# Need help with Gambrel roof angles

• posted on October 10, 2007, 12:23 am
Okay, so I missed this class in Geometry... the gambrel, barn, dutch, or mansard-type roof (or whatever it is called)
Next month I plan to build a 20 x 20 shed for my trailers with a 6' rise to the ridge (from the plane of the top plates). I want the upper and lower sections to be the same.
I googled around and could not find the angles. Help will be appreciated.
woodstuff
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• posted on October 10, 2007, 3:06 am
wrote:

http://www.roofingchildsplay.com/calculators/gambrel_roof_calculator.php
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• posted on October 10, 2007, 8:25 pm
"Jim Behning" wrote in message:
| wrote: | | >Okay, so I missed this class in Geometry... the gambrel, barn, dutch, or | >mansard-type roof (or whatever it is called) | > | >Next month I plan to build a 20 x 20 shed for my trailers with a 6' rise to | >the ridge (from the plane of the top plates). I want the upper and lower | >sections to be the same. | > | >I googled around and could not find the angles. Help will be appreciated. | > | >woodstuff | > | > | > | google gambrel roof calculator. Lots of hits | | http://www.roofingchildsplay.com/calculators/gambrel_roof_calculator.php
I also found lotsa hits and found the above also. Maybe this will help, thanks
woodstuff
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• posted on October 10, 2007, 3:48 am

Constrained by the parameters you gave, and assuming the flattest portion of the roof needs at least 3 on 12 pitch for adequate runoff: The bottom section would have a pitch of 13 1/4" rise per foot of run (48 degrees from horizontal) and the top section would have 3" of rise per foot of run (14 degrees from horizontal. Each rafter would be slightly over 6 feet in length (exclusive of tail).
However, these dimensions will yeild a very squatty gambrel roof. If you can raise the center to 8 feet or so, the proportions would be more traditional and make the loft more useable too. In that case, I'd make the bottom section 60 degrees from horizontal and the top section 14 degrees from horizontal. Rafter lengths would go to 6.5 and 7.5 feet respectively (exlusive of tail).
DonkeyHody "In theory, theory and practice are the same, but in practice, they are not."
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• posted on October 10, 2007, 11:05 am

I should have said the rafter lengths would go to 6.5 feet on the top section and 7.5 feet on the bottom section.
DonkeyHody
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• posted on October 10, 2007, 8:37 pm
"DonkeyHody" wrote in message: | On Oct 9, 10:48 pm, DonkeyHody wrote: | > On Oct 9, 7:23 pm, "woodstuff" wrote: | > | > > Okay, so I missed this class in Geometry... the gambrel, barn, dutch, or | > > mansard-type roof (or whatever it is called) | > | > > Next month I plan to build a 20 x 20 shed for my trailers with a 6' rise to | > > the ridge (from the plane of the top plates). I want the upper and lower | > > sections to be the same. | > | > > I googled around and could not find the angles. Help will be appreciated. | > | > > woodstuff | > | > Constrained by the parameters you gave, and assuming the flattest | > portion of the roof needs at least 3 on 12 pitch for adequate runoff: | > The bottom section would have a pitch of 13 1/4" rise per foot of run | > (48 degrees from horizontal) and the top section would have 3" of rise | > per foot of run (14 degrees from horizontal. Each rafter would be | > slightly over 6 feet in length (exclusive of tail). | > | > However, these dimensions will yeild a very squatty gambrel roof. If | > you can raise the center to 8 feet or so, the proportions would be | > more traditional and make the loft more useable too. In that case, | > I'd make the bottom section 60 degrees from horizontal and the top | > section 14 degrees from horizontal. Rafter lengths would go to 6.5 | > and 7.5 feet respectively (exlusive of tail). | > | > DonkeyHody | > "In theory, theory and practice are the same, but in practice, they | > are not." | | I should have said the rafter lengths would go to 6.5 feet on the top | section and 7.5 feet on the bottom section. | | DonkeyHody
thanks for the work! I may well go this way and lower the sidewalls to 7'.. I am buying an enclosed trailer for my work that is 7'11" high and 8'6" wide (outside of the wheels). The other trailer is just as wide at the wheels, buy is a low utility trailer. Maybe it wouldn't be so bad to just build a mezzanine on top for some type of storage, rather than wasting the space. Just now I can't think of anything to put up that high....
with appreciation,
woodstuff
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• posted on October 10, 2007, 7:57 am
woodstuff wrote: | Okay, so I missed this class in Geometry... the gambrel, barn, | dutch, or mansard-type roof (or whatever it is called) | | Next month I plan to build a 20 x 20 shed for my trailers with a 6' | rise to the ridge (from the plane of the top plates). I want the | upper and lower sections to be the same. | | I googled around and could not find the angles. Help will be | appreciated.
The traditional gambrel roof is one-half of a regular octagon. That means that your rise at the ridge would be ten feet.
I'm not an architect or builder, but it seems to me that if you squash that rise down to six feet, then the pitch between the purlin and the ridge may not be adequate.
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto /
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• posted on October 10, 2007, 8:42 pm
"Morris Dovey" wrote in message: | woodstuff wrote: | | Okay, so I missed this class in Geometry... the gambrel, barn, <snip> | | The traditional gambrel roof is one-half of a regular octagon. That | means that your rise at the ridge would be ten feet. | | I'm not an architect or builder, but it seems to me that if you squash | that rise down to six feet, then the pitch between the purlin and the | ridge may not be adequate. | | -- | Morris Dovey
You might well be right... gotta draw this to scale and see what it looks like. Also, the roof is metal and I could seal it well. My shop building has a 2 1/2 / 12 pitch and doesn't leak.
woodstuff
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• posted on October 11, 2007, 12:07 am
woodstuff wrote: | "Morris Dovey" wrote in message: || woodstuff wrote: ||| Okay, so I missed this class in Geometry... the gambrel, barn, | <snip> || || The traditional gambrel roof is one-half of a regular octagon. That || means that your rise at the ridge would be ten feet. || || I'm not an architect or builder, but it seems to me that if you || squash that rise down to six feet, then the pitch between the || purlin and the ridge may not be adequate. | | You might well be right... gotta draw this to scale and see what it | looks like. | Also, the roof is metal and I could seal it well. My shop building | has a 2 1/2 / 12 pitch and doesn't leak.
Ok. I found a sketch I made for a friend who wanted a gambrel roof on a new garden shed and posted it to news:alt.binaries.pictures.woodworking
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto /