What is the most I can cantalevier a deck joist using 2x10s? I am spacing 16 OC. jeffysan
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With a thousand pound a foot load you can't.
With a support under them every eight feet and no load, forever.
In your case, with the information given, somewhere in between.
SamT
Edited 1/5/2006 10:22 am by SamT
I thought the rule of all-thumbs was 3 times the height of the joist.
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
My own rule of sore thumbs is if it's more than the height of the joist call an engineer.
SamT
Yesterday I had the inspector raise an eyebrow at my deck for cantilevering 4', His first comment was that 2 feet was the max, then that maybe 40" would be OK, then he said he'd get back to me. The deck is 16' square, so there are 12' of regularly supported 2x10. I'm also spaced 16"o.c. Or at least my deck joists are.
Code issues aside, the 4' cantilever feels very solid.
Here in NC decks cannot extend beyond 2' cantilever - code. Other rule of thumb is 25% cantilever on flooring - ie 12' supported x .25 = 3' cantilever max.But that is just a rule of thumb.Let's not confuse the issue with facts!
>>Here in NC decks cannot extend beyond 2' cantilever - code. << and, I'd like to add, min 2x10 16" O.C are required.
I'd be real surprized if any inspector would pass a 4' cantalever unless it was engineered.
Will it be loaded with a roof, a rail, some snow?
Load a roof on it and the max here would be 9.25" the same as the depth of the joist.
otherwise it also depends on how long the joist is overall.
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Assume 1000 psi wood
First, you DO NEED TO GO TO THE LIBRARY AND CONSULT SOME ENG TEXTS TO BE SURE YOU UNDERSTAND THE DERIVATION AND IMPLICATIONS OF THE BELOW CALCULATIONS BEFORE PROCEEDING.
As others said, if incapable of that, you gotta hire somebody (by implication) smarter than you - now you got incentive to go the the library, huh <G>
Assume 16" spacing
Assume 40# sq ft loading
4.4#/in beam loading
Moment = 4.4*L*L/2 =2.2*L^2 = strength * section modulus=1000*1.5*9.25^2/6 = 14.2K in-#
thus L = 80 inches = 6.7 feet
If you dont understand or cannot go to the library to figure them out, hang 2 94# bags of cement from the end of each joist, then go stand on the end with a safety harness on and jump up and down on the end. If you feel uncomfortable, the cantilever is NOT OK.
BTW, deck on own house has 2x10 at only 3.8 ft long cantilever at 16" spacing; plus, 2 directional support from deck board also taken into account.
Oh, BTW2, I never do these on-line calculations unless inebriated, so beware, be sure to go to the library!
Edit BTW#3, on decks, some codes assume a group of linemen along the deck rail, so the assumption of 40# sq ft equal loading DOES NOT apply, you gotta put a line of linebackers along the rail for the calculations.
Edited 1/5/2006 11:24 pm ET by junkhound
Edited 1/5/2006 11:30 pm ET by junkhound
Edited 1/5/2006 11:34 pm ET by junkhound
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My deck which just happens to be my floor joist extending out from the house, is cantalevered 6'.
They are 2x10's on 16" centers.
Now Junkhound has given ya the load formulas -- so I'm not going to attempt to give ya load calcs of a 2x10----- but in my neck of the woods when you cantalever anything your limit is also based on that you will not go over 1/3 of the total length of the board.
I framed an add-a-level last year with 12" I-joists at 16' oc and I sistered 2x10's along side them with a 3-1/2" x 9-1/2" microlam at each end with a 3'8" cantilever. I never use the same size joists that are the same as the house though. We always go one size down from the joists when we do decks like that. I always go back the closet bearing wall which in my case was 16' back.Joe Carola
In canada, the national building code is also 2' when 2x10 or larger floor joists are used, but where cantilevered floor joists are orientated at 90 degrees to the main floor joists, you can extend the catilever at a 6:1 ratio (meaning if you want a 4' cantilever, you would need a 24' joist)...
jeffysan..........When I started 30 yrs ago, we cantlivered decks , twice the distance inside as what would go outside. I've seen some that decayed and failed because we "Pinta " treated for waterproofing but not because ofstructural problems. Now before anybody has a cow I'm glad we have new codes and I adhere to them religiously . Sounds like I pray no one finds out I built them that way in the begining hehe.