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deck

linnrg

Sawhorse
Joined
Mar 17, 2015
Messages
516
Location
Sterling Alaska
IRC 2009 had allowances for 4"x4" post for decks (up to 6'9") but the DCA 6 requires only 6"x6" posts. IRC 2012 dropped the deck post table. 2018 IRC allows for the 4x4

Why did this change at the DCA 6 to only allow 6x6?
 
IRC 2009 had allowances for 4"x4" post for decks (up to 6'9") but the DCA 6 requires only 6"x6" posts. IRC 2012 dropped the deck post table. 2018 IRC allows for the 4x4

Why did this change at the DCA 6 to only allow 6x6?

Okay... lots here to clear up. Please take no offense (seems you have to put that disclaimer on the internet if you are going to just talk straight)

1) Deck posts were never addressed in the IRC until the 2015 edition. I know, because I was part of the group that wrote the proposal. I also wrote ICC's 2009 IRC deck book. There is nothing at all, period, in any earlier edition than 2015.

2) Do not get the IRC confused with the DCA 6. They are NOT the same. The DCA 6 is NOT a minimum standard guide. The AWC will tell you this directly.

3) The limit for 6' 9" is only in the 2018 IRC and is only when a 4x4 is supporting a 3-ply beam. See the footnote in the table that returns the maximum 4x4 height to 8 ft. when supporting a 2-ply beam.

4) We revised the table again for the 2021 and it is going to be AWESOME. It was expanded considerably. It now provides for different species of lumber and different snow loads. It is also based on the actual tributary area supported by the post (not the very conservative assumption of loads based on beam plies). Under certain design conditions, a 4x4 can now be up to 14 ft. tall. You could use this now to size posts supporting multiple deck levels or a deck and a roof. Same for the footing table. Did I say "awesome" yet?

5) My 2nd edition ICC deck code and commentary book will be released this Fall and it will include both the 2018 and the 2021 codes. I encourage everyone to allow the 2021 provisions as an "alternative". They are much better provisions that will broaden prescriptive design.

6) If you ever get a chance to attend my live classes, webinars, or on-demand deck code courses, you will get a very detailed and visual explanation to all these post sizing codes. I just presented this subject last month in an ICC webinar. Maybe I should edit this part out into a short youtube video... Hmmmm....

Any questions? I'm happy to provide answers.

You can view the different IRC versions for free at codes.iccsafe.org
 
when a 4x4 is supporting a 3-ply beam.
How do you do that? Is the middle ply supposed to be centered on the post, with each outside ply getting equal partial support? Or do you prefer to have 2 plys fully supported and the 3rd getting very little support?
 
I'm not going to miss a thread titled "decks" ha, ha!
I have no doubt in that...

I am passionate about decks, as I in another life enjoyed designing and building them. That said, I like to throw in some input here and there. But this one, I know my place and will gladly step aside to you sir.

This one was right up your alley and you were the man with the answer, that is for sure.
 
Okay... lots here to clear up. Please take no offense (seems you have to put that disclaimer on the internet if you are going to just talk straight)

1) Deck posts were never addressed in the IRC until the 2015 edition. I know, because I was part of the group that wrote the proposal. I also wrote ICC's 2009 IRC deck book. There is nothing at all, period, in any earlier edition than 2015.

2) Do not get the IRC confused with the DCA 6. They are NOT the same. The DCA 6 is NOT a minimum standard guide. The AWC will tell you this directly.

3) The limit for 6' 9" is only in the 2018 IRC and is only when a 4x4 is supporting a 3-ply beam. See the footnote in the table that returns the maximum 4x4 height to 8 ft. when supporting a 2-ply beam.

4) We revised the table again for the 2021 and it is going to be AWESOME. It was expanded considerably. It now provides for different species of lumber and different snow loads. It is also based on the actual tributary area supported by the post (not the very conservative assumption of loads based on beam plies). Under certain design conditions, a 4x4 can now be up to 14 ft. tall. You could use this now to size posts supporting multiple deck levels or a deck and a roof. Same for the footing table. Did I say "awesome" yet?

5) My 2nd edition ICC deck code and commentary book will be released this Fall and it will include both the 2018 and the 2021 codes. I encourage everyone to allow the 2021 provisions as an "alternative". They are much better provisions that will broaden prescriptive design.

