How to Size a Deck Beam
A beam is a solid structural member that is supported by posts and footings that accepts and transfers the load from joists. Once you know the distance between support posts and the length of the joists that will be supported you can determine the required size by checking our beam-sizing chart. The size of a beam is a function of the amount of weight it must support and the distance it must span.
A common beam is composed of the same size and type of lumber used for the joists by nailing 2 or 3 together side by side. Even if you are allowed to use a smaller beam, you should maintain the same depth of material as the joists to present a uniform appearance. Never position your post “sandwiched” between two boards as is sometimes seen as a beam construction technique. The relationship between directly applied and fastened boards is what bonds the strength of a multiply beam.
Occasionally a beam application may require spanning a long distance that exceeds the design limits for conventional beams. In these cases you may have to use an engineered beam to meet the required load capacities. Engineered beams are fairly expensive, so you might want to add another post to reduce the span if possible. Your local building supplier should be capable to use your plans to determine which size and type of beam will work. Steel I beams are the strongest form of beam available and can be used to carry extremely long spans 20 ft + but are very expensive, heavy and difficult to work with.
How to Decorate Deck Support Columns
Browse some examples of decorative deck support posts for tall decks.
Building A Deck Over An Air Conditioner
Things to consider when building a deck near an air conditioning unit. You may want to relocate the AC unit if possible to avoid some problems.
Beam Span Chart
Learn how to size your deck beam using this easy-to-use span table. Just cross-reference the post spacing and joist length to determine the beam size.
Anatomy of a Deck
A comprehensive guide to help you learn the names and understand the functions of every part of your deck.
Dos & Don'ts for Homeowners to Consider When Building a Deck
Your dream deck can take whatever shape you like. The trick is making it fit your budget and site conditions. While the deck doesn’t have to be built as a rectangle, there could be good reasons for doing just that.
Best Hidden Fasteners for Decking
Hidden fasteners create a clean deck surface and can be used with composite, wood and other materials. Learn about hidden deck fasteners at Decks.com.
More Helpful Resources
Explore Articles by Topic
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Railings
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Learn about permits and working with contractors
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Build a covered deck to enjoy all seasons
Ledger
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Care
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Materials
An overview on water drainage, benches, planters and lights
Why is Joist Protection so Important for Your Deck?
If you’ve ever seen a piece of wood left out in the weather for any period of time, you know what happens: decay. Whether through wet rot, insect damage, or mildew, the fibers begin to break down.
How to Angle Corners and Joists
Learn how to frame a deck with angled or clipped 45-degree corners using a cantilever beam.
How to Attach Deck Post Bases to Concrete Footers
Follow our step-by-step instructions on how to install a support post to a concrete deck footing using a post base connector and anchor.
What to Consider When Building A Wrap-Around Deck
Looking to add a wrap-around deck to your home but unsure of what the process involves? Check out this guide to learn more about top considerations when building a wrap-around deck.
How to Demolish & Remove a Deck
At some point, it might become necessary to remove an old deck, due to age or condition. Learn more about what's involved in a deck demolition and removal project.
Explore Articles by Topic
Footings
Information related to installing frost footings for decks
Framing
Learn structural framing methods
Decking
Learn about wood and composite decking materials
Stairs
An in-depth look at the complex issue of how to build stairs
Railings
How to install guardrails and handrails to meet IRC code
Features
An overview on water drainage, benches, planters and lights
Design
The basics of deck design
Planning
Learn about permits and working with contractors
Porches & Patios
Build a covered deck to enjoy all seasons
Ledger
Proper attachment techniques
Care
Maintain your deck to maintain your investment
Materials
An overview on water drainage, benches, planters and lights