# Brain Tease:  Deck plan submittal



## jar546 (Feb 20, 2011)

You are given a set of drawings made by the contractor for a proposed deck attached to a SFR made with nominal lumber, platform construction.

The deck is planned to be 16' in length along the house and project out 12'6".  There will be a properly sized beam approximately 10' from the home and the balance of the 2'6" will be cantilevered using 2x8 treated SYP @ 16" o.c.

Piers, post connections, etc. are all good.  Ledger board attachment is with 1/2" lags as required.  Railings are compliant.  This is only a question on 1 item so again, please don't read into the question.

The contractor has specified that the joist ends will be attached to the ledger board by notching the ends (within limits) and resting directly on a nominal 2x4 which will be attached to the bottom of the 2x12 ledger in compliance with R502.6.

Is this type of connection allowed for this deck?

If not, why and what code section?


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## KZQuixote (Feb 20, 2011)

I think that you could meet the lateral anchorage requirements by power blocking and cross nailing the portion of the joist ends above the notches. 

Proally have to lag the power blocks as well.

Bill


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## DRP (Feb 20, 2011)

Load the cantilever and check the uplift at the house connection.


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## pyrguy (Feb 20, 2011)

DRP said:
			
		

> Load the cantilever and check the uplift at the house connection.


'Xactly


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## jar546 (Feb 20, 2011)

You guys are good.  That is exactly what I was looking for.

In this case I would required joist hangars that are rated for the uplift or ask them to have a licensed DP sign off on their intended method.


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## dhengr (Feb 20, 2011)

Is this football or building construction?  What is power blocking and cross nailing?  Those two terms could mean many different things to me.  How should the 2x4 ledger be attached to the larger ledger and to the house?

What loads should be considered in checking that 2.5' canti. and the potential joist uplift (unloading) at the ledger beam?  What does that loading diagram look like on those joists?  What loading condition produces the max. bending stress in the joists?  Should there be blocking btwn. the deck joists over the beam out at 10'?


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## GHRoberts (Feb 20, 2011)

moment due to the overhang is something like 50*2.5/2 ftlbs. About 62ftlbs.

Uplift at the house is 62/12.5 pounds. About 5 pounds/ft. 5*16/12 pounds per joist. Less than 8 pounds/sqft of uplift. If I include the weight of the railings, joists, and deck ...

No problem.

Get some common sense.


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## KZQuixote (Feb 20, 2011)

dhengr said:
			
		

> Is this football or building construction?  What is power blocking and cross nailing?  Those two terms could mean many different things to me.  How should the 2x4 ledger be attached to the larger ledger and to the house?What loads should be considered in checking that 2.5' canti. and the potential joist uplift (unloading) at the ledger beam?  What does that loading diagram look like on those joists?  What loading condition produces the max. bending stress in the joists?  Should there be blocking btwn. the deck joists over the beam out at 10'?


Hi dhengr,

Check out my post near the end of this thread.

http://www.inspectpa.com/forum/showthread.php?3037-pressue-blocking/page5

Basically it's a technique to avoid using another hanger and, IMO, match or exceed the pull out (lateral) and shear of a hanger. If you've never nailed drywall to a ceiling with hangers that don't plane out, you won't appreciate the elegance and simplicity.

Bill


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## DRP (Feb 20, 2011)

Here's how I'm seeing it, feel free to correct my thinking.

If we load the overhang only there would be 50psf x 1.33'x2.5'=166.25 lbs/joist.

If I gang that load up on the outer rail the max moment is 166.25 lbs x 2.5 feet or 416 ft-lbs.

Dividing that by the backspan 416/10=41.6 lbs of uplift at the house.

Ignoring the self weight of the deck I think one nail at the house is going to take care of the uplift.

I believe it is required to block over the main beam on any cantilever.

Uniformly loading it was a bit closer with a max moment at midspan of ~1100 ft lbs. 1100 ft-lbs x 12"=13200 in-lbs/13.14"│ =1004psi stress

#2 syp has a base Fb of 1200. it'll get bumped up 15% for repetitive member and docked 15% for wet service so Fb=1200 as I see it. If it were me I'd see if they would go for 2x10's but I don't believe they have to.


