Gambrel pitch and height
Hi, i'm building a gambrel roof barn that'll be 30'x50', but i'm having trouble figuring out the pitch and height i want. most of the new designs look too "squatty" compared to the old gambrels in my area. is there a resource for figuring this out? are there traditional dimensions or formulas to guide in laying these things out?
Well there are about as many different gambrel roof configurations out there as there are gambrel roofs. There really isn't a standard, however I know exactly what you mean about the squatty appearance of your modern gambrel trusses.
Most of your pre-made trusses that are designed as a gambrel consist of roughly a 20/12 bottom pitch and a 4/12 top pitch. So you have a really steep bottom pitch and a really flat top pitch. This results in that "squatty" appearance.
Now, I am going to give you a design secret that I have discovered free of charge. ;)
The rule of thumb that I use when designing a gambrel is that the top pitch should be no less than half the pitch of the bottom. In other words if you start with a say 14/12 bottom pitch your top pitch should be 7/12 or greater. If at all possible it looks the best at exactly half. The shallower the top pitch the more "squatty" it will look.
My go to pitch combo is usually 14/12 bottom and 7/12 top. A 12/12, 6/12 combo will work, and so will a 16/12, 8/12. On your 30' wide barn that 14/12, 7/12 combo should work well. Wider barns will start to need a shallower pitch if the goal is to limit the height of the barn. The opposite is true with a narrower barn you may need to start going steeper to give enough head room in the loft.