jack rafter angle

Jack Rafter angles all depend on the geometry of the roof. Although they run into hip rafters and these (hip rafters)  are usually (but not always) at an angle of 45 degrees (looking straight down on a plan view), you have to bear in mind that the hip rafter runs upwards at an angle. Therefore the jack rafter has a compound cut, which can be very difficult (but not impossible) with a circular, or compound mitre saw. So the simple answer is  No, jack rafters are not always 45 degrees

 

THe angle of the cut isn't 45 degrees though. For instance let's say the pitch of the roof was 22 degrees. For the common rafters the plumb cut will be 68 degrees. For the jack rafters the plumb cut will be 68 degrees, but,,, the angled cut (cheek cut) would only be just about 43 degrees. (The same applies for crippled jack rafters running into a valley btw) The calculations are a bit difficult to explain, but a quick google search for setting out jack rafters will show you how to do it.

 

I used to cut them by hand on a saw horse (some years ago now) A rough and ready way to mark the angle is to mark the plumb cut then mark another line the thickness of the rafter parallel with it. Where it meets the top edge of the rafter, square across to the other edge . Where it meets is approximately where to mark the other plumb cut ( where it will meet the hip) Join these two and the angle between one side and the other is roughly the angle the cut is at (measure this and you'll see it's not 45 degreees (unless the pitch of the roof is 45 degrees too))

 

hello
quite intrigued! why is it not 45? i know that it relies  on the angle that the hip rafter actually rests on the wall plate from the ridge but are you saying that if its a true 22.5 split it still isn't 45? if so why the hell not??? maths eh!

 

hello
big as you can get compound chop saw! should do up to about 6x2! unless you have a 10 degree pitch!

 

hello
still don't get it! if its 45 on plan view  then surely you have to cut it at 45? im not saying you are wrong, im just trying to imagine where the difference is!

 

hi mak, it is 45 deg' but only on plan, as soon as you incline the jack rafter it changes, what is known as edge bevel, (the plumb cut will be the same as for common rafters) this will be a sharper angle the more steeper the pitch becomes. i've made an app for you roofing carpenters called "jack rafter" check out short YouTube video clip here its available for iphone and android...good luck

 

Set your circular saw to 45 and you will be right if its an equal hip or valley

 

I wouldn't dare use a circular saw for cutting this jack rafter edge bevel, I always used a hand saw when I was on the tools. Not sure what you mean when you r saying (Set your circular saw to 45 and you will be right if its an equal hip or valley) I think you'd benefit from my "jack rafter roofing calculator.

 

You are obviously not that experienced at roofing then if you mess about with handsaws,

If you set your circular saw at 45deg you will achieve the correct side angle, I learned this from books 30years ago and I know it from experience doing hundreds of hip roofs since ,

 

Good man wuddy