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Is your deck designed to handle a crowd?


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What I see as most informative is that newer composite decking floats on joists giving little lateral resistance. Good to look out for. Cross bracing joists from beneath would fix this.

From the Don Bender news story:

"One fairly recent development in wood and WPC deckboards is "hidden fasteners" that fit in a slot on the side of each board. Great idea right? You don't see the fastener, and the slot allows the board to slip so that thermal expansion and shrinkage won't cause the boards to buckle.

The problem is that since the fasteners allow slip, the deck diaphragm has almost no stiffness from side-to-side. This means that the deck substructure must provide nearly all of the resistance to lateral loads. This can result in a complicated design that should be performed by a registered design professional."

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I have never considered structural issues with the "cool" new floorboard fastening systems; just kinda slipped by me while I was admiring how wonderful it looks without fasteners.

Note to self.....stop being seduced by pretty things....and it's corollary, imbuing pretty things with characteristics they don't have......

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What I see as most informative is that newer composite decking floats on joists giving little lateral resistance. Good to look out for. Cross bracing joists from beneath would fix this.

To meet or exceed the lateral resistance of wood decking:

How big should this cross bracing be?

How many cross braces should be there?

What sort of fasteners should be used and how many?

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What I see as most informative is that newer composite decking floats on joists giving little lateral resistance. Good to look out for. Cross bracing joists from beneath would fix this.

To meet or exceed the lateral resistance of wood decking:

How big should this cross bracing be?

How many cross braces should be there?

What sort of fasteners should be used and how many?

One cross brace. I might try a 2x10 diagonal from outside corner of deck to opposite ledger. 3 screws in each joist. 3" deck screws would do.

A steel corner iron could do this, fastened right.

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One cross brace. I might try a 2x10 diagonal from outside corner of deck to opposite ledger. 3 screws in each joist. 3" deck screws would do.

A steel corner iron could do this, fastened right.

In your backyard, in your friend's backyard, maybe in my backyard. Elsewhere, punt it. The codes don't cover it.

'Course we all know this.

Marc

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What I see as most informative is that newer composite decking floats on joists giving little lateral resistance. Good to look out for. Cross bracing joists from beneath would fix this.

To meet or exceed the lateral resistance of wood decking:

How big should this cross bracing be?

How many cross braces should be there?

What sort of fasteners should be used and how many?

One cross brace. I might try a 2x10 diagonal from outside corner of deck to opposite ledger. 3 screws in each joist. 3" deck screws would do.

A steel corner iron could do this, fastened right.

Hmm. Given a 12x12 deck with joists at 24" oc, and 2x6 decking, there would be about 336 3-inch screws holding traditional wood boards to the deck. Even if the boards are not running diagonally, that's a fair bit of lateral strength. (It would be greater if the boards were wider or if they were run diagonally, but it's still a lot of strength.) You're plan would replace that strength with 21 screws in a single board. What value are you using for the shear strength of the screws? Are you derating for wet conditions? Are you sure that your screws in that orientation are going to provide 16 times the strength of the screws in the original configuration?

I only pose these questions because this stuff isn't as straightforward as it seems as first. It's easy for us to say, "just put a diagonal batten under the joists," but the details are often more complicated.

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What I see as most informative is that newer composite decking floats on joists giving little lateral resistance. Good to look out for. Cross bracing joists from beneath would fix this.

To meet or exceed the lateral resistance of wood decking:

How big should this cross bracing be?

How many cross braces should be there?

What sort of fasteners should be used and how many?

One cross brace. I might try a 2x10 diagonal from outside corner of deck to opposite ledger. 3 screws in each joist. 3" deck screws would do.

A steel corner iron could do this, fastened right.

"Deck" screws are not rated for structural applications.

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It is not an easy question to answer because lateral loads on decks are not well understood. I think a worst case lateral load for a deck is about 12 psf. So with a 15x15 deck that would be 2700 pounds. Then try to figure out the stiffness of the decking and how the forces are transferred into the brace. Force is proportional to deflection, so as the deck sways a little the fasteners in the brace near the outside edge of the deck see more of the force.

If the deck is high, then bracing the columns is also advisable, but the columns have to be large enough so they are not overloaded in bending.

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What is the lateral force of 12 heavy adults dancing the polka, not necessarily in time, on a 12' x 12' deck, 12' from the ground? An HI might especially consider this on a deck with hidden fastener composite decking.

Luckily as an HI I don't do that kind of arithmetic.

I have been on some really scary decks that were owner/uncle/buddy-built. One had hardiboard, thinset, and grouted ceramic tile piled high onto 5/4 pine on spindly 4X posts.

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