Imagine you put weeks of work into building a deck and now it's time to enjoy it. You step on your deck and you just find out it is swaying to the left and right as you walk on it. It creates an unstable surface which is not just unpleasant to be on but also a great tripping hazard as it can mess up your balance and you could fall.
Read more: How to Build a Raised Deck
Bracing a deck is extremely important to maintain the integrity of the structure and to ensure your outdoor space is safe for you, your family, and your guests.
In order to brace your deck properly, there are just a few things that you need to keep in mind, you wouldn't need a lot of materials and the process is actually fairly simple:
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Identify where you will be positioning the braces and measure the distance
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Cut the braces on a 30-45 degree angle
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Attach the braces using structural screws
This article will go fairly in-depth about the entire process of installing diagonal braces, as they are the most common and generally the easiest to install. However, there will also be discussions on different bracing methods based on height or even for what kind of deck you might have.
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Are Deck Braces Necessary?
You might be thinking that if a deck might be wavering then it's not that big of a deal, as long as its footings remain solid and the deck boards are properly laid then what could the issue be? There is as a matter of fact a very big issue as choosing not to brace your deck can have very serious consequences.
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A deck without braces can be a very unstable structure that can very easily collapse if some weight is put on it. Imagine that, one of your guests walks out on the deck and the structure starts swaying left and right, this movement would loosen the joints and the connection and would cause the deck to collapse.
It might even be required by your local building code to brace a deck properly from swaying. It is always recommended to fasten the deck to your house unless it is situated in a place where that cannot be done.
Read more: How to Build a Freestanding Deck
Deck Bracing Techniques
As we have mentioned, diagonal bracing is usually the way that people go when they have to brace their decks. This involves fastening a 4x4 piece of wood to a 6x6 Column, as well as the underside of the deck's beam.
When you're done, you will have a V shape on either side of the column. Diagonal bracing is generally much more suitable for all standard-size decks.
Another bracing method is cross bracing. This form of bracing, on the other hand, is normally reserved for decks that are not attached to a structure. It entails connecting a 24 or 26-inch piece of wood on either side of the 6-6 column to form an "X" configuration.
Cross bracing is typically exclusively used on freestanding decks because it provides one of the most effective forms of anti-sway lateral support, which a freestanding deck requires more than a secured deck
Installing a continuous footing and wall for decks 6' to 8' or taller is often the most structurally sound choice. This approach entails creating a continuous concrete footing and then constructing a wall between the footing and main beams (made up of pressure-treated studs and pressure-treated plywood or skirting material).
A wall provides lateral support in each direction, ensuring that the deck is stable and sway-free. This may take longer, but it will provide a significant structural benefit to a larger deck.
How to Brace a Deck from Swaying
Materials you will need:
Before you are starting with your project here's a list of tools and materials that you will require:
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4 x 4 posts
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Structural Screws
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12” Miter saw or hand saw
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Impact Driver
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Drill
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Safety glasses
Step 1: Measure the distance between your deck column and beam using a 30-45 degree angle as your guide. Using this 30-45 degree angle gives you the highest amount of structural strength, so it's really important to make sure you stay within this limit.
Step 2: Cut the 4x4 posts that will act as your braces with a 12" miter saw or hand saw once you've calculated the distance and determined the angle you'll be cutting on. Before beginning any cutting, always put on safety eyewear.
Read more: How to Remove Paint from a Wood Deck
Step 3: With the braces measured properly and cut, it's time to fasten them. If you are using structural screws that are 5/16 thick x 6” long, you will need two screws per brace side. Using either an impact driver or drill, fasten your screws into the post and through the column which is perpendicular to the brace. You are done fastening the post to the column, repeat these steps and screw the post to the deck's beam.
Step 4: Make sure that you are fastening the posts diagonally on each side of the column around the perimeter of your deck. This form of structural support holds the deck properly together, preventing any sway from making your deck collapse.
FAQs about Brace a Deck from Swaying
What actually causes a deck to “sway,” and what’s the first fix?
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Sway is lateral racking from wind, live loads, or flexible frames. The fastest cure is diagonal bracing: add knee braces (post-to-beam) at corners and/or X-bracing between posts; on attached decks you can also use V-bracing under joists. Aim for ~45–60° brace angles for best stiffness.
If my deck is ledger-attached to the house, do I still need bracing?
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You still need a lateral-load path. The IRC permits lateral load connectors that provide 1,500 lb (6.7 kN) each at both ends of the ledger (or an engineered alternative). These resist horizontal pull-out; perimeter bracing can still be added if needed.
Where should knee braces go—can I put them on center posts?
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Most guidance puts knee braces at corner posts, not mid-line/center posts (risk of overstressing heavily loaded interior posts). Use X-bracing between posts instead if you need stiffness at interior bays.
What size, angle, and fasteners are typical for knee braces?
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Common field practice is 2×6 or 4×4 braces set at ~45–60°, landing at least one-third down from the top of a tall post; fasten with bolts or listed structural screws per connector specs. (Through-bolting or code-listed screws from reputable hardware makers is preferred.)
How do I brace a freestanding deck (no ledger)?
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Freestanding decks must resist lateral forces in both directions on all sides. Use knee braces at corner posts, plus X-bracing between posts (parallel and perpendicular to beams) to lock the frame.
My deck feels “bouncy” more than “swaying”—is bracing the fix?
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“Bounce” is vertical deflection; fix it by shortening spans (add a beam/posts), stiffening beams/joists, or increasing joist depth—not by lateral bracing. Add knee/X-bracing only for true side-to-side sway.
Do I ever need bracing under the joists (not just at posts)?
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Some jurisdictions require under-joist diagonal bracing (2×6) at 45–60° when posts exceed certain heights or when using specific hidden-fastener systems—run the braces ledger to beam and attach to every joist. Check your local detail sheet.
When does bracing need an engineer?
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Tall decks (long posts), multi-level decks, or unusual geometry often require engineered bracing plans. Some departments also allow embedded posts as an alternative for freestanding decks at lower heights—verify locally.
Do guardrails and posts help stop sway?
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Guards aren’t a substitute for bracing, but the 2021 IRC R507.10 demands guard loads transfer via a continuous load path into joists/beams. Make these connections robust; then add bracing to control sway.
Any alternatives if I can’t add knee braces at corners?
- Two common options: (a) Diagonal decking (board layout at ~45°) can stiffen the diaphragm and reduce the need for separate sway bracing; and (b) where permitted, post embedment can provide lateral stability for low, freestanding decks. Always confirm with your AHJ.
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