Forest Management
North American and European hardwood sources; request order-specific certification when required.
THERMOStart your projectBUILDERS FIRSTSOURCE · ISSAQUAHGet a local Maximo consultation
Botanical: Fraxinus excelsior / americana · Maximo Collection
Thermo AshProfile by profile.
Thermo Ash is the dense hardwood option in the Maximo collection. The catalog identifies it as Class 1 durable and suitable for demanding architectural applications, with lower moisture uptake than untreated lumber and no added wood-preservative chemicals in the thermal process.
MAXIMO SPECIESThermo Ash · 5 catalog profiles
Class 1Durability class
1,320Janka hardness
38.5Installed density
20 YearLimited warranty
Moisture Movement
Tangential: 1.4% | Radial: 0.9% · Equilibrium moisture: 5.2% (vs 16.5% for untreated ash)
Thermal Conductivity
λ = 0.12 W/(m·K) · Confirm assembly-level energy calculations with the project designer.
Aesthetic Character
Bold, expressive cathedral grain with deep chocolate-brown caramelized tones throughout the entire cross-section.
Machining, fastening & finishing
Precision fabrication &
long-term surface care.
Thermal modification changes the way wood machines and responds to moisture. Use sharp tools, support the board near the cut and follow the current Maximo fastening and finish guidance for Thermo Ash.
Machining & Fastening Guidelines:
- Sharp, well-maintained tooling with the board fully supported
- Pre-drilling recommended for all fasteners, especially near ends and edges
- Exterior-grade stainless steel fasteners selected for the profile and substrate
- Treat field cuts and exposed end grain according to the finish and installation guidance
Recommended Finish Systems:
- Penetrating exterior wood oils with trans-oxide UV pigments
- Compatible factory-prefinished coating options, subject to confirmation
- Natural weathering to clean architectural silver-gray patina
High-temperature processing reduces volatile resins; inspect and finish for the intended exposure.
Thermal modification changes the wood through its cross-section rather than creating a surface-only stain.
Request order-specific certification when chain-of-custody documentation is required.
Documented product warranty for listed interior and exterior uses.
Available Thermo Ash Profiles
5 Cataloged models in
Thermo Ash.
Choose a profile to review dimensions, intended applications and side-by-side comparisons with Western Red Cedar, Hemlock and Douglas Fir.
1x6 PlusS4S E4E End MatchSiding & Cladding · Ceilings & Soffits · DeckingCompare profile →
5/4x6S4S E4E End MatchSiding & Cladding · Ceilings & Soffits · DeckingCompare profile →
2x4S4S E4EDecking · Trim & MouldingCompare profile →
2x6S4S E4EDecking · Trim & MouldingCompare profile →
1x10S4S E4ETrim & MouldingCompare profile →Applications for Thermo Ash
Plan the material by
architectural application.
APPLICATION GUIDE
Thermo Ash for Siding & Cladding
Profile options, fastening considerations and assembly questions for King County projects.
Open guide →APPLICATION GUIDE
Thermo Ash for Ceilings & Soffits
Profile options, fastening considerations and assembly questions for King County projects.
Open guide →APPLICATION GUIDE
Thermo Ash for Decking
Profile options, fastening considerations and assembly questions for King County projects.
Open guide →APPLICATION GUIDE
Thermo Ash for Trim & Moulding
Profile options, fastening considerations and assembly questions for King County projects.
Open guide →Where to buy in Issaquah
Builders FirstSource Issaquah
Catalog available by consultation. Contact the Issaquah team to confirm availability, sample kits, and lead time for your selected Maximo profile.
Issaquah, WA 98029
(425) 391-8000
Monday–Friday, 7:00 AM–4:00 PMDealer information verified August 31, 2026. No in-stock claim is made on this site.
Request a local quote
Put this profile
on your project.
Tell us what you are building. Our team will review your wood selection and contact you to coordinate a Maximo consultation with Builders FirstSource Issaquah.
Thermo Ash FAQs
Material &
project questions.
Is Thermo Ash considered a hardwood or softwood?+
Thermo Ash is a botanical hardwood. Thermal modification lowers its moisture response and improves documented durability while retaining a dense, pronounced-grain surface.
How does Thermo Ash resist Pacific Northwest rain and rot?+
High-heat steam modification changes moisture-attracting components in the wood and lowers equilibrium moisture content. This improves dimensional stability and biological durability, but the installed assembly still needs correct drainage, ventilation and maintenance.
What happens to Thermo Ash if left uncoated?+
Uncoated Thermo Ash changes from deep brown toward a silver-gray surface under UV and weather exposure. The timing and uniformity vary with orientation, shelter, drainage and maintenance.
Product and installation references
Confirm performance for the exact species and profile using current manufacturer documents.