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Hi everyone-
I posted this in another forum but thought I’d put it on over here and see if anyone else had some input.
It’s been a while, so….
How do you all generally layout your rafters for a hip roof? I am fine with all the cutting and geometry. What I am wondering is “the big picture;” how you all lay them out across the plates? We are doing our house 24″ o.c. and it is a rectangle 27″ 2″ x 30′ 7″ with ridge parallel with 30′ 7″ wall (obviously!)Do you all normally just layout 24″ o.c. from, say, the back left corner of the house all the way across the plate to the back right corner (similiar to gable roof layout) and just set end and king common rafters independent of your 24″ o.c.? Or do you layout from center line of building left and right on 24″ o.c.? Or layout your jack rafters using common difference and 24″ o.c. from the end king commons? Just curuious how others do their layout with all these options! I want to see the best way to make sure the plywood decking fits with minimal cutting.
As well, one question I also have is how you layout for where the hip jacks ties into the hip rafter. The few hip roofs I’ve done I’ve just hooked my tape on the last o.c. rafter and pulled over until the layout mark hits the ridge. It works, but not the most accurate. One book I have states the following formula:
Multiply rafter spacing X 2. Look up in rafter tables the hip/val length using the above answer as the span. The result is the distance between hip jacks from edge to edge. For example, 24″ o.c. x 2 = 48″. Hip rafter length for 4/12 pitch and 48″ span = 2′ 10 7/8″. Thus hip jacks, from edge to edge would be spaced along the hip rafter 2′ 10 7/8″. Has anyone used this formula? Is it accurate? Do you need to make shortening deductions such as you do for thickness of ridge for commons and 1/2 45- dgree thickness of hip rafter for jacks?
Thanks-
Israel
Replies
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Israel, If you allow for your soffit width, 12" for example and pull your sixteens from there, then the sheeting will run out to the edge of the roof and break on a rafter without having to cut too much for waste. We have done the layout for jacks like you stated but if your house is perfectly square (should be), once you have one jack cut, you can use the jack difference given by reichers in his rafter book. works like a charm. Probably not the way everyone does it, but it works for us. Mike
*Israel, usually we install all cut roofs on 16" oc. We then stack them over the stud layout. But, it really doesn't matter.There probably isn't any cost savings, no matter where you start. blue
*Yo Israel, If you want your jack rafters to meet at the same point on the hip and your building dimensions aren't a multiple of 4' (for 16" o.c.) then you have to lay out for rafters differently than usual. Example: Your going to frame a hip roof on a 26' x 36' house. You can lay out the front and back wall (long walls) from either end. Lay out is 16" to the center of rafter. Now the end walls need to be layed out from each corner towards the center. What this will do for you is make all the jack rafters the the same length and they will meet at the hip rafter. In other words you will have 8 jack rafters of each length. Four with the long point of the jack on left side and four on the right. When you get your longest jack rafter measurment just use the square to tell you the difference in length for each one. If I confused you, draw a rectangle on a piece of paper. Draw in the hips and then the longest length jacks. You will see that there are 8 jacks all the same length, 4 rights and 4 lefts. Thinking about them as lefts and rights really helps me visualize in my head. Make sure you take great pains to insure that the hip rafters and the common rafters "plane out". Run a string hip to hip right above the plates on the corner of the hips. Your string should be right on the commons heightwise. If the commons bow up your string, your hips are too low. If the string is riding above the commons than you have to lower the hips. I hope I haven't put you in a cloud with my descriptions. If you need for me to clarify anything, ring me up.
*I like to lay out from one edn of the ridge and center the end wall layout. This way you can put a set of commons on the end of the ridge an a single common off the end of the ridge to the center of the end wall and your ridge and common wiil be automatically plumbed.Used a 2x for the ridgeridge length will be the long dimension minus the short dimension minus 1-1/2" for the ridge.I like this technique because after you put the single common on the end everything is plumb and braced in both directions.Happy framing!Mr T
*Mr.T I also put a common rafter on the end of the ridge. I usually end up cutting the sheet of ply on the ends of the building to 88" and putting this in the middle to make the transition from layout on each end. I find it much easier to cut a few sheets than cutting various length jack rafters. Do your jack rafters meet at the hip or are they offset?