Hewn’s Class A ignition-resistant cedar siding combines the visual warmth and character of real cedar with a specialized treatment that provides a Class A fire rating under ASTM E84 (with flame spread index of 25 or less). It is created via a vacuum-impregnated process that modifies the wood throughout, enabling compliance with many fire code requirements while retaining natural texture.
Class A Exterior Pressure Treated Ignition Resistant Siding
Hewn believes that the quest for safer, ignition-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 Ignition 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 ignition 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 ignition resistant products are subjected to industry-standard accelerated weathering tests (ASTM D-2898), Flame Spread (ASTM E-84), and are verified by International Code Counsel ESR-1159 and ESL-1021.
Cedar STK Project Gallery
Click below to view projects featuring Hewn’s Cedar STK.
Specifications
Wood Species
Western Red Cedar
Grade
Select Tight Knot
Standard Thickness
13/16″
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)
Flame Spread Index
25 (or less)
V.O.C. Content
< 550 g/L
Smoke Developed Index
45 (or less)
Testing Information
QAI Laboratories
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.
Textures
- Brushed
- Rough ··
- Resawn ··
- Smooth Light Brushed *
- Smooth Brushed *
- Smooth Vertical Brushed *
- Smooth Heavy Brushed *
- Vertical Brushed †
- Double Brushed *
- Circle Sawn *
- Shipwreck ‴
* Custom Option
† Default on Peppercorn, Desert Sand, and Mushroom
‴ Specific to the Shipwreck finish
·· Available on Cinder, Hight Desert, Snow Fence, and Timberline
Natural Wood Variation
Every Cedar STK board has its own character. Natural differences in grain, tone and knot structure create variation within each species and grade. These boards show an example of the range you may see across samples, mock-ups, and full installations.
These boards illustrate the wood’s natural variation before any ignition-resistant treatment.
Visible and Decorative Metals and Stonework with Class A Siding
Class A Exterior Cedar Siding contains naturally occurring tannins, organic acids, and other water-soluble elements. During the initial maturing and weathering period, these elements may be carried by rainwater runoff and can react with certain metals, alkaline stone materials, and other exterior surfaces.
For any metal on, or in contact with, the building facade, we recommend using either a pre-painted baked enamel or stainless steel product. When using copper, anodized, or any other non-coated metal, please coat the surface with a quality protective enamel finish. When possible, apply two coats to help protect the metal from reacting with runoff from the Class A product.
Decorative stonework should also be considered when it is located below Class A Siding. This is especially important when runoff from the siding can sit on the stone rather than drain away. Limestone, marble, and travertine are particularly sensitive because they contain alkaline properties, which can react with acids.
Considerations should be made when storing any Class A material on decorative stonework surfaces during installation. We recommend a simple waterproof barrier between any stored material and the stonework. After installation, during the first wet season while the cedar is initially maturing, make sure runoff from the siding does not collect on alkaline stone, decorative metals, or in bodies of water. Once the material has matured and weathered, the risk of reaction is reduced.
Materials to Consider
Metals
- Windows
- Gutters
- Downspouts
- Flashing
- Valleys
- Fixtures
Stonework
- Limestone
- Marble
- Travertine
* These materials are most likely to be affected when they are located below Class A Exterior Cedar Siding and runoff from the siding is allowed to sit on the surface. If runoff drains away properly, the risk of reaction is reduced.
All Cedar Siding must be installed using only stainless steel fasteners.
For any questions or concerns about using decorative metals or stonework with our Class A Siding, email us at info@hewn.com.
Standard Milling Profiles
Hewn’s Class A Ignition Resistant Exterior Cedar Siding is available in a variety of milling profiles, designed to fit the individual needs of your project. Our most common milling profiles, listed on this page, assume our standard thickness of 13/16”.
Our Class A Ignition Resistant Exterior Cedar Siding is milled to your requested specifications in-house, allowing for the highest level of oversight throughout the entire production process.
Board-to-Board
T&G Milling Profiles
Hewn’s Class A Ignition Resistant Exterior Cedar Siding is sold in widths of 1×4, 1×6, 1×8, 1×10, and 1×12. T&G 1×4 and 1×6 profiles come standard with a ¼” tongue. T&G 1×8, 1×10, and 1×12 T&G profiles require a ⅜” tongue, instead of a ¼” tongue. Profiles for our most common widths (1×6 and 1×8) are shown below. For more profiles, please refer to our Specification Sheet.
Hewn has the capability to create custom milling knives in-house. For more information on custom milling options, please contact one of our sales representatives.
1x6 T&G Milling Profiles
T&G 1x6 Tight
T&G 1x6 1/16" Fineline
T&G 1x6 1/8" Fineline
T&G 1x6 1/4" Fineline
1x8 T&G Milling Profiles*
T&G 1x8 Tight
T&G 1x8 1/16" Fineline
T&G 1x8 1/8" Fineline
T&G 1x8 1/4" Fineline
* 1×8, 1×10, and 1×12 T&G profiles require a ⅜” tongue, instead of a ¼” tongue.
Shiplap Profiles
Hewn’s Class A Ignition Resistant Exterior Cedar Siding is sold in widths of 1×4, 1×6, 1×8, 1×10, and 1×12. Profiles for our most common widths (1×6 and 1×8) are shown below. For more profiles, please refer to our Specification Sheet.
Hewn has the capability to create custom milling knives in-house. For more information on custom milling options, please contact one of our sales representatives.
1x6 Shiplap Milling Profiles
Shiplap 1x6 Tight
Shiplap 1x6 1/16" Fineline
Shiplap 1x6 1/8" Fineline
Shiplap 1x6 1/4" Fineline
1x8 Shiplap Milling Profiles
Shiplap 1x8 Tight
Shiplap 1x8 1/16" Fineline
Shiplap 1x8 1/8" Fineline
Shiplap 1x8 1/4" Fineline
Exterior Siding Accessory Profiles
Standard Milling Profile Widths
Square Edge
1×4 (3½” face)
1×6 (5½” face)
1×8 (7¼” face)
1×10 (9¼” face)
1×12 (11¼” face)
Tongue & Groove
1×4 (3⅛” face)
1×6 (5″ face)
1×8 (6 ⅝” face)
1×10 (8 ⅝” face)
1×12 (10 ⅝” face)
Shiplap
1×4 (2¾” face)
1×6 (4¾” face)
1×8 (6½” face)
1×10 (8½” face)
1×12 (10½” face)
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.
