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Old 04-23-2012, 09:30 AM   #1
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Adding 16.5" to length of deck, sistering 2x6


Adding 16.5" to the end of my deck. It will be in the same direction as the joists so I just need to sister some additional pieces to the end of the joists.

The total cantilever will only be 26" and I have read that maximum cantilever for 2x6 joists is 30" so I should be ok in that regard.

I just have the sistered boards attached to joists with a couple screws and going to pick up additional hardware tonight to finish. Should I use carriage bolts to secure the additional pieces to the existing joists? How many is necessary? Is there a rule of thumb?

Thank for your time everyone!

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Old 04-23-2012, 09:35 AM   #2
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Adding 16.5" to length of deck, sistering 2x6


How far back are the sistered cantlivered joist going into the existing joists?


Last edited by hammerlane; 04-23-2012 at 09:39 AM.
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Old 04-23-2012, 09:41 AM   #3
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Adding 16.5" to length of deck, sistering 2x6


They are 8 foot boards right now, there are 8 joists with additions being added to them. I was undecided if I would cut them shorter or not, depending if the full 8' was needed or not. As I said they are just temporarily screwed in for now.

Trying to figure out what type of hardware I should use and how much of said hardware. Carriage bolts, lag bolts, some sort of brackets, etc.?
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Old 04-23-2012, 09:46 AM   #4
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Adding 16.5" to length of deck, sistering 2x6


Quote:
Originally Posted by NickWa View Post
They are 8 foot boards right now, there are 8 joists with additions being added to them. I was undecided if I would cut them shorter or not, depending if the full 8' was needed or not. As I said they are just temporarily screwed in for now.

Trying to figure out what type of hardware I should use and how much of said hardware. Carriage bolts, lag bolts, some sort of brackets, etc.?
So you have 8 foot 2x6's that you want to cantilever out 26 inches. That leaves you with 5 feet 10 inches of the sisterd 2x6 going back into the existing joist. You should verify that is enough lumber for that amount of overhang. Ive read some posts where it says 4 foot back for every 1 foot overhang. Maybe a 2x6x10 would be a safer choice.
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Old 04-23-2012, 09:54 AM   #5
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Adding 16.5" to length of deck, sistering 2x6


That is true, although I am not sure if it makes a difference that they will be attached to existing joists which are cantilevered out 9.5" right now? These existing joists are full 2x6x16 boards. Thus the total unsupported cantilevered addition will be 16.5" with 9.5" of sistered joist cantilever.

If I were to use 2x10, would I just notch out for the beam? I can't have the sistered addition be higher than my existing joist!
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Old 04-23-2012, 10:05 AM   #6
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Adding 16.5" to length of deck, sistering 2x6


SO right now you have a 9.5" cantilever off of a 2x6x16 joist. And to this you want to add 16.5" more.
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Old 04-23-2012, 10:16 AM   #7
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Adding 16.5" to length of deck, sistering 2x6


I will try and clarify

Right now, 16' 2x6 are being used for my joists of which are cantilevered 9.5" past my final beam. Thus, I have 9.5" of unsupported board out of a total 16' 2x6.

I want to extend the deck by 3 deck boards (16.5") which would create a total cantilever of 26" of which 16.5" would be unsupported totally and 9.5" would be supported by the existing 2x6 joist cantilever and however long the rest of my board ends up, will be supported by the 2x6 joist over the joist span.
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Old 04-23-2012, 10:22 AM   #8
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Adding 16.5" to length of deck, sistering 2x6


OK I get the picture now. Trying to look up how far back the sistered joists need to be on the existing joist.
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Old 04-23-2012, 11:14 AM   #9
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Adding 16.5" to length of deck, sistering 2x6


You may want to discuss this with your building inspector, assuming you have a building inspector (you have not told us where you live). Where I am, the minimum size for a joist is 2x8, so clearly you either work off a different code, or possibly your deck predates code, or maybe there is no code where you are. The L/4 maximum cantilever rule only applies to allowable size joists, so in my town (which uses IRC 2006), even if your deck predated existing code, you would not be allowed to extend the overhang since the building inspector would then require you to bring the deck up to minimum code, which among other things requires minimum 2x8 joists.
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Old 04-23-2012, 11:55 AM   #10
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Adding 16.5" to length of deck, sistering 2x6


So if 2x6 were allowed, one could do 16/4 = 4 foot cantilever? I am only going 26". My deck is rock solid and has never bounced or flexed whatsoever, even with multi-family bbq's and such.

I will tell you right now, I am not rebuilding deck with 2x8 joists just to add 16.5" to the length - that is just silly.

If a person had a deck built with 2x8 joists and was extending it in the same manner as I would like to, how would they secure the sistered joists to the original/beam?
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Old 04-23-2012, 12:15 PM   #11
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Adding 16.5" to length of deck, sistering 2x6


Quote:
Originally Posted by NickWa View Post
If a person had a deck built with 2x8 joists and was extending it in the same manner as I would like to, how would they secure the sistered joists to the original/beam?
Do you mean how would they secure the sistered joists to the original joists?

Also how high is your existing deck from the ground?
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Old 04-23-2012, 12:23 PM   #12
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Adding 16.5" to length of deck, sistering 2x6


Yes how would secure a sistered joists to original joists which are up to current code standards. Top of the deck surface above grade is 22".
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Old 04-23-2012, 12:25 PM   #13
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Adding 16.5" to length of deck, sistering 2x6


If you decide to go along with your plan of sistering 2x6's to the original joists, go as long as you can for the back-span part of the sisters.

Few tips:
-use construction adhesive along with lag bolts
-use larger diameter washers to spread the force of the bolts out over a larger area.
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Last edited by hammerlane; 04-23-2012 at 12:29 PM.
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Old 04-23-2012, 12:33 PM   #14
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Adding 16.5" to length of deck, sistering 2x6


Was indeed planning to use an adhesive between the two boards.

I am thinking to just leave the boards at the full 8', adhesive them together and bolt every 16" with 3/8x4" hex head bolts and multi-sized washers.

To me this seems like it would be adequate but I came here to look for advice so I will take any and all into consideration.
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Old 04-23-2012, 12:34 PM   #15
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Adding 16.5" to length of deck, sistering 2x6


something else found at: http://decks.com/
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Last edited by hammerlane; 04-24-2012 at 07:45 AM.
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