Essentially, timber is treated to add an extra layer of durability, enhancing its suitability for purpose and extending its service life. These treatments permeate wood cells, creating a resistance against decay, pests, weather, fire, or general day to day use. The exact type of treatment will vary according to purpose. For example, timber used for fencing will need a coating to protect against weathering, which will usually be a UC3 or UC4 pressure treatment. Most timber will be treated against boring insects and decay, both of which can substantially reduce its structural integrity.