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Tool Talk Discussion Forum

Framing Carpenter ???

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john in la

02-11-2006 18:19:49




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Can some one tell me how to figure board lengths on a hip roof.
Size is 28' x 28' w/1' over hang; 4/12 pitch; 16" O/C
Trying to figure out how many of what length boards I would need.

I know how to figure a gable roof which would be..... ....
28/2=14+1 foot over hang = 15'
15' x 1.05 (pitch factor) = 15.75ft long boards
So I would need 48 16' boards for a gable roof plus 2 boards for the ridge board.

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Dave NE IA

02-12-2006 08:31:17




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 Re: Framing Carpenter ??? in reply to john in la, 02-11-2006 18:19:49  
There is a very simple formula for square root. This formula can be used to square up any flat surface. A rafter if you lay the rafter down on the ground is a flat surface. I usually carry it out to only 1/16th of a inch, as that is close enough for all my applications. Hip roofs, (double slope on each 1/2 of the rafter plus a little duck bill for a overhang) I seldom do anymore, but if you know the pitch or raise per ft it is easy to figure.each 1/2 of your total rafter will require 14ft nine and one sixteenth of a inch plus a additional 12 inches for your overhang. Your building will require twenty rafters plus what is called specials for the endwalls you need two--they usualy have lumber running horizonal for your siding--usually cost 15% more than the standard rafter.
this is for a double sloped roof. Some areas call a double slope on each side a gable roof.So I am going with (calling that a hip roof) probably called that in your area by your measurements. You must remenber that each rafter requires double the 14'9 1/16 lumber. If you want me to figure all the lumber required to build the rafters I can sure do that if you can provide the quality lumber, snow load ratings etc. in detail. Otherwise a lumberyard can do this on paper in front of you and probably make better sence. Dave NE IA

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john in la

02-12-2006 17:15:23




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 Re: Framing Carpenter ??? in reply to Dave NE IA, 02-12-2006 08:31:17  
Thanks;
Either I am not following or you are figuring what we call a gable roof. A roof with 2 sides and the siding in the front and rear goes all the way to the peak.
I am looking for a hip roof. 4 sided or sloped to all 4 walls.



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Dave NE IA

02-12-2006 19:12:01




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 Re: Framing Carpenter ??? in reply to john in la, 02-12-2006 17:15:23  
I certianly understand your hip roof, and yes I can figure it but wow I havent done one for a lot of years. Yes there is a formula for jack rafters (the short ones going to your hip rafter) you have of course four hip rafters. I'm not so sure but what your building will be shedding water before I can come up with the jack rafter lengths. We pretty much buy rafters anymore with all the law suits and poor quality lumber. I will look as soon as I can think where it may be. Had my business computer poo poo. Dave NE IA

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Butcher

02-12-2006 07:17:49




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 Re: Framing Carpenter ??? in reply to john in la, 02-11-2006 18:19:49  
Hip rafters are measured at 17" for the run of the rafter rather than 12" like commons. The jack rafters(those running from the plate and ending at the hip rafter)are measured the same as commons. The math for finding the lengths of hip and jacks is kind of complicated. I've found that scaling it out on graph paper is easyest. Your 4 hip rafters will need to be 21'9 and 5/8".



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john in la

02-12-2006 17:27:20




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 Re: Framing Carpenter ??? in reply to Butcher, 02-12-2006 07:17:49  
Thanks;
Yes I know the cuts are figured on 17 and not 12 but do not know how to figure the run.
Very complicated as you say.

This roof will not have a ridge board or any common rafters since it is a square. It is really a Pyramid Hip Roof and all 4 sides will be the same.

The problem I am having in figuring the differant lengths is the fact that the hip rafter goes up at a 45 deg angle to the walls.

I think I will take your advise and use some graft paper using 1" to 1' scale to figure it out.

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steve from mo - dangit!

02-12-2006 07:38:16




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 Framing Square. in reply to Butcher, 02-12-2006 07:17:49  
A good framing square will come with a manual that explains how to do it with the square. You could also use the math functions on a computer spreadsheet program.



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