Reading Specifications for Thermally Modified Wood Before Placing an Order

Understanding Dimensions and Profiles

Thermally modified wood is available in various dimensions and profiles, each designed for specific applications and aesthetic outcomes. Dimensions typically refer to the thickness, width, and length of the boards. Profiles describe the shape of the board's edges, such as tongue-and-groove, shiplap, or square-edge.

For example, a common profile for exterior siding might be a shiplap board, which creates an overlapping joint that helps shed water. Interior applications might favor a tongue-and-groove profile for a seamless appearance. The specific dimensions (e.g., 1x6 inch, 1x8 inch nominal sizes) will influence the overall scale and proportion of your design. Always check the actual finished dimensions, as nominal sizes can differ from the true measurements.

Considering the NORX brand, their thermally modified wood is offered in various siding profiles. The 'Square Edge' profile provides a contemporary, minimalist look suitable for vertical or horizontal applications. The 'Shiplap' profile, with its characteristic overlap, creates distinct shadow lines and is often used for exterior cladding. Another option is the 'Rain Screen' profile, specifically designed to promote airflow behind the siding, which is important for moisture management in certain wall assemblies. Each profile has specific installation requirements and achieves a different visual effect. Maximo Accoya, another thermally modified product, also offers a range of profiles and dimensions, often tailored for decking and siding applications.

Approved Applications and Limitations

Thermally modified wood is known for its enhanced stability and durability, making it suitable for a range of applications. However, it is essential to review the manufacturer's approved uses and any stated limitations for the specific product you are considering. Not all thermally modified wood products are suitable for every environment or structural purpose.

Typically, thermally modified wood is recommended for exterior siding, soffits, and interior feature walls. Its improved resistance to decay and moisture absorption makes it a good choice for outdoor exposures. However, it is generally not intended for structural load-bearing applications unless explicitly stated and engineered for such use. For instance, while it excels as a non-structural cladding, it would not replace a structural beam without specific engineering approval and product certification.

Some products may have limitations regarding direct ground contact, exposure to standing water, or specific fire ratings. For example, while thermally modified wood performs well in many outdoor settings, prolonged direct contact with soil or consistent immersion in water might still require additional protection or a different material choice. Always consult the product's technical data sheets to confirm its suitability for your project's environmental conditions and functional requirements.

Moisture Content and Stability

One of the primary benefits of thermal modification is the reduction in wood's hygroscopicity, meaning its tendency to absorb and release moisture. This process significantly improves dimensional stability, reducing swelling, shrinking, and warping compared to untreated wood. However, understanding the specified moisture content range is still important.

Thermally modified wood typically has a very low equilibrium moisture content. This stability is crucial for outdoor applications where temperature and humidity fluctuations are common. It minimizes the risk of movement after installation, contributing to a more durable and aesthetically consistent finish over time. For instance, a facade installed with properly specified thermally modified wood is less likely to show gaps or buckling due to seasonal changes.

While more stable, thermally modified wood is still a natural material and will experience some movement, especially in extreme conditions. Always ensure that the product you select is appropriate for the expected moisture and temperature ranges of your project site.

Surface Finish and Appearance

The thermal modification process itself imparts a distinct, darker color to the wood, often described as a rich, caramel hue. This color penetrates throughout the wood, not just on the surface. However, the final appearance can vary based on the original wood species and whether the product is supplied unfinished or with a factory-applied finish.

If left unfinished and exposed to UV radiation and weathering, thermally modified wood will naturally weather to a silvery-gray patina over time, similar to other wood species. If you wish to maintain the original color, a UV-protective finish will be necessary and will require periodic reapplication. The choice of finish, or no finish, should be a conscious decision made during the specification phase, as it impacts long-term maintenance and the aesthetic evolution of the material.

For example, a project aiming for a consistent dark facade might specify a factory-finished product or plan for regular application of a suitable exterior oil. Conversely, a design embracing natural aging might opt for unfinished material, allowing it to weather gracefully.

A Worked Example: Siding for a 20-Foot Feature Wall

Let's consider a hypothetical project: cladding a 20-foot wide by 9-foot high feature wall on a home's exterior using NORX Thermally Modified Wood Siding. The design calls for horizontal shiplap boards with minimal visible fasteners.

First, we confirm the dimensions and profile. We identify 'NORX Thermally Modified Pine Siding, Shiplap Profile' with a finished dimension of 0.75 inches thick by 5.5 inches wide (actual, not nominal). The specific shiplap overlap provides an effective coverage of 5.125 inches per board.

The total area to cover is 20 feet x 9 feet = 180 square feet. To calculate the number of linear feet needed, we divide the total area by the effective width of one board: 180 sq ft / (5.125 inches / 12 inches/foot) = 180 sq ft / 0.427 ft = approximately 421.5 linear feet.

If the NORX siding is commonly supplied in 8-foot, 12-foot, and 16-foot lengths, we must plan for cuts and waste. For a 20-foot wall, using 12-foot lengths would mean each course requires one 12-foot board and one 8-foot board (20 feet total). For a 9-foot height, we need 9 feet / (5.125 inches / 12 inches/foot) = 9 feet / 0.427 ft = approximately 21.08 courses. We'll round up to 22 courses to be safe and account for top/bottom trim.

So, for 22 courses, we'd need 22 x 12-foot boards and 22 x 8-foot boards. This totals (22 x 12) + (22 x 8) = 264 + 176 = 440 linear feet. This is slightly more than the area-based calculation, accounting for cuts and full board purchases. We should also add a waste factor, typically 5-10%, depending on the complexity of cuts and installer experience. For this project, a 5% waste factor would add 440 * 0.05 = 22 linear feet, bringing the total to 462 linear feet. This example highlights how actual board lengths and effective coverage impact the final quantity.

Finally, we'd confirm the fastening system specified for the shiplap profile to ensure it aligns with the 'minimal visible fasteners' requirement, often achieved with blind fastening or specific clip systems recommended for thermally modified wood.

Before you order

• Confirm actual finished dimensions versus nominal sizes.
• Verify the specific profile (e.g., shiplap, tongue-and-groove, square edge) matches your design intent and installation method.
• Check manufacturer's approved applications for the product (e.g., exterior siding, interior wall, soffit).
• Identify any limitations or conditions of use (e.g., ground contact, structural limits, specific climate suitability).
• Understand the expected moisture content range for dimensional stability.
• Decide on the desired long-term appearance: natural weathering to gray or maintaining original color with a finish.
• Confirm compatible fasteners and installation methods for the chosen profile.
• Calculate linear footage needed based on effective coverage and account for waste and available board lengths.

Confirm installation details, approved uses and warranty terms in the current instructions for the exact product and profile. Your installer should verify the substrate, structure and applicable project requirements.

Questions to help you decide

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