# deck



## linnrg (Jul 9, 2020)

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?


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## classicT (Jul 9, 2020)

Oh Glenn....ya around to answer this one?

BTW, we need a way to tag a member.


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## Pcinspector1 (Jul 9, 2020)

Kinda hard to do that Ty, You have to stay 6-ft away!


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## Glenn (Jul 9, 2020)

linnrg said:


> 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


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## Glenn (Jul 9, 2020)

Ty J. said:


> Oh Glenn....ya around to answer this one?
> 
> BTW, we need a way to tag a member.


I'm not going to miss a thread titled "decks"  ha, ha!


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## ADAguy (Jul 9, 2020)

Fa LA La too (smiling)

Thanks for your efforts.


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## e hilton (Jul 9, 2020)

Glenn said:


> 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?


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## classicT (Jul 9, 2020)

Glenn said:


> 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.


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## linnrg (Jul 9, 2020)

Glenn said:


> 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.
> 
> ...




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!


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## Glenn (Jul 9, 2020)

e hilton said:


> 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


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## Glenn (Jul 9, 2020)

linnrg said:


> 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...


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## Glenn (Jul 9, 2020)

Ty J. said:


> 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!


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## e hilton (Jul 9, 2020)

Glenn said:


> Ya gots to read the footnote!


I would have, but you didn’t include it in your response.  :}


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## Rick18071 (Jul 10, 2020)

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.


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## steveray (Jul 10, 2020)

Rick18071 said:


> 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...


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## e hilton (Jul 10, 2020)

Glenn said:


> 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


Ok ... need help.  I read through the document you linked ... carefully ... including footnotes.  I don’t see one that applies.


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## classicT (Jul 10, 2020)

e hilton said:


> 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.




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?


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## my250r11 (Jul 10, 2020)

Ty J. said:


> BTW, we need a way to tag a member.



THAT'S A GOOD IDEA. Maybe Jeff can do it with our tiny budget.


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## steveray (Jul 10, 2020)

3ply beam WITH a post cap......


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## Glenn (Jul 10, 2020)

steveray said:


> 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.


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## e hilton (Jul 10, 2020)

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.


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## classicT (Jul 10, 2020)

e hilton said:


> 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.


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## classicT (Jul 10, 2020)

Or there is the Simpson CC64









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


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## Glenn (Jul 10, 2020)

Ty J. said:


> 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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## classicT (Jul 10, 2020)

Glenn said:


> "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.
> 
> ...


Why was it added as a footnote to the post sizing table, and not as an exemption to 507.5.1? Great, you have a post cap that can fit a 5.5-in wide beam and connect to a 4x4 post, but it does not meet 507.5.1 which requires full bearing width.


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## Glenn (Jul 10, 2020)

Ty J. said:


> Why was it added as a footnote to the post sizing table, and not as an exemption to 507.5.1? Great, you have a post cap that can fit a 5.5-in wide beam and connect to a 4x4 post, but it does not meet 507.5.1 which requires full bearing width.



You. Are. Killing. Me.  Ha, ha!

It's a tested post cap.  Every single mechanical connector is an alternative.  You don't write exceptions for alternatives, you review the evidence submitted and you approve them.  R507.5.1 is not about beams bearing in alternative bearing devices.  Again, the 1 1/2" bearing lengths DO NOT APPLY TO CONNECTORS.  Alternatives (connectors) can appear like magic when compared to prescriptive design.  Prescriptive design is like making a meal from the better homes and garden cookbook all our grandmas have.  VERY LIMITED.  A tested post cap is like having Wolfgang Puck come to your home and make dinner.  His methods will be quite different than the cook book.

"most" post caps are only designed for uplift and lateral displacement, but "some" post caps include bearing enhancing, like the ones we are talking about.  You approve the alternative bearing as an alternative to 507.5.1.  This is no different than...

"most" trusses get a truss clip for uplift, but "some" trusses with larger bearing loads, also get a truss bearing enhancement (TBE).  Same thing.  Its an alternative to providing a thicker wall for more bearing area.

It has to be in the post sizing table because (dear Lord, I'm saying it again), the post height limits are based on an assumed maximum tributary area of a 2-ply beam!  8 ft. is too tall for maximum loads with a IRC designed 3-ply beam.

I hope I don't confuse this, but think of approving a really tall and long 3.5" wide glued-laminated beam through a beam span table provided by the manufacturer.  You will suddenly be able to get a really long beam (longer than a prescriptive 2 2x12) and you will put way more tributary area on a 4x4 post than the IRC table was ever designed for.  The IRC, however, is clear the post supporting that glue-lam can no longer be sized with the IRC table we are discussing.