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## jar546 (Feb 20, 2011)

A few things to the DP:

Prescriptively, 2x8 syp makes this span acceptable.

Prescriptively, we have no way of knowing what the actual uplift is but there is a code requirement for the uplift.  We have 2 choices.  The use of joist hangars that address uplift or require a DP to sign off on it.  Inspectors are not designers.

At one time, there was a school of thought that required the cantilevered portion to be calculated the same as a balcony at 60psf live load.  This would not apply here.  Food for thought.

If we went to 24" oc framing, I am not sure that the uplift would change significantly due to the lesser framing members.  Food for thought.

The point of this was to bring attention to potential uplift which is required to be addressed in the code although there is no prescriptive method to determine what it is.


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## jar546 (Feb 20, 2011)

GHRoberts said:
			
		

> Get some common sense.


George, you are on thin ice with that comment.  There is agreeing and disagreeing, debating and there are malicious statements.  That is uncalled for.


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## Yankee (Feb 20, 2011)

> I believe it is required to block over the main beam on any cantilever.


I don't read that into the code, I know it has been discussed before but can we go over it again?


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## TimNY (Feb 20, 2011)

When somebody decides whether or not we are engineers.. please let me know.

Honestly I had no idea if the uplift was considerable or not.  Follow the prescriptive or have it signed off.  Moment due to overhang wha?


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## Architect1281 (Feb 20, 2011)

Jar a thought provoking question

to take it the extra step could there be a Simpsonless compliant deck?

I've tried (only as a DRP) to come up with one - It ain't as easy as it sounds but it is possible

my attempt was to avoid the question of corrsivness to the hangers and the fasteners.

here in RI at the coast line the small gage nails and screws are attacked by not only the Pressure treatment but the Salt air as well

the i-1/2" ledgers do not provide enough nailing capacity to resist both uplift and lateral shear or displacement so I've attained some satisfactory results

by using 2x12 ledgers with 4x4 botom ledger extensions - thus introducing the problem of water collection in concealed spaces

the galvanized gage nails tend to disintegrate rather quickly not a good senario


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## jar546 (Feb 20, 2011)

Architect1281 said:
			
		

> Jar a thought provoking question to take it the extra step could there be a Simpsonless compliant deck?
> 
> I've tried (only as a DRP) to come up with one - It ain't as easy as it sounds but it is possible
> 
> ...


Simpson will definitely tell you to use stainless hangars and fasteners on the coast.  I did 2 different seminars with them over the years and was consistently told that.  Hot galvanized double dipped won't help you there according to them and I agree with what I see on lakefronts that get wind and spray.  Could only imagine salt spray and sand.

Whatever fasteners that you use in treated lumber other than stainless will still have problems regardless of hangar use.


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## DRP (Feb 20, 2011)

Table R502.3.3(2) could be applied here as well.  I think again we are in the realm of nails. Never done it this way, still just teasing my brain. Yankee check footnote e.

Now I don't know if y'all think I'm a DP or just DRP the carpenter


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## TimNY (Feb 20, 2011)

Yeah, unfortunately Simpson only "recommends" 316 stainless in ocean environments.  They have a chart in the beginning of their catalog.

In the end, it boils down to service life.  You could use HDG or Zmax and it will work.. for a few years... just like a 3-tab shingle.


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## jar546 (Feb 20, 2011)

DRP said:
			
		

> Table R502.3.3(2) should apply here as well.  I think again we are in the realm of nails. Never done it this way, still just teasing my brain. Yankee check footnote e.Hell, now I don't know if y'all think I'm a DP or just DRP the carpenter


I want to throw a wrench into that statement.  That table is for cantilevered balconies that are part of floor framing assemblies and take into consideration ground snow load.  A cantilevered portion of a deck is not a balcony.  Or is it?  Would that even apply?


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## Architect1281 (Feb 20, 2011)

Yeah salt spary is vicious and the 12 and 16 p commons go to 50% dia in MONTHS in some conditions

(usually inexpensive dipped galv product)

even the sill plates at the foundation so I've been over thinking ways to not use'em at all


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## DRP (Feb 20, 2011)

Don't know jar, I was actually looking for the blocking requirement and decided to throw it into the mix.


