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I’ve been framing for a while now and most things are pretty cut and dry with the exception of jack rafter spacing on different roof pitches. When I have an “A” California the same pitch I just use my rafter book. Usually on the houses I frame, they have an 8 on the main roof with a calafornia A on top, which is a 12. Or I have a room over the garage, which is the same thing except I have 2 king valleys running down from the ridge. This is also an 8-12 on the main roof and the other a 12-12. My question is how do you figure the jack rafter spacing. My stuff is 16″ on center so there is usually quite a few rafters to cut. When cutting them I always try figure it out mathematically, then get upset and end up taking my tape out and messuring them. I’ll be the first to admit it’s a pretty “cave man” way of doing it, but could someone please tell me the right way. I can get mine to work so everything breaks and there straight but I know there’s a better way out there.
Zack
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Spacing or length?....Ken drake....Joe....Where are you two?
near the head scratchin stream,
aj
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length. i know they go 16 on center.
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Zack...the guys I mentioned will answer this for you the best...I use construction master 4...trial, measure and no error, and or full size layout on the deck...once you know the length of one...the rest are easy with the calculator...Your best bet would be to hire an expert in your area and have him teach you how to cut a few roofs...then you will really know what you need to know...
near the stream,
aj
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thanks. I considered purchesing one of those calculators but instead invested my money in some of peters framing videos. should have gone with the calculator.zack
*Hey Zack-Unequal pitch rafters, are impossible to line up on the hip. Jack rafters will always be at different offsets from each other on unequal pitched roofs. I would suggest you spend about 20 bucks on the "Roof Framers Bible" by Barry D. Mussell. You can order from any bigger bookstores online, or many of them carry it. The information for unequal pitch roofs is the best available at any price. My preferred layout for the King common rafter, is from the center of what you're referring to as the A, I think. Layout whatever spacing your using from there. It also covers rafters with layout from the outside wall. As usual more than one way to do things. Were these Peter's Videos more on methods or did they try an teach layout? Let us know what you thought.P.S. Construction master IV, will serve you well, it has explanations of how to use many differant ways. I have a couple of Computer programs that give some slick information for all types of roofs. If you're interested let me know, Michael Leistiko
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Zack, you sound like a person that is truly interested in learning. That is to be commended.
ONe of the problems about learning, especially for apprentices, is not knowing the proper nonclementure (terms). Basically you have asked "how do I figure the rafter spacing?", then answered the question yourself by saying that you space them 16"o.c..
You are on the right track about learning if you are seeking outside information. buying a video is helpful, but not the endall. You probably will have to invest in many more books, and tools (the calculator is one piece of the puzzle), and a lot of time.
Here's one way that I learned to accurately figure, and cut unequal pitch rafters. I basically compbined the caveman method with the scientific method. I used to figure out the theoretical length of the rafter, then measure it caveman style. If it seemed to be close, I'd cut it to the theoretical dimension. If it was wrong, I'd backtrack and re-figure until I could finally calculate things right.
Yes, it took longer on the first few, but now I can stand at the pile and cut every rafter, with absolute confidence. And the best thing about confidence is speed. I never look back!
blue
Ps. plus, I'm a master boogerer for when I screw up!
pss What are you really asking? I'm sure someone in here can help.
*Let's see if this helps. These formulas make sense to me, but then again I scribbled them down in my own shorthand code. I'll try to decifer. Hip Jack(layed out from commom) =Theoretical common rafter minus common difference(CD)Hip Jack(First hip starts from corner) =First hip jack IS C.D.Hip Jack(does not start from corner or common) =unit rise(squared) + unit run((12") squared) = square root times total run of hip jack(in feet)Common Difference = unit rise(squared) + unit rise((12") squared) = square root of , times the on center(in feet) 16"oc =1.3333333ft.Valley Jacks ...depends where they are lated out from. Use Common Difference(as Hip Jack)Valley Cripple Jack = twice the length of the valley jack that it is across from.(it runs between the valley and valley)(supporting to shortened)Hip Valley Cripple Jack =unit rise(squared) + unit run(squared) = sqaure root of , times total run of H.V.C.J.(in feet) these are the steps to key into a basic scientific calculator. try a few examples on roofs that you already know the answers to. All basic geometry. think of everything on the roof as a triangle. a(squared) + b(squared) = C(squared) Common Difference is the key. It's the (consistent) amount that each rafter is shorter than the next. Gable end longest is 10ft. Next is 8ft. Then 6 ft,4ft,2ft,Zero. Common Difference is 2ft. Common Diff. is also in Swansons Blue Book, with speed squares, and probably in the R.F. Bible. On some framing squares too. I use the math method.Hope I actually understood the original Q. Jeff
*I thought what he meant was how does he figure where to place each rafter against the hip rafter so that when they are all layed out they are 16 oc. (ie you may have to layout marks at every 18 inches along the hip rafter in order to achieve 16 oc spacing between your rafters.Just thinking,Pete
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Thanks for the insight and information. I guess I confused everyone with the wording of my question. I've only been framing for two years but the funny thing about it is that I've worked my way up to lead carpenter in the company I work for. So Blue is right because I get my terms confused and mixed up. I know what I'm trying to ask so let me reword it. The houses I typically frame has a 7 or 8/12 on the main roof. Then the plans call for a "california A" on top or to valley rafters running down and the pitch of this "A" is a 12/12. I know the plans call for rafters to be placed 16" on center. I then lay out my ridge 16" on center. Pete has the right idea in that the valley rafter may have to be laid out 18" on center to achieve this 16 inch spacing. However, I do not want to lay out my vally, but want to be able to go to my bench and with my gable end measurement and be able to cut all my jack rafters so when I nail them against the ridge at my 16 inch marks they will swing into the valley rafter and maintain their 16 inch spacing.
