Ok, I’ve been arguing with my framing partner for two days now. I say that when you are using double cheek cut hips, you have to lengthen the ridge at each end, by one half the thickness of the common rafter. I’ve drawn this out for him, I’ve shown him the drawing in Marshal Gross’ book. He still will not agree. He thinks that it should grow by one half the thickness of the ridge and that the thickness of the common rafter is irrelevant.
Here is where he has now got me confused; the reason the ridge is lengthened is so that the framing point where all the roof planes come together will be the same as it would be if we snapped them out on a deck. They are transferred vertically from the the plan view. We adjust the ridge length because we have the thickness of the materials we are working with, specifically the commons and the hips.
Here is where he makes a valid point. He says that when we drop the ridge to account for it’s thickness and make the plane from the commons come together at a point (like trusses do, or if the rafters touch at the plumb cuts and there is no ridge) above the ridge, we should also lengthen the ridge by that amount. After all there is a common rafter butting the ridge (parallel to it). Now this makes sense. If I have a ridge that is 12 inches wide on a 12inch rise roof, I drop the ridge 6 inches. Shouldn’t we lengthen the ridge6 inches? If we don’t, then the pitch on the hip side will change.
Can someone explain this to me? I know that even if we do this, we would still have to take into account the thickness of the common rafter and adjust the ridge for that. Do we do both?
Any help you have would benefit me greatly (especially if I can prove him wrong) 🙂
Replies
Tim,
I think you would have to increase the length of the ridge by one half it's width and not add half the rafter width to this.
I also think your partner is correct in that the rafter width is irrelevant,you determined the common rafter length by subtracting half the ridge width so the ridge would have to grow by half it's width at each end to accommadate the common rafter length at the hip .
Vince Carbone
Edited 4/6/2002 6:04:48 AM ET by Vince Carbone
Edited 4/6/2002 6:08:11 AM ET by Vince Carbone
You want to use all the brain power of this thread? Give the rise and run , pitch etc of the common and sit back and wait a few hours. I would be greatly surprised if the exact length wouldn't appear on your moniter.
I think the ridge thickness only has to do with the length if it's a single side cut hip. If it's a double side cut hip only the thickness of the common rafter is used. Adding the thickness of one common rafter to the ridge length when using a double side cut hip.
Tim,
I'm with Vince on this. You will add half the ridge width to the length of ridge at each end. The width of the common rafter shouldn't have any effect. Think of it this way. The hip is nothing more than the intersection of the planes of your common rafters top faces.
Bish
For the practicality of a double 45 beveled hip fitting centered at the ridge end on ridges of greater or less thickness than the commons, the ridge can be lengthened by half the thickness of the common, the end parallel with the ridge common shortened by half the thickness of the common and the hip shortened by half the 45* thickness of the common.On a ridge thicker than the common , the parallel to the ridge common will sit high of the ridge and the double 45 hip will drop in and plane in to the two roof planes.On a ridge less thick than the commons , the end parallel to the ridge common will sit low of the ridge and the ridge and a little of the two other king commons will need to be whacked off a little.That the parallel to the ridge common is cut " special " as Marshall Gross says in his book "ROOF FRAMING" and that it sits higher or lower than the ridge when the ridge is thicker or thinner than the commons is key to seeing how it works.If the ridge grew by half its thickness on a doubled lvl ridge with 2x commons and the commons cut accordingly , than the hips don't have a corner to snug into unless cut special or the commons padded or somthing.So for double 45 beveled hips the ridge grows by 1/2 the thickness of the common, the hip shortens by 1/2 the 45*thickness of the common and the end common is shortened by 1/2 the thickness of the common and sits level, high or low on the ridge depending on it's thickness.For a long time i thought Gross was wrong but i didn't get that the "special common"set high or low on the ridge.
Thanks Bill for your explanation. That makes a lot of sense. I just couldn't see the Marshall Gross could be wrong.
My framing partner doesn't like to cut the roof and install it all at once. We usually set the ridge and just measure from the top of the ridge to the plates. We have found on a medium to small roof that it is faster to do it this way. He thinks it is a waste of time to draw the roof on paper in plan view and figure the roof. He might be right, but I want to be able to do it both ways.
Thanks again for your response.
Tim
It would seem to me that a common rafter is a common rafter and wouldn't need to be cut "special" for the roof end parallel to the ridge if the ridge length were adjusted by it's half thickness.Maybe I'm missing something but I can't see how the width of the rafter changes it's length a 2x common or a 4x common would still be the same length on the same roof.
Imagine if you could stand all the common rafters up from their heel cuts without the ridge all the commons would be at the same height off the top plate on all four sides of the roof.you could then cut the ridge length to fit in between the two commons that run parallel to the ridge.
Vince Carbone
Vince, with a ridge the same thickness as your commons a double 45* beveled hip will fit in fine up top with the commons cut the same length adjusted for half the ridge thickness. With a ridge thinner or thicker than the commons you lose that centered intersection up top if you cut the parallel to the ridge common minus for half the ridge . You could do it but in both instances it makes for more work. For a thinner ridge you'ed have to move your perp to the ridge commons off center to allow for the parallel to the ridge common to butt the ridge and you would have to double 45* bevel your hip off center to be true , plus clip a little of the perp commons.For the thicker ridge if your 3 king commons are on regular layout and cut for minus half the ridge thickness, a double 45* beveled hip hits the outside corner of the ridge with no commons to bear against.You could pad the sides of the common but another possibility is to cut the thicker ridge on each hip end 1/2 the thickness of the common long( instead of half the thickness of the ridge) , cut the parallel to the ridge common 1/2 the thickness( levelwise) of the commons shorter , cut the double 45* beveled hip 1/2 the 45* thickness(levelwise) of the common shorter, cut the perp to the ridge commons 1/2 the thickness of the ridge( levelwise) short and just remember to let the parallel to the ridge common sit high of the ridge since the level of the ridge is at the height of the shorter commons. If you draw out in plan view all of this it makes it easier to understand, especially if you start with same size common and ridge thickness and then thicken or thin the ridge with your commons staying centered on layout and staying the same thickness.Remember though on thicker ridges the end common is higher and on thinner the end common is lower . ( for lower you have to shave the ridge and some of the other two commons a little.)Personally i've never set a thinner than the commons ridge, but a few double lvl ridges or built up 2x.