how do I figure what angle to cut my boards for a roof?

Question

I want to add a room to a manufactured home,The roof is slopped in the back and I am going out with a triangular roofstarting from the middle of the house and going over 24 ft.Neither side of the new room will be at the end of the manufactured home so I am joining one roof running one direction with another going another direction, which is going to form a valley on each side of my room.How do i figure the angle to cut my boards as i move up the roof with the new addition?

Answer 1

If your existing roof is sloped at 4:12 (typical for a trailer), use a framing square and set it on the board (rafter) at 4" on one leg and 12" on the other. Instead of using the leg that is on the 4" mark, use the one that is on the 12". This is called the 'long cut'. The other is used for where the rater meets the ridge board.

The long cut is also used where the ridge board lays on the existing roof.

The ANGLE (bevel) would be determined by using a speed square and finding out what degree a 4:12 would correlate to on the 'common' scale. I never use the hip-val scale to mark rafters b/c a speed square won't give you a line all the way across the board.

Another thought. You could buy a 12" speed sq. and use the hip-val scale. (that's the tool that's shaped like a triangle). Just line up the 4 (for a 4:12 pitch) on the hip-val scale with the edge of the board and mark it. You still need to determine what degree you need to bevel it at, though. I don't have my sq. at hand, so...

You will know that you are right if the difference in rafter lengths is the same all the way up the roof. If your first rafter is 59 in, and your second rafter is 52 1/2, your third rafter should be 46 (6 1/2 difference), etc. After 3 rafters, I can usually cut them without getting a measurement from the guys on the roof. Don't try that yourself, though. I've been doing this for a long time.

Remember to check your spacing at the bottom squarely from rafter to rafter. Don't measure up the roof.

Good luck.

Answer 2

How To Figure Angle Cuts

Answer 3

Ussually a slope of a roof is refered to "a number" over 12.
Eg. 5/12 6/12 7/12

A 5/12 roof is not as steep as a 7/12 pitch roof. All that means when you cut the rafter is you put the framing square on the number 12 and the other whatever pitch roof you have. The angle of your blade is the calculated by the pitch of your roof also.

Also

"A" squared + "B" squared ="C" squared is a formula for triagles often used connected one roof to another.

Answer 4

fast, easy, fool proof way is to go to Lowes or Home Depot and get a construction calculator. Read the instructions and it will tell you what board to cut, how long to make it and what angels need to go where.

Answer 5

that would require a long answer for here-- the best way is go buy a "speed square"-- it will come with a direction booklet to show you how pitch works