Timber Used With Paving
The use of timber, especially ‘sleepers’ or lengths of wood 100mm x 200mm x 2400mm as risers
under steps, and as ‘walls’ under raised patios, or as edging against paved areas as a support to
retain the MOT Type 1 sub-base should be considered poor practice for several reasons.
Timber, even when treated to confirm to Class 4 or Class 5 (the most durable, suitable for
contact with the soil) may be fine inasmuch as meeting durability when measured against a
certain class table showing various uses for such grades of timber, but when used in conjunction
with, and adjacent to, rigid paving projects such as steps and underneath raised areas of paving
slabs, they may be the cause of many problems, causing cracking, delamination, lifting of
slabs and crushing (if there is no room for flexing or expansion for the slab due to restricted
spaces e.g. against a house wall).
Timber constantly flexes, expanding and contracting with temperature and ambient air
moisture content, as well as standing/running water, and will move at a vastly different rate
than rigid paving materials and their laying beds.
If a project does call for timber as part of the design, ensure that the wooden features are kept
away from rigid paving and foundations, with fibre boards or free draining shingle between
the two materials to allow for the varying movements.
Never use timber as risers for steps, as the paving slabs of the treads will work loose very
quickly, and may become dangerous.
