12”oc Ceiling Joists w/ 16oc Rafters?
NYFLOORGUY
| Posted in Construction Techniques on
My plans call for the above requirements. When a rafter falls in between
the ceiling joists and not directly next to, should I put some blocks on my double top plate for stability? Any input would be appreciated. I’m building a 450 sq.ft. addition over my garage, which will connect to the existing house on the 1st floor. I’m working on the pictures, and intend to post my progress (it’s just so time consuming!). I know flooring very well, so feel free to ask any questions about ceramic tile, hardwood, laminate, subfloors, etc.
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Just did this last week - again.
You may want to check with your inspector to make sure he's ok with it.
Around here ( nNW OH) we run them 16oc and double every third joist. Solves those messy spacing problems.
Remodeling Contractor just on the other side of the Glass City
round here .. the joists sit on top of the double plate and are end nailed, nope, toenailed into the rim joist. We then lay a 2 X 4 on top (flat) of the rim joist and partly over the ends of the cieling joist to lock everything together and make a base for the rafters ..
This is how I always did it. Added advantage is better insulation over the top plates of the outside walls.
Any cvhance you could increase the size of the ceiling joists so they would work at 16" O.C.?
Most things I see that require 12" O.C. spacing are undersized and/or over spanned.
I'm with you. What's the point in spec'ing 12" OC, and going through extra blocking, instead of upping the rafter size. If it's just money, spend it.
The reason for specing 12" oc, in my case is quite simple.
24 x 24 garage.
For 40 PSF limited attic storage, 2x12x 24 won't quite make the grade at a 24' span / 16 oc.
VERY simple fix - spend the money and drop an additional one in every third and keep on rolling. At that point it is more than adequate strengh wise, I didn't need to order any "special" material - and wait for it to come in.
Hard to up the size past 2x12 around here. Unless I go with i-joists, and then I would have to screw around with web stiffeners and blocking - waste time.
Added six more joists - that I was already set up to run anyway - six minutes tops, no blocking, then on to cutting rafters. - Simple.Remodeling Contractor just on the other side of the Glass City
Make sense....note that you are actually doubling every third, instead of going 12" OC....KISS rules
found a pic ..
I am not using a rim joist for airflow purposes (A vented soffit and ridge vent). I was thinking of laying 2x 6's flat on the top plate in between the rafters and ceiling joists where need, to add stability. As for the 12'' oc (2 x 10) ceiling joists, I hear everyone on the overspanned thing. I wanted to use an lvl down the middle to reduce the requirement, but my engineer didn't draw it, so I went as drawn. Partly because it was the weekend when I started this part, and had to keep going. I live in southern NY (Dutchess County).
Edited 10/22/2008 3:45 pm ET by NYFLOORGUY
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I usually do what you said you wanted too and break it up with a beam. But I wouldn't deviate from the plans where you live. Tough area, so I've heard.
The simple answer to your question is that I would put two good strong backs on top of the joist and maybe a row or two of bridging/blocking. Maybe block about 4' from the ends. That should be more than adequate.
I don't like the 2"x10"s spanning 24' though. Even with no attic storage I think that will have to much deflection. I would use a min. 2x12.
The span is 21'-9'' from interior of top plate to interior of top plate. I do have a 2x10 2 or 3 feet in, on top of the ceiling joists. We did this to keep them stable while we work. I also have 7/16'' osb in the middle 8 feet (4' from each side of the ridge board). Are you saying leave the 2x10 (strongbacks) and add blocking on the interior. I attached a pdf w/ some hand drawn sketching to illustrate what I was thinking of doing. I'd just like to point out that the building inspector was very cool. He mentioned that they "work for the homeowner" and that if I was a builder I better "do it right because it's the homeowner's money". He even said to call him and he would come out and show me what I should do. Please let me know if there is a problem w/ the attached file, what format, etc.EDIT/update: My apologies. I didn't know what a "strongback" was. I spoke to the building inspector and he explained (before I asked) what one was, and how to do it. He did ask that it be put on my plans by the engineer. To those who don't know, a strongback is a member layed flat over the joists (midspan), with a vertical member nailed to it. Making a "T". You then nail it to the ceiling joists (in the attic space). It helps deflection.
As for the "free standing" rafters, they sit on the top plate w/ no blocking. He said I can put hurricane clips on them if It makes me sleep better!
Edited 10/23/2008 4:57 pm ET by NYFLOORGUY
It sounds like the Inspector you have is a good guy and sort of a partner in this project, giving helpful advice when you need it.
What do you think your finished cost will be?
Bill
Strongbacks help with deflection and Bridging will help with twisting if installed near the ends and middle and also with some some deflection. The nice thing about a proper strongback is that it does a good job at tranfering the load across several joist, so that if you joist are pushing the limits of thier span as I think yours are, a good strongback will atleast make any deflection uniform. Ex. If one joist tries to sag then the strongback will transfer some of the load across to several other joist and they willhelp support each other. The ceiling will also be straighter as a result of this.