NADRA CODE UPDATE

August 14th, 2019

By: Glenn Mathewson

Proposal RB190 – Table R507.5

Through the efforts of NADRA.org and other organizations and professionals, the 2015 IRC revealed the first deck beam-sizing table (Table R507.5) to ever be included in a US model code.  It provides maximum spans of simple deck beams based on different loading, species, profiles, and number of plies of common lumber.  It was a welcome addition for building departments that have long struggled to approve deck designs without requiring an engineer and without having to develop their own span tables, as many had done.  The American Wood Council (AWC) created their popular document, DCA6, to help alleviate this problem and provide pre-engineered design tables.  These tables would become the 2015 provisions, and still today the AWC provides the engineering for most of the new deck structural provisions.  For contractors working in regions not utilizing the DCA6, the new tables came as a little shock.  In comparing the beams spans that have been acceptable, the new IRC tables cut them down dramatically.  Why?

Creating a pre-engineered design table is not necessarily simple, specifically for beams.  To provide a maximum allowable beam span, the load the beam is supporting has to be known.  In its most simple form, a beam supports joists of the same length and carries half that length.  A ledger, presumably, is carrying the other half.  Those same joists, however, could cantilever beyond the beam, and the beam would support the entire load of the cantilever.  This is just one design variable of many.  A beam could be at an angle and support a non-uniform load along its length, or it could be supporting joists spanning from both sides.  Currently none of those variables are provided in the code.

Why did many allowable beam spans suddenly reduce with the new code?  The table is calculated on the assumption that every beam is supporting maximum-cantilevered joists.  In many cases, joists can cantilever beyond the beam up to 1/4 their span, and that’s a lot of added load…load that is being designed for every time, whether there or not.  Consider a deck with a 12 ft. joist span and no cantilever.  The beam is actually carrying 6 feet of joist, but the code is sizing it as if it’s carrying 9 ft., because it’s assuming the maximum allowable 3 ft. joist cantilever is there.  If you did cantilever the joist the maximum distance, the table is accurate.  If you didn’t, your beam spans are unnecessarily restricted…significantly.  Okay—Let’s fix that!

The NADRA proposal RB190 adds a footnote to the beam span table with a set of modifiers.  The modifiers allow you to alter the input “joist span” in the beam span table based on different percentages of joist cantilever from zero to one-fourth.  Included are cantilevers of 1/12, 1/10, 1/8, 1/6, and the maximum 1/4 of the joist span.  Currently, a (2) 2×10 southern pine beam supporting a 12 ft. joist span is restricted 7 ft. – 4 in., REGARDLESS of whether the joists cantilever or not.  With RB190’s modifiers, if the joists don’t cantilever, the 12 ft. span can be multiplied by .66 to yield an equivalent span of 8 ft.  Using this value in the table results in an accurate maximum beam span of 9 ft.  That’s no small margin from the current 7 ft. – 4 inch maximum!  There is no reason not to allow beams to be sized for their actual loads, and possibly reduce some costs or visually obstructive posts from our neighbors’ backyards.

Proposal RB190 was prompted by NADRA, developed with the help of the Deck Code Coalition, and engineered by the American Wood Council.  It is solid engineering in a solid concept.  It was approved at the Committee Action Hearings with no opposition.  There is good reason to believe it will make it through the last part of the ICC code development process, the Final Action Hearing.

Please support proposal RB190 and let’s maintain an appropriate balance between safety, design freedom, and affordability. 

Please contact NADRA for any questions or concerns regarding this proposal.  We welcome your conversation. You can send an email to Info@NADRA.org

NADRA Code Update

July 3rd, 2019

By: Glenn Mathewson

To finish a marathon, you’ve got to push through the last mile.  Such is the same with developing a new edition of the International Residential Code.  Thousands of people are currently running a marathon toward the 2021 IRC, and though they are halfway through, there’s no telling who (or who’s proposals) will make it to the finish line.  While it’s too soon to start cheering, it’s not to soon to feel confident and strong, and that’s how the NADRA and Deck Code Coalition proposals are looking.

