Re: Hip roof design
#24204
08/18/10 09:53 PM
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Joined: Apr 2009
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Thane O'Dell
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Good idea Mo. That will give better Relish. Will M&T be required here or will large screws work just as well. Why the GRK screw. Never heard of them before. I will reduce the Jacks at the ends to 6 in.
Thane
Life is short so put your heart into something that will last a long time.
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Re: Hip roof design
#24205
08/18/10 10:18 PM
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Joined: Jan 2008
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bmike
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Thane - M&T at that location may remove too much material. I usually do the girt shoulder joint with lags. You need to figure out how much relish you need, and then you run in lags from the top. As to jack rafters... do not M&T them. Housing of appropriate depth with panel screws or lags from the top. You can do an adzed or band saw reduction curve to bring the jacks down to size so they fit in the hips. And - you may not need to push the hips all the way up to a fine point. A 1" or slightly larger flat on the top works just as well. If the jacks are properly sized, you can always up the size of the hips to make life a bit easier. Here are the screws I like: http://www.ozarkloghomes.com/loghogscrew.html
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Re: Hip roof design
[Re: bmike]
#24206
08/18/10 10:46 PM
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Joined: Nov 2006
Posts: 850
mo
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Some food for thought: I do not like to reduce the depth to fit the joining member. Reason being, is that I am under the philosphy that your timber is only as strong as its weakest section. I wouldn't want to create a possible shear point there. I would just upsize accordingly.
I recently had to wrap my head around something like you are doing now. It was a 24' X 24' 4 hip structure with a 3/4 pitch instead of your 1/3 pitch. It was a doozy. One thing that I learned though from it and recommend to you is that you find your longest rafter (excluding principals) and determine what cross section that needs to be and work back to the principles from there. A 24' triangular roof plane is a lot to fill in.
I'd be happy to show you an easy way to find the angles for the top of your jack rafters, as well as the backing cut of your hip, when you get to that if you like
Last edited by mo; 08/18/10 10:47 PM.
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Re: Hip roof design
#24207
08/18/10 11:09 PM
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Joined: Feb 1999
Posts: 137
Paul Freeman
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In a simply supported, uniformly loaded beam, shear requires a significantly smaller section than bending. Therefore a truly "form following function" timber in this condition would look like a whale or for those familiar with Monty Python: the "theory of the Brontosaurus".
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Re: Hip roof design
#24208
08/18/10 11:35 PM
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Joined: Nov 2006
Posts: 850
mo
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Paul, You lost me! Does that mean it is ok to reduce at the joint between hip and jack? Can you explain further please? Thanks.
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Re: Hip roof design
[Re: mo]
#24209
08/19/10 12:02 AM
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Joined: Nov 2006
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mo
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"My theory by A. Elk, brackets, Miss, brackets. This theory goes as follows and begins now. All brontosauruses are thin at one end, much much thicker in the middle, and the thin again at the far end. That is my theory, it is mine, and it belongs to me, and I own it, and what it is, too."
EUREKA! This makes things a little easier. Learn something new everyday. Thank you.
P.S You know my father told me something once, he said, "You are not stupid if you don't know something, its just that you have not yet learned otherwise."
Last edited by mo; 08/19/10 12:07 AM.
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Re: Hip roof design
#24210
08/19/10 01:08 AM
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Joined: Dec 2007
Posts: 1,882
TIMBEAL
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It is my understanding that a timber needs more size in the middle section. It can be reduced at the ends where, as Paul points out shear could require a smaller section. So, an adzed reduction would be pretty sexy. Brontosaurus went extent a while back. More screws http://www.grkfasteners.com/en/RSS_1_2_information.htmTim
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Re: Hip roof design
#24217
08/19/10 02:08 PM
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Joined: Apr 2009
Posts: 235
Thane O'Dell
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Does anyone supply Adze handles? I have a good head for one which I have never used. Another option would be a drawing of one showing length and shape. I will have some time to practice once the timbers are ordered. Also, it would be nice to make some braces with curves.
Thane
Life is short so put your heart into something that will last a long time.
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Re: Hip roof design
[Re: Thane O'Dell]
#24221
08/19/10 09:10 PM
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Joined: Apr 2009
Posts: 235
Thane O'Dell
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Finished design concept for client approval. posts- 8x10 plates- 8x10 hip rafter- 8x8 jack rafter- 6x8 collar tie- 8x8 & 8x10 corner brace- 8x10 king pin- 12x12 queen pin- 8x8 Oak braces & Splines 8:12 pitch roof Roof decking- 1.5x5 t&g pine stone wall around perimeter installed after frame.
Life is short so put your heart into something that will last a long time.
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Re: Hip roof design
#24222
08/19/10 09:30 PM
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Joined: Feb 1999
Posts: 137
Paul Freeman
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Wow! That is a thing of beauty, I like it.
Engineering fee will be high:
Check for uplift at the outside corners Check the size of the corner crossing ties Heavy load at the ends of the crossing ties Check shear in the through tenons
phew...that gets complicated, its sort of like a hammerbeam truss except there's no buttress or big ass post to anchor the outside.... on the other hand you could argue a well fastened roof diaphragm could do much for this frame...
but its very creative...looks great!
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