Cantilevered Deck

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#1

Originally Posted By: kmcmahon
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How far can 2x8 floor joist cantelever without support posts?


Trying to find something in Code Check.
![](upload://pLZXM1fVqZG5BdNrVN9kSboGxz4.jpeg)

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#2

Originally Posted By: rchoreyii
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The length of the joist cantilever should not exceed 1/3 to 1/6 of the total joist length. Depends on the area you are in. Someplaces allow 1/3, some only 1/6. Basically if 8 feet is sticking out, the joist should be at least 24 foot long for 1/3.


At least that is the info I have. Hope it helps

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Ron Chorey
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#3

Originally Posted By: ssopha
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It looks awful long to me to be safe. I wouldn’t want too many heavy weights on that porch.

#4

Originally Posted By: Joe DiGiacomo
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I don’t understand how the longer the lumber (which is supported between two points) can increase your allowable cantilever projection. Wouldn’t the type, thickness and ht. of the joist determine the max. cantilever allowed, no matter what the overall length of the joist is? Can you please explain. Thanks

#5

Originally Posted By: jpeck
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This is the way it is figured.


You can cantilever out 1/3 of the span rating.

I.e., if you have a lumber sized to give a 9' span between supports over three supports (two spans), then you can cantilever out 3'.

If you need to cantilever out 6', you would need to use something with a span rating 18'. That's some heavy timber, truss joists, steel beams, or something equally strong.

To go out 8', the span rating would have to be 24', you are talking trusses here.

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Jerry Peck
South Florida

#6

Originally Posted By: kmcmahon
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So, What you are saying Jerry, that with 2x8 joists at 16" O.C. spacing the Max Spans would be 12’7" and the max cantilever would be 1/3 of that or 4’2". So this 8’ cantilever would be way to far of a cantilever.


Is this a correct assessment?

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#7

Originally Posted By: kmcmahon
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Now I would think that the size(depth) of the joist would have some bearing on how far to cantilever as Jerry Peck stated, but not according to this detail?????

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#8

Originally Posted By: rchoreyii
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Kevin


I just gave you what was taught to me in the class I took. I looked up in code check also and found nothing about catilevered joists. Maybe you should call your local codes enforcement and see what they say. I know we don’t inspect to code but you don’t want to have a situation on your hands where the front line for some football team is out there with their beers and babes and it comes crashing down.


cheers

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Ron Chorey
LAS CRUCES Home Inspections
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#9

Originally Posted By: rchoreyii
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Joe,


Typical cantilever is a 2X6. According to my info it can only be 1/3rd the length of the over all length of the joist. The rest must be attached to ceiling joists on the interior or second floor joists. This is the only info I have and I could be wrong. If anyone has any other info please respond.

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Ron Chorey
LAS CRUCES Home Inspections
rchorey@comcast.net
rchoreyii@nm.nachi.org

#10

Originally Posted By: kmcmahon
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Thanks for the clip…after you sent it to me, I looked and took the above clip from the NACHI education site. It’s a valid detail, I would think that the overall depth of the member would play a part. If I had a 2x4 100’ long, it would mean I could cantilever 33’…just doesn’t compute ya know? Just looking for other thoughts. Doing the report for the people right now and running out of time to stall them.


Thanks everyone.

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#11

Originally Posted By: kluce
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I agree, there has to be other factors - Size and length and type of material. I ran into this one time and informed my clients that further evaluation is needed by a structural engineer to determine if structure is properly installed. Then I add a note informing the client that there was no visible problems seen at this time.


If my clients called me (which they didn't) with questions on this subject, I would just inform them that the cantilever cannot be installed in that way without approval from a structural engineer and recommend having the owner show the buyer that approval or get one.

If there was no signs of damage, you might what to write this up to cover your butt so someday, when the new homeowner are having a party on that cantilever and something bad happens, you don't get a phone call.

Im my case, it was obvious that the cantilever was sticking out too far.

#12

Originally Posted By: ccoombs
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The rule of thumb given above is based on the code span tables for a given floor joist. If the code span tables allow a 2x8 to span 12 feet, then the cantilever can be 3 feet.


The deck you have shown is way too much for normal 2x members. The live load for a cant. deck is much higher than the live load for a deck with posts. Add in additional loading if you get snow in the area.

This could be a life safety issue. I would recommend further investigation by an engineer.

#13

Originally Posted By: kmcmahon
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Curtis, I would have to agree with your entire statement. That’s basically how I stated it in my report.


