This story shows how to lay out the site for a two-level deluxe deck.
A concrete slab runs alongside this house -- a fairly common situation. In some cases you can lay joists directly on top of a slab. However, a slab is probably no more than 4 inches thick, so it cannot support posts.
The first step is to install one ledger for each level. Place the ledger 1 inch plus the thickness of the decking below the bottom of the door sill. If the house has beveled siding, cut the siding or shim it with cedar siding so that the ledgers will be vertically plumb.
The footings and posts for the upper level are set into the ground beyond the slab. The photos at right show layout for the lower-level post, which will be set on piers that go through the slab.
Once the ledger is installed, several hours to build batterboards, run string lines and check them for square, and mark the slab for the footing locations
Tape measure, hammer, sledgehammer, carpenter's level, drill, chalk line, mason's line, a jackhammer if a concrete patio is in the way
Building batterboards, measuring, checking lines for square
Install the ledger boards
1x2 and 1x4 for batterboards, a straight board, deck screws
Use a plumb bob or carpenter's level to reference down from the edge of the ledger to the slab. (Note that the shims are 1 1/2 inches longer than the ledger to accommodate the thickness of the rim joist.) To draw a line exactly perpendicular to the house, lay a straight board on the slab, and use a 3-4-5 triangle to square it with the foundation. Draw a line on the slab along the edge of the board. This line indicates the edge of an outside joist for the lower level.
If a vent must run through the ledger, remove the vent cap and its tailpiece. If the vent does not fall between joists, you may need to frame out to make room for the vent. Measure for the center of the hole and use a hole saw to cut the hole. Hole saws can bind and buck; practice with the tool before cutting the ledger board. You may need to attach a longer pipe to the vent cap before replacing it.