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Redefining Natural Timber Performance for Modern Architecture.
Why Thermally Modified Timber Matters Now?
New Zealand faces the challenge of building more homes and commercial spaces while reducing environmental impact. Thermally Modified Timber (TMT) offers a natural timber solution that enhances stability and performance through heat and steam - without added chemicals. With over 125 years of experience as a New Zealand-owned timber manufacturer and supplier, JSC supports architects, builders, and homeowners in confidently adopting TMT across projects.
The Natural Process that Transforms Timber.
What is Thermally Modified Timber?
Thermally Modified Timber is produced through a carefully controlled heat-and-steam process that changes the timber’s cell structure, reducing moisture uptake and increasing stability. Unlike traditional preservative treatments, this modification is completely chemical-free, relying only on heat, steam, and time.
Thermal modification provides a sustainable and effective solution for enhancing a timber's properties, ensuring durability and stability in construction projects worldwide.
Phase 1: Heat Treatment
Timber is heated to extreme temperatures in a humidity-controlled environment with restricted oxygen supply to prevent combustion, and water is removed from the timber.
Phase 2: Thermal Modification - Structural Changes
All extractives are removed from the timber. The heating process is applied for a few hours and begins to bake the sugars and tannins in the wood, removing the food source from fungi and insects. The wood darkens and hardens.
Phase 3: Conditioning - Moisture Reintroduction
Temperatures are slowly lowered, and water and steam are reintroduced to stabilise the wood and prevent it from drying out completely. The timber is cooled slowly to minimise stresses on the wood as it cools.
After modification, the timber becomes more dimensionally stable, lighter in weight, and darker in colour, without compromising performance. Over time, if only clear coated, it will develop a soft silver-grey patina, maintaining its natural beauty while performing consistently across environments.
JSC TMT® - Thermally Modified for NZ’s Diverse Environment
Performance in New Zealand Conditions
The JSC TMT® range is exceptionally well-suited to New Zealand’s diverse environments - including harsh cold, windy, and exposed areas as well as hot salt-laden air areas. The process of thermal modification gives the timber greater dimensional stability, meaning less movement as temperature and humidity fluctuate.
While specific results vary depending on the species, profile, and coating system used, thermally modified timbers typically experience significantly less swelling and shrinkage than untreated softwoods under comparable conditions. This increased stability allows architects and builders more flexibility in design, especially when selecting darker coatings, which traditionally place more stress on exterior timber surfaces.
Other performance benefits include:
- Reduced susceptibility to fungi and decay, thanks to the removal of sugars and extractives that fungi feed on.
- Improved coating adhesion and longevity, as the low-moisture surface enhances oil or stain penetration.
- Lower thermal conductivity, helping create more comfortable indoor environments.
- Lighter weight, which makes the timber easier to handle and install without compromising structural integrity.
- JSC TMT® can be incorporated confidently into both residential and commercial builds when used within our CodeMark certified cladding systems.
- JSC can refer specifiers to experienced intumescent coating suppliers where project requirements include Group 1S interiors and Type A/B external wall assemblies.
⚠ Note: JSC does not test, certify, or warrant fire performance. Designers should seek confirmation from a fire engineer or other suitably qualified professionals.
A renewable choice for long-lasting design
Applications for Architects, Builders & Designers
The JSC TMT® range offers architects, builders, and designers remarkable versatility across both residential and commercial projects. Whether the goal is to achieve a natural, textural façade or a refined, contemporary interior, JSC TMT® provides a stable, chemical-free timber solution that performs beautifully across applications.
- Cladding
When used within JSC’s CodeMark certified cladding systems, JSC TMT® offers confidence in both performance and compliance. Suitable for a variety of profiles including VertiClad®, BevelClad®, RustiClad®, and Board & Batten, it delivers proven stability and dimensional consistency. - Screens & Battens
JSC TMT® battens and screens combine function with design freedom. They’re ideal for creating depth, rhythm, and privacy - providing visual interest while allowing for airflow and shade control. These elements perform equally well in exterior façades and interior feature walls. - Interior Panelling & Ceilings
JSC TMT® brings warmth and natural beauty indoors. Its low moisture content ensures reliable performance in interior environments, with the added benefit of being low-VOC and no added chemicals - ideal for health-conscious or sustainability-led builds.
Across all applications, the JSC TMT® range offers true design flexibility - through combinations of profiles, surface finishes (such as Brushed, Bandsawn, or Dressed), and coating options from JSC’s Coda® & JSC Scumble® Wood Oil range, architects and homeowners can achieve an exceptional level of creative expression while maintaining performance integrity
Sustainability
Extending Timber’s Life
Sustainability sits at the core of JSC TMT®. By extending the usable life of timber, the thermal modification process supports a circular approach to construction - keeping carbon locked away for longer and reducing the need for replacement materials.
All JSC TMT® timber is sourced from responsibly managed forests, where long-term renewal and biodiversity are prioritised. Through modification, the timber’s service life is increased, helping to reduce embodied carbon across a building’s lifecycle.
Key sustainability benefits of JSC TMT® include:
- ♻ Renewable resource: Responsibly sourced from sustainably managed forests where growth exceeds harvest rates.
- 🌿 Low-impact modification: Produced using only heat and steam - no added chemicals, preservatives, or added compounds.
- 🌏 Extended service life: Longer-lasting façades and interiors mean fewer replacements and less resource consumption over time.
- 💨 Carbon retention: Timber continues storing carbon for decades within the building structure.
- 🚫 Non-toxic at end of life: Can be reused, recycled, or safely disposed of without environmental harm.
- 🏡 Supports sustainable building standards: Contributes to Green Star, Passive House, and broader low-carbon building principles.
JSC TMT® offers a sustainable pathway for modern construction, combining natural performance, visual warmth, and environmental responsibility in one material.
Expertise that Stands Behind Every Project.
Support & Technical Resources from JSC
JSC provides more than just products - we back projects with technical resources and expertise:
- NZIA-accredited CPD presentations.
- Technical guides, drawings (PDF/DWG), and installation manuals.
- Nationwide support and project-specific advice.
- A legacy of 125 years supplying premium architectural timber solutions.
Build with Confidence
JSC TMT delivers stability, performance, and sustainability for future-focused building in New Zealand. Whether for cladding, battens, or interiors, JSC’s TMT range gives professionals and homeowners the confidence to design and build resilient, beautiful, and responsible projects.
