An overview of how NTR classification works
The NTR system is built around defined wood protection classes that specify durability requirements for different end uses and exposure conditions. These classes form the basis for certification, third-party quality control and the right to use the NTR mark.
NTR classification is not automatic. Each producer must apply for the relevant NTR classes, and only approved classes are included in the scope of certification and third-party control.
The role of NTR classes
NTR classes define:
- the intended use and exposure conditions of the product
- the required level of durability against biological deterioration
- the technical requirements for treatment or modification
- the scope of quality control and audits
Only products produced in accordance with an approved NTR class, and verified through third party control, may be marketed as NTR-certified.
NTR documents and production types
The NTR class system is defined through a set of NTR documents, each covering specific production types and materials. Together, these documents form the technical backbone of the NTR Quality System.
Preservative-treated softwood
Covers Scots pine and other permeable softwoods used in a wide range of construction and infrastructure applications.
Preservative-treated spruce (GRAN)
Covers defined applications for preservative-treated spruce, where specific requirements apply due to material properties and intended use.
Preservative-treated heartwood and special products
Covers products and applications where particular material characteristics require adapted requirements and control principles.
Modified wood
Covers wood products where durability is achieved through modification processes rather than traditional wood preservatives.
Each document defines which NTR classes are available, how they are applied and how compliance is verified.
Application and approval of NTR classes
When joining the NTR system, a producer must:
- apply for specific NTR classes relevant to its products
- demonstrate that production, processes and competence meet the requirements
- include the approved classes in third-party quality control
Only the NTR classes explicitly certified and approved for a production site are valid for marking and marketing. Changes in production type or product scope require a corresponding update of the approved NTR classes.
NTR classes and third-party quality control
All approved NTR classes are subject to independent third-party control carried out by an NWPC-approved control body. The scope of control is directly linked to the applied and approved classes.
This ensures that:
- certification is objective and impartial
- requirements are applied consistently across producers and countries
- trust in the NTR mark is maintained over time
Where to find detailed requirements
Detailed technical requirements, class definitions and control rules are specified in the relevant NTR documents. These documents are the authoritative reference for producers, control bodies and other stakeholders.
Next step
Learn how independent audits and inspections ensure compliance with approved NTR classes.
