls, Manitou Springs, Fountain, Calhan and unincorporated El Paso County.

The practical answer is the same one we give inside the city: we confirm the governing jurisdiction and the current requirement for your address before we specify materials. We have run jobs in Woodland Park, Cascade, Monument, Black Forest and the Springs, and they are not the same job.

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Frequently Asked Questions