# Deck rail strength and amount of acceptable deflection



## Buelligan (Jun 6, 2015)

Ok I have another contractor disagreeing with my interpretation of code intent.

I cannot find any reference to deck rail construction except the table R301.5 requires 200 lb/sqft as live load on guardrails and handrails.

I failed this deck twice. 16x10 deck and the 16' side of the deck having one rail in the middle, 8' span between posts. This post was attached to the band joist with lag screws that did not protrude through, so I had no idea how deep it was into the band. I also could flex the band board by moving the top of the post more than an inch without much effort.

So he replaces the lags with through carriage bolts, which may be another issue as I believe washers inside and out are needed. But he did not address the flexing of the band with either brackets per DCA6 or some type of blocking to decrease the deflection. He comes in to discuss the failure as he doesn't understand why this failed. He stated that he put 200lbs of force on the rail and it deflected 3.5" and did not fail so it meets code!!

My response was that it should not deflect that much but did not have an immediate answer for an allowable amount of deflection. He agreed to install a bracket per DCA 6 and left. But I really would like to understand what an allowable amount of deflection is commonly accepted so I may better enforce the rails being installed on decks.

I spoke with several engineers and also did some research online and it was unanimous that the formula H/60 was commonly used for rail deflection design. This was referenced to 1604.3 in the IBC as a cantilevered member. I'm not quite clear how they arrive at that but as it was an acceptable criteria for my building official.

Well after much time spent on this one answer I have come here with several different schools of thought on the matter with hopes of some wise advice from my fellow code geeks LOL.

I personally like the common engineered practice of H/60. I have found the ICC test standard for rails AC273 but it seems to allow about 2.5" of deflection on the rail system. I am confused by the report as it states to apply 500lbs but measure the deflection at 200lbs. 2.5" at 200lbs seems very excessive to me, anyone else? This morning I have found a chart in the IRC, table R301.7 that has "All other structural members" L/240 as maximum deflection. This is right after the live loads chart. That is even more restrictive so I'm just so confused. HELP!!

So the numbers look like this:

Engineer     36"(H)/60 = *.60 deflection*

AC273        36"(H)/24+96"(L)/96 = *2.5" of deflection on midpoint     *Link to AC273

IRC table    72"(H)/240 =* .30 of deflection *(72" per footnote b, L shall be twice the cantilever length.)

So am I putting too much thought into this or what? I'm sorry but the perception for many is the reality and the homeowner was terrified at the amount of movement in the rail. As was I when I did the throw a hip into it test and felt like I was going fall off the deck! I feel that 1/2" to 1" of deflection at 200lbs should be sufficient to meet the intent of code when it comes to the safety of guardrails.

Thoughts?


----------



## ICE (Jun 6, 2015)

Should the rail be 42" high?  What do you mean by "one rail in the middle"?  If it were up to me the guardrail would not deflect at all under a 250lb point load.  But then I wouldn't know what the code says without looking it up.


----------



## Mark K (Jun 6, 2015)

There are no deflection criteria for hand railings.  I have discussed this with other engineers and could not find a code requirement.

AC273 is not code.

You enforce code provisions not the intent.  The intent is used to help interpret the specific provisions but should not be used to create additional requirements.  Similarly you do not enforce common practice.

What code are you using?  If the IRC was adopted how do you get to the IBC?  The applicant is allowed to use the IBC to justify something not allowed by the IRC but the building official cannot require compliance with the IBC if what they are doing is compliant with the IRC.

While I am not recommending flexible railings they may actually result in fewer problems.  If the occupants perceive the railing to be flexible they are likely not to lean on or get close to the railing.  In terms of safety it is strength that is more important than stiffness.  In any case I do not see where the IRC provides any criteria.

The 2105 IBC does not provide deflection criteria for railings.  In Table 1604.3 the closest you come are the provisions for exterior walls and interior partitions which provide criteria for snow and wind load.  The 200 pound load you mentioned is a live load and in that column there are no deflection criteria for exterior walls and interior partitions.

