Deck lateral supports

[Joe Funderburk, CMI]

How high does a deck post need to be before it needs lateral supports? Can't get a clear answer to that question in the IRC.

[ccurrins]

POST REQUIREMENTS

[R407]

All deck post sizes shall be 6x6 (nominal) or larger, and

the maximum height shall be 14'-0" measured to the

underside of the beam. Posts shall be centered on

footings. Cut ends of posts shall be field treated with an

approved preservative (such as copper naphthenate)

[R402.1.2]. The beam shall be attached to the post by

notching the 6x6 as shown in Figure 8 or by providing
an approved post cap to connect the beam and post as

shown in Figure 10. All 3-ply beams shall be connected

to the post by a post cap. All thru-bolts shall have

washers at the bolt head and nut. Attachment of the
beam to the side of the post without notching is

prohibited (see Figure 9).

This doesn't mention lateral support, only max. height.

[Marcel R. Cyr]

Originally Posted by jfunderburk

How high does a deck post need to be before it needs lateral supports? Can't get a clear answer to that question in the IRC.

Attachment 27807

Hi. Joe.

Unfortunately there are no hard rules regarding bracing. You will probably not be required to install bracing but it is an option worth considering because it will increase the strength of your deck. Bracing between posts using X or K bracing can be also be used to make a deck more rigid. In this method you attach 2x4’s or 2x6’x from the top of one post to the bottom of the next and vice versa resembling the understructure of a wooden railroad bridge. This technique is rarely used because it is obstructive and unattractive. One of the only situations where you would be likely to need X bracing would be if your deck had long support posts and was sited on a sloping lot.

http://www.decks.com/article82.aspx

My opinion, on this would be to install solid bridging at a 45 degree to the outside corners back to the house attachment or install the decking boards at a 45 degree to parallel and this would only be done when the sway stability of a deck is in question.
Typically, the deck boards provide enough stability for the sway and the
knee bracing is not necessary.
Unless the support post exceed the axial stability under load due to extreme heights.

Hope this helps.

Marcel

[Kenton H. Shepard, CMI]

Stand at the front edge of the deck (or balcony), spread your legs apart, grab the handrail and shift your weight left and right real hard to try to make the deck rock back and forth... if it feels solid, it's OK. If it moves very much... recommend diagonal (also know as "knee") braces be installed by a qualified contractor.

Sellers will whine and whine about this, but it's a cheap fix, and if you get 25 people dancing to a beat on a 2nd story deck and it collapses (and it can) , people can get badly hurt and you may be liable.

It's really an engineering question and you can also recommend a structural engineer, but the braces can be installed for as much or less than the cost of an engineer. If it moves much, an engineer will recommend braces anyway. Those guys are terrified of liability.