Does wood need
The answer to this question depends on:
1. a component's intended application and bio-deterioration risk as defined in British Standard Use Classes;
2. the consequences of premature failure and;
3. the natural durability of the wood to be used.
All you need to know about wood preservation can be found in the WPA Manual now free to download: WPA Manual: Industrial Wood Preservation
The level of protection conferred by a wood preservative depends on its method of application. Brush, dip or spray applied products will afford a degree of protection but for extended service lives of 15, 30 or 60 years typically only wood pre-treated by an industrial penetrating process can give the required level of protection for the life of the component.