Deck Beam cantilever?

[3rdgendslmech]

Getting ready to add a 10x12 deck addition onto my ground level deck.
There's a 6x6 post in concrete right at the corner of the existing deck. My plan was so go 2' to the left and sink a post in conrete which would leave me with about 20" or so of cantilever beam.
I looked on my county's deck guide but it doesn't give a spec for beam cantilever, just joist cantilever.

 

[The Tool Tyrant]

One third overall length is the norm for a deck cantilever...example: 12' beam= 4' cantilever

 

[jkeyser14]

In my county the regulation is maximum 23.9 in. cantilever.
It is worth a call to your permitting office.

 

[K'ledgeBldr]

Most AHJ's use the "one third of the overall length" rule.

 

[bczygan]

Most AHJ's use the "one third of the overall length" rule.

On a 12' overall length beam that would be 8' span and 4' cantilever.

Way too much.

It's 1/3 of span.

Of the span is 9' the cantilever is 3'. Total beam length is 12'.

Bill

 

[BFHtime]

It will ultimately come down to what the local inspector wants. If you are going get it inspected which means you need a permit. This is the reason why so things do not collapse and people do not get hurt. Imagine if the deck was 20 feet above ground.

A lot deck fail at the ledger board. from rot not water proofed correctly or not enough fastening to the structure.

 

[The Tool Tyrant]

On a 12' overall length beam that would be 8' span and 4' cantilever.

Way too much.

It's 1/3 of span.

Of the span is 9' the cantilever is 3'. Total beam length is 12'.

Bill

Back during my 32 years as a framing contractor in San Diego, the 2/3 in, 1/3 out rule was standard, so as I stated, 12' beam, 8' in (bearing), 4' out (cantilever). This would of course be for a 'simple cantilever' as in a deck and would take into account that the beam was sized correctly for the load imposed on it.

 

[mike93lx]

Lookup the American wood council deck guide. It will have absolutely everything you need to build a solid deck that meets US code

 

[Jking24]

Back during my 32 years as a framing contractor in San Diego, the 2/3 in, 1/3 out rule was standard, so as I stated, 12' beam, 8' in (bearing), 4' out (cantilever). This would of course be for a 'simple cantilever' as in a deck and would take into account that the beam was sized correctly for the load imposed on it.

Not to dispute your experience but this is what i always thought it was aswell but i was informed that it's not 1/3 it's for every one out you need three in essentially making it a1/4 and that is span vs cantilevered section. 8' span would equal a little over 2" allowable cantilever

 

[Slednut]

I don't know if this applies to a deck, when we framed up my addition the code was 8' with a 4' cantilever.

 

[mike93lx]

I don't know if this applies to a deck, when we framed up my addition the code was 8' with a 4' cantilever.

8' Wide? Width doesn't matter and that cantilever is different than a deck.

Looks nice though. Do you use it?

 

[Slednut]

8' Wide? Width doesn't matter and that cantilever is different than a deck.

Looks nice though. Do you use it?

Sorry I don't know the builder language. Those are 12' long, with a 4 foot cantilever. We really don't use it, I cut my fingernails out there once in a while.

I wish I wouldn't have done it. I got the bright idea to build a 4 foot soffit above it which wasn't the funnest job to finish off.

 

[3onthetree]

Rather than 6 more pages of back and forth how each commenter did it, here is AWC code. Check if AHJ has something more stringent. Google AWC Prescriptive Residential Wood Deck Construction Guide as someone mentioned.

 

[Milzo]

I work for a deck building company as operations manager. We do 350 decks a season in NE Ohio. AWC DCA-6 as other mentioned can be viewed here https://awc.org/pdf/codes-standards/publications/dca/AWC-DCA62015-DeckGuide-1804.pdf

Currently the AWC recommends 1/4 of the span for beam cantilevers.