6) If you ever get a chance to attend my live classes, webinars, or on-demand deck code courses, you will get a very detailed and visual explanation to all these post sizing codes. I just presented this subject last month in an ICC webinar. Maybe I should edit this part out into a short youtube video... Hmmmm....

Any questions? I'm happy to provide answers.

You can view the different IRC versions for free at codes.iccsafe.org


Thank You

I also have other problems because we have 70# ground snow load. The applicant for the deck I am reviewing is one who carries a gun 24/7 (legally!) so I don't want to tell him that his little deck had to have 6x6 posts!
 
How do you do that? Is the middle ply supposed to be centered on the post, with each outside ply getting equal partial support? Or do you prefer to have 2 plys fully supported and the 3rd getting very little support?
Ya gots to read the footnote! Never forget ye footnotes, my grandpapa used to say! I can give you a fish or teach you to fish. Your answer is in the footnote. Here is the link directly to section 507. https://codes.iccsafe.org/content/IRC2018P3/chapter-5-floors#IRC2018P3_Pt03_Ch05_SecR507
 
Thank You

I also have other problems because we have 70# ground snow load. The applicant for the deck I am reviewing is one who carries a gun 24/7 (legally!) so I don't want to tell him that his little deck had to have 6x6 posts!
Send me an email to my first name @ buildingcodecollege.com (or use the contact page there) and I will send you over the approved post sizing table for 2021 IRC. It includes 70 psf snow loads now. Use it as an alternative to give your citizen the most freedom of design... or to keep from getting shot! ha, ha!

It may still have to be a 6x6 though, depending on height and area supported. Sorry...
 
I have no doubt in that...

I am passionate about decks, as I in another life enjoyed designing and building them. That said, I like to throw in some input here and there. But this one, I know my place and will gladly step aside to you sir.

This one was right up your alley and you were the man with the answer, that is for sure.
Heck ya, throw in that input! Other perspectives, experiences, regional norms, and the like will make us all more educated in our discussions. There is SO much work yet to be done in developing a quality set of minimum standards for decks. All are welcome.

It did feel nice though to be called out for this discussion. Thanks!
 
Glenn, I was wondering if you ever tried to get rid of the requirements for the deck lateral load connection because of all the testing that you posted about it before that showed that they were not really needed.
 
Glenn, I was wondering if you ever tried to get rid of the requirements for the deck lateral load connection because of all the testing that you posted about it before that showed that they were not really needed.

The "connection" is not required.....Technically

R507.1 Decks. Wood-framed decks shall be in accordance
with this section or Section R301 for materials and conditions
not prescribed herein. Where supported by attachment to an
exterior wall, decks shall be positively anchored to the primary
structure and designed for both vertical and lateral
loads.

R507.2.4 Deck lateral load connection. The lateral load
connection required by Section R507.1
shall be permitted
to be in accordance with Figure R507.2.3(1) or
R507.2.3(2).

Those just give a prescriptive way....We still don't have anything prescriptive about stringers, but hey...
 
Ok ... need help. I read through the document you linked ... carefully ... including footnotes. I don’t see one that applies.
I am with you E Hilton....

R507.5.1 (2018 IRC) indicates that beams must have bearing for the entire width of the beam. A 3-ply girder therefore cannot bear on a 4x4.

upload_2020-7-10_11-6-12.png

It seems to me that the second sentence of Footnote C of R507.4 (2018 IRC) is conflicting with R507.5.1 as it indicates that a 4x4 post less than 6-ft 9-in in height can be suitable for a 3-ply beam. Bearing width of the beam is 4.5-in; post is 3.5-in wide; what makes up for the 1-in of the beam without direct bearing?

upload_2020-7-10_11-8-16.png
 
3ply beam WITH a post cap......
We have a winner! steveray! This is exactly what I was trying get folks to read.

Here was the issue. Minimum bearing is required for conventional, prescriptive construction. It has NOTHING to do with hangers or any other metal connectors, as those are all "alternatives". FYI: despite common misconceptions, you do not need prescriptive bearing length in the saddle of a tested (alternative) hanger, unless directed as such within the design of the hanger.

Manufacturers can come up with endless ideas to transfer bearing pressures, provide they perform. Think about bearing enhancers for larger girder trusses. Manufacturers have post caps designed and tested to provide sufficient bearing and load transfer between a 3 ply beam and a 4x4. They work. They are okay. They still have to be "approved" by the BO.