In terms of the 200 lb load how can you determine compliance unless they either test it or an engineer prepares calculations which are submitted?


----------



## cda (Jun 6, 2015)

The International Building Code does not prescriptively address allowable or tolerable rail deflections.  According to a staff member of the International Code Council, the code has no deflection limits for handrails and guards.  Good design practice would limit how much a handrail or guard could be pushed outward or downward.  Regardless of the IBC silence on this matter, it remains a very important aspect in the construction and design of railings, and thus must be considered.


----------



## cda (Jun 6, 2015)

http://www.deckmagazine.com/codes-and-standards/2015-deck-code-update.aspx


----------



## ICE (Jun 6, 2015)

cda said:
			
		

> The International Building Code does not prescriptively address allowable or tolerable rail deflections.  According to a staff member of the International Code Council, the code has no deflection limits for handrails and guards.  Good design practice would limit how much a handrail or guard could be pushed outward or downward.  Regardless of the IBC silence on this matter, it remains a very important aspect in the construction and design of railings, and thus must be considered.


Kinda like how there is no deflection tolerance for a foundation or....well what else can I think of.... How about an oak tree.  If there is no tolerance stated that just might be because there is no tolerance.  As in we will not tolerate any deflection.  That would work way better than scaring the shlt out of the owner.


----------



## cda (Jun 6, 2015)

ICE said:
			
		

> Kinda like how there is no deflection tolerance for a foundation or....well what else can I think of.... How about an oak tree.  If there is no tolerance stated that just might be because there is no tolerance.  As in we will not tolerate any deflection.  That would work way better than scaring the shlt out of the owner.


But

Is it no deflection tolareance when the eighty pound inspector pushes on it

Or

The three hundred and eighty pound inspector, who just ate lunch, pushes on it?


----------



## ICE (Jun 6, 2015)

cda said:
			
		

> ButIs it no deflection tolareance when the three hundred and eighty pound inspector, who just ate lunch, pushes on it?


One of my great friends is that man.  Well 340 anyway.  You should see him on a warehouse plywood panel roof.  He's come across guardrails that he wouldn't try out.  It isn't that difficult to build a stout guardrail that has little to no movement.


----------



## Sifu (Jun 7, 2015)

Can't remember where I read it, may have been a JLC article so you might check the archives.  I will see if I can find it.  It was a pretty good article about this.  Basically they tested just about every known method of guard post and rail attachment and every one of them failed but one.  The only one that actually passed used a combination of a tension tie and threaded rod.  I don't remember the exact hardware that was used.  Still waiting to actually see that method used!  It should be noted that they tested based on the 200lb load WITH the safety factors which might be where the 500lb number you saw came from.  The article seemed to be illustrating more about which methods absolutely don't work under any circumstances that it was about getting us to use the only method that did work since it was a bit complicated and prohibitive.  It did a good job at illustrating that the most common methods such as a couple lags on a notched post didn't even come close.  Personally I give a good hard shove and if I am comfortable with it I move on, if not I require more.  If I see a notched post I really give it the ole' stink eye.  It would be nice to have a more specific criteria but outside of that I exercise due diligence and move on.


----------



## MASSDRIVER (Jun 7, 2015)

http://www.deckmagazine.com/structure/question---answer-2.aspx

Brent.


----------



## ICE (Jun 7, 2015)

After reading that article it is apparent that it is plenty difficult to build a safe guardrail around a deck with wood unless HDs are added.  I didn't know that a guardrail needs to withstand 500 lbs. but that does make sense.

And that's just for the post.  Attention to detail with the rail is next.


----------



## Sifu (Jun 7, 2015)

The article mentioned in the post from Brent is the one I remember.  Thanks.  I will see if it is the archives.


----------



## MASSDRIVER (Jun 7, 2015)

The only flaw I see there is they focus on a single post. Now it depends on construction, but I typically put a post at the end of the line on each corner, so each corner gets two posts. Then withe the top rail I use a 3x6 with a peaked top milled at about 20 degrees, and put a biscuit at the miter, and if it's long biscuit the joint.

