Photo: Mike Guertin

For years, the IRC has required that deck top railings be strong enough to resist 200-lb. concentrated loads applied at any point and in any direction along the top of the top rail. The purpose of the 200-lb. load requirement, of course, is to prevent someone from falling from an elevated deck for any number of reasons, including simply tripping on the deck surface. Unfortunately, despite efforts to introduce prescriptive guard post connection details into the code that would meet the 200-lb. outward load requirement (see Looking Ahead to the 2018 IRC, by Chuck Bajnai, PDB September 2016), the 2015 (or 2018) IRC doesn’t offer guidance for builders or inspectors on how to connect the guard post to the deck structure, meeting the IRC requirement.

But there’s another potential avenue for getting guard post design details into the hands of builders and building officials: By creating an ICC Guideline. Though not a code or standard, and therefore not mandatory, an ICC guideline could be used to provide a pathway to details that could eventually be adopted by the IRC. In the meantime, the Guideline development process could open the door for input by all stakeholders, especially deck contractors and practicing engineers, and result in a useful benchmark for the design and construction of guards until it is codified.

What We Know About Guard Post Connections
When someone falls through a deck guard and is either hurt or killed, the failure point is typically the connection of the guard post to the deck structure. While the outward force of a 200-lb. person simply leaning against a residential deck rail is relatively small, if that person trips the dynamic load on the top rail can easily reach 200-lbs. or more. And as our testing at Virginia Tech has shown (see Tested Guardrail Post Connections for Residential Decks, Structure Magazine, July 2007, and Strong Rail-Post Connections for Wooden Decks, JLC, February 2005), guard posts and their connection to the deck (or balcony) structure are most highly stressed when loads are applied at the top of the post and in an outward direction.

Without guidance from the code community, many deck contractors “guess” as to what detail constitutes a safe guard post connection, typically followed by a plan reviewer or building inspector making an approval decision without guidance beyond what they may have seen used in the past. Because of the lack of prescriptive detail in the IRC, some building inspectors use the “push test” to evaluate a guard, where they apply a small load - maybe 15 lbs. – and observe how much the guard deflects. But this test is a measure of stiffness, not strength: A dangerous nailed-on guard post could appear stiff when loaded by a small outward load, yet with a slightly larger load, the post connection to the deck band can suddenly fail, resulting in total collapse of the guard section.

For comparison, think about pulling out a nail with a claw hammer or crow bar. On the first attempt, the nail may not even budge, but a second and more forceful attempt can produce nearly total withdrawal of the nail. Pushing on a constructed guard post is analogous to the first attempt at removing the nail with a claw hammer; tripping and falling against the post is analogous to the second, more forceful attempt.

Here is the simulated deck joist/band/guard post configuration tested by the team at Virginia Tech. A chain was attached 37.5-inches (36” code required+1.5”) above the joists, over to a pulley, and up to a load cell. The test was conducted by raising the test machine load head which produced a horizontal force on the guard post.
Here is the simulated deck joist/band/guard post configuration tested by the team at Virginia Tech. A chain was attached 37.5-inches (36” code required+1.5”) above the joists, over to a pulley, and up to a load cell. The test was conducted by raising the test machine load head which produced a horizontal force on the guard post.

Our team at Virginia Tech University tested stress-rated 4x4 guard post connections from 2004 through 2008. Our lab test specimens were “perfectly fabricated” using new No.2 Southern Pine lumber for the framing, and 4x4 guard posts. Over the 5-year period of our research, the tests were witnessed by hundreds of continuing education course participants, about a quarter of them code officials, inspectors, or plan reviewers. What we found is that common guard post connections typically would fail at loads between 20 percent and 75 percent of the target test load of 500 lbs.

Why 500 lbs., instead of the IRC-designated 200-lbs? The purpose of a test safety factor is to account for a number of variables, including the fact that actual deck guard post connections are never “perfectly fabricated” in the field. Other variables include the near weakest post in the tested grade and species, the near lowest density of the joists that holds the bolts or screws, and uncertainty about the maximum load the post connection will experience in-service. Based on our judgment, we selected a test load safety factor of 2.5, which was also the minimum test safety factor in previous editions of the model building codes.

This post detail - which relies on blocking, ½-inch bolts, and screws - failed the load test. In fact, the only post details that passed the authors' testing were ones made with load-rated metal connectors. Without the connector approach, the deck band “peels off” at load levels between 20-75 percent of the test requirement.
This post detail - which relies on blocking, ½-inch bolts, and screws - failed the load test. In fact, the only post details that passed the authors' testing were ones made with load-rated metal connectors. Without the connector approach, the deck band “peels off” at load levels between 20-75 percent of the test requirement.

After a long series of unsuccessful test configurations, we finally figured out a way to build a guard post connection that could resist the 500-lb. test load at the top of the post. The solution was to use load-rated connector rather than a “fasteners only” approach. The “connector solution” for attaching a guard post to decks has been widely published in contractor magazines and engineering journals. In fact, the American Wood Council’s popular DCA-6 includes a detail for connecting a 4x4 post to a deck, which is based on our published research on guard post connection testing. This is a resource that often is used by deck builders, building code jurisdictions, and by homeowners, many of whom rely on its deck post connection recommendation. To our knowledge, at least three manufacturers now market metal hardware specifically designed to be used for connecting guard posts to decks. However, despite these efforts, none of these solutions are in the IRC code.

The AWC's DCA-6 guard post connection detail, which is strong enough to meet code requirements.
American Wood Council The AWC's DCA-6 guard post connection detail, which is strong enough to meet code requirements.

The Value of an ICC Guideline
Plan reviewers and inspectors are left without guidance - beyond DCA-6 - on any proposed alternative details that would have sufficient strength to safely resist the code-mandated 200-lb. concentrated load requirement. Some contractors argue – without any testing evidence – that there are other 4x4 guard post connection details that are safe. But without that evidence, and because of the gap in the current IRC on how to prescriptively construct a guard post attachment to a deck, the code community faces the near impossible task of ensuring that deck guard constructions they approve will in fact safely resist the code specified design load in-service.
Until a proposal to the IRC for prescriptive guard post details is finally approved and adopted, an ICC Guideline could be valuable in an attempt to protect life and prevent fall injuries/fatalities from decks and balconies. Plan reviewers need a concise document that addresses the complicated issue of guard post attachment to decks. The value of the proposed Guideline is vast—all residential plan reviewers can benefit from an ICC published Guideline by using it in deck/balcony plan checking and inspection until this life safety issue is addressed by the IRC, hopefully within the next decade.