Laying Out the Site

Laying Out the Site

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.

Prestart Checklist

Time
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

Tools
Tape measure, hammer, sledgehammer, carpenter's level, drill, chalk line, mason's line, a jackhammer if a concrete patio is in the way

Skills
Building batterboards, measuring, checking lines for square

Prep
Install the ledger boards

Materials
1x2 and 1x4 for batterboards, a straight board, deck screws

Previous | Next

Overall Layout

Each level has its own ledger and beam, so the beams are laid out separately using a combination of batterboards and chalk lines.

Previous | Next

Step 1

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.

Previous | Next

Refresher Course: Fastening a ledger

Attach the ledger with a pair of lag screws about every 16 inches. The screws must be long enough to go through the entire thickness of the framing member behind the siding. Place the screws where they will not get in the way of the joists, and counterbore the holes if you want to recess the heads.

Step 2

Snap chalk lines on the slab indicating the outside of the joists. Measure from those lines to locate the footings. Check and recheck your work.

Previous | Next

Step 3

Where the ledger runs past the house, reference down with a carpenter's level or a plumb line and use batterboards and mason's line to mark the footing locations.

Previous | Next

Step 4

Rent a jackhammer to cut holes in the concrete slab to accommodate the footings. Make the holes a few inches wider than the tube forms.

Previous | Next

What If... A vent must go through the ledger?

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.

Previous | Next

Comments