An on-going series of inquiries from consumers & industry professionals sent to Info@NADRA.org.
“I am planning a deck on the back of my home. I am wondering if I am missing something.
I want to use 6×6 post and notch them for my beam and rim joist as one, then just carry it up to be my hand rail posts also. Other than maybe cost and the extra work of dealing with the heavier pieces this seems like the way to go but I don’t see anyone doing it. Am I missing something as a non professional as to why this would not work?
Other details: Deck height on one end will reach 36 inches. Total deck size will be about 24 feet along the house and a max of 12 feet out away from the house.”
Answer provided by Glenn Mathewson, NADRA Technical Advisor:
Thank you for reaching out to us for assistance. The NADRA membership supports the organization to offer commentary to those seeking a better understanding of the deck and railing industry. The International Residential Code (IRC) is a model code developed by the International Code Council. Government authorities very often reference this document for the regulation of single family homes, but they often make amendments to change the rules. The guidance herein is only in regard to the unamended model code, as we are unaware of your locally adopted building code. The subject of guards may or may not be amended. have reached out to our advisors to provide you assistance.
What you are proposing is not unusual in anyway and can produce a very sound and beautiful deck and guard. Being a technical subject, it is important we clarify that you are referring to “guards” and not “handrails”. Handrails are only the graspable rail found beside stairs and ramps to assist in ascending and descending. A guard is a feature at the edge of an elevated walking surface meant reduce the likelihood of a fall off the edge. Presuming you are speaking of a guard, we will continue.
According to the 2018 IRC, guards must be designed to resist a 200 lb load placed at the top of the guard, currently in any direction. To achieve this design load through testing, an ultimate strength of no less than 2.5 x the load must be resisted. This is a 500 lb test load. Research has been done on this load for guard post connections and found that a 4×4 post could not be notched at the point of connection. No testing occurred on a 6×6. In the development of the next edition of the IRC, the 2021, much discussion was made by industry professionals on the subject of notched guard posts. A proposal was submitted and approved for this code, based on the research and engineering analysis, that prohibits the notching of 4×4 posts. In the discussion for this proposal, 6×6 posts were brought up. When notched to retain at least 3.5 inches of material in the “flange” it was agreed that notching a 6×6 should not be prohibited by code at this time and without further research. No code provisions were approved with relation to 6×6 posts.
In the absence of prescriptive design methods or provisions provided by the code, a design professional is necessary to validate structural performance. Therefore, we cannot provide you any definitive answer, as there is not yet an established accepted and generic practice to notching 6×6 guard posts. We can tell you that it can be achieved sufficiently, and is a design seen in the industry. Here are some things to consider as you make your decision:
- 1) Determine if there are local design standards required by your local building department.
- 2) Discuss the design with your local building department.
- 3) The design of your guard assembly as a whole can have an impact on the load resistance the post to beam connection must resist. Evaluate this.
- 4) Notching of material must be done with consideration to any knots, wane, or damage to the member near and at the notch location.
- 5) Do not overcut your notches with a circular saw, as this equates to a deeper notch.
- 6) If it is preservative treated lumber, you need to field treat the inside of the notch. If cedar, you do not.
- 7) At a minimum, do not leave less than 3.5 inches of material remaining in the untouched portion.
We hope this information will be helpful to you in your project.