Building a roof on a pergola is really a simple project. The variety of materials that are available to roof a pergola are so numerous, easy to use and adaptable for any situation that the average person, who has little skill with tools, is capable of performing the task. A pergola roof should allow sunlight in but keep the heat of the sun out. The pergola roof should protect guests from sudden rainstorms while still making it possible to enjoy the beauty and ambiance of the garden. A roof that satisfies all of these requirements and can be installed by the homeowner in a weekend is a great choice for the pergola.
Determine that the pergola is built strongly enough to bear the additional weight of the roof. The upright support posts of the pergola should be anchored in concrete. During high winds the roof will act as a sail, placing great stress on the upright posts and crossbeams. Roof the pergola only after it is determined that the structure is soundly built. A city building inspector can provide all the information needed to make assess the strength of the pergola.
Use high strength corrugated fiberglass panels, available at home improvement stores, to roof the pergola. They are translucent and allow sunlight in but keep the heat of the sun out. The panels will also shield against sudden rainstorms.
Measure and determine the span of the framework that the fiberglass panels will rest upon. The fiberglass panels come in different sizes designed to fit various size ranges of roof framework. It should be noted that the panels are not designed to bear any additional weight. The panels can be cut to size with hand or power saws fitted with fine toothed carbide tipped blades while wearing safety glasses, dust mask and gloves.
Fasten the panels through the crown at every second corrugation by drilling holes in the panels on 12-inch centers using a drill bit that is one and one sixteenth inch larger than the diameter of the wood screw that will be utilized. Use three inch long wood screws along with armored neoprene washers, available at home improvement stores.
Determine in which direction prevailing winds blow and start laying the panels on the roof from the leeward side and work toward the wind. Overlap each succeeding layer of panels over the panel that was just laid so that the wind blows over it and does not catch the edge of the panel.
Place the panels a minimum of two layers deep on each side of the pergola roof for additional strength.