Pergolas are outdoor structures intended to provide shade and cover walkways, patios or sitting areas. They are typically constructed to hold an overhead trellis and support a vine or climbing plant. The most important thing to remember when constructing a pergola, especially one that is to support a vine, is that it needs to be durable and weather resistant. Once constructed it is difficult to repair or replace a pergola without damaging the vine.
If you choose to use untreated wood in order to allow a patina on the surface to give a rustic look, opt for softer woods only for the overhead lattice structure. Hard woods, such as maple or oak, should be used for the support structure that will come in contact with the ground. They are more rot resistant and can better support the weight of a vine. Stain or seal the entire structure to increase the wood's longevity.
Pressure Treated Wood
Pressure treated wood can be used for a pergola. In years past, pressure treated wood contained and leached dangerous chemicals like arsenic. Modern pressure treated wood contains high levels of copper, which will make any fasteners in contact with the wood rust more rapidly, but will not poison the soil or your vine. Choose pressure treated wood in conjunction with rust-proof zinc or stainless steel fasteners to have the best of both worlds.
Many homeowners opt to use rough-hewn landscaping timbers for their pergola in order to give the structure a more rustic look. This is a great choice, but care should be taken to ensure any vines or plants growing on the pergola can be safely supported while rotten timbers are swapped out for new wood every four or five seasons. This can be accomplished by using a backup system of steel rods and wire to support the actual weight of the vine, and using your landscaping timbers for aesthetic purposes only.
Synthetic Decking Material
Synthetic wood, or synthetic decking material, is a wood and plastic based alternative to traditional wood or pressure treated varieties. The benefits of synthetic decking material are that it does not corrode in damp conditions, and is termite-resistant. However, synthetic decking material typically has a somewhat "manufactured" appearance and color. Due to its appearance, it may not be a good choice for individuals wishing to have a pergola with a wooden or natural appearance.
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How to Build a Pergola Using Pressure Treated Wood
A pergola can be built as a freestanding structure supported by four or more posts, or it can be attached to a...