The problem with the 2015 table is there was no mention of this what-so-ever. There is no understanding of how the height limits were derived provided in the code text. Those of us that developed them knew, but the code did not reveal. The 8 ft. height is based on the largest tributary area you could "prescriptively" place on a 4x4. This was 2x12 joists 12" OC and a (2) 2x12 beam on a center post (beam off both sides). Okay... but nothing in the 2015 IRC would alarm a designer that selected a 3-ply beam on an approved post cap on a 4x4. However, this would exceed the loading assumed in the prescriptive table.

For this reason, the 2018 changed as you see. I was not involved with creating the 2018 as I had more pressing stuff in life going on. What is bad about the 2018 is it's backwards. The 8 ft. should be the tabular value and the footnote should modify it to 6' 9".

It matters not. DO NOT BOTHER with the 2018 or 2015 post provisions. The 2021 table is amazing and is absolutely an acceptable "alternative". Start using it now.

Hopefully that provides the details to this. Ask questions if you have any.
 
Ok. I don’t mean to be difficult ... but ... looking in the simpson catalog for post caps, I don’t find one for 3@2x beams on a 4x post. The closest one is BC46 but the beam width is 5-1/2” ... too wide for the triple beam.
 
Ok. I don’t mean to be difficult ... but ... looking in the simpson catalog for post caps, I don’t find one for 3@2x beams on a 4x post. The closest one is BC46 but the beam width is 5-1/2” ... too wide for the triple beam.
I am in agreement Hilton....

The modifications to the 2018 related to posts seem to muddy the waters, as an approved bracket has always been acceptable where bearing conditions are larger than the post. Why the table was modified to put in a caveat for a non-prescriptive design, we may never fully know.

That said, the only product that I am aware of that allows less than full direct bearing is the following by Simpson. And to be honest, I am not a fan of these.

 
Or there is the Simpson CC64

upload_2020-7-10_13-34-13.png
upload_2020-7-10_13-36-22.png
upload_2020-7-10_13-35-0.png

But we are really starting to get into the realm of an engineering design if it is making it this far.
 
I am in agreement Hilton....

The modifications to the 2018 related to posts seem to muddy the waters, as an approved bracket has always been acceptable where bearing conditions are larger than the post. Why the table was modified to put in a caveat for a non-prescriptive design, we may never fully know.

That said, the only product that I am aware of that allows less than full direct bearing is the following by Simpson. And to be honest, I am not a fan of these.

"we may never fully know..." UH... yeah, it's no secret. I know and I'm trying to help you know, so that "we can fully know". I know all the people that created it and I worked with them on 2015, 2021 and already starting on 2024 If you're looking for hidden agendas, they aren't there. It's collaborative work by many different parties.

I'll try one more time to explain why the 2018 change was important.

This has nothing to do with approving a post cap. It has everything to do with approving a post height from a table who's engineering is only based on a 2 ply beam max span, and the maximum trib area that can be created, and then also approving a post cap to bear a three ply beam which can be sized by the code. It was a mistake in the assumptions made that a 4x4 would always only carry a 2-ply beam. A code user that does not realize the derivation of the maximum 4x4 height would not have been prompted to question it supporting a 3-ply for any reason other than the beam bearing. Such as:

"OH! you have a tested post cap for that 3-ply beam on a 4x4. No problem then." The problem is there is a problem, but it's not the beam or post cap. It's the load on the post from a three ply beam (and resulting trib area) that may now exceed what the post sizing was based on.

This is not anywhere near engineering necessity. It's a tested post cap.

I don't really know how else I can explain this. Its the inherent difficult of created pre-engineered tables. Assumptions have to be made, but they also have to be known.

Truthfully, deck codes are a brand new work in progress in codes that have been in works for over a hundred years. The 2015 and 2018 provisions should be thrown away as trial and error that has brought us to the 2021. When 2024 is done, I will say the same of throwing away the 2021. It is going to take a few cycles to plateau at a complete prescriptive set of deck structural codes.

Again, happy to answer questions, but I'm starting to feel like maybe you've already made up your minds. If you had seen my visual presentation in my recent webinar, I think you would fully see whats going on.
 
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