Figuring compound angles of two joining ridges

I am building a screen between our home and the neighbors. It is going to have a Japanese-style to it and will look like a shoji screen. I have made 8" boxes around 4 x 4 ten foot high posts. I cut the sides of these box posts that run with the stringers into 45° angles and they look like the front of a bird house without a hole. The sides of the post that face our side of the fence and the neighbor’s side have been cut down to the height of the lowest angle . The roof has a 45° bevel on each side of the roof so when it meets the roof will be at a 45° angle… and will rest on the sides of the “house shaped” cuts on the posts. I have 22’ of screen and then a two foot return that joins the house.

I have calculated that the roof needs to be trimmmed back from the edge half the distance of the distance between the two edges. Thus the roof is 11" on a side. The space between the edges is 15" m/l… I divided the 15" in half and measured back 7.5" and drew a line from that point to the outside edge and the opposite way to the “inside” corner of the joint. This all meets up very nicely, but now the question:

for the boards to join nicely what angle should I cut the above cut on the edge of the boards for the two roofs to have a lovely mitered joint? Won’t a straight cut leave an odd look where the cuts meet? I think there should be some angle, but don’t know where to beging to figure it. I can post photos of the finished shoji… I’m getting psyched to see this done. It ought to look very nice.

Your help is most appreciated.

the “img” button didn’t work for me. So will need to look into it later.

Just get yourself a speed square and do some research on what all the numbers on it means.

Its really easy

Well, I do use a Swanson S.S., but only for what I know how to do. I have not at the “Little Blue Book” for since the last century. But I have never framed and needed to know about roofs before.

Since your post I have read and watched info on using the SSS, but have yet to find info that is specific to my quest.

I have written to SSS requesting a replacement booklet or a pdf that I can read on line. I also suggested that they put short videos on their website, just to help others like me with issues of comprehension.

(Wish my dad were still alive, he could do this stuff in his sleep)

Thanks for the reminder about going back to a great tool. I had forgotten its original purpose.

Still I’d enjoy a quick visual, if you know of a site with one. (I’m more of a visual learner. All text can be daunting to me… may be my age… or just my learning style)


Even the cheap ones come with the book.


If I understand you correctly, just cut the angle just under a 90. This way just the very top of the board will touch. This will keep the joint tight.