With the publishing of the final report from the Committee Action Hearings, the public can not only see the results of the hearing, but also a summary of the comments made by the committee.  There are three result categories, but since those aren’t “final” results, the comments should be the focus.  The committee comments could be looked at as spectators cheering on or booing the runners.  They provide direction, encouragement, and suggestions, much like “you got this! Keep going! You’re so close”.  Unfortunately, sometimes the comments can feel more like “you’re never going to make it! Give up now!  You look so tired!”

The race is not over until you pass the finish line, and sometimes people get a second wind.  That’s what the next phase of the code modification process can offer—a second chance.  Regardless of the committee result, every proposal can receive a public comment modification, and if received, the proposal will be heard again at the final hearings, where a final vote will be made…but not really.  The final vote is actually made online a few weeks after the hearing.  In this vote, only governmental ICC members can cast the final thumbs up or thumbs down.   These members could vote down a proposal approved by the committee, and likewise, the members could turn around a proposal disapproved by the committee.

Public comments to the committee results are due July 24th and these will be the catalyst for the next step in the process.  A proposal that does not receive a public comment is almost certain to be finalized as-is in the “bulk vote” where the governmental members vote for the entire package of proposals.  Having not received any disagreement from the public, the assumption is that the committee opinion is good to go.  Here is the part to pay close attention to:

If the committee result for a proposal is not challenged by July 24th, consider it done.  If there is something you don’t like, silence is equivalent to support.

So let me put it this way…  “Speak now or forever hold your peace”.

Okay…that’s not exactly true, but you would have to hold it until the 2024 IRC code development hearings where everything is on the table again.

Thanks to select NADRA members that have financially supported NADRA representation in the code modification process, I am working alongside other professionals in the Deck Code Coaltion and we are preparing public comments.  We are running this marathon until the end.  I hope you are on the sidelines cheering us on.  Here are the results and comments from the Committee Action Hearings that have us in a runner’s high.  You can view all the Group B ICC documents and the live video from the Group B hearing at this link:  https://www.iccsafe.org/products-and-services/i-codes/code-development/

RB184: Disapproved

Committee Reason:  There were multiple corrections expressed in a modification that the committee felt was too extensive. The wording in Section 507.4 is confusing. The committee urges that the corrections should be brought forward in a public comment. The collaborative effort, and inclusion of engineers in the effort, was a positive aspect for this proposal. (Vote: 10-1)

RB185: Approved As Modified

Committee Reason: The modification to Section R507.10.1.2 removed ‘approved’ because this adjective cannot be applied to manufacture’s instructions. The modification to Section to R507.10.2 reworded the two sentences for clarity. The modification to Section R507.10.4 removes ‘approved’ because this would be confusing to the homeowner. The proposal provided good general prescriptive language for guards that will reduce the need for engineering of guards. The committee had several suggestions for better wording that should come forward in a public comment: Add ‘also’ to Section R312.1.4; ‘design’ instead of ‘construction’ in Section 507.10; revise ‘prevent’ to ‘limit’ in Section R507.10.1.1; joists are part of the deck framing, so the language in Section R507.10.1 is confusing. (Vote: 9-2)

RB186: Approved As Modified

Committee Reason: The modification restores rivets and puts in the term ‘glulam’ to be consistent with the term used in ASTM F1667. Adding the Class D is appropriate for this product. (Vote: 11-0)

RB187: Approved As Submitted

Committee Reason: The committee felt that the overall proposal is a good reorganization that add clarity to the code requirements. Item 3 in Section R507.3.3 is an alternative means that is currently allowed in Chapter 1. (Vote: 11-0)

RB188: Approved As Submitted

Committee Reason: This revision will clarify the engineering option for deck beams where fastened together. (Vote: 11-0)

RB189: Approved As Submitted

Committee Reason: This change clarifies the cantilever limitations. (Vote: 11-0)

RB190: Approved As Submitted

Committee Reason: The proposed footnote allows for a design that does not use the full cantilever, which will allow for a more efficient design. If you do not use this option, the table is more conservative. The commentary should include an example. (Vote: 11-0)

RB191: Approved As Submitted

Committee Reason: The revisions add clarification to the code and allows for better design practice for wood decking. (Vote 11-0)