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-   -   Cantilever Deck (http://www.diychatroom.com/f19/cantilever-deck-149873/)

CarpenterCaleb 07-11-2012 12:17 AM

Cantilever Deck
 
I recently was reading some threads about cantilevered decks and don't quite understand why everyone is scared of the 3:1 rule. A couple weeks ago we rebuilt a deck that grew from the old size and the plans called for 2 piles on the cantilevered part that the stairs came down from. These pilings would have been in the homeowners garden and therefore I contacted a couple engineers and questioned on whether they were needed. The total length of the deck was 15'3" and the beam was set at 11'9". I tripled up the beam that the stairs (12 risers double stringers) supports, doubled up the outside ply, and blocked the whole dock mid way. The engineers told me that a double was necessary to carry the load of the stairs and anything else was overkill according to their programs. This makes me wonder why everyone is so worried about using the 3:1 rule. Also the stairs and cantilevered section is just as sturdy as any flush beam constructed deck that I have ever been on. Just looking to hear some input as to why other contractors are hesitant to utilize cantilevers, as I believe they look so much better and if 2 engineers agree there is absolutely 0 problem with this in my eyes, as they have made me do some ridiculous things in the past according to their program. Thanx guys just looking for some feedback

GBrackins 07-11-2012 12:20 AM

what is the 3:1 rule? do you mean 3x the back span vs the cantilever?

joecaption 07-11-2012 09:22 AM

Done with the right width floor joist and proper attachment points that's fine. But how many times have we all seen DIY decks where they cheaped out and use something like 2 X 6's, 24" on center with to long a span.
I'll try and post a picture of one in my area that the home owner built.
He thought it needed a slope so on a 12' deep deck it drops about 6". He nailed the ledger right through the vinyl siding. No joist hangers.
The over hang is about 4' from the beam, and over the years from the beam to the end of the deck the joist have sagged at least 2".
Not bad enough he then just set the 4 X 4 post for the railings on the deck and toe nailed them through the decking with finish nails, no blocking, not bolted to the floor joist.

Last but not least he used a 2 X 4 for the end post againt the house and used spikes to just nail them right though the siding.

GBrackins 07-11-2012 09:56 AM

I like cantilevered decks, so when I design one I perform the following calculations:

determine design live load (based upon building code requirements plus experience/judgement, always at least 40 pounds per square feet per building code)
determine dead load based upon construction/materials for deck

1. live load + dead load over backspan and live load + dead load over cantilever (even loading)
2. live load + dead load over backspan and 0 live load + dead load over cantilever (causes end of cantilever to rise)
3. 0 live load + dead load over backspan and live load + dead load over cantilever. (causes backspan to rise)

joists are sized based upon the most restrictive of the three conditions. I typically use 12" o.c. joist spacing to keep composite decking from being bouncy (subjective from person to person)

just my humble opinion ....

sierra1 09-12-2012 07:09 AM

floating stairs
 
You seem pretty knowledgable....got info on constructing wood floating stairs for the exterior? Thanks...

GBrackins 09-12-2012 08:51 AM

sierra1,

what do you mean by wood floating stairs?

if you're wanting information in regards to your project you should start your own tread. gets confusing when trying to discuss two different projects in the same tread.


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