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## GHRoberts (Feb 20, 2011)

jar546 said:
			
		

> George, you are on thin ice with that comment.  There is agreeing and disagreeing, debating and there are malicious statements.  That is uncalled for.


There is nothing uncalled for here.

I recall a reply a couple days ago that echoed a reoccurring opinion: that AHJs get to use their judgment.

Well, get some common sense and professional judgment.

You wrote the initial post asking for what is wrong. What is wrong is that you use your "certifications" to bludgeon professionals. You are bringing back memories of why we have national and state building codes: inspectors were failing work unless they got a bribe. And builders had little or no option but to pay.


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## Yankee (Feb 20, 2011)

DRP said:
			
		

> Don't know jar, I was actually looking for the blocking requirement and decided to throw it into the mix.


Like my old dad would say

"I thought!"


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## jar546 (Feb 20, 2011)

Elaborate on how certified code inspectors are "bludgeoning" professionals?


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## Yankee (Feb 20, 2011)

jar546 said:
			
		

> Elaborate on how certified code inspectors are "bludgeoning" professionals?


He must mean your statement when you said



> "In this case I would required joist hangars that are rated for the uplift *or ask them to have a licensed DP sign off on their intended method*."


Ya. bloody. horrible.


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## jar546 (Feb 20, 2011)

Yankee said:
			
		

> He must mean your statement when you saidYa. bloody. horrible.


Still don't get it.  If they don't want to use an engineered product such as a Simpson or USP product that has an uplift rating and prescriptively we don't know what the uplift is except that is more than likely potentially exists and there is no prescriptive method to address it, we then need engineering.


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## jar546 (Feb 20, 2011)

How do we as inspectors know how much uplift exists?

What if the deck was framed with 2x12s and had 42" of cantilever?  Would the uplift change?  Where is the IRC prescriptive in this case?  Since decks are post and beam, they are not really covered under the IRC to begin with on a technical note.


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## Yankee (Feb 20, 2011)

jar546 said:
			
		

> Still don't get it.  If they don't want to use an engineered product such as a Simpson or USP product that has an uplift rating and prescriptively we don't know what the uplift is except that is more than likely potentially exists and there is no prescriptive method to address it, we then need engineering.


I wonder if the uplift amount is negligible up to the permitted cantilevered length.


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## DRP (Feb 20, 2011)

Guys...

Throw out all the big engineer terms and go back to the playground. It's a seesaw. jar's example was excellent. The backspan was exactly 4 times the cantilever. Big Sally weighs 166 pounds, Freddy jr sits 4 times as far from the pivot point as Big Sally, how much does Freddy jr weigh?


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## dhengr (Feb 21, 2011)

DRP:

One correct answer, given the info provided, is that Freddy weights 23# and his feet never touch the ground.  The answer you probably hoped for was that Freddy weight 166/4 = 41.5# and they are balanced on the seesaw.

An engineer would say that the moments about the pivot point are equal, for example; (166)(X) = (41.5)(4X).  See, I saw.


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## dhengr (Feb 21, 2011)

You guys are too darn fast for me, I’m still thinking and working around posts #7 - 13.  I suspect that your balcony table R502.3.3(2) is pretty much on the money, but it’ll take me awhile to get to that post and think on it a bit.  At the moment, I can’t think of why I wouldn’t treat the balcony essentially the same as this deck and handrail canti.  Except it does appear that there is a difference in the IRC LL’s, with decks at 40#/sf and balconies at 60#/sf.

TimNY.....   I don’t think most of you are engineers, but some of you have a pretty good feel for some of the engineering involved.  And, what I have tried to say is you should be very careful about pretending to practice engineering if you don’t know what you’re doing; but also to do your job well you must have a fair amount of basic engineering intuition to understand, interpret and enforce the code.  This is doubly true because no prescriptive code (any code for that matter) can possibly cover every condition under every situation, and yet you are being asked every day to stretch the IRC; but please don’t make me go see an engineer and have to pay him for his advice, and use him as our insurance of last resort.

GH....  I think you might want to get your calculator recalibrated, maybe even overhauled, before you do any more PEing.  You do some unusual engineering, post #7.

