How to Build an Octagonal Deck

Step 3: Level the support board.

If the entire deck is elevated you will need to find the height of the first 4"x4" post to determine your starting point. First determine your reference point for the top of the deck surface. This may be the threshold of a door or a point on the siding. Mark a line level with this point that will extend near the first block. From this line, hold a level out over the block and measure from the bottom of the level to the pocket of the block. From this measurement, subtract the thickness of the surface board and the thickness of the support board (1 1/2" + 5 1/2" = 7"). Cut the first 4"x4" post at this measurement and

If the deck is placed next to a door, the deck should be between 1/2" and 1" below the door's threshold. Or if you want a step up to the door, the deck should be between 6-7 inches below the door. You don't want anything between 1-6 inches; this will create a trip hazard.