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How To Build an Octagon Deck

When designing an octagon deck, maintaining its squareness and levelness is of the utmost importance and should take up the majority of your attention. To begin, we suggest positioning the pre-notched posts at each corner at an angle of 22.5 degrees. This will serve as the beginning point. You are going to put twin flush beams in this space between each of these posts. Make sure that each beam is the same length and that it is the same distance from one side to the other.


You will have some wiggle room to make adjustments to the framing around the perimeter before you add any more framing. While you are working on the frame, you should use temporary supports to stabilize it. After ensuring that the perimeter of the deck is straight and level, the octagon frame can next be strengthened by installing joists using angled joist hangers. If you want to avoid interfering with the post beam notch connections, you should avoid inserting joists near the corner intersections of the building. Strength and structural stability of the octagon can be improved by incorporating decking and bracing into the design.


If you want to put a gazebo on top of the octagon, you need to make sure that the footings you use are strong enough to take the additional weight that will be caused by the roof, and that the gazebo is correctly linked to the octagon's frame.

Materials Needed:

  • 2x8x14’ Pressure Treated Lumber

  • 2x8x8’ Pressure Treated Lumber

  • 4x4x8 Pressure Treated Lumber

  • 1-1/4x6x8 Cedar Decking

  • Cement Mix

  • 10” x 8’ Sonotube

  • 6” x 4’ Sonotube

  • Sonotube Saddles

  • 4” Bolts, Nuts, Washers

  • Screws

  • Joist Hangers

  • Wall Anchors

  • Cabot Deck Coating

  • Wood Glue

Tools Needed:

  • Hammer

  • Clam Shell Shovel or Post Hole Auger

  • Cordless Drill

  • Hand Circular Saw

  • Shovel

  • Wheelbarrow

  • String line

  • Chalk