gambrel roof angles

[infernocapt]

I plan on building a gambrel roof over a small garage. I was wondering, how do you figure the angle cuts on the ridge, base plate, and knuckle joints?

[Rich]

I've always drawn it out on a piece of paper or in cad. But the basic idea of a true gambrel roof is to take a line from edge to edge of the full roof width. So from the bottom outside edge of the overhang to the bottom outside edge of the opposite side. Create a half circle with the middle of that line being the center of the circle. Along the length of that line you will want to split it into 6ths.. now where the outside 6ths line crosses the half circle is where one of the joints will be.. and of course the center of the line will cross the circle at the highest point. I hope that makes sense.. and again that is just what I do. I'll see if I can find a true design formula.

[Rich]

I did find this article on the subject..
http://www.taunton.com/finehomebuilding/pages/h00130.asp

[infernocapt]

thanks, that part about dividing it into 6ths helps a lot. But i'm still at a loss as to what angle do you cut the joists at the knuckle and ridge. is there a set degree angle?

[Rich]

It will change depending on what width and height you have. Even if you use my formula of 1/6ths and using the circle it will change. I'm still looking through some old framing books that might have something.

[doyle]

I realize this post is 2 months old, but just in case you are still looking for those "definite" angles, I might be of some help. I build storage buildings for a living, which you can see on my website. I feel that I have fine-tuned my angles over the years to provide the most eye-appealing gambrel roofline.

The angle that sits on top of the side wall is 23 degrees, the angle at the ridge beam is 18 degrees, and the other 2 angles that butt up against each other are each 24-1/2 degrees. All those degrees added up will be 90 degrees.

I use 1/2" plywood gusset plates on both sides of the butt-joints and also use an oversize ridge beam so there's no fear of the roof sagging from all the extra weight and stress of this style roof. Example...use 2x6 rafters and a 2x8 ridge beam.

[Rich]

Some nice designs you have doyle. I like how you've done the ceilings in a couple of the tall wall barns (open).

[doyle]

Thanks, Rich!

[ETofwow]

After searching for several months I have determined there really
isnt a specific (perfect) Gambrel Roof angle.

Doyle uses 2 set angles of; top = 18 degrees and side = 23 degrees.

Rich has chosen to use a half circle to determine his calculation. Using
Richs' formulae you will get; top = 21 degrees and side = 24 degrees.

Both of these produce a asthetic roof line. but where I live in the mountains 6500' elevation most gambrel roofs have a much steeper top slope because of snow loading.

Currently I am building a small Tool Shed using 22.5 degree angles for both the top and sides using the half circle as my height guide.

When I draw all three of these techniques on top of each other they all look pretty close.

Ed