Whether timber is air dried or kiln dried there will always be a small variation in the moisture content of individual boards and even within the same board. Depending on the moisture content of the board when it commences its service life it will take up moisture from the air and in some cases the reverse will happen and moisture is lost. When timber takes in moisture it expands and when it loses moisture it shrinks. Expansion can result in board movement which will cause gaps between boards to close and where insufficient clearance has been allowed in the construction, the boards will buckle. Shrinkage can result in hairline cracks at joints and around panels and splits in wider boards or panels. These are rarely detrimental and may well become more or less visible at certain times as the moisture content varies relative to the climatic conditions applicable to the location of the door.
In all cases newly fitted timber doors will take time to adjust to their environment. The length of time will be conditional on various factors for example the specie of timber, the paint or stain finish, the operational use of the door, as well as the extremes of temperature, humidity and weather it is exposed to. Although there can be no firm timescale, generally timber doors will take a minimum of 2 years to settle into their service surroundings.