Is it possible to build a deck without a support beam?

I’m building a new deck (well, remodeling an existing one, but that’s another story) and don’t want a support beam. Anyway, it’s about 18 feet wide and I don’t want any support posts in the center, under the beam. 

I’ve spoken with several contractors and, honestly, I’m kind of at the mercy of what they tell me. But I want to be informed. Can this be done? What should I be asking?

Lauren Shepard

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Here’s what you need to know.

Yes, building a deck without a support beam can be done—barely. Eighteen feet is a long way to span and in order to get a clear span underneath the deck structure. You need what’s called an engineered post and beam system. This means a number of things:

1. Choose engineered material and not regular framing lumber. Examples inlcude jargon like PSL or glue-lam. If your contractor isn’t using this jargon—or worse, doesn’t know what it means when you do, run screaming.

2. Engineered lumber also comes with engineering. There are different sizes of these items and it usually requires an engineer to do the proper calculations to specify the right beam.

3. The posts will probably need to be engineered as well. Make sure to have this conversation with your contractor and ask about the size of the posts, too.

4. All of this impacts cost. The product simply costs more  to purchase—you’re talking a couple thousand dollars easily. Second, installation is more expensive because these engineered products are massively heavy and take more time and skill to work with. the contractor may need to rent or own a piece of equipment in order to move or lift a beam that heavy.

So, building a deck without a support beam is possible, but it takes careful design and execution. It’s essential to ask all of your questions before handing over a deposit, signing a contract, and greenlighting the project. Your contractor may order materials swiftly, and then you may not have as many options to change the plan mid-stream due to cost and time constraints.

Best of luck to you. If you have more questions, please send us a note. 

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