Hello. How does one go about using 2×12 ceiling joist and make them fit under a 4/12 hip roof with 2×6 rafters?
There is only about 6″ between the top plate and top of the 2×6 rafters. Am I correct that you would have to clip more than allowed off of the joist to make them fit under the roof sheathing?
Thanks
Replies
Normally, you nail the joists to the side of the rafters. The top of the joist that sticks above the rafter gets cut on that angle. You should be fine as long as you have good purchase on the top plate, with 4" +- at the short point. Spike it tight to the rafters.
Beat it to fit / Paint it to match
Your pitch cut on the 2 x 12's will effectively reduce their ability to span the ceiling.
You are entering into creative thinking land....
Bob's next test date: 12/10/07
Joists don't need as much "meat" at the ends as they do in the middle, so it's usually ok to cut them to match the slope of the roof. The ends are mostly in shear, so as long as enough wood remains to resist shear you'll be ok.
A 2x6 rafter doesn't leave you very much joist though. Any way you can change the design and have the joists run to the outside wall, and set the rafters on top of the joists? Your eaves would be a few inches higher; would it matter in your case?
I would try to detail it like Mike said. Frame the floor, then a plate to set the roof rafters on. That might require a shorter wall though if you are trying to match the existing roof line for an addition. Then a shorter wall and lower ceiling can mean different harddware for the garage doors....
This is why the architect is supposed to work these things out ahead of time.
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As Jim says, it does reduce the allowable span, but in real life I think it depends on what the span of the 2x12 is, and the demand placed on it. I know that, obviously, cutting a tapered wedge out of the top of the 2x12 doesn't weaken it anywhere near as much as notching the same amount from the bottom. Notching the bottom reduces the strength of the whole joist to whatever is left after the notch; I would think that with the tapered cut, you have full 2x12 somewhere around 16" in from the wall. An engineer could tell you better than I could how much this reduces it's strength, but my gut and practical experience tell me not a whole lot. If anything a plywood gusset 16" in would give you full 2x12 at the bearing point. ( I don't think it's necessary, but it may make the building inspector happier........Someone with more experience regarding engineered lumber allowable spans might be able to chime in as to how much of a 9-1/2" TJI or the like can be clipped at the top, and what the span would be.Is this existing roof with floor being added or new? If new, then what the other guys said...taller rafter=higher height at plate, or blocking under 2x6 for inc in height
Bing
Edited 4/5/2008 6:14 pm ET by Bing187
i would add rim joists and blocks and frame the roof on top of the rim joists.
you might have to add soffit etc, to get the elevation to look right but i think it could be done.
only if he dropped the wall height.
Piffins right, this is what you pay the architect for. You have an incomplete blue print.
This is why you are on a website trying to figure it out.
why would he have to drop the wall height?
if you run rafter tails long, and have wide fascia, and a soffit, you would be able to return the soffit to the structure at a height that is in proportion and pleasing to the eye. it just has to be worked out.
If he uses 2x12 joistes, the minimun would be 2x10 rafters. In order for it to line up with the rest of the house facia he would drop the walls.
this would allow for min. clipping of the top of the rafters.
I still belive he would be much better off with trusses. Espicially if he is not familiar how to cut rafters with a hip. I belive he said he had 5/15 pitch, which would give him very minimal clearance for storage anyway.
It also might be a less expensice option. I know around here 2x12x24'
are pricey.
What kind of span do you have that you'd need 2x12 ceiling joists? That's hefty even for a floor joist.
What kind of span do you have that you'd need 2x12 ceiling joists? That's hefty even for a floor joist
I'll bet it's to hit a mandated R value rather than a span value--2x6 rafter does not suggest a long roof span that would also need hugely-deep joists, too.
But I could be wrong.Occupational hazard of my occupation not being around (sorry Bubba)
2x6 rafter on a 4/12 could be a 22' wide house with a 12' common rafter and a 22' wide room w/no bearing walls. Could be a lotta things. Without some more info from op, it's moot.
Bing
PS. sure does look nice in your neck of the woods ( saw pix) "sigh" I can't wait for good weather.
Edited 4/6/2008 6:47 pm ET by Bing187
can't wait for good weather
This is our good weather. About two more weeks, three, tops, and the heat will start cranking in. Pleasant days in the 70s turn to roasters in the 80s in a hearbeat. Thne June rolls around and the lows at 70s and the highs 90s.
Fleeting is the word.