Jeff...   The OP was a good question, and my additional questions (brain teasers) were just to see if anyone knew how to start approaching this problem.  The code’s admonition about the potential for uplift at the house ledger is an important one, and if you don’t have a feel for how to do this problem, how do you know when to say, ‘get an engineer to design this.’  And, I’m not trying to turn any of you into an engineer, I’m just trying to teach you how to think a little like an engineer on the questions I chime in on, or to help you know when you should stand your ground and say, “this doesn’t comply with the IRC, get an engineer’s help, then come back for your  permit.  That still doesn’t assure you it’ll get built right, but it’s a step in the right direct.  When you switch to 24" o/c jst. spacing the uplift/ft. on the ledger doesn’t change at all, but the uplift per jst. or on each jst. connection increases by a factor of 24/12 or 24/16.

I’m a fairly conservative old guy, but the way I see the deck cantilever (canti.) is as follows:

1.)    The uniform fl. ld. gives you a canti. moment of, -M = wa^2/2, or (50#/sf)(2.5')^2/2 = 156.25'#/ft. of width, or 208.33'#/jst.

2.)    The hand rail at 15 or 20#/ft. gives a -M = Pa, or (20#/ft.)(2.5') = 50'#/ft. of width, or 66.67'#/jst., but this may really only be applied in a more concentrated fashion to one jst. ever 5 or 6' at a guardrail post.

3.)    The 200# horiz. load on the handrail at 36" high causes another -M = (200#)(3') = 600'#, the worst case is this horiz. load at a handrail post, and this moment goes into 1 or 2 jsts. depending upon how you attach the post to the deck framing system.

4.)    I would check a single jst. canti. with the sum of these three -M’s, shears and the resulting uplifts, the worst case condition, and maybe adjust my framing and attachment details if I had trouble making a single jst. work for the size jst. dictated by the simple beam backspan condition.

5.)    I believe the 40 or 60#/sf LL debate goes something like this: we have the normal 40# fl. load, and we have a 40# snow load, and decks are notoriously prone to drifting off the adjacent higher roof.  Now, it’s not likely that anyone would hold a dance party in a snow drift, but either the drift or some people out on the deck with some snow is highly likely.  Otherwise, the difference btwn. a deck (LL = 40#/sf) and a balcony (LL = 60#/sf) might be some conservatism because the balcony is solely dependent upon canti. action off the exterior wall, while the deck is simply supported by a ledger and a beam near the other end of the fl. jsts., a more forgiving structural system.  It would be interesting to hear what a real code historian had to say about this, if any one of you know some of those type people.  On commercial balconies you have vibration considerations, and the potential of everyone in the stands stamping their feet after the touchdown, or the whole crowd moving at once. the wave or at exit time.  This is akin to the soldiers marching in unison and bringing the bridge down.


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## GHRoberts (Feb 21, 2011)

dhengr said:
			
		

> GH....  I think you might want to get your calculator recalibrated, maybe even overhauled, before you do any more PEing.  You do some unusual engineering, post #7.


There is no need to do accurate engineering. No need to do the correct engineering. Just a need to get a correct solution. The engineering I do shows that in most cases 1 8d nail is sufficient to handle uplift.

dhengr you seem to roll up a lot of cases and consider the sum of them. You seem a bit uncertain about the live load requirements. I suppose you should show where your model is a prescriptive code requirement.

I found several different models on the internet. The modelers seem to make up a lot. They all seem to get different answers.

Uplift is a made up concern. Made up by people who don't know how to engineer.


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## KZQuixote (Feb 21, 2011)

dhengr,

Would you please elaborate on:

The uniform fl. ld. gives you a canti. moment of, -M = wa^2/2, or (50#/sf)(2.5')^2/2 = 156.25'#/ft. of width, or 208.33'#/jst.