I also double up my rim or use 4x material then through bolt that and use malleable washers.

I'm confident I could have a full on brawl bar fight against ICE, Jar, Mark Handler and ADA GUY ( I mean, just to make it fair) and that rail will be just fine. You can't just focus on one component.

Brent.


----------



## conarb (Jun 7, 2015)

\ said:
			
		

> I'm confident I could have a full on brawl bar fight against ICE, Jar, Mark Handler and ADA GUY ( I mean, just to make it fair) and that rail will be just fine.


Brent:

Got a story for you, back in the early 50s I was working on a crew where the builder had hired an Oakie guy as a laborer, he was strange, never said anything and ate his lunch far away from the rest of us, he had several kids and was building a shack for his family with left-over materials and whatever he could scrounge up.   The County caught him and red-tagged his house, he went into the county building department took his hammer and literately beat the brains out of the CBO.

After he was in jail we called for a foundation inspection on a down-slope house we were building, the inspector showed up, parked his car on the street above us and yelled through his open window to bring the permit card up to him, since I was the kid on the job I was told to bring him the card, when I got to his car he said: "You guys are crazy, I'm not going down there", he signed the card, handed it back to me and was on his way.  The laborer didn't have any money but wanted to hire a prominent lawyer that we had built a house for, he said to the lawyer that God had told him to do it and had told him to go to a tree and dig at the roots, that God had put money there to pay the lawyer.  I guess sometimes beating the brains out of CBOs works, God works in strange ways.


----------



## ICE (Jun 7, 2015)

MASSDRIVER said:
			
		

> I'm confident I could have a full on brawl bar fight against ICE, Jar, Mark Handler and ADA GUY ( I mean, just to make it fair)


I don't know about the other guys but I would never mess with a man in a dress....I guess it's the Comanche in me.


----------



## ICE (Jun 7, 2015)

MASSDRIVER said:
			
		

> I typically put a post at the end of the line on each corner, so each corner gets two posts. Then withe the top rail I use a 3x6 with a peaked top milled at about 20 degrees, and put a biscuit at the miter, and if it's long biscuit the joint. I also double up my rim or use 4x material then through bolt that and use malleable washers.


Conarb could smack into that with his Prius.


----------



## MASSDRIVER (Jun 7, 2015)

ICE said:
			
		

> Conarb could smack into that with his Prius.


He seems like a Prius kinda guy huh? I bet he hates his Viper so much he would just give it to me if I asked nice.

Brent.


----------



## ICE (Jun 7, 2015)

If he has a Prius it's a lifeboat for a land yacht.


----------



## MASSDRIVER (Jun 7, 2015)

ICE said:
			
		

> I don't know about the other guys but I would never mess with a man in a dress....I guess it's the Comanche in me.


Or maybe the Apache in me.  





Brent


----------



## cda (Jun 7, 2015)

O



			
				conarb said:
			
		

> Brent:Got a story for you, back in the early 50s I was working on a crew where the builder had hired an Oakie guy as a laborer, he was strange, never said anything and ate his lunch far away from the rest of us, he had several kids and was building a shack for his family with left-over materials and whatever he could scrounge up.   The County caught him and red-tagged his house, he went into the county building department took his hammer and literately beat the brains out of the CBO.
> 
> After he was in jail we called for a foundation inspection on a down-slope house we were building, the inspector showed up, parked his car on the street above us and yelled through his open window to bring the permit card up to him, since I was the kid on the job I was told to bring him the card, when I got to his car he said: "You guys are crazy, I'm not going down there", he signed the card, handed it back to me and was on his way.  The laborer didn't have any money but wanted to hire a prominent lawyer that we had built a house for, he said to the lawyer that God had told him to do it and had told him to go to a tree and dig at the roots, that God had put money there to pay the lawyer.  I guess sometimes beating the brains out of CBOs works, God works in strange ways.


So which edition of Hammurabi's was adopted than??


----------



## MASSDRIVER (Jun 7, 2015)

conarb said:
			
		

> Brent:  The County caught him and red-tagged his house, he went into the county building department took his hammer and literately beat the brains out of the CBO.


