How to Build an Attached 16x20 Pergola on an Existing Deck

Cameron Easey

Pergolas are structures that provide shade over a deck or a patio during the summer months. A pergola can be a free standing structure or you can construct one that attaches to the side of your house.

Building an attached pergola, 16 feet by 20 feet, on your deck can be done by first determining if your deck is big enough for this size of pergola.


You can use mounting brackets to secure the cross beams if you do not want to cut notches.


Measuring incorrectly will leave you will wood boards that you may not be able to use.

  1. Measure out and mark a 16 foot by 20 foot outline on your deck using a tape measure and a pencil.

  2. Install a ledger board that will be used to secure the support beams to the side of the house. Mount a 16 foot, 1-by-6 board for the ledger section of the pergola to the side of your house. Drill holes into the 1-by-6 board and into the framing of your house with the power drill.

  3. Insert lag screws into the holes and tighten them with the socket wrench.

  4. Place the post brackets on the corners of the outline you drew on the deck in step 1. Make sure the corner of the bracket is setting flush with the outline on the deck.

  5. Secure the post brackets to the deck with screws using the power drill.

  6. Insert the 4-by-4 posts for the pergola into the post brackets and secure them with the nails. Hammer the nails through the brackets and into the posts.

  7. Attach two of the 20 foot 1-by-6 boards to each of the 4-by-4 pergola posts for the side beams. Place the first two boards on the left and right side of one of the 4-by-4 posts. Repeat this process for the other 4-by-4 post.

  8. Place mounting brackets at the ends of the 20 foot, 1-by-6 boards and attach them to the ledger.

  9. Place one of the16 foot, 1-by-6 boards, for the cross beams, on top of the pergola frame and mark the location for wood notches with a pencil.

  10. Cut the wood notches into the 1-by-6 board with a dado blade using the table saw.

  11. Mark each additional cross beam using the board with the notches as a template.

  12. Cut the notches in the rest of the cross beams using the table saw with the dado blade

  13. Set one of the 1-by-6 boards on top of the side beams of the frame and secure it with nails or screws. Hammer a nail or drive a screw down into the 1-by-6 board and into the side beams.

  14. Repeat the previous step to finish securing the cross beams and to complete the project.