Deck Railing failure accounts for a large portion of the injuries and deaths involving structural failure of decks. Let’s take a look at why, and discuss some fairly simple measures we can take to make sure our railings comply.
First, what does the code say? The IRC 2009 requires the railing be a min. 36″ above the deck surface. Commercial codes often require 42″ heights, in part to insure it is higher than a tall persons center of gravity. The IRC requires that the railing be able to resist a 200-pound concentrated load applied along the top in any direction. With a 36″ height, that 200 lb. load becomes very large, 2000# or more. Bolting the posts to the decks Rim joist, or Band joist would seem to be fine, but that’s not where the problem exists.
According to a study by researchers at Virginia Tech, it is nearly impossible to meet these requirements building with generally accepted practices. Even when placing the post on the inside of the band and blocking behind the post, the blocking will fail where the nails or screws come out the side of the blocking. In general it is good to remember that endgrain is not our friend. The PDF shows how each technique failed except those setups that involved Lateral tension connection, like you get using the Simpson DTT2 Deck post connector. These are modified versions of the hold-downs we use for Earthquake tiedown requirements on the west coast. This hardware is screwed in with 8 SDS 1/4″ x 1 1/2″ screws , and it has a cousin, the HD2AHDG, which is bolted.
It turns out that very often the point of failure is the Band joist being pulled away from the Deck joists. Often band joists were nailed to the deck-joists, which over time will not prove to be the best. Now they are more often screwed in, and that is better as long as the right screws are used, (more on that in a later blog perhaps). While it is best to use one holddown on each railing post, using a min of 2 holddowns per length of band-joist will provide a code passing connection that will also provide an extralevel of insurance, whether your a contractor, worried about warranty work or lawsuits, or your a homeowner worried about the safety of your family. It is not necessary to place the holddown next to the band joist, and in fact I think it works better if it is backed off, that way it will always be in tension even as the wood expands and contracts.
The railings connection to the Posts is another overlooked connection and I was going to consider that here but I think it deserves a post of its own with some graphics, so I will address that in a later post.
Many contractors are going to moan and complain and try to charge a lot more if we start specifying these on our deck designs, but they don’t really take that long to install and often it can replace blocking that would have to be included and take longer to install if the hardware was not used, so I don’t think its really a valid argument. There is an excellent article by Mike Guertin from Professional Deck Builder Magazine that covers many innovative ways to use the hardware.
Again, if you have any Questions about your deck, would like a certified inspection, or help in the design, engineering, and plan preparation of your deck, we are here at Nolan Engineering to help.