NADRA Code Update: Should Decks be Built Like Stairs?

October 2019 Update

By: Glenn Mathewson

Some believe they should.  Stair treads must resist the same uniform load as decking, but with an added requirement to resist a 300 lb. concentrated load at mid span.  Consider the impact your feet place on treads as you come running down them. This extra requirement is not without consequences, as spans allowed for composite decking are often reduced when used for stair treads.  Many products require minimum 12- or 10-inch stringer spacing. This could be the future for joist spacing. Do I have your attention?

Though NADRA has been involved in the International Residential Code modification process, there are many other organizations and processes that affect the codes and standards of the decking and railing industry.  The American Society of Civil Engineers is one such organization. They develop the ASCE 7 standard, Minimum Design Loads for Buildings and Other Structures, which establishes the minimum design loads historically copied into the International Code Council’s (ICC) building and residential codes.  

In the ICC hearings, NADRA has supported a proposal to adjust the loading direction required of guards that was submitted to the International Residential Code (IRC) development process this year.  At the ICC hearings, the committee did not approve the change and requested it first be made in the ASCE 7 standard. We will contest this at the IRC final hearings this week, but we also turned our attention to the ASCE standard development process.  Last week, by luck, the ASCE committee was meeting in Denver, and with a short drive and NADRA support, I was able to attend.

Though I was going there for the guard proposal, another one came up, and my concerns for guards were quickly replaced with decking.  A proposal was received to require all deck boards to resist a 300 lb. concentrated load at mid span, just as is required for stair treads.  The committee discussed the reasoning, that ladders can place a concentrated load on a single deck board upwards of this magnitude. Prior to closing their discussion, they invited comment from guests. .

I shared concerns of proposals that place additional loads on decks different than inside a house, where ladders could similarly be used.  I explained how composite decking spans are reduced when used on stairs and subjected to a 300 lb. design load. I asked if they had the data on how wood and manufactured decking product maximum spans would be affected by the proposal.

It appeared this analysis was not included with the proposal, but the committee was interested.  They turned the question back to me—to NADRA… Now the ball is in our court to answer. How will this affect our industry?  Will current composite decking formulations on the market require a reduction of joist spacing to support this load? Will manufacturers “simply” change formulations and retest in order to maintain current spans?  Will joist spacing for wood decking require reduction?

We are working on some of these answers, but you should be too.

Because this could become the new rule.

Leave a Reply