I’m about to try my first hip roof–on an 8×12 garden shed. One thing I’m unclear about is the birdsmouth on the hip rafter. Do you cut a sort of 45 degree notch on the corner of the plate? Or what?
I found a great online calculator for hip roofs, for anyone interested:
Could a building code update make your go-to materials obsolete?
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial NowGet instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
Replies
You can, John Carrols recent article shows you that way.
I would cut the birdsmouth for your pitch but don't forget the hip rafter gets a 17 horizontal instead of the usual 12.(or multiple, for example if you are using a roof pitch of 6-12 your common rafter birdsmouth could be 3-6, and then your hip birdsmouth could be 3-8 1/2) If you leave the same amount of wood above your birdsmouth (vertically measured) as your common rafters then your sheathing will lie flat.
Remember the information on the back of the blade of a stanely (or equivilent) framing square, it saves you alot of mathematics.
Have a good day
Cliffy
I don't think I made my question clear.The birdsmouth is square to the plate in all cases except on the hip rafter, where there's what seems to me an ill-fitting joint, where the heel cut is at a 45 degree angle to the corner of the wall/plate. I guess a Japanese joiner would chisel out the interior of the heel to make the plate corner "pocket" into it. But I sorta doubt that regular carpenters do that. So, what DO they do? Sorry if this sounds nitpicky, but I come from more of a furniture-building background.
What DO they do?
They whack off the interfering corner of the wall. Think of your Japanese joiner, and what he would remove from the hip timber, then think inside-out, and apply that same little wood-removal theory to the wall structure.
Perfect little opportunity to use that nice large ryoba saw you have been saving for this kind of cut.
View Image
I get your question now. Yes it is an ill fitting joint, but that joint is structurally sound and in pretty much 99 percent of the roofs it is hidden by soffit.
Pesonally I don't get overly concerned about that ill fittin joint. I'm more concerned that the ridge is level, the commons are all the same, the fascia is all straight and the roof is strong.
Have a good day
Cliffy
Go and look at the online roof calculator for which the OP showed us the link.
I just downloaded it to my cell phone, so now I can throw away all my squares and calculators! ;-)
Hey that is a pretty impressive program. Notice the angle of the sheathing? It is not 45 degrees. The last three articles in the mag (Authored by John Carrol, Mike Guertin, and Larry Haun) all state that hips intersect the commons at the Ridge at 45 degrees, as if the last few lines of info on the framing square don't exist. Not even a mention that it is only 45 degrees on a flat roof and the steeper the pitch the further from 45 it gets.
Have a great day
Cliffy
PS I remember you as the Lake Placid Guy! (I've been there a few times and thoroughly enjoyed myself!)
>> One thing I'm unclear about is the birdsmouth on the hip rafter. Do you cut a sort of 45 degree notch on the corner of the plate? Or what? <<
You don't notch anything. Whatever the H.A.P. (Height above Plate) cut for your common rafter is, you come in from the outside corner where you measure your hip from with a plumbcut line half the thickness of the hip and then scribe down from the top of the hip the same H.A.AP. cut as the common rafter.
C'mon, Joe! Anybody coulda told him that!
He's a furnituremaker, for cryin' out loud. He wants to have some fun joining this little structure. Its not like, $4.50/sf, slam-bam-we're-outa-here.
Didja put that little roof cutting download into your blackberry yet?
;-)
>>Didja put that little roof cutting download into your blackberry yet? <<No, my CM is is way faster and blows that away.........;-)Besides, I don't even have a blackberry.Joe Carola
"Whatever the H.A.P. (Height above Plate) cut for your common rafter is, you come in from the outside corner where you measure your hip from with a plumbcut line half the thickness of the hip and then scribe down from the top of the hip the same H.A.AP. cut as the common rafter.Joe Carola"Man, I wish I understood this. Or the attached drawing, which I didn't. I think I'mjust going to have build it, and see what's what.But that corner just doesn't make sense to me, unles you whack the corner of the plate. But then I do't know what happens to the geometry of the whole thing.
Thanks, I remember learning that in carpentry school almost 30 yrs. ago, and promptly forgot it. Been fussin' and guessin' ever since. Always made it work, just couldn't tell you how.
As an apprentice many moons ago, my Boss (Dad) made me cut the corner of the plates to the same width as the hip rafter. However, I've since found that cutting the birdsmouth longer to clear the corner works just as well. Just remember the depth of the birdsmouth where it crosses the outside of the plate should be the same as your common rafters.
I'm going to work on that, but it still seems funny that a 90 meets a 45 that way.
I cut the plumb cut of the birdsmouth at a 45 bevel so that the middle of the rafter sits on the corner.
Not quite sure what you mean, but I've been foolin around in Vectorworks. "A" seems like what one guy said. "B" is my notion of notching the plates, which gets crazy, because you'd have to notch the rest of the plate, plus the corner 2x post. "C" probably requires that I get some Tabi boots.Could you explain the 45 bevel?
I'll bet you can handsaw off the corner, both plates plus however much you need more out of the cornerstud below, quicker than you can chisel out the hip.
The relieved hip is an ordinary feature of a two-ply hip, with each ply a mirror of the other at the birdsmouth. Most framers just whack the notch with its plumbcut offset outboard, but I thought you wanted a jointed look.
Gene, let me say that I haven't meant to apply furniture-level joinery to house framing. Just trying to understand what good carpenters do, out there in the real world. I think what I oughta do is drive around where new houses are going up, and when I see a hip roof, stop and talk to the guys. (Mainly because I'm having a hard time visualizing the verbal descriptions you and others are providing.)Again, though, thanks.
Your pic A is what you do when you're framing.
B is what you do when you calculate wrong or are too 'whatever' to correct the birdmouth. Depending on the extent of the chopping it may even be a code compliance issue since the effectivenes of the top plates is compromised.
C is what you do if you were building furniture.
Jawjuh,A is the way you do it. No notching anything or making a diamond cut. The diamond cut is for something that exposed and has a nice finish.Your A drawing, I made the blue line where you would mark the same H.A.P. cut height as the common which is half the thickness of the hip and in as my drawing before.Joe Carola
Joe, thanks, and I think it's penetrating my thick skull........
thats good advice for dropping the hip. in my neck of the woods, we call the "height above plate" the "deadrise".
Jay,I've heard it mentioned "Heel Stand", "Heel", "Throat", but "Deadrise" is a new one.Joe Carola
Jawjuh,You don't have a thick skull at all. If you didn't come here and ask a good question like that, then I'd say you have a thick skull. BTW, that was a good drawing also.Joe Carola