I’m planning to build a 24′ x 36′ attached garage with a room overhead. My plan is to frame the 36′ walls with 14′ 2×6’s and dado in a 2×6 ledger board approximately 10′ up on each of the long walls. I will then run 24′ I-joists between the two walls to form the floor of the overhead room at an elevation of approximately 11′. The I-joists will rest on the ledger that I let-in to the 2×6 walls (I also plan to glue and nail an additional 2×6 to the ledger to provide a full 3 inches of bearing for each end of the I-joists). This will leave me approximately 3′ of wall above the floor on each side. As for a roof, my plan is to run I-joist rafters from the top of those 3′ walls to a ridge board that runs the full length of the garage. Can someone give me an idea if I’m totally out to lunch or does this sound plausible?
Thank you!
John
Replies
I have a couple of problems with your ideas.
First - Why go to all the trouble of notching in a ledger? Build your walls at about 10' then set the I-joists on the top plate and use a rim board on the outside. Then build a kneewall on top of that.
Second - If you're using I-joists for rafters you have to have a ridge BEAM instead of a ridge BOARD. Hangers, web fillers, and/or blocking may also be required, depending on your loading and the manufacturer's recommendations. You'll proabby need a pretty large beam if you have to span 24' or so.
The following PDF file gives a few roof details:
http://www.gp.com/englumber/pdf/123040/20,28,29.pdf
Or look at the file I have attached - It has some more details.
One other alternative comes to mind - Use attic trusses. They can probably be manufactured to do what you're trying to do. I can probably post a pic if you give me a pitch to work with.
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I originally planned the wall details like you suggest but was told that that would not work due to the fact that the knee walls were not tied together with joists of any sort. The way I understand it, without the joists tying them together, the tops of the knee wall would be subject to forces that would tend to drive them out from the center of the garage - the joists are necessary to counteract that force. If that's not true, I'd much prefer to follow your suggestion! I'm planning a 12/6 pitch on the roof and would like at least an 8' ceiling within the middle 4-6' of the room. The supplier I checked with, told me that that would not be possible with a truss. Again, if that's incorrect, then I am all ears - I'd much prefer to use trusses. Thanks for the note.
"without the joists tying them together, the tops of the knee wall would be subject to forces that would tend to drive them out from the center of the garage"
If you have a ridge beam, you don't have horizontal thrust at the tops of the walls. Even without it, I doubt you could connect the floor joists to a ledger, and the ledger to the wall well enough to hold the forces involved.
Are you clear on what the difference is between a ridge beam and a ridge board?
When you say a 12/6 pitch, I assume you mean 6/12? Otherwise you're gonna have one heck of a steep roof.
Have a look at the picture I attached, and see if it's roughly what you have in mind. You'll gain a lot of headroom if you increase the pitch a bit. I had a good wife once. Then she went home to her husband.
Sco is describing balloon framing which we do all the time around here for kneewall situations like this. It's worked for a couple of centuries, so I'm sure it can work for him too. He needs either the ballooon walls or a strctural ridge, but not necessaryuilly both.
He should only let the ledger in 3/4" though or use 2x6 walls to maintain enough strength in the studs to resist the lateral roof thrust.
I agree that the pitch is too low to make good use of space. Ours is typically a four foot to 54" kneewall and a 12/12 roof on a 22' to 224' width.
That ridge beam would be the long length and not the 24'. right?
The other concern is that there woiuld need to be firestop blocking in the stud wall at the floor frame level..
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Your solution creates a hinge at the floor line which has no resistance to any horizontal force (wind, thrust, etc..). Balloon framing solves that issue.
Boss Hog's alternative was standard platform framing with a structural ridge. There are no problems with horizontal forces in this scenario if the structural ridge is properly sized. It will be huge if it is 36 feet long but that is another issue.
Boss Hog's real suggestion was to use attic trusses.
We have used balloon framing in this situation a number of times and would do so again. This biggest problem for us is framing long walls that are that tall, especially when they are 2x6's. We do is so infrequently that we forget all the tricks we used ten years ago.
That's where those proctor wall jacks come in handy..
Excellence is its own reward!
Thank you all very much for your input!
I did mean to say a 6/12 pitch - I wanted it to match the house. The more I think about what you have all said, I guess I'd be willing to steepen the pitch of the garage even though it wouldn't match the house. Personally, I don't think it would look bad, although I'm not so sure my wife would agree.
Boss Hog, thanks for the diagram of the attic truss - that is something I've never seen before (as y'all might have guessed, I'm not a professional carpenter - not even close). I like the concept but don't like the fact that I'll lose so much space down the center of the structure.
I now understand the difference between a ridge board and a ridge beam. Given the length of the room and lack of support columns under the room, I suspect a ridge beam would be out of the question. That leads me back to my original design, or some other option. If I balloon framed it, I was planning to use 2x6's for the walls and letting in the ledger a full 1.5" on the outside of the walls. I was also going to scab another ledger parallel to that one on the inside of the wall to provide extra bearing for the I-joists. I was also hoping that I could find some sort of strap to help hold the I-joists to the veritcal 2x6's and/or the outside ledger. Last night it occurred to me that this would put quite a bit of tensional force on the I-joists. Can someone tell me if they are designed to withstand those type forces?
As an alternative, I'm now considering standard platform framing with a 4-5' kneewall and 8/12 or 10/12 scissors trusses on top of that. Any thoughts on how a 10/12 pitch roof would look attached to a house with a 6/12 pitched roof?
Thank you all again for your help!
Sco
"Your solution creates a hinge at the floor line which has no resistance to any horizontal force "
Not really - It's typical platform framing. The diaphram action of the roof sheathing will transfer any horizontal forced to the gable walls. Love is like the sun: when it's there, you just want to wallow in its glow, and when it's gone, you just want to sleep and drink hot chocolate.
Gotta disagree wit you on this one Boss man.
Balloon framing is the way to go.
Or are you trying to sell this guy some trusses?
:)Mr T
Do not try this at home!
I am an Experienced Professional!
Aw, come on Mr. T - You know trusses are the answer to ALL framing problems..................(-:
Seriously - (If you can believe I'm ever serious) I realize there's a lot of room for personal preference on stuff like this.
My preference would be trusses - In this case I believe they would be easier, cheaper, and stronger.
But I also realize there is a lot of room for disagreement.
Being as I have no clue where this guy lives, I have no hope of selling him anything. Heck, we're so busy we don't NEED any new custoners. Romeo's last wish was to be laid by Juliet.