SO, YOU'RE actually building your own deck. Not having fun yet? Well, if you've done the concrete footers (to support the posts that support the deck) and the ledger board (which allows fastening the deck to the house), you've probably done the most strenuous part.
Now it's time to start creating the structure of your deck. Cheer up -- this part is only painstaking and tedious.
First step, the posts: These will support the edge of the deck on the opposite side from the ledger, in other words, the yard side.
Find the best 6-by-6 pressure-treated posts that you possibly can. Make sure that they are square and virtually free of cracks. You need to make braces to support the posts while they're being installed. Drive stakes into the ground at each post location about three feet out at perpendicular angles -- one off the front face, say, and one off the side face. Use one nail to tack furring strips to each of the perpendicular sides of the posts about halfway up so the strips can be swiveled to form a 45-degree angle when they are attached to the stakes.
Attach the post anchors to the posts, making sure the post bottoms are cut square and treated with extra wood preservative. Check that the posts are plumb (perfectly vertical) from two adjacent sides, then secure the braces to the stakes.
Clamping levels to two adjacent sides of the post will free your hands while you are manipulating the post to get it plumb. This step is important, so make sure that you take your time and get it right. You may want to use a long level, such as a 6-foot framing level, to check because posts are sometimes bowed, and you want to span the bows.
Plumb all the posts and use string to make sure they are lined up equidistant from the house. Do not tighten the post bases yet, because you will most likely be taking the posts down again to cut notches in the top to support the main sandwich beam of the deck.
There are two ways to mark the top of your posts for cutting. The first is to lay a straight 2-by-4 on top of the ledger (sight along the top of the board to check its straightness). Lay your level on top of the 2-by-4 and adjust the board until it is level and then mark where the bottom of the 2-by-4 hits on the post. This will give you the same point on each post as the top of the ledger. Then measure down from that mark the depth of the ledger and mark that. The posts will be cut off even with the bottom of the ledger.
Most decks are supported on the outside edge by a beam that is notched into the post tops. The beam supports the joists, which are also mounted on the ledger.
Measure the depth of your beam lumber on the inside and the outside of the post, starting with the level mark. (The beams are usually 2-by-10s or 2-by-12s. Lumber is actually a half-inch smaller than its stated measurement, so a 2-by-10 would be 1 1/2 inches thick and 9 1/2 inches deep). When the tops of the posts are cut off, they will also be level with the tops of the beams.
Measure the width of the beam that you are mounting on top of the posts (usually 1 1/2 inches). Mark this point on the posts. Set the saw to a 1 1/2-inch depth and make repeated horizontal cuts on the inside and outside of the post, chiseling out the waste to leave a tongue of wood between the notches. Do this on each post. Once the notches are cut, place the beams in the notches and drill holes 1 1/2 inches from the top and from the bottom on each post, through the outside beam, the tongue of the post, and the inside beam. Insert 1/2-inch carriage bolts about 7 inches long to accommodate a washer and a nut on the inside of the beam.
There is another way to mark your posts. You may want to borrow or buy a water level (they are not expensive). They're extremely accurate and come in handy when you have to make repeated marks at the same height. Most water levels come with 25 or 50 feet of tubing. Once the level is set up, one person can easily mark all the posts. You do have to make sure that the water is carefully filled in the tubing so there are no bubbles to make your measurements inaccurate.
The safest place to cut the posts is on sawhorses on the ground. It's possible to cut a post in place, but it requires great care. You need a place to stand that is solid, such as scaffolding -- or on the ground if your posts are low enough. Don't stand on the top of a stepladder or trash can with a saw that can remove digits.
However, if you insist on sawing the post in place, brace it firmly. You may want to clamp a carpenter's square to the post to guide and support the saw as it cuts. If you will be cutting off more than a foot of waste, have someone hold the scrap top to keep it from falling on you or binding the saw blade.