Diagonal boards to reduce deck racking?

[Zaf]

I've just completed a new 14'x16' deck. I used 2x10 joists, a (3)

2x10 beam (16') and (3) 6x6 posts. The deck surface is 9' above grade, footings are 12" diam 42" below grade. While the framing is well beyond code, it does still rack a little bit. I think if I put a few 2x6"s on the bottom of the deck DIAGNOLLY accross the joists, this would reduce racking. Has anyone tried this? I really dont what to put cross braces on the posts (too ugly). If diagnot boards don't help, I'm thinking one sheet of marine plywood on the bottom.

[Jeff Wisnia]

You have hit upon the correct solution. A single diagonal 2 by 6 screwed or nailed onto the bottom of the joists from corner to corner will add a huge amount of anti-racking stiffness to your deck. You could fasteners it to every joist, just to "gild the turd", but every other joist would be plenty sufficient.

If you can't easily get a 2 by 6 long enough, use a pair of shorter ones in a vee pattern running from near the two outer corners of the desk to a point near the center of the header.

I used exactly that technique on my 14 by 12 foot deck which sits on 8 foot high 4 by 4 legs.

Jeff

[Zaf]

Tx for confirmation Jeff. BTW, I also surmize that the most effective section of the diagonal piece is that of the beam edge of the deck as this is where racking will be mose pronounced. By the house edge, the movement should be minimal.

[Jeff Wisnia]

I think I follow what you're saying, but I'm not sure I agree with what you said there.

True, the absolute displacement of the racking will be maximum at the beam edge of the deck, but that's because it's the integral of the movement all along the length of the joists. I believe the most effective single diagonal brace should form the hypotenous of the right triange formed be either side and the beam edge of the deck.

And, as I mentioned, if you can't readily get a single piece long enough to span that distance, then run two pieces from the outer two corners to a point near the center of the header, forming the shape of the letter"M".

Jeff

-- Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"If you can keep smiling when things go wrong, you've thought of someone to place the blame on."