In timber-frame structures
The movement in a timber frame structure caused by joint settlement, shrinkage, and deformation from loads is known as differential movement. It is important that consideration is taken at design stage of differential movement and its effect on the building. Hard points (e.g. eaves, heads, heads, portal frames, etc.) are specific areas where this movement should be allowed for. The level of differential movement is proportionate to the building: the maximum movement i experienced at the top of the building and the minimum at the bottom.
Therefore, the level of protection required against differential movement is relative to the height of the building. Some provisions can be made for timber frame components to reduce the amount of differential movement, such as:
Protecting timber components once delivered to site.
Minimizing the amount of cross-grain timber that is used in the building.
Using timber frame components of a specific moisture level. (e.g. low moisture proprietary L-Joists)
Avoiding, where possible, using a mixture of materials with contrasting moisture levels.
Design stage considerations
Weather and air tightness (e.g. windows, doors, etc.) should not be compromised when allowing for deferential movement at the design stage.
Additional consideration for differential movement needs to be taken in the following cases:
Where additional sole plates are going to be used at ground floor level.
Where balconies or perches are supported by the timber frame structure.
Where cladding systems are supported by the timber frame structure but about the masonry leaf.
Where compressible seals are used, e.g. window sills.