I've heard this mentioned before and would be interested if anyone knows about this and that is swinging a valley rafter one way or the other so it will allow for jack rafters to line up so you do not have to cut one side more than a 60 degree angle(which i do not have a saw to do.)
About the Steve Peters framing videos, they were helpfull in that he taught me his methods in doing things. I only got the basic and advanced and he did not deal with this topic. He does have a super advanced one that I heard does deal with different plate heights and unequal pitchs and I probable will end up getting it. there kinda expensive (i think i paid 150 for the two i got and the other is 170) but their good refreshers and you get a couple of ideas from him. the only thing is that your walls are'nt always perfectly straight and 2 foot high so you can hold your ridge from the ground with 5 foot long 2 by 4 rafters. if you got some young guys working for you it can be a real investment in making them watch it then applying it out on the jobsite instead of explaining everything out on the field for them.
jeff you may have answered my question but i have to print out your system and read it a couple of times till i figure it out. thanks
thanks
zack
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O.K., let's see if I got ya now. The term "California A" is throwing me. I'm assuming a dormer or intersecting roof. You have a main ridge and a intersecting ridge comming off the main(at a 90 deg. angle to the main) You also have a valley on either side of the intersecting ridge.You need to fill/connect between the main ridge and the valley. And the intersecting ridge and the valley.These will be your valley jacks. your plumb cut(on the long face)on the main ridge end of the VJ will be 7 or 8/12 with no side cut(or to say a normal side cut of 90deg. across the 2x edge).the "bottom" cut will require a 12/12 face cut(long face) and a side cut to fit the angle against the VJ. The VJ will fall in plane with the common rafters 7 or 8/12, and will require a 7 or 8/17 face cut, with a side cut pulled off the charts. My example in the book(framing square is out in the van) shows a 7in rise, and the side cut dimension is 11 1/16". Lay the square across the 2x side, with the blade reading 11 1/16 and the tongue reading 12in. Mark the 12in. side and that's the side cut. Now layout from the ridge, check with the framing square for square , and the side cut should make the valley end of the jack fall right where it should. Remember to shorten the valley jack as you would a hip or valley, but on both ends. Am I any closer to the question at hand, or is there just no hope for me? Hope this helps.
The book I was taught from is "Carpentry" by Leonard Koel.It has a workbook too. ISBN #0-8269-0732-6. Very good, indepth coverage of complete building process, and alot of illustrations. Its a good size text book, about 700 some pages, and probably about $100. It's the one I learned from, so unfortunately I can only think along their terms! Was I close? Jeff
*Zack,
View Image © 1999-2000"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Zack, I was about to gove you some help, and then I came upon your statement "However, I do not want to lay out my vally, but want to be able to go to my bench and with my gable end measurement and be able to cut all my jack rafters so when I nail them against the ridge at my 16 inch marks they will swing into the valley rafter and maintain their 16 inch spacing."That was the clue that I needed to help you.Heres how I cut the rafters on the bench by using the gable end measurement. I'm assuming (some of your terms are regional, so I'm guessing a bit) that you have an 8/12 main roof, with a 12/12 roof intersecting into it over the front porch (quite common here in michigan). Here's what I do: First, I sheet the main roof, then lay on the 12/12 onto it using 1x valley boards, and 2x ridge and rafters. I calculate the length of ridge like this: Meausure the height of the ridge above the plywood (remember to "drop" your ridge [3/4"]),divide by 8(the unit rise of the main roof, and multiply by 12 (the number of unit runs that are need to achieve the height). This number equals the length of your ridge.Cut the ridge square on the gable end, and on an 8/12 (mark the 12) on the layon end. Your over all length is long point to square end.I then calculate the difference in length of the rafters. This number is calculated like this: 16/12x8=10.66 (rise of the first jack@16"oc) The square root of 10.66x10.66 x2= 15.08"15.08 is your common difference for a 12/12 layon roof at 16"oc, onto an 8/12 main roof.I then simply cut one at 15.08, the next at 30.16, the next at 45.24, etc. There will usually be a narrow span between the last jack and the gable. I usually do this cutting right up there on the roof bccause I don't like to carry large numbers of small parts up there; I prefer to lean a few long 2xs and pull them up as needed. I usually cut only one or two and nail them up to get them out of the way. I'm not big on huge stacks of staged parts.Hope this helps. bluePs Joe has given you a formula for an equal pitched roof with the valleys running at 45 degrees. This is not the case for your roof.pss The calculation for jacks that run into a true valley are figured the same. The cuts that are greater than 45 degrees are cut by tipping the saw. I usually cut the rafters square first, then tip my blade at the required degree. Since I only use a 71/4 blade, the degree is limited to the depth of the blade, unless I "shave" the remainder with my saw.
