- Structural-Commercial Only (to be called for after old roof tear-off)
- Ice Shield (if applicable)
- Final
When it comes to protecting your home, your roof’s fire rating makes a big difference. Roofs are graded as Class A, B, or C—like a report card for fire safety. Class A roofs provide the strongest defense because they are the best at resisting flames and embers. This fire-resistiveness limits a fire’s ability to spread to neighboring properties and surrounding areas.
These ratings aren’t just about the materials you can see; they measure how the entire roof assembly performs during a fire. A roof assembly is like a sandwich made up of roofing, underlayment, and decking materials. This “sandwich” is designed to stand up to fire and wind-blown embers, and the specific combination of materials is tested by rating and certification agencies like Underwriters Laboratories (UL) in real world situations.
When applying to Los Alamos County, customers are required to submit manufacturer specification sheets verifying Class A ratings for ALL roofing materials.
Why do I need a Class A roof assembly?
After facing multiple wildfires over the years, the county adopted an ordinance in 2025 requiring Class A roof assemblies (the highest fire-resistance rating) and tempered glass skylights (Ordinance No. 02-368). These rules aren’t just red tape—they’re designed to give homes a fighting chance in a wildfire. Since Los Alamos is officially classified as an area where neighborhoods meet fire-prone landscapes (Wildland-Urban Interface, or WUI), these protections help reduce risk and keep the community safer.
Understanding the Rating:
Class A is the highest fire-resistant rating given by testing and certification agencies like UL. This indicates the roof assembly can resist serious fire exposure without igniting, cracking, or warping. It meets the requirements for resisting flame spread and preventing fire penetration into the structure.
For Pitched Roofs:
Shingle and metal roof assemblies and the underlayment material(s) are required to be tested in accordance with ASTM E108/UL790 to achieve a Class A fire resistance rating. The Los Alamos County Building Division requires manufacturer specifications sheets showing materials have been tested to meet a Class A rating be submitted as part of the application.
For Low Slope (Flat) Roofs:
Minimum of quarter in. per foot slope required for Los Alamos County Thermoplastic Polyolefin (TPO) or modified bitumen membranes are required to be tested in accordance with ASTM E108/UL790 and achieve a Class A fire resistance rating. These assemblies are designed by the manufacturer(s) and tested by the Underwriters Laboratory (UL) and bear a UL certification stating Class A. Los Alamos County Building Division requires manufacturer specifications sheets showing materials have been tested to meet a Class A rating be submitted as part of the application.
Questions? Need examples of assemblies or cut sheets? Contact us.
building@lacnm.us
505-662-8120