How to build a pergola on an existing deck

Updated July 20, 2017

Adding a pergola to your existing deck can help to give your outdoor space some dimension. These four-sided structures have four posts that hold up a trellis-style roof. Putting a pergola in place can help to create an "outdoor room." Place a table and chairs under the pergola, and you have a new gathering space. You also can plant vines and flowers at the base of the pergola, and allow them to creep up around the posts to the roof. For this example, the pergola will be 8-by-8-feet.

Drive a wood stake in the ground at the four corners of the existing deck. Measure the distance between each stake to make sure that each side is of equal distance.

Dig a 2-foot-deep hole at the location of each stake. Pour 6 inches of gravel into each hole. Next, place a 10-foot-tall post in each of the holes. With 2 feet of the post under the ground, the height of the pergola will reach 8 feet. Make sure that each post is standing upright.

Mix a batch of concrete and pour it into each of the four holes. Pour the concrete until it reaches the soil line. Then use a trowel to smooth out the surface of the concrete. Allow the concrete to dry overnight.

Set up a ladder next to one of the posts. Climb the ladder to the top of the post. Then use a tape measure to measure 7 1/4 inches down from the top. Use a marker to mark this spot on the left and right side of the post. Repeat this step on all four posts.

Return to the first post. Climb the ladder and lift one of the 10-foot beams just below the marked spot on the post. Have an assistant on another ladder at the opposite post to hold the other end of the beam. Each main beam will hang over the end of the posts by 1 foot. Drill two holes parallel to each other through the beam and into the post. Attach the beam to the post with carriage bolts. Repeat this process on the other end where your assistant is holding the beam. Then attach another beam on the other side of the same two posts. When you are finished, two beams will run parallel to each other with two posts in the middle.

Repeat Step 5 on the two posts on the opposite side. Install two 10-foot beams on each side of the posts. Once finished, you will have four beams running parallel to each other.

Climb a ladder to the top of the first post and place a crossbeam directly above the two main beams. The crossbeam will run perpendicular to the main beams. Drill two holes through the crossbeam and into the post. Attach with two carriage bolts. Make sure that each crossbeam hangs over the end of the post by 1 foot on each side. Repeat on the opposite end of the crossbeam. Then place another crossbeam on the other end of the crossbeam you just installed. Again, drill two holes through each end and attach carriage bolts. Add two more crossbeams on the opposite side of the pergola. The posts will be holding up a square when you are finished.

Take 10-foot-long wood slats and nail them an angle at each end of the crossbeams. Allow the slats to hang over the crossbeams by 1 foot. These slats will run parallel to the main beams and perpendicular to the crossbeams. For this example, if you leave a 6-inch distance between each slat, you will have enough room to install eight roof slats.

Things You'll Need

  • Wood stakes
  • Shovel
  • Gravel
  • Concrete
  • Trowel
  • 4 wood posts, 10-feet long, 4-by-4-inches
  • 8 wood beams, 10-feet-long, 2-by-8-inches
  • Ladder
  • Tape measure
  • Marker
  • Nails
  • Drill
  • Carriage bolts
  • 8 wood slats, 10-feet-long, 2-by-6 inches
  • Assistant
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About the Author

James J. Siegel is a journalist with over ten years of experience. He graduated from Bowling Green State University and works as an editor for a trade magazine. His freelance work has appeared in San Francisco Apartment Magazine and