 

[3rdgendslmech]

I work for a deck building company as operations manager. We do 350 decks a season in NE Ohio. AWC DCA-6 as other mentioned can be viewed here https://awc.org/pdf/codes-standards/publications/dca/AWC-DCA62015-DeckGuide-1804.pdf

Currently the AWC recommends 1/4 of the span for beam cantilevers.

Thanks Milzo! I just needed about 2 feet to get away from the other footer that the old deck post is in. I'm def good by AHJ accounts.
It's a ground level deck being only maybe 22" off the ground at the lowes point of the yard. I called my local permit office and they said due to the size, since it wasn't attached to the house, and ground level.

 

[pmiranda]

So, speaking of the AWC, I was looking at their cantilever chart and am deeply confused. The first two rows look like a mistake in that the allowable overhang _increases_ with joist spacing!?

https://awc.org/pdf/codes-standards/publications/dca/AWC-DCA62015-DeckGuide-1804.pdf

 

[mike93lx]

So, speaking of the AWC, I was looking at their cantilever chart and am deeply confused. The first two rows look like a mistake in that the allowable overhang _increases_ with joist spacing!?

https://awc.org/pdf/codes-standards/publications/dca/AWC-DCA62015-DeckGuide-1804.pdf

I have noticed that as well, but don't know why it would be the case. I doubt it is a typo, but maybe if you email them, they can shine some light on it

 

[pmiranda]

Oh, I see there's a FAQ.. https://awc.org/faqs/awc-support/dc...sometimes-increase-as-joist-spacing-increases

Basically, a longer span has less stiffness, and the maximum span is assumed for the purposes of calculating maximum overhang. I'd have to crack open a book and find the deflection formulas and the right values to plug in to understand more, but I'd wager that using a larger joist still allows the overhang of a smaller joist, if you limit the span to that of the smaller joist.

In the problem I'm working on today, it turns out that going to the next larger joist size allows both a larger overhang and wider spacing, so I might do that anyway!

 

[mike93lx]

Oh, I see there's a FAQ.. https://awc.org/faqs/awc-support/dc...sometimes-increase-as-joist-spacing-increases

Basically, a longer span has less stiffness, and the maximum span is assumed for the purposes of calculating maximum overhang. I'd have to crack open a book and find the deflection formulas and the right values to plug in to understand more, but I'd wager that using a larger joist still allows the overhang of a smaller joist, if you limit the span to that of the smaller joist.

In the problem I'm working on today, it turns out that going to the next larger joist size allows both a larger overhang and wider spacing, so I might do that anyway!

Remember that wider joist spacing will increase bounce in the decking

 

[gearhead1]

The code around here allows an overhang or cantilever and the amount depends on what size lumber is used. Obviously a 2x12 will support more than a 2x6.

 

[Joemctag]

Rather than 6 more pages of back and forth how each commenter did it, here is AWC code. Check if AHJ has something more stringent. Google AWC Prescriptive Residential Wood Deck Construction Guide as someone mentioned.

I think that the term “span” means the distance (center-to-center) that a beam, a sheet of plywood, steel deck, etc. spans between beams, columns, etc. that support it. For example, if your joist “spans” 8’-0” from support to support, then cantilevers, and the table says allowable cantilever is L/4, where L is the joist’s “span”, then allowable cantilever would be 2’-0”.
Of course, many structures are built using the 1/3 -of-the/total-length rule-of-thumb and are approved by an inspector, therefore making them legal. Doesn’t mean it’s what an engineer intended.

 

[Joemctag]

In the deck-building spec. that milzo and 3onthetree refer to, the paragraph titled “Joist Size” on page 3 says it more clearly than I did. And they don’t want you to just use a larger joist size to get a greater cantilever, so they explicitly limit the overhang to 1/4 of the “span”, not the total length. You can certainly get an engineer to design a structure with a greater cantilever, but if no engineering then it’s the table.

 

[pmiranda]

Yeah, if you want to cantilever more than 1/4 span it needs more thought. But what I was noticing is that there are circumstances where too small of a joist doesn't allow even 1/4.