The requirements for wood preservatives differ depending on the hazards the supporting wood components are exposed to::
Hazard Class O
Wood in interior use, which is constantly dry, is not exposed to hazards.
It does not have to be impregnated with a wood preservative.
Hazard Class 1
Under certain circumstances wood in interior use has a certain risk of being exposed to insects. In this case, it is necessary to treat the wood with a wood preservative that has the test mark Iv.
Hazard Class 2
Wood that is not in ground contact nor is directly exposed to weather influences or leaching (temporary wetting is possible) has to be treated with a wood preservative that has the test marks P and Iv.
Hazard Class 3
Wood that is not in ground contact, but is exposed to weather influences or condensation has to be treated with a wood preservative with the test marks P, Iv, and W.
Hazard Class 4
Wood that is in constant ground contact or permanently exposed to wetting has to be impregnated with a wood preservative with the test marks P, Iv, W, and E.
For wood in hazard class 4, sufficient protection can only be achieved using vacuum pressure impregnation.
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