How to build a pergola
Measurements for the uprights of a pergola should be around 2.7m (9ft) from ground level so that climbers can trail down to some degree without impeding passage.
The width across the path between the uprights should be approx. the same as the height to achieve a degree of balance. The space between posts within each of the two parallel rows can vary from 0.9–3.7m (3–12ft).
The best types of timber are larch, Douglas fir or oak. Pine is sometimes used, but tends to rot more quickly than other timbers.
Vertical supporting columns may need to be set 45–60cm (18in–2ft) into the soil. Treat their bases with a wood preservative and extend their life span further by placing 5–7cm (2–3in) of course gravel at the base of the hole, then setting the post inside a large drainpipe with the rim just above soil level, filling around with gravel and capping with cement.
Pergolas need to be of quite solid construction as they may be required to support a considerable weight of foliage, and when in open situations, withstand considerable wind buffeting. Uprights should therefore be a minimum of 5x5cm (2x2in) and ideally 8x8cm (3½x3½in). The latter size would support crossbeams of up to 15x5cm (6x2in) and laterals of up to 5x2½cm (2x1in) at a spacing of around 60cm (2ft) apart.