Framing Your Deck

Posts and beams

Once you've laid out for the footing holes, follow instructions to dig and pour the footings. Footings should be at least 2 inches above grade at all points; on a sloped site they'll stick up higher on the down side of the slope.

Keep things level, plumb, and straight
Take a little extra time to precisely align all the framing members. Double-check posts for plumb and adjust the braces if necessary. When using a mason's line to set a row of posts, keep the line about 1/8 inch away from the posts so the line stays straight. Framing members often get bumped during construction, so go back and check all the posts just before installing the beam, and check the beam just before installing the joists.

Prestart Checklist

Time
Two days with a helper to install posts, beams, and joists for a medium-size deck

Tools
Tape measure, hammer, drill, circular saw, handsaw, layout square, chalk line, post level, carpenter's level, mason's line

Skills
Measuring and cutting boards, checking for level and plumb, following a framing plan

Prep
Install the footings with J-bolts and allow the concrete to set; draw layout lines on the ledger and the header

Materials
Lumber for posts, beams, joists, blocking, and braces, 16d galvanized nails or 3-inch deck screws, joist hangers, hurricane ties

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Step 1

Install post anchors on the footings. The day before you set the posts, square one end, seal them, and cut them about a foot longer than needed. Install and brace the corner posts plumb in both directions, sealed end down. Align the line posts with the corner posts and brace them.

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Step 2

Hold a carpenter's level on top of a straight board. Set one end of the board on top of the ledger and hold the other against an outside post. Draw a mark on the post that is level with the top of the ledger.

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Step 3

To determine the height at which the post should be cut, measure down twice: Use a scrap piece of joist lumber to measure down the width of the joists and a scrap piece of beam lumber to measure down the width of the beam.

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Refresher Course: Beam options

Beams for decks are usually made of 2x lumber rather than a single piece of 4x lumber. (Thick lumber is more prone to crack and warp than two or three 2xs fastened together.)

For the simplest method of beam construction, just fasten two 2xs together. Drive two or three 10d nails or 2-1/2-inch screws every 16 inches, unless your inspector specifies otherwise. The resulting beam is 3 inches thick, but a post bracket is 3-1/2 inches thick. To make up the difference add a 1/2-inch plywood shim at the post.

Beam with spacers. Beams that will be set on posts should have pointed pressure-treated plywood spacers to increase rigidity and allow water and debris to fall through. Locate the spacers 12 to 18 inches apart. Some inspectors prefer a continuous strip of plywood the same width as the 2xs for added strength.

Two-part beam. A two-part beam is made by attaching 2xs to both sides of the posts, then cutting the posts. Because this method adds lateral stability to the deck, it is often used for second-story decks with long posts.

Step 4

Mark the cut line on the corner posts and hold a chalk line between the marks. Then snap the line to mark the interior posts for cutting. For the posts that will support the angled beam, use a carpenter's level to mark for cutting.

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Step 5

To cut a post, mark all four sides with a layout square and cut with a circular saw or reciprocating saw. If the post is a 6x6, you'll need to finish a circular saw cut with a handsaw.

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Step 6

Make the beams longer than they need to be (you'll trim them later). Lay one 2x on top of another with the crowns facing the same direction and the cupped sides facing each other.

To keep the top edges flush, you may need to use clamps. Drive two or three 10d nails or 2-1/2-inch screws every 16 inches unless your building codes have specific fastening requirements.

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Step 7

In this deck plan one end of each beam is cut at a 45-degree angle. Cut only this end now; cut the other end after the joists are installed and the frame is squared. Set a circular saw at 45 degrees (test it for accuracy on a scrap). Using a layout square as a guide, cut through one of the boards. Flip the beam over. Use a square to mark the other board with the same angle. Complete the cut.

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