While that is a great, wholesome and heartwarming story, I must now categorically state that I do not, nor have ever condoned the practice of beating inspectors to death. Not to death.

Furthermore, I have to question the validity of the tale as you mentioned "brains", and "out of", and that probably is not possible at a building department.

:lol::twisted:

The one and only time I ever beat on an inspector was not because he WAS an inspector, or anything he did as a result of being an inspector, but because he was a loudmouth, insulting, arrogant, feltching, abborant a-hole, and made the mistake of threatening to kick my a55. I returned the favor, pre-favor, as it were, and made him bleed. I think he got fired some time later for being a drunk and a liar.

I was young.

Brent


----------



## ICE (Jun 7, 2015)

The thread has





Well then Buelligan, apparently the answer to your dilemma is not to be found in code and the best we have come up with is Brent in a bar fight.


----------



## conarb (Jun 7, 2015)

\ said:
			
		

> I think he got fired some time later for being a drunk and a liar.I was young.
> 
> Brent


Got another inspector story for you from the late 50s, I was starting a room addition and had it formed, called for inspection and concrete on Christmas eve, the truck arrived but no inspector, the ready-mix driver said: "Don't wait for him, the last pour I had he showed up late drunk as a skunk", so I went ahead and poured and about half-way through the inspector showed up sober as a judge and started screaming at us, I took him to the driver and he explained what he had seen and told me describing the drunk inspector so the sober inspector told me to go ahead but never do it again, even if the inspector is drunk.  We contractors all have our inspector stories, most of them were one of us,  architects or contractors who went broke and got city jobs to make a living.


----------



## tmurray (Jun 8, 2015)

Buelligan said:
			
		

> So he replaces the lags with through carriage bolts, which may be another issue as I believe washers inside and out are needed. But he did not address the flexing of the band with either brackets per DCA6 or some type of blocking to decrease the deflection. He comes in to discuss the failure as he doesn't understand why this failed. He stated that he put 200lbs of force on the rail and it deflected 3.5" and did not fail so it meets code!!


Unless otherwise defined in the code "failure" would be when the component is no longer able to perform its intended purpose. In my opinion, a failure would be when the guard no longer provides the intended level of safety to occupants (too low, no longer in place, etc.).


----------



## mtlogcabin (Jun 8, 2015)

I believe you could use this section for deflection requirements for guardrails.

R301.7 Deflection.

The allowable deflection of any structural member under the live load listed in Sections R301.5 and R301.6 or wind loads determined by Section R301.2.1 shall not exceed the values in Table R301.7.

All other structural members    L/240

Guardrails are listed in R301.5. there is no definition of a structural member in the IRC. The minimum allowable deflection limit in R301.5 is L/180.

BTW my 40 foot guardrail in my loft with 4 post only deflect's about 1/4 inch but then again it has a 6"w X 4"h glue-lam for a top rail. I would suggest stiffening the top rail would be easier and more efficient then adding more post and special fasteners.


----------



## ICE (Jun 8, 2015)

deleted duplicate


----------



## ICE (Jun 8, 2015)

MASSDRIVER said:
			
		

> Or maybe the Apache in me.
> 
> 
> 
> Brent


You could hide a couple of them under your skirt.  You're a dangerous man there Brent.


----------



## jdfruit (Jun 8, 2015)

Man did this thread run out into the weeds.

I think mtlogcabin has the most reasonable approach to deflection so far unless something more definitive shows up.

Another question on the whole issue is: why wasn't the potential problem addressed during plan review?


----------



## Glenn (Jun 8, 2015)

There was a proposal for this subject to the 2015 IRC, but it was not approved.  It matched the deflection limits for composite guards as required by the reference standard ASTM D 7032.  I spoke against it because it may be a good standard for a manufacturer, but not something that anyone could have feasible utilized in the field.


----------



## JBI (Jun 8, 2015)

My deck railing has zero deflection (and all I used was 3" deck screws). I also left my 4 x 4's 4 x 4's and didn't cut them down to 2 x 4's.