Funny thing was the homeowner/broker/builder (same person) was adamant that he is a retired Union carpenter, and he assured me first thing he pointed out when I got out of my truck, that the cantilever was adequate and the boards stretched half way thru the home. ![icon_rolleyes.gif](upload://iqxt7ABYC2TEBomNkCmZARIrQr6.gif)

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#14

Originally Posted By: rmoore
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Kevin…


I think we all agree that this looks wrong (and scary). The fix seems simple enough, especially as it's only a storage area underneath. A couple of good footings, a pair of 4x4 treated posts on screw adjustable hardware, and a 4-by treated beam (plus a little connection hardware). Probably cost about the same as getting a structural engineer out there. I know we're not supposed to do engineering but, in this case, I think it might be appropriate to recommend structural evaluation OR installation of additional support by a qualified contractor. They are almost certainly going to have to do the latter anyway...might as well give them a choice.

I know I'm stepping into a gray area here, but the "repair" here seems obvious.

BTW...did the homeowner/builder also assure you that the baluster spacing was OK? ![icon_wink.gif](upload://ssT9V5t45yjlgXqiFRXL04eXtqw.gif)

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Richard Moore
Rest Assured Inspection Services
Seattle, WA
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#15

Originally Posted By: James D Mosier
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kmcmahon wrote:
Curtis, I would have to agree with your entire statement. That's basically how I stated it in my report.

Funny thing was the homeowner/broker/builder (same person) was adamant that he is a retired Union carpenter, and he assured me first thing he pointed out when I got out of my truck, that the cantilever was adequate and the boards stretched half way thru the home. ![icon_rolleyes.gif](upload://iqxt7ABYC2TEBomNkCmZARIrQr6.gif)


The main thing that caught my eye in this post is the capitalized "U" word. He might know how it's always been done. He may know how to do it with toothpicks. He probably knows how to get around the AHJ, but it doesn't mean he knows how to do it right.

I'm not sure I would recommend repairs by a qualified contractor either. Could end up with the contractor this guy retired from. Yes it may deferr the responsibility from you, but is it really helping your client?

--
Jim Mosier
#16

Originally Posted By: kmcmahon
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rmoore wrote:
Kevin...



BTW...did the homeowner/builder also assure you that the baluster spacing was OK? ![icon_wink.gif](upload://ssT9V5t45yjlgXqiFRXL04eXtqw.gif)


No, but I did catch it there and on the inside where the balcony guardrail is only 24" high!

Also, where the guardrail is missing on this deck!



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#17

Originally Posted By: roconnor
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and stability. Dont confuse the two.


Strength: Cantilever span should be no more than 1/4 the allowable joist span rating ... for bending resistance.

Stability: Cantilever span should be no more than 1/3 the back span ... to prevent uplift
[from IRC R502.3.3 ... more restrictive than the old stability rule of 1-out & 2-in ... or cantilever no more than 1/3 total length]

So a typical 2x8 DF#2 joist with a span rating of say 12-feet should not cantilever out more than 3-feet (1/4 span rating), and for stability it should extend into the house at least 9-feet [cantilever 1/3 the back span ... or back span 3 times the cantilever]

Note that those rules of thumb are only for nominal snow load areas, and do not apply to cantilevers supporting an outside wall ... where the limit of the cantilever would be 2-4 times the joist depth depending on the details.

Hope that helps ... ![icon_wink.gif](upload://ssT9V5t45yjlgXqiFRXL04eXtqw.gif)

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Robert O'Connor, PE
Eagle Engineering ?
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I am absolutely amazed sometimes by how much thought goes into doing things wrong

#18

Originally Posted By: jpope
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Come on Kevin. Don't you know a diving platform when you see one?

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Jeff Pope
JPI Home Inspection Service
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#19

Originally Posted By: kmcmahon
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jpope wrote:
[/img]

Come on Kevin. Don't you know a diving platform when you see one? ![icon_biggrin.gif](upload://iKNGSw3qcRIEmXySa8gItY6Gczg.gif)

I had the exact same thought! ![icon_biggrin.gif](upload://iKNGSw3qcRIEmXySa8gItY6Gczg.gif)

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#20

Originally Posted By: roconnor
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That does look like a diving board … icon_lol.gif … flag right there …


Did ya see any noticeable deflection on the outer edge of the span, and were you brave enough to go out on the deck to see if it "felt" flexible ... ... it does look like the cantilever joists may be over-spanned from the rules of thumb above.

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Robert O'Connor, PE
Eagle Engineering ?
Eagle Eye Inspections ?
NACHI Education Committee

I am absolutely amazed sometimes by how much thought goes into doing things wrong