Cut and Set Posts
Install pressure-treated 6x6 posts in anchors, leaving them long for final trimming. Secure each post with two diagonal braces to keep them plumb during construction.
Quick Summary
20-30 minutes
6x6 pressure-treated
2 diagonal braces
4-foot level
Why Proper Post Installation Matters
The Backbone of Your Deck
Posts are the vertical structural members that transfer the entire weight of your deck - decking, joists, beams, furniture, people, and snow loads - down to the footings. Posts that aren't plumb create cascading alignment problems with beams, joists, and decking. Taking time to install posts correctly is essential for a deck that looks professional and lasts decades.
The key to success at this stage is precision and patience. Each post must be perfectly plumb (vertical) in both directions - when you check with a level against one face, then rotate 90 degrees and check again, both readings must show level. A post that's even 1/4" out of plumb at the bottom can be noticeably crooked at the top.
Temporary bracing is critical. Without proper bracing, posts will shift during construction, especially when you're working on them to install beams and joists. Good bracing takes extra time upfront but prevents frustrating problems later.
Choosing the Right Posts
6x6 Posts (Recommended)
- Higher load capacity
- Better lateral resistance
- Required for elevated decks (most codes)
- More substantial appearance
- Accommodates notching for beams
4x4 Posts (Limited Use)
- Only for low decks (under 3 ft)
- Limited to short spans
- May not meet code requirements
- Cannot be notched safely
- Lower cost but higher risk
Treatment Rating Requirements
Even though deck posts sit in metal anchors above concrete, they should be rated for ground contact (UC4A or UC4B treatment level). This provides maximum protection against moisture that may wick up from the footing or collect at the base. Look for the treatment stamp on the end of each post.
Step-by-Step Installation
Calculate Post Length
Measure from the top of each post anchor to your desired deck surface height. Then subtract the thickness of your decking (typically 1" for 5/4 decking or 1.5" for 2x), the joist depth (typically 9.25" for 2x10 or 11.25" for 2x12), and the beam depth (typically 9.25" for doubled 2x10s).
Deck surface height from anchor: 48"
Minus decking (5/4): -1"
Minus joists (2x10): -9.25"
Minus beam (doubled 2x10): -9.25"
Post length = 28.5"
Cut Posts to Rough Length
Using your calculated length plus extra, mark and cut each post. A circular saw won't cut through a 6x6 in one pass - you'll need to cut from multiple sides. Use a speed square to mark a line around all four faces of the post for accurate cuts.
Cutting technique: Set your circular saw to maximum depth (about 2.5"). Cut along your line on one face, rotate the post 90 degrees, cut again. Repeat until you've cut all four sides. The center may need finishing with a reciprocating saw or hand saw.
Set Post in Anchor
Lift the post and place it in the anchor bracket. The post should fit snugly but not be forced - if it's too tight, the anchor may be slightly out of square. Ensure the post sits fully down in the bracket with no gap.
Before securing, orient the post so any bow or crown faces in a direction that won't affect your beam installation. Also check for any splits or defects and orient them away from visible areas.
Plumb the Post
This is the most critical step. Hold a 4-foot level against one face of the post and note if the bubble is centered. Have a helper push the post in the necessary direction while you watch the level. Once that face is plumb, rotate 90 degrees and repeat.
Check both directions multiple times. When you adjust one direction, it can affect the other. Keep adjusting until the post is perfectly plumb on both faces simultaneously.
Install Temporary Bracing
With the post held plumb (helper needed), attach diagonal braces to hold it in position. Each post needs two braces positioned roughly 90 degrees apart to prevent movement in any direction.
Brace setup: Use 8-10 foot 2x4s. Attach one end to the post about 4 feet up using a single screw (allows adjustment). The other end attaches to a stake driven firmly into the ground. Position braces at roughly 45-degree angles from the post.
Secure Post to Anchor
Once the post is plumb and braced, permanently secure it to the anchor bracket. Use the fasteners specified for your anchor type - typically structural screws or hot-dipped galvanized nails through all provided holes.
Don't skip any holes. Each fastener contributes to the anchor's load capacity. Using undersized or fewer fasteners than specified can result in anchor failure under load.
Proper Bracing Techniques
Why Two Braces Per Post?
A single brace only prevents movement in one plane - the post can still pivot around the brace axis. Two braces at 90 degrees prevent movement in all directions. Think of it like holding a pole: one hand won't keep it steady, but two hands at different positions will.
Brace Length
8-10 feet long 2x4s work well for most applications
Attachment Height
Attach to post about 3-4 feet above the anchor
Ground Stakes
Use 2x4 pointed stakes driven at least 18" deep
Keep Braces Until Beams Are Installed
Do not remove temporary bracing until beams and at least some joists are installed. The bracing holds posts plumb during all the bumping, lifting, and hammering of beam installation. Removing braces too soon results in posts shifting out of plumb, requiring you to start over.
Common Mistakes to Avoid
Cutting Posts to Final Length Too Early
Never cut posts to final height before installation. Variations in footing heights and anchor positions mean each post may need to be a slightly different length. Always leave posts long and mark the final cut line after all posts are installed using a laser level or water level.
Inadequate Bracing
A single brace or flimsy bracing allows posts to shift during construction. You won't notice until the beam is installed crooked. Use substantial 2x4 braces firmly staked and screwed - not propped or wedged.
Not Checking Plumb in Both Directions
A post can be perfectly plumb in one direction while severely leaning in the other. Always check both faces at 90 degrees to each other. Recheck after installing braces and again before installing beams.
Using Wet or Warped Posts
Pressure-treated lumber is often sold wet and will twist and check as it dries. Select the straightest posts available and let them acclimate (stickered and covered) for a week or two before installation if possible. Severely warped posts should be rejected.
Frequently Asked Questions
Should I use 4x4 or 6x6 posts for my deck?
6x6 posts are recommended for most decks, especially those more than 3 feet above grade or with beam spans over 6 feet. 6x6 posts provide greater load capacity, better resistance to lateral forces, and create a more substantial appearance. Many building codes require 6x6 posts for elevated decks.
Why should I leave posts long and cut later?
Leaving posts long (6-12 inches extra) allows you to mark and cut them to precise heights after installation. This accounts for variations in footing heights and ensures all posts are cut to create a perfectly level beam surface. Cutting posts too short is a costly mistake that's hard to fix.
How many braces do I need per post?
Each post should have two diagonal braces positioned at roughly 90 degrees to each other. This prevents the post from moving in any direction. Braces should run from about 4 feet up the post down to stakes driven firmly into the ground. Leave braces in place until beams and joists are installed.
What type of wood should deck posts be?
Deck posts should be pressure-treated lumber rated for ground contact (marked UC4A or UC4B). This treatment protects against rot and insect damage. Common species include Southern Yellow Pine, Douglas Fir, and Hem-Fir. Always use posts rated for structural use - not landscape timbers or fence posts.