Companies that industrially manufacture wood with improved durability can become NTR-certified if the production takes place in accordance with the quality rules of the NTR documents and is connected to third-party control.
Manufacturers of wood preservatives or wood modification processes can also apply for certification of wood preservatives or wood preservation process and be approved and included on the NWPC list of approved wood preservatives.
In accordance with the NWPC documents, timber producers and manufacturers of wood preservatives or wood protection processes of the following may be admitted as members:
- Pressure impregnation
- Vacuum impregnation
- Supercritical impregnation
- Heat treatment
- Heartwood protection treatment
Current rules are stated in the NTR documents