How do I Build a Pergola With Composite Materials?
Working with composite materials is similar to working with wood, with a couple of important differences. Many contractors say that designing a pergola with composite materials is a challenge, and many of them won't do it. It can be done; this pergola just needs a little more support than others do. Does this Spark an idea?
Things You'll Need
- 12 columns or 4-inch by 4-inch by 12-foot composite posts
- 12 bolt-down post-holder brackets
- 12 2-inch by 6-inch by 4-foot composite beams
- Piece of scrap wood (optional)
- Router and bits (optional)
- 6 1-inch by 6-inch by 12-foot composite decking planks or traditional wood boards
- 24 hurricane ties
- 48 lag bolts measuring 1/4 inch by 3 inches
- 48 washers for bolts
- Socket adapter for cordless drill
- Cordless drill
- Drill bit set
- Compound miter saw or table saw
- Saber saw
- Sander
- Sandpaper
- Box of 3-inch wood screws
Instructions
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1
Determine whether you're going to use composite materials for just the support posts and the beams (the frame) or for the entire pergola. Composite material often sags under its own weight, so contractors say it's normally not recommended to span more than two feet without support.
Because it won't be holding any additional weight in a pergola, as it would when being used in a deck, the span can be a little longer. Composite materials would work for the beams that run along the outside of this pergola, because they rest on support columns every four feet. To use it for the rafters, you'll need to run beams out from the house every eight feet. This would make for a broken-up pergola, which may or may not be desirable, depending on your tastes. Using both composite materials and real wood solves this problem. You can use traditional wood boards for the rafters, and if you'd like, use composite materials for the columns and the beams that rest on the columns.
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2
Insert the upright posts into the post-holder brackets. If you don't have post-holder brackets in place, install them or have them installed every four feet around the perimeter now, then insert the posts into the brackets.
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3
Measure the wood for the pergola. Use the compound miter saw or table saw to cut all of the pieces of composite materials and traditional wood boards to the proper size and shape. If you're going to have rounded ends, use a router and do them all at the same time so they are uniform. Cut a pattern in scrap wood, and use it to cut the pieces. Cut square notches out of the rafters with the table saw or saber saw so they can slide down over the outside beams. Sand them all at the same time, using a sander to save time.
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4
Predrill the holes for the lag bolts and the screws. Predrilling will make it easy to slide in the bolts, and it will help to avoid mushrooming around the heads of the screws. You may wish to have a helper lift a board into place so you can mark the location of the bolts and screws, then remove the board and predrill the holes.
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Mark the location of the hurricane clips, then attach them to the traditional wood boards. The other ends will attach to the beams in another step.
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Assemble the pergola. Have a helper lift one beam section into place at the top of and between two composite posts. Have the helper hold the beam section still while you attach it to each of the posts with the lag bolts and a socket adapter for your cordless drill. Two beam sections will meet in the middle of each vertical post, so position them accordingly. Allow for expansion in the composite material that will occur as a result of temperature changes; do not tighten the bolts completely. The beams will run around the outside edge of the pergola, making a frame attached to the upright posts.
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Mark the location of the rafters on the beams. Lift one 2-inch by 6-inch by 12-foot board onto the tops of the beams (real wood boards are recommended for this). Start at the middle and work toward the edges, placing a board about every two feet. Slide the boards down into place by sliding the slots down over the composite beams, but do not attach them yet.
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Position the boards about every two feet, avoiding the vertical posts. When you have them where you want them, attach them to the beams using 3-inch-long wood screws and hurricane ties. Remember to leave room for expansion. Traditional wood could be notched in both boards and screwed down through the top of the rafter into the beam (see references), but composite materials need more room for movement.
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Decorate your pergola as desired. Plant vining or climbing plants, weave fabric through the 2-inch by
6-inch boards, or whatever fits your style.
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Tips & Warnings
Composite decking does expand and contract a great deal with temperature changes. This needs to be accommodated by using different methods for fastening and leaving space to allow for expansion and contraction.
Expect movement in the pergola, especially if it is freestanding.
Check with your local home improvement store to see what manufacturers recommend for use with the columns or posts you want.
Keep like items together to stay organized while you work.
Check your local building codes before beginning this or any project.
Fastening composite decking material securely presents a challenge.
Predrilling is important to prevent mushrooming, which is a mound of the material developing around the head of the screw.
Contrary to many advertising claims, composite decking materials do decay, and some mold and rot rather quickly. If you're going to use composite decking material, use one that has zinc borate added to the wood fibers to prevent rot.
There have been recalls on some composite materials because degradation in the planks creates fall hazards.
Do not overtighten the lag bolts
References
- Photo Credit raisin image by pat fauve from Fotolia.com