What is it that you mean by "^2/2"

TIA

Bill


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## dhengr (Feb 21, 2011)

GH.....  You are correct, many problems do not require elaborate and exacting engineering to arrive at a satisfactory solution, when you have the engineering experience and judgement and confidence in your own abilities to save some calc. steps.  I just see no sense in being inaccurate when with so little extra effort it can be shown correctly.  So, just to confuse the issue, I don’t see any sense in doing something wrong, certainly not intentionally, when I am trying to help these guys understand what we do and how that relates to what they do.  While, in an out and out shooting match, I may be able to win the day, I have rarely found it beneficial to antagonize BO’s, if I can help it.  I pick my fights with them very carefully, and not for the fun of it.  I’d sooner drink with them than fight with them.  They have many ways to make life miserable for me, maybe just put my plans or letter at the bottom of the pile, and screw up my client’s schedule.  I have never needed a restraining order against the AHJ yet, and my plans always end up on the top of the pile, all because I’m so damn good looking, agreeable, and easy to get along with.  And, they actually come to me with code clarification questions, not hassle me because of them.

I design for the worst possible combination of load which could occur.  That’s in keeping with good sound engineering judgement; the old std. ‘design in accordance with accepted engineering practice,’ this is akin to combining DL and LL for the fl. load since they might happen at the same time.  The combining of the canti. uniform fl. loading, plus the DL of the railing system, plus the horiz. load on the handrail, is quite in keeping with the facts of life.  That’s a bunch of frat boys on the deck, with a keg, when one of them tries bull rushing the handrail to impress his girlfriend.  Read the news on deck failures.  I’ve been in court on several deck failures, none of them of my own design.  The 40 or 60#/sf is right out of the IRC2006 for decks and balconies respectively, and I tried to explain some of my thinking on that difference, which had been brought up earlier.

Bill....    For a uniformly loaded cantilever (canti.) beam: w is the load in #/sf, but since I am considering a 1 ft. width of fl. at this stage of my calcs., w is load in #/ft/ft. of width, a is the canti. span length in ft.; and the max. canti. bending moment is -M = (w)(a)(a/2).  a^2 is math or computer programming lingo for (a)(a) or a squared, as in (2.5')(2.5') = 6.23 ft. squared.  Thus, you now have (50#/ft.)(6.25sf)/2 = 156.25'#/ft. of fl. width; then 156.25(16/12) = 208.33'#/jst. at 16" o/c.


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## GHRoberts (Feb 22, 2011)

dhenger ---

You confuse your design requirements and code requirements. Your requirements might be prudent, but they are not required by code. So while I admit my math was outrageously unsuitable, you should admit yours are also.

This question was posed as a code compliance question. Fill in the omitted construction details to the problem and do the computations required by the code. You might find as I always have that uplift might be a real engineering issue, but it is not a real code compliance issue.

---

If you want code compliance based on the engineering model you use, submit it as a code change.

---

I would suggest that you do some real life measuring of frat boys on decks. You might find that you under estimate the loading they can produce.


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## bgingras (Feb 22, 2011)

dhengr said:
			
		

> On commercial balconies you have vibration considerations, and the potential of everyone in the stands stamping their feet after the touchdown, or the whole crowd moving at once. the wave or at exit time.  This is akin to the soldiers marching in unison and bringing the bridge down.


didn't Mythbusters bust that myth?


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## Daddy-0- (Feb 26, 2011)

> and the balance of the 2'6" will be cantilevered


Wouldn't be an issue here. We only allow a max. 24" cantilever on decks. Your design as stated would not make it past plan review. I am not sure if that is a Virginia thing or in the IRC but 24" max is the rule here.


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## DRP (Feb 27, 2011)

It is not a Virginia or IRC thing, I think someone decided "We've always done it this way". Most counties are using the Va "Typical Deck Details" which later was slightly modified and became the AF&PA's DCA6 optimistically labelled "Prescriptive Residential Deck Construction Guide"

The earlier VA versions limited to 3' overhang on the ends and 2' off the sides. DCA6 allows L/4 in either situation.

edit; This is the latest version I could find, it appears to line up with DCA6 on overhangs now;

http://www.fairfaxcounty.gov/dpwes/publications/decks/details.pdf

(Subject to change next week   )

I kept waiting for dhengr to finish, summing his estimates up I came up with ~150lbs of uplift less the dead load on the backspan.


