# Deck Cross Bracing: The prevention of "racking".



## dutchswan0311 (Sep 13, 2011)

Construction of our deck is underway, but I had not considered the many different design methods for the prevention of "racking". In some cases, I see an |X|style bracing between posts created, and in other cases I see a |/ brace for corners and a \|/ brace for middle posts. Which do you all believe is the most effective type of bracing to prevent lateral movement of the deck parallel to the structure? 

Below are the blueprints to our deck, and the latest image that shows our progress. I have employed the use of a full |X| type of brace between the first and second end posts. While it is sturdy to be sure, I am not really sure that I like the "look" of it. Another question I have is how many braces are required? Do we brace just the posts that are farthest from the structure, or do we do all of them? Online research is inconclusive to me because I haven't really seen any decks as large as ours (33' Wide x 20' Deep for the upper & 12' Wide and 14' Deep for the lower). In the blueprint image I have depicted in GREEN my current plan of which posts I intend to brace. Are there are any professionals in the room that can critique this plan? Finally, do I need to brace any posts perpendicular to the structure?


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## Willie T (Jan 29, 2009)

Normally, I wouldn't sweat it, but you COULD have a fair number of people on that deck doing something all together as a group, like line dancing, that might set up a lateral motion that could begin to affect the stability. So, in this case, not a bad idea.

Personally, for aesthetics, I think I would brace only the inside piers... and with cables and turnbuckles, not big fat wood. And the stairs will probably take care of that pair of piers as well as the other outside ones.


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## MTN REMODEL LLC (Sep 11, 2010)

Guys.... I'm not anywhere close to knowing if the below method even effects racking... proably because I'm not entirely sure from an engineering standpoint what racking is.... I kinda think of it as shear on a horizontal surface...:huh:

But on decks that I'm concerned as to possible lateral movement, I'll cross brace the posts as discussed by the OP, where aesthetics isn't a concern.

But where aesthetics is a concern, I use cable, I bolts, and turnbuckles applied as X-bracing under the surface of the deck (not as a replacement for wood x-bracing my posts.

Hopefully, an engineer will jump in with some critique/ explanation /understanding of the issues around racking.

Also, would not racking be less of a concern on the OP's relatively low deck verse a higher deck with taller posting? ( I guess intuitively, racking does not appear to be a primary concern to me on the OP's deck)

TIA for input


EDIT: OP... if you have line dancing on the deck, could not you just divide them in half and have them stand back-to-back. (smiley... not on edit function)

Besides racking, I'm a novice on line dancing also.


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## dutchswan0311 (Sep 13, 2011)

I suppose I should add that the cross-bracing employed on the first set of posts in the picture are 12' 2x6s installed on either side of the 6x6 posts. The ends are fastened using carriage bolts, and I also used a carriage bolt to fasten the middle of the X together using an 8" 6x6.

I had thought of using cables instead of wood, but wasn't sure how readily available such a thing is to the consumer market. I haven't yet checked the big box stores. While I knew bracing would be required, I had not put much thought into how I would do it until now, and have yet to research such alternative methods. (Hence my post on this forum).

With regard to line dancing: I have programmed my deck to self destruct should such a detestable act ever occur on it haha. Then again, you have to give the paying customer what they want. I can only hope the deck line dancing crowd is not among my target audience.


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## MTN REMODEL LLC (Sep 11, 2010)

dutchswan0311 said:


> I suppose I should add that the cross-bracing employed on the first set of posts in the picture are 12' 2x6s installed on either side of the 6x6 posts. The ends are fastened using carriage bolts, and I also used a carriage bolt to fasten the middle of the X together using an 8" 6x6.
> 
> I had thought of using cables instead of wood, but wasn't sure how readily available such a thing is to the consumer market. I haven't yet checked the big box stores. While I knew bracing would be required, I had not put much thought into how I would do it until now, and have yet to research such alternative methods. (Hence my post on this forum).
> 
> *With regard to line dancing: I have programmed my deck to self destruct should such a detestable act ever occur on it haha. Then again, you have to give the paying customer what they want. I can only hope the deck line dancing crowd is not among my target audience*.