----------



## Buelligan (Jun 9, 2015)

mtlogcabin said:
			
		

> I believe you could use this section for deflection requirements for guardrails.R301.7 Deflection.
> 
> The allowable deflection of any structural member under the live load listed in Sections R301.5 and R301.6 or wind loads determined by Section R301.2.1 shall not exceed the values in Table R301.7.
> 
> ...


Thanks! That's the section I saw and was comfortable with using. 3" was WAY TOO LOOSE for me and just seemed to be useless and almost to the point of failure at time of installation. I have inspected ALOT of decks and all guard posts on decks seem to deflect no more than an inch and most of them even less! SO getting the post to be rigid is not that difficult or even too much to ask, I feel. Most good contractor's seem to get that and prefer to err on the side of caution when it comes to "safety" rails. Not sure why he was so comfortable with a rail that was so loose and was almost peeling the band board off the end of the joists.


----------



## Buelligan (Jun 9, 2015)

jdfruit said:
			
		

> Man did this thread run out into the weeds.I think mtlogcabin has the most reasonable approach to deflection so far unless something more definitive shows up.
> 
> Another question on the whole issue is: why wasn't the potential problem addressed during plan review?


I did address it on the plans. I asked for rail post blocking or support details! The response and correction I got was "he has been building decks for 20 years, he knows what they need". so she wrote the statement on the plans "rail posts will be blocked" and that's it. SO I said fine I will accept this but will fail it at inspection if it is not correct. I had that conversation with him when he came in after the second failure. He said it was up to me to tell him what "I wanted" and my response was that" you stated you would block posts to code and it is up to you to provide me with details of how you will accomplish that. I cannot design it for you. Next time provide me with actual detailed plans and I will let you know if it is acceptable. This is why I prefer not to accept just a statement." Didn't want to argue with 20 years of experience.


----------



## jdfruit (Jun 9, 2015)

Buelligan

No good deed goes unpunished


----------



## pete_t (Jun 9, 2015)

Sifu said:
			
		

> Can't remember where I read it, may have been a JLC article so you might check the archives.  I will see if I can find it.  It was a pretty good article about this.  Basically they tested just about every known method of guard post and rail attachment and every one of them failed but one.  The only one that actually passed used a combination of a tension tie and threaded rod.  I don't remember the exact hardware that was used.  Still waiting to actually see that method used!  It should be noted that they tested based on the 200lb load WITH the safety factors which might be where the 500lb number you saw came from.  The article seemed to be illustrating more about which methods absolutely don't work under any circumstances that it was about getting us to use the only method that did work since it was a bit complicated and prohibitive.  It did a good job at illustrating that the most common methods such as a couple lags on a notched post didn't even come close.  Personally I give a good hard shove and if I am comfortable with it I move on, if not I require more.  If I see a notched post I really give it the ole' stink eye.  It would be nice to have a more specific criteria but outside of that I exercise due diligence and move on.


Think this is the one you remember.
	

		
			
		

		
	

View attachment 1198


Deck Guardrails.pdf

Deck Guardrails.pdf


----------



## jdfruit (Jun 10, 2015)

pete

Very good detail & info


----------



## tbz (Jun 14, 2015)

Buelligan said:
			
		

> I did address it on the plans. I asked for rail post blocking or support details! The response and correction I got was "he has been building decks for 20 years, he knows what they need". so she wrote the statement on the plans "rail posts will be blocked" and that's it. SO I said fine I will accept this but will fail it at inspection if it is not correct. I had that conversation with him when he came in after the second failure. He said it was up to me to tell him what "I wanted" and my response was that" you stated you would block posts to code and it is up to you to provide me with details of how you will accomplish that. I cannot design it for you. Next time provide me with actual detailed plans and I will let you know if it is acceptable. This is why I prefer not to accept just a statement." Didn't want to argue with 20 years of experience.


As always late to the party,

As pointed out by some, there is no defelection limit on guards, however the criteria mainly used is that the guards deflection is required to stop without the guards height descending down below the required minimum height, Model IRC code, 36".

