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I’m framing a dormer 16′ wide. This side walled dormer has a roof pitch different than the main roof pitch. 6/12 vs. 8/12
Because the dormer is so wide (almost the width of the roof) the rafter length tables aren’t much help because the rafters end short of the side walls (in the gable of the main roof).
I’ve looked and thought about this so much that right now I’m not sure if I’m dealing with a bastard hip type problem, or an unequal span/pitch addition roof.
Any comments/help?
Replies
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Craig,
Does the dormer have a shed roof? I'm not quite sure I understand what's going on here.
Ed. Williams
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I'm with you on this, Ed. I reread it a couple times and
can't figure out what the problem is, especially if it's
just a shed dormer. How 'bout it, Craig?
*Hey Craig,Does the dormer you're building have a hip instead of a gable on it's end? If so, I think I understand your problem. You've got no place to start from, right? Looks to me like if the slope on the hip is to match the rest of the dormer roof, you could build that portion first to establish the ridge height for the rest of the roof. Once that's done, it should be clear sailing...... If the slope of the hip is to be different than the rest(i.e....matching main slope of the house), you would still to that first to establish the ridge height, but then the slope of the sides would be predetermined by this height and the width of dormer addition and not necessarily what you want.
*Ed, Mad Dog & David:No this is not a shed dormer (although I'm tempted to change it into one).My problem, as David states, is that I have no starting point. One note I left out which adds to the confusion is that the ridge of the dormer is dropped 2' from the main roof ridge. I've been trying to frame this with a long valley rafter (from ridge down) and a short valley rafter hanging off the long one at a point 2' below the main roof ridge. Again, the problem lies in the width of the dormer, which makes the valley rafters theoretical length exted out past the gable end walls of the existing house, and therefore I cannot use the theoretical length to locate the tail end of the valley rafters.Maybe I should go "off plan" and frame the dormer the way you would a small window sized dormer with double rafters on each side, and a header 2' below the ridge.Thanks for any help you can offer.Craig
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Craig,
Joseph Fusco
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"The price of apathy towards public affairs is to be ruled by evil men." -- Plato
*Craig - If you do go with the double rafter and header method, which I think might be simpler in this case, think about making the doubles into triple or even LVL's, same with the header, they will be carrying a lot of weight. And nice heavy framing under the rafter tails to take it down to the foundation.
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Hey Craig......if you can overlook the crudeness of attached sketch.......does it look anything like my sketch?... looking straight down on roof? If it does, there may not be hardly any ridge at all, but you'll still have to know the height it would be.... Looks like the bearing points of the 8/12 valley rafters fall beyond the side walls of the dormer...but the 6/12 hip rafters hit the corners....Maybe you could temp put 8/12 common rafter at the center of the dormer area and measure back 8' from the outside wall,drop a plumb bob from the common to where it intersects the 8', if the dormer is 16' wide then it looks like that point would be the height of the ridge (and the point where the valley rafters meet).
*Sorry...I'll get the hang of it sometime.
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Craig,
You don't have a bastard hip problem. That's where one ridge drops down into another ridge as if it were a hip. It doesn't go all the way to the plate line - hence, "bastard hip".
It seems to me that the valleys for the dormer should end at the point where the dormer walls intersect the main roof. The pitch change between the two roofs should not be a problem as this is done all the time. Your rafter book may not help you in this situation, depending on the book you have. However, it this kind of thing is built all the time.
I wish I could see for myself what it is you have to deal with, but it seems to me that this is one of those situations where you just have to strap on your tools, get a dependable cut man on the ground, and jump in the middle of it. If you can establish your ridge and valley, then it's just a matter of filling in the gaps. I'm not sure that mathmatical equations are what you need unless you're prone to that sort of thing.
Good luck,
Ed. Williams
* Ed,
Joseph Fusco View Image
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Hey guys:
Thanks for the input. It's going to take some time to sort through all this, and I'll let you know how I come out.
Joe Fusco; great info (h.a.p. is a term I'm glad to be introduced to).
Dave Ingle; You understand exactly my problem. Are you by any chance in the cartooning business though?...that's some wiggly old house you're drawing. I hope mine comes out a little straighter.
Nick Pitz; Yeah, all the headers and valleys are doubled
1 3/4" x 12" L.V.L.
Best to you all!
Craig
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Joe,
Thank you for this reply.....that was a big help. I expect no less from you.
As always, I'm sure you will come up with some worthless snappy answer to this post.
Can't wait to see it.
Ed. Williams
* Ed,
Joseph Fusco View Image
*Joe, Joe, Joe,You let me down......You can do better than that.Try again.Ed. Williams
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I'm framing a dormer 16' wide. This side walled dormer has a roof pitch different than the main roof pitch. 6/12 vs. 8/12
Because the dormer is so wide (almost the width of the roof) the rafter length tables aren't much help because the rafters end short of the side walls (in the gable of the main roof).
I've looked and thought about this so much that right now I'm not sure if I'm dealing with a bastard hip type problem, or an unequal span/pitch addition roof.
Any comments/help?