Q: How do we know what is the acceptable deflection for guardrails?

A:  There is no standard acceptable deflection.

So what is the test? Well to achieve a 200 lb concentrated load they use 2.5 (500lb) safety factor to test the assembly (for glass rails the safety factor is 4). This is based on defined testing procedure from the International Building Code (IBC).

(Glass Guardrail deflection with minimal pressure)

2012 IBC Test Procedure- 1710.3.1 Test procedure.

So based on this criteria it was found that most common guardrail assemblies most likely do not meet the requirement defined by the code.

Per Simpson Strong-Tie "The railing connection is a crucial deck connection, and it is often inadequately constructed. In order to provide the required load resistance at the hand rail, the post must not only be fastened to the rim joist, but also be tied back into the joist framing. Machine bolts or lag screws through the post and rim joist alone do not typically meet the performance requirements of the building code. " Link to Strong-Tie PDF -  Code Compliant Guard Rail Post Connections

The American Wood Council has this very informative “Prescriptive Residential Deck Construction Guide”

So what does this mean for us as Home Inspectors in the field inspecting deck? We need to be extra careful of our evaluations. If nothing else presenting proper information to our client so they can make informed decisions when it comes to deck guardrail requirements.

Here is some additional reading-

Code Compliant Guardrails- Deck Magazine

Guardrail Deflection Limits- Matthew Blackmer, M.S.C.E., P.E

Tested Guardrail Post Connections for Residential Decks- Structure Magazine

"To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge."

Nicolaus Copernicus

NCW Home Inspections, LLC  is a Licensed Washington State Home Inspection service located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Oroville, Cle Elum, East Wenatchee, Quincy and many more…  

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