The main thing everyone forgets is that guards are not required to have posts, nor their single attachment required to resist 500 or even 200 lb's, the top of the guard system at any point is required to resist a 200 lb point load.

The blocking, and all the bracket mumbo jumbo is not the correct way or only way, just a tested method.  The testing done was limited to non-real life construction, you are missing the guard, and the full construction of the deck, ie flooring and therefore testing a single part and they come to the deduction, well this is the method we suggest.

As to lags vrs bolts, pretty much all the screw manufactures state and engineers concur, that a minimum of 3" of solid wood is required for a lag to hold loads, thus in order to use the lags, they would need a double rim board.

Also, if they installed a double rim board had every balusters 1.5" square, double lagged to the rim board, installed a 2x4 sub-rail and a 5/4 x 6 top board, all screwed together and then tested for the 200 lb point load at the top, the deflection would be very little and and the guard system would pass and there would be no posts.

The issue here was you felt the guard moved to much and therefore felt unsafe, you failed it and requested it be fixed or proof it met compliance, they had the options, from what I am reading you provided a direction by supplying DCA6, last time I checked DCA6 was not an ICC code, just an AWS pamphlet unless a local AHJ adoptedit, I venture a guess that you noted, well I am not sure how you built this one, but it does not feel safe, it seems to move more than I feel is safe without confirmation from an engineer, but if you follow these pages and diagrams, I know decks built like this in the past, don't seem to move like that.

They might have 20 years, but lots of things change as you noted, DCA6 is not 20 years old I believe, but back to design options, mounting guards to construction structure is and has always been a concern to many and then not to others, NYC is currently requiring all buildings with it's limits to complete facade inspections and bring all the exterior structure and guards up to code compliance, as they have found many of them in place don't comply and or are unsafe.

I guess I went off topic a bit, but I always get a bit of a hair raising when people talk about guard structure and loads and focus on a single post and not the entire system.  I also get a bit off kilter with noting code requires blocking, as there is nothing in the IRC code prior to 2015, and in the new section 507 exterior decks, section 507 it just notes to stop lateral resistance in R507.5.1, it does not say you need to use blocking, only stop the rotation, and if blocking is used then.

However, deflection is measured with engineering testing standards and thus as an inspector, if you fail a guard for deflection, are you not moving this in to an engineers corner period?

For don't you need confirmation, your feel test does not verify it does or does not comply, just notes a flag, if an engineer can validate it complies or it does not comply the question becomes after all my ramblings, if as an inspector you fail a guard for deflection without preforming the proper testing method, how can you then approved your failure flag without a proper engineer sign off or engineers inspection report?

Your failure was a guess, as is your approval now?

Once you fail a project for a structure issue that can only be verified by an engineer, how does one approve and pass that item without an engineers report it complies?

That is my question?

Tom


----------



## ADAguy (Oct 7, 2015)

Brent, thank you for the inclusion in a very esteemed group of Code Junkies.

Just remember to whom your kilt owes its heritage too. My ancesters ruled much of the known world for a brief period.


----------



## MASSDRIVER (Oct 19, 2015)

The Neanderthals?  

Learn something new everyday.

Brent.


----------



## jeffc (Oct 22, 2015)

In a prior post, TBZ stated, "However, deflection is measured with engineering testing standards and thus as an inspector, if you fail a guard for deflection, are you not moving this in to an engineers corner period?" I hope everyone realizes that it does not take a lab coat and an advanced degree to measure deflection. If you know how to apply a force and how to measure displacement, you can perform a deflection test.


----------



## ICE (Oct 22, 2015)

jeffc said:
			
		

> In a prior post, TBZ stated, "However, deflection is measured with engineering testing standards and thus as an inspector, if you fail a guard for deflection, are you not moving this in to an engineers corner period?" I hope everyone realizes that it does not take a lab coat and an advanced degree to measure deflection. If you know how to apply a force and how to measure displacement, you can perform a deflection test.


I push on it.  Real hard...like I am trying to break it.


----------

