How to Set and Cut Deck Posts

Your new deck isn't going to build itself. Get started by setting and cutting the posts that will be the frame for your new favorite hang-out.

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Setting the posts for your deck requires careful work, but it can also be exciting because the posts are the first visible sign that your deck is going up. Even though you still have a lot of work to do after you set the posts, getting them up can make you feel like you're halfway there.

Setting posts will go more than twice as fast if you have someone help you. Two helpers are even better; you won't have to move back and forth from one post to another to adjust them. Follow along with our steps below to get started. 

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Getting Started

Posts must be plumb, so they have to start out with square ends. Check the bottom of each post with a speed square and cut it if necessary. Dip cut ends in a preservative before setting them in the anchors and let the preservative soak in overnight.

To make the job go quickly, do everything in stages—square all the posts, set them in the anchors with a temporary brace, then plumb, align, and brace all of them, letting their height run wild, then mark and cut them to a consistent height.

What You Need

  • Speed square
  • Framing hammer
  • Post level
  • Mason's line
  • Wrench
  • Tape measure
  • Water level
  • Reciprocating saw
  • Lumber
  • Fasteners
  • Masking tape

Setting the Posts

Step 1: Square and Preserve Ends

The day before you set the posts, make sure their ends are square. Mark the cut lines with a speed square and make the cuts with a mitersaw or circular saw. Dip the cut ends in preservative and let them sit overnight.

Step 2: Set Posts

Set each post in its anchor. While someone holds it plumb, drive one nail through the anchor hole and about halfway into the post. This will keep the bottom in place but allow you to move it when you plumb it. Tack 1x4 bracing to the post (see next photo) and stake in position.

Step 3: Brace and Plumb Posts

When you've set and temporarily braced all the posts, restring the mason's lines on the marks that represent the outside edge of the posts. Clamp a second 1x4 brace to the post and stake it. Plumb each post with a post level, keeping its outside face against the mason's line.

Step 4: Align Posts

Recheck the post alignment by sighting down the mason's line. Replumb any post that looks out of line and adjust the bottom of the post if necessary. If you have a post that's plumb but slightly bowed (no more than 1/8 inch), you can force it into place when you install the beams or joists.

How to Adjust the Bottom of the Post

Adjustable post anchors are made to be moved—right up to the last minute. To make an adjustment insert an open-end wrench in the slot and loosen the nut just slightly. Tap the post into place with a hammer and a piece of 2x4 scrap, and retighten the nut.

Step 5: Anchor Posts

Drive the remaining fasteners into the post anchor. Some anchors are made to accept nails or screws only. Others are fabricated to accept a lag screw also. Predrill for the lag screw before driving it.

Cutting The Posts

Step 1: Mark Level Line

Use a water level to establish the height of each post. Fasten one end of the water level so the water line is even with the bottom of the ledger (or level with whatever edge your plan prescribes). Hold the water level on each post and mark the post at the water line. Transfer the mark around the posts as shown on the next page.

Step 2: Make Cut Line

You can mark the cut line for the posts by using the depth of the joist and/or beam, depending on your construction plan. Starting at the line that is level with the bottom of the ledger, measure down the depth of the joist and mark this point.

Step 3: Mark All Posts

Transfer the cut line to all the faces of the posts, using a speed square and a carpenter's pencil. Make this line dark enough so you can see it when the sawdust flies. You will need to be able to see the line to keep the blade from wandering.

Step 4: Cut Posts

Holding the weight of a circular saw at right angles to the post can prove cumbersome (and even dangerous), especially when standing on a ladder for a raised deck. A reciprocating saw will prove more accurate. Keep the shoe of the saw on the surface of the post and make sure the blade cuts straight along the line.

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