Thermo Wood Cladding Guide: Everything You Need to Know

Thermo wood cladding is exterior siding made from wood that has undergone thermal modification — a process that heats the timber to 180–230°C in a controlled, oxygen-free environment using only heat and steam.

This process permanently changes the wood at a cellular level:

• Hemicellulose (the component that attracts moisture) is broken down
• The wood becomes significantly more dimensionally stable
• Decay resistance improves to Class 1–2 (EN 350 standard)
• The color darkens to a rich, warm brown throughout the board
• No chemicals are used at any stage of the process

Thermo wood has gained widespread adoption for several reasons:

• Chemical-free durability: Unlike pressure-treated lumber, thermo wood achieves its decay resistance through heat alone
• Dimensional stability: Reduced moisture absorption means less warping, cupping, and checking
• Consistent quality: Factory-controlled process ensures uniform performance across all boards
• Sustainability: FSC and PEFC certification available. The Ayous species is fast-growing and responsibly harvested
• Design flexibility: Available in multiple profiles (T&G, shiplap, channel, open joint) for diverse architectural styles
• Weight advantage: Thermo Wood Ayous is lighter than most cladding alternatives, reducing structural load and installation effort

Thermo wood cladding comes in several profile options to suit different design approaches:

• Tongue and Groove (T&G): Interlocking boards create a seamless surface. Ideal for a clean, contemporary look.
• Shiplap: Overlapping boards with a subtle shadow line. Classic appearance with excellent weather protection.
• Channel / V-Joint: Similar to T&G but with a visible channel between boards for a defined linear pattern.
• Open Joint: Boards mounted with visible gaps over a dark membrane. Creates a modern, airy facade.

Profile selection depends on the desired aesthetic, building orientation, and local climate conditions.

Thermo wood cladding typically costs $4–$8 per square foot for materials, depending on profile, dimensions, and order volume.

Cost Component	Range per Sq Ft
Thermo wood boards	$4–$8
Battens/furring strips	$0.50–$1.50
Fasteners and clips	$0.50–$1.00
Membrane/housewrap	$0.25–$0.50
Professional installation	$4–$8
Total installed	$9–$19

Proper installation is essential for maximizing the lifespan of thermo wood cladding:

1. Rainscreen principle: Always install over a ventilated cavity (minimum 20mm gap) to allow moisture drainage and air circulation
2. Moisture barrier: Use a breathable housewrap behind the battens
3. Acclimation: Allow boards to acclimate to site conditions for 48–72 hours before installation
4. Fastening: Use stainless steel screws or clips. Pre-drill for face-screwing. Hidden clip systems provide the cleanest appearance.
5. End grain sealing: Seal all cut ends with a wax-based end sealer to prevent moisture ingress
6. Expansion gaps: Leave 2–3mm gaps at board ends and around openings for thermal movement

One of thermo wood cladding's greatest advantages is its low maintenance requirements:

• Unfinished: Left untreated, thermo wood weathers to a consistent silver-gray patina over 6–12 months. This is purely cosmetic — the wood's durability is unaffected.
• Oiled: Apply a UV-protective oil once every 1–2 years to maintain the original warm brown color. Use a pigmented oil for best UV protection.
• Cleaning: Annual wash with mild soap and water. A soft brush or low-pressure wash removes dirt and organic buildup.

Thermo wood does not require sealing, staining, or painting for performance — any finish is purely aesthetic.