12' 2x6 rafter still seems a tad small--not that it's not done, jsut small. That's why my thought was for insulation depth. It also could be a case where this is a one story 'bit" pooched out from under a two-story mass adjacent, so the 2x12 is to keep things aligned/common. We are all still guessing a bit, and need input from OP.Occupational hazard of my occupation not being around (sorry Bubba)
More info is certainly needed. Thats why I left this thread with such a generic response. Yes it can be done but it might cut down the span capability.If it's really critical to add the 2x12, then he could simply run a header and lag it into the studs and plates, then hanger the ceiling joist. This will effectively support the end of the joist at the wall without the overcut for the slope. Where theres a will theres a way. Bob's next test date: 12/10/07
Hello and thanks to all for the help. For those who were asking about the specs.This is for a two car garage addition. The span I need to cover is 23'-3 1/2". The roof is a 4/12 pitch hip with 2x6 rafters since I want to match my existing roof line. The width of the garage is 26'-8". The common rafters of the hip span the 26'-8 with the joists running the 23'-3 1/2". No snow loads (southwest Texas).I was only looking at 2x12's because someone suggested it. I was looking at a ceiling joist span table and it shows I can span 26'-2" at 12" o.c. with Douglas Fir No.2 or better 2x8's. It seems 2x8's will work.
Hello Jim. Here are the specs.
This is for a two car garage addition. The span I need to cover is 23'-3 1/2". The roof is a 4/12 pitch hip with 2x6 rafters since I want to match my existing roof line. The width of the garage is 26'-8". The common rafters of the hip span the 26'-8 with the joists running the 23'-3 1/2". No snow loads (southwest Texas).
I was only looking at 2x12's because someone suggested it.
I was looking at a ceiling joist span table and it shows I can span 26'-2" at 12" o.c. with Douglas Fir No.2 or better 2x8's. It seems 2x8's will work.
Are you really going to use this only to hold up the ceiling or do you plan on storing something in the attic? How high are the walls that your ceiling joist will sit on? There are so many ways to skin this cat, depending on those answers. If the walls are 14' high (yes, I've built garages with 14' studs), then you simply drop the ceiling joist down below the top plates. If you plan on storing stuff in the attic, you will have sag if you follow those charts. You might not mind sag though...I'd look into TGI's. Here in Central Texas, there isn't any doug fir stocked. It's "special order". I'm afraid of what it will look like when it gets here! Bob's next test date: 12/10/07
Hello Jim. Other than the garage door rails and the sheetrock there will be nothing else pulling on the joists. I'm not using it for storage.
The walls are 8', I don't want to change my existing roof line so I can't go any higher.
Actually I just called my local lumber yards (not Lowes or H.D.) and they both have 2x8x24 D.F. No. 2 or BTR in stock in large quantities ($18.49 each).
I will still be strongbacking them to help with the sag.
You'll have no problem putting them in then. Congrats...you have your solution. You'll have to be clever to retrofit these if your roof is already intact. Bob's next test date: 12/10/07
Thanks Jim for all your help on this. I'll be doing the roof at the same time so that should help.
14' walls in a garage? I bet that was one nice garage.
It was not uncommon for garage walls to grow in the rolling subdivision. Usually, the cornice details were tied to the house and we had to keep the roof planes in line for one reason or another. If the property rolled downward on the garage side, we'd simply drop the bottom plates, so tall garages were very common. The last house I owned had 14' 2x6 garage studs. Yes, it was a nice garage indeed but I really didn't need the height. If I had stayed there, I was going to convert that garage into a small gymnasium workout room and add on a "normal" 3 car garage to replace it. I'm glad I moved though.When you mention "doing your roof", does that mean re-shingling or will your roof be open for laying in the new ceiling joists? If you get to lay them in, you will have no problems. If the roof plywood is on, you'll have some challenges, but nothing too catastrophic. Bob's next test date: 12/10/07
Man Jim I just realized you are just up the road in Round Rock, it's a small world.
The roof will be open so that should help.
You ever do any framing in the Lago Vista area? I can't believe the houses that are out there.
I don't know that I've toured the Lago Vista area quite yet. We get busy wherever we are and I'm having a hard time getting about to see everything.We haven't concentrated much effort in getting frames in any area. Bob's next test date: 12/10/07
Is there some reason you are not using pre-made rafters? 24' 4:12 pitch is commonly available, only about $40 each, guaranteed to function properly and easy to install. I even put up a roof with them by myself once (I grunted a lot). Am I missing something?
