OurBarns1 wrote:

"Chris,

Can you explain the "half circle" method or lead me to the post in the earlier thread on this topic. I poked around there but could not find "half circle" described."

Sure. I should clarify first though that there are several methods for drawing the Mansard (most of which I found in James Newland's Carpenter's Assistant), and these methods devolve into two basic approaches:

1. Treat the lower pitched portions as one giant A-frame, then divide the height of that A-frame, truncate it in other words, and construct a slack-pitched roof across the opening.

2. Take the span of the roof, and construct a half circle upon it. Then the circle is divided by various methods to produce the points at which the lower and upper roof meet.

I've played around with these methods, and the one that I liked the results from best goes as follows:

1. Establish roof span:



2. Draw the half circle, centered on span at floor height:



3. Divide each half of the span into thirds:



4. At the marks 1/3 from each end of the span, extend perpendiculars to the half circle arc:



5. Connect the dots and the roof shape is developed:



This is a general approach only - the particulars of your application may demand slight adjustments.

As example, here's the cross section of the building I did, and you can see that the fold in the roof has been moved slightly down from the half-circle:


This drop came about as a result of wanting to keep the upper roof pitches at a certain amount, identical to the each pitches, and some fiddling with framing details at the fold area. I Hope this information proves useful. I think the result it gives is somewhat close to the 1:2, 2:1 method described earlier by another post.