There are examples of the use of timber in historical buildings, many of which may be centuries old, and numerous other applications where wood has been used in exposed situations. However, wood does have enemies and these include fungal decay, woodworm and marine borer, but there are methods that can be used to avoid these hazards.
Fungal attack, or rot and decay, only occurs when there is moisture and oxygen. Keeping timber dry, therefore, avoids this type of damage. Therefore, the use of timber in interior applications, where the moisture content of the atmosphere will be less than 20%, means that decay will not occur.
Wood, once dried from its original green state, will adapt to the moisture content of the atmosphere. Where the atmosphere is damper than the timber it will generally swell and, where dryer, it will tend to shrink, depending on the stability of the chosen species.
Wood which is exposed to damp and rain can be given extra protection with wood preservatives, water repellent preservative systems, or a protective film of paint or varnish. These need to be applied and maintained to ensure that all surfaces are completely sealed, aiming to avoid the trapping of excessive water below them. Timber used in architectural joinery is kiln dried to reduce the moisture content prior to the application of finishes.
Some of the more durable timbers, like oak, can be left untreated but exposure to sunlight and weather will gradually fade the original colour, leaving it silver grey.