Deck Guard Post Code Proposal

[Glenn]

In my work for the North American Deck and Railing Association, I have been representing the industry as a whole in the Deck Code Coalition. Together we put forward a handful of proposals for the 2021 IRC related to decks. I am highlighting them in articles over the next few weeks.
Deck guards are notorious for poor installations. The whole subject is under scrutiny, including the load capacity and direction of loading. Many wanted a prescriptive way to build wood guards, specifically detailed. Others are concerned too much specification in the IRC will limit design freedom. We argued many differences, but agreed on a few problems to address in the IRC in two proposals.
Please read the blog on RB185-19 and RB301-19.
185 was approved by the committee.
301 was disapproved by the committee and we have submitted a public comment.
Please ask me any questions you may have or contribute any of your own ideas and thoughts.
This is NOT an easy subject to tackle in code.
http://www.nadrablog.com/?p=5146

 

[steveray]

Never heard of a notched 4x4 failing....Connectors, yes, but the actual post, no....

 

[Glenn]

Never heard of a notched 4x4 failing....Connectors, yes, but the actual post, no....

I personally have not either. However, many, specifically engineers, will have no talk of notching posts when it comes to legitimizing code provisions. Though myself and NADRA do believe some guard systems (specifically with many corners/turns) could be built just fine with notched guard posts, in working with others to compromise and agree, it was decided to support this prohibition in lieu of a specific guard design detail in the body of the IRC.

Here is the research from 12 years ago that started all the concerns of legitimizing guard post connections. Bear in mind these tests are all on stand alone posts without any guard members helping to support the loads. Here is a quote from the article about notching.

https://www.structuremag.org/wp-content/uploads/2014/09/C-LL_Wood_Post_Connections_by_Loferski1.pdf

"Some configurations included notched 4x4 posts attached with bolts to the band joist. Although none of the 4x4 laboratory test posts failed at the notch, notching reduces the strength of the post significantly; guard-rail posts should not be notched. Repeated in-service moisture cycles typically cause cracks to develop and propagate from the corner of the notch along the slope-of-grain. Thus, notches in a guardrail post, coupled with “grade permitted” slope-of-grain and moisture cycles, can produce a very weak guardrail post during the service life of the deck."

 

[Sifu]

I am sure you and many others have read it but there was a test of these connections at Virginia Tech some years ago. It was good information but without any real ability to limit these connections in the code. I think your proposals offer some prescriptive guidance, which is what the IRC is supposed to do. While I don't personally know of any failures of these connections I can say many times that I have seen deflections far greater than what the code allows. A notched 4x4 post creates an incised cut prone to failure and limiting that seems to be a good step.

 

[Sifu]

You were faster than me......that is the study I referenced!

 

[steveray]

Love engineers.....Solving a problem that does not exist.....Guess we should stop allowing let in bracing and ribbon strips too as they weaken the building.....