I keep asking and he is not responding why no trusses.
he is not responding why no trusses
Several Guesses.
It's an Addition, and small (apx 22 x 26), and may not haveseen them used for that sort of thing.
Also, the closest wood truss supplier is in my town, two hour's drive away (and is also brand new and not in many YP yet). Next nearest (that I know of) would be in Houston. It's that, or drive up to Austin amd hit up one of the bigger suppliers (and Hope lumber is closer to Roundrock) and have them order trusses from his measurements (which might send them off to Illinois or East Texas).Occupational hazard of my occupation not being around (sorry Bubba)
Hello Frammer52, Why no trusses? Well pretty much what CapnMac said. I have not completely ruled it out though.
you wouldn't be going through this now.
When the trusses are made they will desigh them for your print, then
give you a diagram on where they go. Much easier than trying to cut
etc. etc..
Hello NannyGee. Are you talking about trusses?
Oh yeah! Trusses! Dhuh - stupid me. Why didn't I make that connection?
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"Are you talking about trusses?"Yes. Since they account for at least 95% of all roof structures here, the older folks, like my father, often call them rafters to match how they were used to building roofs decades ago. Anyway, If it is at all possible to find them and have them delivered to your site, do it. It is a much more sensible solution, and will likely be cheaper as well as faster and more sturdy. I've had them delivered 60 miles to our cabin (along with the rest of the lumber for about $100 fee) without the retailer batting an eye.If you are daring you can even make them yourself, though no one here would recommend it. They were often built on site decades ago. There is certainly no way I would waste 2x12's in a structure that was not intended to bear weight, just hold up a ceiling.
"Is there some reason you are not using pre-made rafters?"Educate me. In forty years of this, I have never heard of them. Maybe it is special in your area to pay more than twice as much for having them pre-made as just buying the lumber?
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Here in Central Texas
I'm going to guess that you did not click on his profile, he's in San Marcos, just n the other side of Austin from you (and Tom, and possibly, Hiker)
there isn't any doug fir stocked
LoL! Ain't that the truth. Mind you I remember when different varietes of Pine weer in stock, but nowadays, I sometimes cringe to see what's labeled SYP.Occupational hazard of my occupation not being around (sorry Bubba)
We've already seen enough of SYP materials. I've learned that we were spoiled and had a very good lumber supply: lots of choices and a lot of good stock. Bob's next test date: 12/10/07
But over-deep rafters just reduce the R value. Better to cover the tops of them with cells.You're not gonna get any usable space in a 4/12 attic.
What is wanted is not the will to believe, but the will to find out, which is the exact opposite. --Bertrand Russell
Fitting a replacement rafter with heel cut over a plate is awfully hard in the first place. Better to attach a ledger to the wall and hang the ends of the new rafters in my way of thinking.
You'll have a very hard time convincing a sharp inspector that a span that really needs a 2x12 will be fine if you whittle the bearing end down to fit the top plate. It just isn't going to happen since it's outside of normal building practices and goes against code books such as IRC---unless you want to pay an engineer to determine it's okay and get a stamped drawing or letter.
I've done these in the past when repairing snow damage, and it's not uncommon to need something like a 2x12 to take the stress of bending old over spanned 2x4's back into alignment. The new rafter isn't helped by the old, the old sway-back 2x4 in addition to any weight on the roof is actually fighting the new.
Back to the ledger. Hang it like any weight bearing ledger, I like Timberloc or Ledgerloc screws, and use joist hangers to support a 1-1/2" heel cut on the bottom of the rafter. Joist hangers are rated so it's not all that difficult to see which is needed for the weight involved, and often you'll get by with one that fits nicely on the ledger. In worst cases one of the hangers with long straps is used and wrapped around the ledger to get enough nails in it to satisfy the weight requirment.
Another option is placing the ledger under the slight heel cut on the new rafters. You'll lose 1-1/2" of usable space since the wall will now need to be firred out, but that's not all that bad for what you're getting.
I like the ledger between the end of the rafter and the wall because it provides a solid surface to attach a means of jacking the rafter into place. A double 2x12 hanger was long enough we could get them in place with 6 teco's and have enough room to get the new rafter up as far as possible by hand, then jack under the rafter with a hydrolic ram gizmo.
It sounds easier than it is, so hopefully it'll work out.
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