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thanks all. joe, i don't know if you read the entire email but what i need are common valley rafter deductions of bastard valleys or hips. just to clarify, what i'm trying to figure out is rafter deductions on 2 different pitch roofs. ie. a main roof with a 8/12 and a ridge intersecting that is a 12/12. correct me if i'm wrong but you can't make that a 45 degree angle. if you got any more information i'm all ears. by the way that's one killer website you got and thanks for all the info it you put in it.
thanks alot blue. how the heck did you come up with that formula. i hope that fomula wasn't in framing 101 and i have really just been blowing it. thanks a million for the tip.
anyone else out there got any more usefull info on this topic please email cause i'm all ears.
zack
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John,
View Image
© 1999-2000
"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it."
Aristotle
*Zack, the formulas are derived from the basic roof framing formulas. If you look closely, you will see that they are indeed as simple as calculating basic triangles. You are right about the angles not being 45 degrees. And the cuts will not be 45degrees, but they will add up to 90. That means if you have a 60 degree on on one set, you will have a 30 on the other set.Unequal pitch roofs are a bit more challenging, but certainly not rocket science. They are still basic geometry.blue
*Joe, interesting GOOD-or-Interesting BAD? Glad some new blood came in, I'm starting to confuse myself! Jeff
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THAT'S IT. how the heck did you do that and you got some more info to share now that you know what i mean.zack
*blue. i understand what you mean and you got any suggestions for cutting a 70 degree cut with a saw that only goes to 55 degrees.zack
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Yes Zack, i usually cut the rafter square first, then lean it on one horse with one end on the ground. I then tip my saw (by eye for these cuts) and bevel it. It's critical to cut the rafter to length and square first, because the excess material would get in the way and prevent you from tipping the saw, and getting maximum depth off your blade.
blue
*Blue,
View Image © 1999-2000"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*It's possible Joe, I didn't think too hard on it. Which number is not right?blue
*Zack,Probably the simplest way to cut an angle in excess of 55 degrees is to mark it and use your circular saw. You can cut those angles on small pieces of lumber easy enough by rotating them and using a square block but that would surely be too much to handle with a 12' piece of 2x10 for instance.Pete
*Jeff,
View Image © 1999-2000"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
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sorry about confusing you so much jeff i guess i know what i want i'm just wording it the wrong way. but your answer is helpfull. why im at it, since we're talking about valley jacks and stuff does anyone out there know how to get the measurment of a bastard valley or hip rafter (one thats not a true 45 degree) other than just measuring from where the two ridges intersect to where the common rafters from the main roof and the common rafter of the "A" intersect (joe's picture).
since this is email and i'll probably never see anyone i'm writing to i'm going to ask a dumb question. what does everyone in here mean when they say side cut.
zack
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Remember Zack, were not laughing with you, we're laughing at you!
A true valley jack has to have a compound angle cut on the bottom end of the rafter. The degree that you have to set your saw to, to make the cut usually is referred to as the side cut. It is stated as numbers on the framing square, but we usually refer to it in degrees since the power saw was invented.
If I see you trying to tip a handsaw to 45 degrees, I'll know we're making inroads.
blue
*Zack,
View Image © 1999-2000"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Blue,
View Image © 1999-2000"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*
I've been framing for a while now and most things are pretty cut and dry with the exception of jack rafter spacing on different roof pitches. When I have an "A" California the same pitch I just use my rafter book. Usually on the houses I frame, they have an 8 on the main roof with a calafornia A on top, which is a 12. Or I have a room over the garage, which is the same thing except I have 2 king valleys running down from the ridge. This is also an 8-12 on the main roof and the other a 12-12. My question is how do you figure the jack rafter spacing. My stuff is 16" on center so there is usually quite a few rafters to cut. When cutting them I always try figure it out mathematically, then get upset and end up taking my tape out and messuring them. I'll be the first to admit it's a pretty "cave man" way of doing it, but could someone please tell me the right way. I can get mine to work so everything breaks and there straight but I know there's a better way out there.
Zack