:thumbsup:

Dutch.... You may have a torsional issue with dancing poles :thumbup:


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## dutchswan0311 (Sep 13, 2011)

MTN REMODEL LLC said:


> Also, would not racking be less of a concern on the OP's relatively low deck verse a higher deck with taller posting? ( I guess intuitively, racking does not appear to be a primary concern to me on the OP's deck)


Before the application of the bracing you see in the picture, I was able to "wobble" the deck a little by standing next to it and shaking it as hard as I could. This was before the installation of the 3rd and 4th beams on the right, but was quickly neutralized with the installation of the coss-bracing. As it stands right now, I cannot move the deck at all no matter how hard I try. Of course, there is a difference between what a 180lb man can do standing next to the deck, and the kind of lateral movement 10,000 lbs of line dancing folk can generate.


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## MTN REMODEL LLC (Sep 11, 2010)

dutchswan0311 said:


> Before the application of the bracing you see in the picture, I was able to "wobble" the deck a little by standing next to it and shaking it as hard as I could. This was before the installation of the 3rd and 4th beams on the right, but was quickly neutralized with the installation of the coss-bracing. As it stands right now, I cannot move the deck at all no matter how hard I try. Of course, there is a difference between what a 180lb man can do standing next to the deck, and the kind of lateral movement 10,000 lbs of line dancing folk can generate.


Dutch.... Understand what your saying, but you don't have your flooring (decking in this case) on yet. I'm older and weigh 160, and I can push over a stick framned wall with no sheathing. Decking provides a structural, not just an aesthetic element.

However, I agree with you entirely in that the better structurallky you can build,the better. It's just that I can always wobble my rough on a deck (almost always)


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## Willie T (Jan 29, 2009)

An interesting point is that an actual "X" configuration is unnecessary and superfluous since you have more than just two posts to work with.

Start at the outer edge, and attach a cable high up.... run it down to the bottom of the first post inward.... then run it back up to the top of the third post (forming a "V")... and you have achieved the necessary bracing. Half the cable, and it looks twice as good.

In the case of the deck shown already built........ coming from both outer ends, toward the middle, this WILL, unfortunately, end up with an "X" in the center bays. But that's better than having a total of nine "X"s under there.


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## Daniel Holzman (Mar 10, 2009)

The purpose of bracing is to convert a box structure to a truss structure. For those who remember high school geometry, a triangle has the interesting property that it is impossible to rotate any member around a joint (connection) without lengthening or shortening another member. Since wood is stiff and strong is tension and compression, a wooden truss resists rotation around any joint. Since rotation around a joint is what makes a deck wobble, a truss built deck is resistant to wobble, and feels very solid. Hence the purpose of cross bracing.

A deck without cross bracing relies entirely for moment (rotation) resistance on the ability of the posts to resist rotation. Since posts are typically not embedded in concrete, rather they are connected to the sonotube using a non-moment resisting bracket, posts are typically useless in resisting deck rotation either side to side or front to back. This is true of any structure built with rectangular elements, so you will see in high rise buildings that the designer will either specify cross bracing between the bays, or will rely on a moment resisting frame which uses strong plates and welds at the joints.

A house has the same issues, and for moment resistance the house typically relies on rigid sheathing between the studs (usually plywood). This converts a box structure to a rigid diaphragm structure. You could of course do the same with a deck, but it would look pretty strange to have a piece of plywood on the side of your deck.

It is not strictly necessary to brace each post on a deck, but it is required by the Prescriptive Residential Deck Code,if you are following it. From a stiffness standpoint, the best results are obtained if the brace runs from the top of one post to the bottom of the next post (maximum diagonal), however you get very good results using braces that are at least four feet long, set on a 45 degree angle, on both sides of each post, attached to a beam. The Prescriptive Code has a nice picture of the setup.


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## Willie T (Jan 29, 2009)

Great minds, Daniel. Rotational moments of inertia are my pet peeve. :yes:


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