April 1, 2026 was not just another date on the calendar for Colorado builders. It was the deadline by which every municipality and county in a designated Wildland-Urban Interface (WUI) zone was required to formally adopt the Colorado Wildfire Resiliency Code (CWRC) as their minimum building standard. For projects permitted after that date, the rules have changed.
If you are pulling permits in mountain Colorado right now and have not verified your material specs against the CWRC, this post is for you.
The Colorado Wildfire Resiliency Code was adopted by the state in 2025, but local jurisdictions had until April 1, 2026 to formally adopt it. As of this spring, that deadline has passed. Any jurisdiction in a WUI zone that has not yet adopted the CWRC is now out of compliance with state law, and most have moved to adopt it ahead of the deadline.
For builders, this means the CWRC is effectively the law of the land across Colorado's mountain corridor — from the Vail Valley and Summit County to Steamboat Springs, Grand County, and the Front Range foothills. Projects in these areas that spec non-compliant materials are at risk of failing inspection, triggering redesigns, or exposing the builder to liability.
The full compliance deadline (when permits must reflect the new code) is July 1, 2026 for jurisdictions that adopted by the April date. That window is closing fast.
The CWRC establishes three fire intensity zones: Low, Moderate, and High. Most of mountain Colorado falls into Moderate or High. In those zones, exterior cladding, decking, soffits, and fascia must meet one of the following standards:
Standard untreated wood siding, cedar decking, and wood fascia are not permitted as primary materials in Moderate or High zones without a qualifying treatment or rated assembly.
We have been answering WUI compliance questions from builders across Colorado for the past several months. The questions we hear most often come down to three things: what qualifies, what still gives the look of natural wood, and how fast can we get it. Here is what we carry that checks all three boxes.
LP SmartSide carries a Class C (Class 3) fire rating. It performs significantly better than untreated natural wood under fire exposure, but it is not non-combustible and can still ignite under sustained flame. That distinction matters in Colorado WUI zones, where most Class 1 and Class 2 jurisdictions require ratings beyond Class 3 on their own.
LP SmartSide is best suited for projects where the Authority Having Jurisdiction (AHJ) accepts its Class 3 rating, or where it is used as part of a compliant assembly. When paired with 5/8" Type-X gypsum as the rated fire barrier, the assembly can achieve a 1-hour fire rating while preserving the wood-look aesthetic. Always verify with your LP rep and the AHJ before speccing LP in a WUI zone.
RMF's prefinished line delivers the look of natural wood in hundreds of color options with the rated assembly delivered intact. Rocky Mountain Finishes is a direct source. We stock it, know the product line inside and out, and can get it to your jobsite with the documentation you need.
✓ Class C (Class 3) fire rating | ✓ Prefinished, ready to install | ⚠ Verify Class 1 / Class 2 zone acceptance with AHJ before speccing
Fiber cement is noncombustible by definition and compliant in all Colorado WUI zones without any additional testing or documentation. Hardie is the most widely specified fiber cement product in Colorado mountain construction and is recognized by virtually every AHJ in the state.
Rocky Mountain Finishes supplies Hardie in lap, panel, and trim profiles, prefinished to the color of your choosing. Lead times are competitive and we maintain strong inventory for Colorado projects.
✓ Compliant in all WUI zones | ✓ Noncombustible | ✓ AHJ-recognized statewide
Allura is a noncombustible fiber cement alternative to Hardie with the same compliance profile and strong availability for Colorado mountain projects. For builders managing tight timelines or looking for competitive pricing on large exterior packages, Allura is worth a conversation.
✓ Compliant in all WUI zones | ✓ Noncombustible | ✓ Competitive lead times
For projects where real wood character is non-negotiable, pressure-treated FRT lumber carries a documented fire-retardant rating that satisfies the CWRC in most Moderate and High zone applications. FRT wood is a good answer for soffits, accent trim, and secondary cladding where fiber cement would feel out of place aesthetically. For higher end homes, FRT wood may be used as the primary cladding system as budget allows.
We stock FRT STK Cedar, and can supply other FRT-rated wood products and provide the documentation you need for inspection. Verify acceptability with the AHJ for each project and zone classification. FRT wood is good for the lifetime of the treatment material.
✓ Real wood look and feel | ✓ Rated treatment | ✓ Documentation available
This is an option that comes up on projects where an architect or owner has specified natural wood and is not willing to change. A fire-rated coating additive is mixed into standard exterior stain or paint and upgrades it to a fire-retardant rating accepted in a number of Colorado counties.
Important caveats: this solution requires reapplication every few years to maintain its rated performance, and AHJ acceptance varies by jurisdiction. It is best used as a finishing or accent option on projects where the primary cladding is already a compliant material. We always recommend verifying with the AHJ before speccing this as a primary WUI solution.
✓ Preserves natural wood appearance | ✓ Accepted in select Colorado jurisdictions | ⚠ Maintenance required
James Hardie fiber cement installed on a Colorado mountain home. Noncombustible and compliant in all WUI zones.
In most Moderate and High WUI zones, untreated natural wood cannot be the primary exterior cladding. However, FRT-treated wood is permitted in most of these zones, and a fire-rated finish additive on natural wood is accepted in select jurisdictions. Natural wood can still appear on interiors, trim, beams, and accent features where it is not the primary weather-exposed cladding of the exterior envelope.
It depends on the jurisdiction. LP SmartSide carries a Class C (Class 3) fire rating, which is better than untreated wood but does not meet the Class 1 or Class 2 thresholds required in most Colorado WUI zones on its own. In jurisdictions where the AHJ accepts its rating, it qualifies. In stricter zones, the compliant path is to install 5/8" Type-X gypsum as the fire-rated wall barrier and use LP or another decorative wood finish over it, achieving a 1-hour fire-rated assembly. Verify with your LP rep and the AHJ on every project before committing to the spec.
Standard cedar or Douglas fir decking does not qualify in Moderate or High WUI zones. Compliant options are ASTM E84 Class A rated composite decking or FRT lumber. This catches builders off guard more than almost any other item. If your project has an exterior deck, get the decking spec right before you permit.
Rocky Mountain Finishes works with builders across the Vail Valley, Summit County, Steamboat Springs, and the I-70 corridor. We know the products that pass WUI inspection in these jurisdictions and we can help you put together documentation for the AHJ when you need it.
If you are working on a project in a WUI zone and want to talk through your material spec before you pull the permit, reach out. It is a much easier conversation before the permit is submitted than after the inspector flags your siding.
Rocky Mountain Finishes supplies LP SmartSide, James Hardie, Allura, FRT wood, and fire-rated finish additives for Colorado mountain projects. We can help you build a compliant spec and get documentation together for the AHJ.
We serve builders across Steamboat Springs, Vail, Summit County, and the I-70 corridor.
Want to know more? Contact Luke Tyler.