Notice we handled that in R507.4 where it says "beams sized in accordance with Table R507.5..."  So the pointer to the post sizing table restricts it's use to only beams sized by the IRC beam table.  Glue-lams aren't there.  UH-OH... 3-ply beams are... but the larger areas were not part of the engineering behind the limits for a 4x4.


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## e hilton (Jul 10, 2020)

Glenn ... I appreciate what you doing to improve the codes, and I’m not trying to be critical.  Just trying to understand.  I do get your point about 4x4 vs 6x6 posts when height is factored in.  That was good to see.  

Ty ... Why don’t you like the z bracket?   Except that its designed for beams passing along side the post, not bearing on top.


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## classicT (Jul 10, 2020)

e hilton said:


> Ty ... Why don’t you like the z bracket?   Except that its designed for beams passing along side the post, not bearing on top.


Because 9 out of 10 times that I see these submitted, the proponent wants to consider the girder as a 2-ply member when in reality, there is 3.5-in between the plies. The result is the interior member carries the full load until it deflects sufficiently to load the outer member (which at least initially, is in uplift).

Here is my pictorial representation.


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## Glenn (Jul 10, 2020)

Ty J. said:


> Because 9 out of 10 times that I see these submitted, the proponent wants to consider the girder as a 2-ply member when in reality, there is 3.5-in between the plies. The result is the interior member carries the full load until it deflects sufficiently to load the outer member (which at least initially, is in uplift).[/ATTACH]



BAM!  Excellent.  You are spot on.  The other issue is top chord bending.  With less thickness there is less resistance to the beam bending out of plane and thus deflecting more.  You are going to appreciate what we did for the 2021 on this subject.  It's subtle, but it speaks to this issue.

Look at RB188-19 at this link.  It's on page 460 of the PDF.  We added the word "together"  Just to help out a bit with the point.

http://media.iccsafe.org/code-development/group-b/IRC-B-compressed.pdf


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## Glenn (Jul 10, 2020)

e hilton said:


> Glenn ... I appreciate what you doing to improve the codes, and I’m not trying to be critical.  Just trying to understand.  I do get your point about 4x4 vs 6x6 posts when height is factored in.  That was good to see.



Thanks.  I like critical thinking and discussions about this stuff.  I want to the code to be clear.  I actually realized some issues from this conversation that I'll address in 2024.  Such as now that the post sizing table is based on tributary load, R507.4 no longer has to limit to table to prescriptive beams.  Glu-lams, the new treated LVLs, and other longer-spanning beams could have posts sized under Table R507.4.  The minimum bearing area, however, would come from the beam span design, and not the IRC 1 1/2".


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## steveray (Jul 13, 2020)

Ty J. said:


> but it does not meet 507.5.1 which requires full bearing width.



It does bear fully...On the METAL post cap.....More than the prescriptive 1.5".....


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## Paul Sweet (Jul 13, 2020)

Compression perpendicular to the grain usually limits the load of a beam on a post before you reach the limits of bending in the beam or compression of the post (unless it's a long enough post for Euler buckling to limit compression).  You have to check all 3.  Any prescriptive limit will be extremely conservative.


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## steveray (Jul 13, 2020)

Euler? Euler? Euler.......?


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## e hilton (Jul 13, 2020)

Euler buckling ... I’m thinking if you follow Glenn’s guidelines for post size and tributary loads, mr euler will not be a factor.


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## ADAguy (Jul 15, 2020)

!. after "all" this I have not heard mention of research reports or an S.E.'s opinion.
2. Simpson can't be the only" company making tested post caps?
3. This all seems to be directed to DIY'rs, no? They would just toe nail it!
4. Lastly what are the dynamic load limits (safety factors) imposed by deck users shoulder to shoulder with beers and BBQ jumping up and down and moving side to side?


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## e hilton (Jul 16, 2020)

ADAguy said:


> !.
> 2. Simpson can't be the only" company making tested post caps?


Years ago both home depot and lowes carried a wide range of simpson products, then i noticed that one of them ... lowes i think ... switched to a different brand.  Cost saving move I’m sure.  The new brand didn’t seem to have the same quality, and the metal seemed to be a bit thinner.  
On the construction side people bad mouthed simpson, saying they were driving their business by convincing BO’s to spec their product.  Maybe.  But it’s a good product, and if you install it properly it enhances the build.  And for DIY folks it probably prevents a lot of failures.


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