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## dhengr (Feb 27, 2011)

DRP:

I suspect you meant to say you got a canti. moment of ~150'#/ft. of deck width, not “~150lbs of uplift less the dead load on the backspan.”  Looking back at my post #31 1.), I got 156'#/ft., so I won’t argue with you much there.  But what you meant to say is that’s the canti. moment which tends to induce the uplift at the ledger, and that must be divided by 10' to get the actual uplift/ft., so again by my calcs. you get (208.33'#/jst.)/(10') = 20.8# uplift/jst.  For this calc. I’d say only 6#/sf for DL, so the backspan has a downward reaction of (6#/sf)(16"/12")(10'/2) = 40#/jst. downward, vs. 20.8#/jst. uplift, that’s o.k.  I might add most jst. hangers when properly nailed will tolerate some uplift.  Conclusion: the typical jst. is o.k. for this canti. condition.  And, this is the kind of calc. which was done, under worst possible conditions, to arrive at the max. allowable canti. length of L/4 in your Deck Building Guide.

Boy, I did all the calcs. for you and now I gotta add them up too, next you’ll want me to eat your lunch for you too.      I was waiting for the builder to tell me how he was going to space the guardrail posts.  Let’s say the posts are spaced at 5' - 4", every 4 jst. spaces, and that we are going to frame that post to that single jst.  So, at that jst. we have the above uplift calc. for the floor loads, plus negative moments for the handrail weight and for the lateral load on the handrail at 36" ht.  By the way, what does the latest IRC say about that lateral loading, is it 200# anyplace and any direction, or is it 250#?  Seems to me I’ve heard both numbers batted around.  The worst case condition for the post or a single jst. attachment is with the 200# lat. load applied to a single post, and my guardrail has a t&b rail with balusters btwn. them and not attached at the deck.  Thus, the guardrail weight adds a -M = (50'#/ft.)(5.33') = 266.5'# to that single jst., and the lateral load adds another 600'#, these are my items 2.) & 3.) from post #31.  These moments are additive, and cause uplift just like the fl. load on the canti. does, therefore we have (866.5'#/jst.)/(10') = 87# of uplift at the ledger, which must be added to the 20.8#/jst. from fl. load above, for a total of 107.8# uplift on the jsts. supporting a guardrail posts.  So, we need a joist hanger which will take (107.8 - 40) = 68# uplift x 1.5 or 2 F of S.  For significant uplift loads, I’ve actually spec’ed. two jst. hangers, one below for normal gravity load reaction and one on the top edge for the uplift.

Did your Deck Bldg. Guide originate from work done at V.Tech., they’ve done a bunch of research on that issue haven’t they?  Take a look at that T&G decking thread for a follow up on your last post there.


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## Daddy-0- (Mar 2, 2011)

DRP

Here is ours if it works. Scroll down a few pages to the cantilever plans. 24" max. Must be a County amendment.


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## Daddy-0- (Mar 2, 2011)

Trying again

http://www.chesterfield.gov/WorkArea/DownloadAsset.aspx?id=4142


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## DRP (Mar 3, 2011)

thanks dhengr and Daddy-O-

I know the ledger and post connection details are VT, not sure about the rest of the deck guide. I'm still getting back up and running after a lightning strike and haven't had time to really think about it. #200 in any direction is IRC. I believe a nail, or any rated connector already has the F of S in the allowable design values so no need to apply it twice. The take away I see from your calcs is that the uplift is insignificant at these cantilevers. So a question, has anyone ever seen a canti deck fail by uplift at the house and if so what were the circumstances.

The Chesterfield guide looks pretty good to me at a quick glance. I typically build a flush deck. I would fail there as I notch my 6x6 posts 2-1/4" deep to set the rims in and then continue that up for the rail. DCA6 and the VA deck details do not allow simply bolting the girder to the post, which is one of the Chesterfield details, I do agree with the prohibition. My reason for continuing the post thru is I don't believe I've ever seen an attached wood post and rail that could actually take a 200 lb load, mine probably wouldn't either but feels better to me.


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## Daddy-0- (Mar 3, 2011)

DRP

Our guide is a hybrid of the VT and Fairfax. I appreciate your input and information. Your knowledge and common sense are refreshing. I enjoy the Va spin on some of these threads.


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