Fire Resistant Exterior Cedar

After witnessing the devastating destruction in California these past many fire seasons, as well as our own catastrophic fires in the Pacific Northwest, Hewn has allocated an unprecedented amount of resources towards creating new solutions to age-old fire protection problems. These products are designed to meet state and international guidelines on fire protection, without sacrificing the ultimate ideal of having genuine wood siding on nature-adjacent structures.

Hewn is dedicated to developing new California Wildland-Urban Interface (WUI) compliant and Class A fire rated real-wood siding to the market. Hewn’s fire-conscious offerings are the first-of-their-kind in the industry, continuing Hewn’s trend of industry-disrupting innovation to meet the needs of architects, designers, builders, and the public at large.

Class A Exterior Pressure Treated Fire Resistant Siding

Hewn believes that the quest for safer, fire-resistant siding should not result in sub-par products that mimic the look of wood siding. Wood siding has a long history of use in North America, and we aim to continue these generations-old traditions by developing real-wood exterior siding that is designed to meet the ever-increasing need for fire safety in our changing natural landscape.

Our Class A Exterior Pressure Treated Fire Retardant Lumber maintains the visual look and feel of our traditional exterior cedar siding, while implementing an industry-leading fire treatment process that modifies the wood to its core. These products resist the spread of fire, helping your project meet any major fire codes present in your area, and protecting your property in ways that were previously out of reach on a commercial scale. 

In addition to their fire resistant properties, our treatment process has the added benefit of slowing the aging process of the wood itself, protecting against ultraviolet degradation and extending the lifetime of the material. 

Our fire resistant products are subjected to industry-standard accelerated weathering tests (ASTM D-2898), Flame Spread (ASTM D-84), and are verified by International Code Counsel ESR-1159 and ESL-1021.


Samples of our Class A Fire Resistant Exterior Cedar Siding are available for online purchase. Please allow up to ten business days for production.


Samples of our Fire Resistant Exterior Cedar Siding can be obtaining by contacting our sales team, who can assist you in the sample selection and approval process. Due to excessive demand, sample shipments may be delayed 2-4 weeks at the current moment.


Wood Species

Western Red Cedar


Select Tight Knot

Standard Thickness


Standard Widths (Nominal)

1×4, 1×6, 1×8, 1×10, 1×12

Milling Profile

Tongue & Groove or Shiplap (Multiple Options)

Moisture Content

Kiln Dried – Average 10-14%

Fire Resistance

Hewn Thermex-FR®

Process Type

Vacuum-Impregnated Treatment

Class Rating

Class A (ASTM E84)

Possible LEED Credits

MR 5 – Regional Materials

Flame Spread Index

25 (or less)

V.O.C. Content

< 550 g/L

Smoke Developed Index

45 (or less)

Testing Lab

QAI Laboratories

Report Number

IAS Report No. AA-635

Treatment Notes

ICC ES Report ESR-1159 ESL 1021. Tested per ASTM E84 / UL 723. Extended for 30 min, no increase in listed classification subjected to standard rain test (ASTM D2898). KDAT.

Milling Profiles

Hewn’s Class A Exterior Pressure Treated Fire Retardant Lumber is available in a variety of milling profiles, designed to fit the individual needs of your project. Our most common milling profiles, shown below, assume our standard thickness of 13/16”.

Our fire resistant lumber is milled to your requested specifications in-house, allowing for the highest level of oversight throughout the entire production process.

T&G Milling Profiles

T&G 1/16" Fine Line

T&G 1/8" Fine Line

T&G 1/4" Fine Line

Shiplap Profiles

Shiplap 1/16" Fine Line

Shiplap 1/8" Fine Line

Shiplap 1/4" Fine Line

Fostering Local Partnerships

Hewn believes in the power of strong local economies. Our Class A Exterior Pressure Treated Fire Retardant Lumber is made in partnership with Chemco Inc, a local company here in the Pacific Northwest with forty years of experience in research and development of wood enhancement technology for fire-resistant products. We combine Chemco’s unmatched fire treatment processes with Hewn’s proprietary color and finishing techniques to create unique wood siding products designed for installation in the toughest of fire-code regions and environments, ensuring our customers a safe and beautiful product without compromise.

Support Documents

Specification Sheets

Installation Guide

Fire Certifications