How many supports beams needed

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m2244

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Hello,

I am building a deck this week. I called the lumber yard and the guy there seems to think that I only need one support beam but It seems that 2 would be better. The deck is 15 x 20, the 15 dimension is out from the house, so the support beam would be 20' long and roughly 13 feet out from the house (I think). So does a 15 span out from the house need more than 1 support beam?
 
He is right if you are using 2x10s for joists If your close the ground or what is below isn't important, I would go with the extra beam and have no bounce. The beam wants 3 posts under it. The beam wants to be at least 2 2x10s.
 
If you plan to make the deck free-standing (with no ledger attached to the house), you obviously need 2 support beams. Doing so is the preferred method, as it eliminates the need for the ledger and its associated, long-term performance problems. Locating the joists with 2' cantilevers at each end will work well, resulting in a balanced design with minimal deflections if you space the 2 x 10 joists at 16" centers. If you're only using 3 posts (6 x 6s recommended by the IRC), I'd suggest cantilevering both ends of each beam to shorten the continuous spans to 8' each. Less "wiggle" and deflections when you hold those big parties on the deck.
 
Last edited:
m2244 said:
Hello,

I am building a deck this week. I called the lumber yard and the guy there seems to think that I only need one support beam but It seems that 2 would be better. The deck is 15 x 20, the 15 dimension is out from the house, so the support beam would be 20' long and roughly 13 feet out from the house (I think). So does a 15 span out from the house need more than 1 support beam?
Click to expand...

I think that it does need another support beem because if you are after the right balance for your deck then yu need to use another support beam for it...
 
My suggestion is to have this designed for you, pull permits and have inspected.

Andy.
 
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