In contemporary architecture, material selection plays a critical role in defining the aesthetic and sustainability of a building. While traditional wood was often used in designs that featured roof overhangs to protect exterior walls, modern designs tend to favour exposed surfaces and sleek lines, making materials more vulnerable to weathering. This shift in design preferences has led to the growing use of thermally modified wood (TMW), a material that combines durability, beauty, and sustainability.
Thermally modified wood is a product of an innovative heat treatment process that alters the wood’s structure, enhancing its performance while maintaining its natural aesthetics. This transformation has made TMW a popular choice among architects, where there is increasing pressure to balance striking design with environmental responsibility. As TMW gains traction, it is proving to be an ideal material for architects seeking to create buildings that are not only visually appealing but also environmentally conscious.
Aesthetics and Performance: The Vision Behind TMW
Architect Mari Hunt, renowned for her work with wooden structures, emphasises how thermally modified wood aligns perfectly with her design philosophy. “The material supports that vision beautifully,” she says, highlighting how TMW integrates seamlessly into her designs, reflecting both the natural surroundings and her client’s expectations.
One of her standout projects, the Kaseke micro hotel at Maidla Nature Resort in Estonia, demonstrates the versatility of TMW. From terraces to façades, roof surfaces to interior spaces, the entire structure is clad in thermally modified wood. “I wanted to use the same material throughout the building,” Hunt explains. “TMW was the only choice to achieve the aesthetic of a unified material that feels both durable and soft for visitors.” Hunt’s use of TMW underscores its flexibility and ability to evoke warmth and elegance, features that are often lacking in other materials such as stone, glass, or plastic.
Hunt also chose TMW for an eco-hotel project in Spain. Due to intense sun exposure, the wood naturally weathers over time, turning a distinguished grey that complements the building’s rustic aesthetic. “Thermal pine is the most common thermally modified wood that I work with,” she adds. “It’s ideal for terraces, while for interior spaces like saunas, we use thermally modified deciduous trees.”
Sustainability and Environmental Benefits
While architects like Hunt appreciate TMW’s aesthetic value, manufacturers and suppliers highlight its sustainability benefits. Jason Martell, Project Manager at Thermalwood Canada, notes that architects are increasingly choosing TMW as an environmentally responsible alternative to exotic woods. “Once architects use thermally modified wood in a project, they keep coming back,” Martell says. “They see the positive feedback and results.”
The environmental impact of TMW is notable. Thermalwood Canada uses clean-burning propane to power its kilns, with the wood modification process relying solely on heat and steam. By sourcing almost all of its wood locally from Quebec, the company’s approach supports net-zero emissions projects, which is critical for architects striving to meet sustainable building certifications such as LEED and WELL.
Additionally, TMW’s durability, stability, and long-term resistance to rot, decay, and weathering make it a highly reliable material. The modification process improves the wood’s performance without the need for harmful chemicals, aligning with the growing demand for sustainable materials in the construction industry.
Quality Assurance and Standards
Thermally modified wood must meet high standards to ensure consistency and reliability across various applications. The International ThermoWood Association (ITWA) has established strict guidelines for manufacturers to follow, including a recipe-based approach to treatment that uses specific temperature, time, and steam conditions for each wood species. This process permanently alters the chemical structure of the wood, improving its performance across multiple environmental factors.
“Thermally modified wood has a 25-year warranty on decking and a 60-year warranty on cladding,” explains Martell. “Architects also appreciate its better fire rating compared to rough lumber.” These warranties reflect the material’s durability and its suitability for long-term use in demanding conditions.
Overcoming Challenges and Misconceptions
Despite its growing popularity, TMW faces some misconceptions. Architects often worry about its cost, assuming that it will push a project over budget. “Architects sometimes think it will be over budget,” Martell admits. However, by using species like Canadian Ash, Thermalwood Canada can provide high-quality products at competitive prices, making TMW accessible to a wider range of projects.
Another challenge is ensuring that contractors adhere to specifications. “We often see contractors pivot to lower-grade products to cut costs, despite what was specified,” Martell notes. This is a common issue in the industry, but architects who specify TMW are finding that the material’s long-term benefits far outweigh any initial cost concerns.
The Future of TMW in Architecture
Looking ahead, the future of TMW in North America appears promising. In 2024, consumption of thermally modified wood reached over 850,000 cubic meters, driven by the demand for sustainable construction in the U.S. and Canada. Decking sales alone grew by 22% year-on-year in 2022. Furthermore, a 2023 survey revealed that 32% of North American architects now specify TMW for moisture-prone areas, a significant increase from 18% in 2020.
The rise of TMW reflects a broader trend in the lumber industry, where sustainability, precision, and reliability are becoming essential criteria for architects. As TMW continues to evolve, it will play an increasingly vital role in meeting the growing demands of modern construction, combining performance, aesthetics, and environmental responsibility in one versatile material.
In conclusion, thermally modified wood is reshaping the way architects approach material selection, offering a sustainable, durable, and aesthetically pleasing option for contemporary architecture. As the industry moves towards greener, more responsible building practices, TMW is poised to become a staple in the design and construction of eco-friendly, high-performance buildings.
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