Timber pergolas and how to build them

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All of the pergolas shown in these images are constructed from tanalised timber. Harmless to plants; no further treatment required; guaranteed for 15 years against rot. It is important to treat any cuts with a proper sealing agent for treated timbers. The timber used for these pergolas will blend in with any deck, for all exterior timber will tone down to a grey colour unless stained or otherwise treated.

Pergolas built near the house, can provide a good shade area - especially if built on a sunny wall. Bear in mind that once clad with plants, your pergola could also cause considerable darkening of adjoining room. Take into account the position of the sun at various times of the day, to see how best to orientate your pergola rafters.

A sturdy timber pergola can be built without having to dig deep foundation holes to support it. Simple bracing of the timbers will make it sturdy enough with just a shallow support hole. Most of the movement in a substantial pergola will come from the sheer weight above ground level. All well constructed pergolas will be top heavy to say the least!

In order to prevent the whiplash effect, angled strut can be used. These will prevent any sideways movement at the top of the pergola. The bracing struts are best secured by using coach screws or other exterior screw-type fittings.

Main support beams for building a pergola, should be in the region of 6x2in - 150x50mm - with span of not more that 3.00 metres (9 feet). Whilst the beam will be well capable of the weight normally associated with pergolas and plants, any wider span than that suggested, will lead to natural sagging of the beam over the years. The span of the pergola main beam can be increased by the use of sturdy angled bracing struts, for the span will then be measured from the contact point of the supporting struts.

All of the pergolas above were built without the use of angled braces, to give a clean line. They are sturdy enough not to need the struts. All fastening was done with 12 mm coach bolts, and 'hidden' top bracing was used to ensure no wobble.

Normal beams of the pergola can be either 4x2in (100x50mm) or 5x2in (125x50mm). The thickness is less important then the depth of the timbers in this case. Instead of 2in (50mm) timbers, 1.5in (38mm) thickness can be used, but then preferably with 5in depth of timbers.

The upright posts should be min of 4in (100x100mm) treated timber. (3in will lead to whiplashing effect.)

When building your pergola, the size can be increased quite considerably by overhanging the rafter beams. Typically, a 4in or 5in rafter can be overhung by 900mm (3 feet) without any problems. If the timbers are 'notched' instead of simply laid and fastened on top of the main beam, than a shorter overhang of the pergola rafters would be better - maybe 600mm.

As seen above and below, different shapes can be obtained with pergolas. They need not be rectangular. It is a good idea to 'build' your pergola on the ground - using either clamps or light screwing to try out different designs and to ensure that everything fits. Much easier to rectify at ground level than 2 or 3 metres high! Using substantial timbers will invariably mean enlisting help. Pre-drilled support holes and sturdy clamps should also be part of the construction process of building your own pergola.

Garden Timber Pergolas and Ideas of how to build them.