How to Build a Pergola on a Deck

Once you've added a deck to your home, you may find it's too hot and sunny to enjoy in midsummer.

Prepare to Build the Pergola

You can add a freestanding pergola to your deck to create a room outside, with crossbeams for shade and a trellis to add plants to one or more sides, to keep it even cooler. Build it from the same wood as the deck so it blends in naturally.

Choose a basic blueprint for an 8-by-8-foot pergola from the many available on the Internet. Check with your city or county building department to learn if there are any building codes that may affect the construction of your pergola, and whether or not you need to get a building permit. If so, obtain the proper permits before you start construction.

Make sure your deck is large enough to hold the pergola, and that it's raised high enough from the ground so that you can get underneath it to fasten the upright beams to the deck's joists. For an 8-by-8-foot pergola, you'll need at least 4 feet on two sides of it, and more unless you want the pergola to completely fill the deck.

Obtain the materials required in the plan. This will include posts, boards, screws and a variety of tools.

Lay out the 8-by-8-foot area the pergola will occupy. Use a tape measure to carefully measure the length from the outside of each support post to the outside of the adjacent support post. Set it up so that the posts are next to the inside edge of a joist. Use chalk to mark where the posts should go.

Build the Pergola

Find the inside edge of a joist under the deck. This will be your starting point, so mark it with chalk. Use the tape to measure 8 feet along the joist, and make another mark there. Use a chalk line to mark the line between these two points on top of the deck.

Mark the points with a 6-penny nail. Measure the other three legs of the pergola the same way, and mark each corner with a nail.

Start at the first corner and use one of the 4-by-4-inch posts to draw the shape of the hole on the decking. Cut the 4-by-4-inch hole with a jigsaw or circular saw. With your assistant, stand one of the posts on its end and put it in the hole.

Drill 2.5-inch holes through the joist and the post. Fasten the pole to the joist with a 6-by-1/2-inch carriage bolt. Repeat for the other three 4-by-4-inch posts. Measure each post to a height of 8 feet from the deck, mark the 8-foot line all the way around the post, and cut them off at that height.

Line up two of the 2-by-8-inch-by-10-foot boards to use as crossbeams. Screw them together with wood screws, working from both sides. Repeat with the other two boards that size.

Attach one pair of the boards, or crossbeam, to the 4-by-4-inch posts using two of the 7-by-1/2-inch carriage bolts. The top edge of the crossbeam must be even with the top of the post, and the edges of the crossbeam must extend the same distance on each side. Repeat on the opposite side so that the crossbeams are parallel to each other.

Take the five 2-by-6-inch-by-10-foot boards (the rafters) and mark the center of each. Lay them across the crossbeams so that two of them cross the support posts and the other three are all the same distance from each other. Make sure that the same amount extends over the crossbeams, then secure them to both crossbeams with wood screws.

Finish the Pergola

Stain the wood of the pergola to match your deck, if your deck is stained. Seal the wood after staining it.

Set a long rectangular planter along the sunniest side of the pergola. Fasten a trellis to that side. Plant climbing plants in the planter so that they grow up the trellis and provide more shade.

Fasten a sunshade across the top of the pergola if the rafters don't provide as much shade as you want.

Things You Will Need

  • Pergola blueprint
  • Permit(s), if necessary
  • Tape measure
  • Chalk
  • Chalk line
  • 4 6-penny nails
  • 4 4-by-4-inch posts, 9 feet long
  • Jigsaw
  • Circular saw
  • Drill
  • 4 6-by-1/2-inch carriage bolts
  • Ratchet for bolts
  • 4 2-by-8-inch-by-10-foot boards
  • Several 2 1/2-inch galvanized wood screws
  • 8 7-by-1/2-inch carriage bolts
  • 5 2-by-6-inch-by-10-foot boards
  • Wood stain
  • Wood sealant
  • Paintbrushes
  • 3-by-8-foot planter
  • Trellis
  • Climbing plants
  • Sunshade (optional)

Tips

  • Building a pergola is a two-person job, at the very least. Get a friend or two to help you with the job, and you may be able to finish it in one weekend.
  • You can find free plans for building pergolas at the BuildEazy and Woodworkers Woodshop websites, and for sale at the Garden Structure website. You local lumber store and DIY store may also have free plans.
  • Remember the old adage, measure twice, cut once. You'll need it with this project.
  • Cedar is one of the best woods to use for outdoor structures like decks, steps, pergolas and terraces. It doesn't rot easily and is rarely infected by insects.
  • Any time you work with power tools and wood, be sure to use the proper safety equipment, including gloves and safety goggles. Make sure you have enough light to see well.
  • The offset holes help to keep the structure sturdy.
  • You can use a jigsaw or router to give the ends of the crossbeams and rafters a design.
  • Flowering plants on a trellis make a great wall for sun protection and further decorate the pergola. They can also make a screen for greater privacy from neighbors.