#1421 - 09/06/05 12:53 PM
Deck Improvement: Sistering & Cantilevers
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ChicagoNature
Returning Do It Yourselfer
Registered: 09/06/05
Posts: 3
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Hi,
This is a first time project for me and I don't know all the terms, so please bear with me.
My existing deck is rectangular, 8'x32'. As you can see it's pretty narrow. The house surrounds the deck along an "L" (on two sides).
8ft. 2x8 joists are 16" apart and run across the short distance of the deck from the joist hangers on the ledger board on the house to two 2x8 rim joists that are resting on 5 cement footings that run along the length of the deck.
All the joists are in good condition.
My goal is to get an extra two feet of width (10 feet) so that the deck is more usable. Building code allows me to perform a 2-foot cantilever. But, I'm trying to make life easy and taking out every joist and replacing them seems like a big job. That is, I'd use install new 10 foot joists.
However, I was wondering if I could simple sister onto the sides of each joist to extend out 2 extra feet. I guess sistering a cantilever section would require two feet out and 4 to 6 feet in. I'm not sure about this.
But, will this idea work and is it safe?
And, if so, what bolts do I use to sister the joists and where should they be placed.
Thanks so much!
Mike
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#1422 - 09/06/05 09:49 PM
Re: Deck Improvement: Sistering & Cantilevers
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provip
Super Do It Yourselfer
Registered: 03/03/01
Posts: 1153
Loc: Victoria, BC, Canada
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Code requirements differ from region to region but the rule of thumb is 3:1. So in your case you would go in minimum 6 feet past the point of support. 2x8's on an 8' span 16"oc is giving you a very strong deck to begin with provided your ledger is installed properly and everything has proper nailing.
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Bart Blainey, B.E.R.
Consultant/Journeyman Carpenter
Building Envelope Specialist
Master Renovator
provip@prodeck.org
http://www.prodeck.org
Barton Blainey (provip) specifically assumes no legal liability or responsibility for the accuracy, completeness or usefulness of any information or process disclosed. The above further expressly advises that any use of or reliance upon the information and or opinion disclosed is at your risk .
_________________________
Bart Blainey, B.E.R. Consultant/Journeyman Carpenter Building Envelope Specialist Master Renovator provip@prodeck.org http://www.prodeck.orgBarton Blainey (provip) specifically assumes no legal liability or responsibility for the accuracy, completeness or usefulness of any information or process disclosed. The above further expressly advises that any use of or reliance upon the information and or opinion disclosed is at your risk .
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#1423 - 09/06/05 11:16 PM
Re: Deck Improvement: Sistering & Cantilevers
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ChicagoNature
Returning Do It Yourselfer
Registered: 09/06/05
Posts: 3
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Thanks Bart!
By the way, I went to the hardware store to buy 4 inch carriage bolts (96 of them) and it costs $1.40/each not including the washer and nut. Woah!
This is assuming 4 carriage bolts for each of the 24 joists (and sisters). I'd probably place 2 of them 6 inches from the ends.
Anyway, is there an equivalently strong way of sistering that would save some money?
Thanks,
Mike
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#1424 - 09/07/05 12:20 AM
Re: Deck Improvement: Sistering & Cantilevers
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provip
Super Do It Yourselfer
Registered: 03/03/01
Posts: 1153
Loc: Victoria, BC, Canada
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Carriage bolts are overkill. 3" galvanized nails (spikes) will do the job. Nail in rows of 3 nails about 8" to 12" apart and do this on both sides.
If you are concerned and there doesn't appear to be any reason to be in this case. Use full 10' joists to sister on and brackets or hangers at the ledger board.
In any case, make sure the ledger board is well fastened to the house and that the hangers are well nailed. Special care is required in these areas when joists are cantilevered.
------------------
Bart Blainey, B.E.R.
Consultant/Journeyman Carpenter
Building Envelope Specialist
Master Renovator
provip@prodeck.org
http://www.prodeck.org
Barton Blainey (provip) specifically assumes no legal liability or responsibility for the accuracy, completeness or usefulness of any information or process disclosed. The above further expressly advises that any use of or reliance upon the information and or opinion disclosed is at your risk .
_________________________
Bart Blainey, B.E.R. Consultant/Journeyman Carpenter Building Envelope Specialist Master Renovator provip@prodeck.org http://www.prodeck.orgBarton Blainey (provip) specifically assumes no legal liability or responsibility for the accuracy, completeness or usefulness of any information or process disclosed. The above further expressly advises that any use of or reliance upon the information and or opinion disclosed is at your risk .
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#1425 - 09/07/05 10:13 AM
Re: Deck Improvement: Sistering & Cantilevers
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ChicagoNature
Returning Do It Yourselfer
Registered: 09/06/05
Posts: 3
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One other concern I have is that the new boards that I will be using to sister (2x8x6') will be slightly wider than the existing joists that rest on two boards extending along the cement footings.
The existing joists are about 7-1/8" and the new ones are coming today and they're bound to be 7-1/4" to 7-1/2". If it's just 1/8" difference, I was told to just lift the existing joist and shim it. But, if it's larger, shimming may not be an option.
What do you suggest?
Thanks for all the help!
Mike
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#1426 - 09/07/05 05:50 PM
Re: Deck Improvement: Sistering & Cantilevers
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provip
Super Do It Yourselfer
Registered: 03/03/01
Posts: 1153
Loc: Victoria, BC, Canada
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First, the boards you have coming should be 8' allowing 2' for cantilever and 6' back in on the other joists. Remember the 3:1 ratio, so you should be back 3'for every foot cantilevered.
The existing joists are probably secured to the support beam so my choice is to cut the new joists to match.
_________________________
Bart Blainey, B.E.R. Consultant/Journeyman Carpenter Building Envelope Specialist Master Renovator provip@prodeck.org http://www.prodeck.orgBarton Blainey (provip) specifically assumes no legal liability or responsibility for the accuracy, completeness or usefulness of any information or process disclosed. The above further expressly advises that any use of or reliance upon the information and or opinion disclosed is at your risk .
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