A pergola is a classic outdoor structure that creates a dramatic addition to the space. Its commanding presence within a backyard calls for a creeping and colorful vine to cover its components. It also beckons for a set of comfortable chairs to be placed underneath for an outdoor living area to enjoy year-round.
The column is the decorative component of the trellis that holds up the top parts of the pergola, including the rafter, purlins and beams. Round and square columns are the most popular shapes and are available in different types of material like wood, plastic and composite. Prefabricated columns are built in various finishes including smooth, fluted and paneled. The diameter of the columns ranges in size and can be as wide as 30 inches.
Also called lintels, beams are used to support the rafters on the pergola. The key component of the beam is the interior substructure that prevents dropping or bending. White oak is the an ideal wood for pergola beams because of its long lasting and durable structure, not to mention it's one of the hardest woods.
Rafters are the components of the pergola that rest on top of the lintels or beams. They are typically spaced 16 inches apart but can be closer. The design of a rafter has carved ends that add a decorative touch to the space and give the pergola its characteristic design.
Purlins rest on top of the rafters and are set at the same spacing as the rafters for a sturdy pergola. A purlin's main function is to increase the amount of shade below and to help the rafters from twisting and turning. Think of the purlin as the bracing mechanism or component of the pergola. Typically, there are the same number of purlins as there are rafters. Creeping vines, when planted around a pergola, will cover the purlin for a shaded "roof" to the structure.