Before installing the posts, you’ll need to remove the mason’s line centered over the footings. Before doing so, however, you might want to add another line to help you to align the posts. For 4x4 posts, set this line 1 3/4 inches (half the actual width of a 4x4) from the existing line. Then set the posts in place with the face of the post just touching the newly placed line.
Tools: Hammer, cordless drill or screwdriver, level.
Cut Your Posts Down to Size - Always rough-cut posts longer than actually needed. With the post braced in place, the extra length allows you to plumb it easily. This is important if you are building a low deck whose posts might finally be only 1 or 2 feet high. Also, the extra length provides you with some working space for transferring the ledger height to the post and measuring down the post to the proper post height. Once you have double-checked your marks, detach the post from the bracing and cut it to the proper length, or cut in place.
1. Set and brace the posts. Measure and cut the posts so they are higher than the bottom of the ledger. For each post, you’ll need two stakes and two braces. Insert the post into the post anchor. Hold it as straight as possible and attach the braces with one screw so they pivot. Drive the stakes into the ground next to each brace. Using a level, plumb two adjacent sides of each post. Holding the post plumb, have a helper attach the braces to the stakes.
2. Fasten the posts. Before attaching the post to the post anchor, recheck the post for plumb. When the post is plumb, drive nails or screws through the anchor into the post. Post anchors and caps vary, so be sure to use the type and number of fasteners specified by the manufacturer. Take care when driving fasteners that you don’t move the post out of alignment. When finished, recheck the post for plumb. Finally, use a utility knife to cut away any of the fiber-form tube that remains above ground level.
Marking and Cutting Posts
Marking and cutting posts is a relatively delicate operation. If you get it right, your deck will be level and the rest of the job will be easier. Get it wrong, and you’ll mar the appearance and actually complicate later steps. So don’t rush this step. Enlist an assistant if possible to help with transferring level marks. If time has passed since you set your posts, check them for plumb. Often, posts get bumped or bracing gets kicked, knocking your supports out of plumb. Readjust if necessary.
Tools: A long straight board, carpenter’s level or water level, pencil, tape measure tape, circular saw, chisel.
Caution! Treating Cut Posts - If you are using pressure-treated lumber for your deck, have a supply of wood preservative on hand. Although the treated wood absorbs a good dose of the chemicals used in preserving the wood, the coverage is most thorough on the outer surfaces. When you cut a treated post or board, you expose wood that is less-thoroughly treated. To avoid future maintenance problems with your deck, brush some preservative on the cut ends. Because they'll be most exposed to weather, horizontal surfaces, such as posts ends, particularly need this treatment.
1. Establish post height. Rest one end of a long straight board on top of the ledger. Hold the other end against a corner post. Place a level on top of the board and level it. Mark where the bottom of the board touches the post. Next, measure down from that mark the depth of a joist (For a 2x8 joist, measure down 7 1/4 inches). Measure down from this second mark the depth of the beam (for a 10-inch beam, this would be 9 1/4 inches). Make a level mark at this location around the post. This is the post cutoff line.
2. Cut posts to length. After the cutoff lines are marked on each post, double-check your measurements by placing a long board and level along the line of posts. Make sure the cutoff lines are level with each other. Set your circular saw for a maximum depth of cut, then cut from opposite sides of each post, taking care to follow the lines. If you have trouble making level cuts, tack a board across the posts to rest the baseplate of the saw on. If necessary, use a sharp chisel to clean off the post top.