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I have found if you use the points of your 12 sided roof as the commons, it is easy enough to head off the jacks and tape them. Then mass produce those jacks and so on. You know the meathod… I too like to know the math behind it. Let me know what you find out.
Please note: I am in the middle of building a round turret roof which I will build on the ground and crane it into place. Better than stick building up 30′ in the air. Good luck!
Kelly
Replies
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I have found if you use the points of your 12 sided roof as the commons, it is easy enough to head off the jacks and tape them. Then mass produce those jacks and so on. You know the meathod... I too like to know the math behind it. Let me know what you find out.
Please note: I am in the middle of building a round turret roof which I will build on the ground and crane it into place. Better than stick building up 30' in the air. Good luck!
Kelly
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Hey Joe
Nice to see you've got sumthin' to smile about again.. . don't be stingy with the drawings, hell do 'em in colour!
-Pat
*Framing an any-sided structure can be solved on a framing square. We all know that the hip on a rectangular structure uses 17 as the run vs 12 for the common. The no. 17 can be arrived at as follows: Let N=no. of sides of structure (for a rectangular structure, we use 4). Let H=run for hip rafter. Let alpha = angle between hip and common rafetr for N-sided structure. b alpha= 1/2 * (360/N) alpha= 45 degrees for 4 sided structureb N=12/cos alphaN=16.97 (17" close enough)Therefore we have the formula for hips and commons for any sided structure, and only need to apply the basics of roof framing as we learned in the little booklet supplied w/ our framing square (don't tell me you threw it out).For 12-sided structure:alpha = 1/2*(360/12)=15 degreesH = 12/cos 15 = 12.42" or about 12 7/16" on your framing square.
*Fred, What about a circle?
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You folks, must be west coasters, 'cause you're all up so late. Any how, the posts look helpfull and I will review them more this eve. Joe, I will scan in the plan and post it(need instruction, I know you are good at this) or email it to you ( need your email ), It looks like its right up you alley!
I think alot of guys could benefit from this. I am puttin up the first floor exteriors on the dodecagon, and I know enough to know they gotta be dead nut to facilitate the rest of the framing.
Thanks, and look for posts tonight.
Tom
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RKELLY:
Good question! You can see the answer by increasing
b N
,the # of sides. If you go through the formula, we see a 4 sided structure to have a hip run of 17, an 8 sided structure having a hip run of 13, a twelve sided structure having a run of 12 7/16". We really should think of a circle as a infinitely sided structure (that is how the formula for area of a circle is derived). Therefore, a circle "hip" run will approach 12, i.e. technically all of the "hip" rafters on a circle are really common rafters. I've never framed a circular turret, but the problem would be one of when all the rafters converge. I believe this is usually solved by having a king post at the center with as many sides as their are commons. I'd have to think about cutting the jacks, but I probably have a text, or someone out there with firsthand experience can describe it. Anyone?
*Tom; It looks like you have been blessed with a project that will be fun. Hope your span isnt too large or you will be up there in jack and the beanstalk land. I have never framed a dodecagon, and actually wonder why they didnt just make it a circle instead. I would do my layout work as if it is a circle any way. I would cut my plates on an armout of plywood to the diameter of hip rafter to hip rafter and then make tangent cuts the lengthof the sides off of the radiused plates. To get the length of the tangent cuts for the sides I would divide the circumference of the diameter by 12. Depending on how they intend to cap this off, weather vane,or ridge cap, whatever I think I would use a center post with a diameter of 5.729 inches and at least 12 inches in depthto accomadate the plumb cut on a 2x6 rafter. The centerpost of this diameter will give you a circumference of 18 inches so all of the common rafters will have a space to nail. The lengthof the rafters will be 21 and5/8 ths of an inchper foot of run. Be sure to deduct the 1/2 widthof the center post about 2 7/8 of an inch from your rafter run when calculating run or half span of the rafters. Also be sure to deduct the tangent cut off of the radial plate from your span. Your hip rafters should have a very longside cut that will be 15 degrees on both sides of the rafters. The saw bevel cut will not be 15 degrees so you will have to play with that to getthe correct bevel set on your saw. If there is a need for jack rafters, just header off at the height the need occurs and tape your jacks to and attach to the header blocks. There is going to be a whole lot of nailing going on in one particular place, so dont shoot anybody. Have fun ,brisketbean
*Thanks to all the well educated minds out there. I will need to thouroughly digest all this info.TOMMY B. --don't forget to brace the heck out of your dodec. at every point. That is the reason I chose a circular turret I'm working at my home: To avoid the chance of racking and keeping strength in the walls.Kelly
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Just some simple arithmetic that may or may not help.Whenever you build a shape where all sides are equal in length, divide the number of sides into 180 and you will have the number for your degree of angle.
For instance, if you were building a perfectly square pyramid, you would have 4 sides, therefore the angle to cut at the tops of your boards is 180/4 or 45 degrees. this angle needs to be cut twice actually at the intersecting ends of all runs to the center so that each board is pointed at the end like an arrow. (sheesh, it's always so hard to explain these things in type.)
This math is based on the principle of 360 degrees making a complete circle. As above it is based on 180 degrees but there are 2 cuts per side of the square...therefore actually 8 cuts. 360/8 is 45.
Did this help or confuse any of you? Its confusing me and I know what it means!
For the twelve sides the cuts would be 15 degrees on both sides of each board end. I wish to God I could just draw a picture on this damn thing.
Best wishes,
Pete Draganic
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Didn't think you would Joe. I have trusses coming next wednesday, and after that I will be into it for real.
Tom
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Tommy,
It's difficult for me to picture exactly what it is that you are building but here is a little math that may be useful, if the shape of the roof is actually a twelve sided hip roof ( or part of one), and not a cone.
b The Common Rafters
For plumb cuts on commons and jacks, set the stair gauges at 18 and 12 on a framing square. If you prefer to use an "angle square" (speed square) the angle for the plumb cut would be 56.3 degrees.
If you allow any common rafters to run all the way from the plate to the peak, first find the run of the commons by taking half of the span of the room, then look up the length in rafter tables or use Construction Master Calc.if you have one, or, multiply the run of the common rafter by 1.8028. You should get the same result with all three methods. Shorten the rafters appropriately if you are using some type of center piece to nail the commons to.
b The Hip Rafters
For the plumb cut set the stair gauges at 18 and 12 7/16, which would be 55.4 degrees using an angle square.
To find the length of the hip rafters, multiply half the span of the room ( the run of the commons ) by 1.8226 This would give the correct length if the hip rafters run all the way from the corners to the peak. Shorten for center piece as necessary
b Dropping The Hips
If the hip rafters are 2x stock, drop the seat cut 5/16ths of an inch so that the edges of the hip rafter "plane" with the jacks and commons.
I would use header blocks for the jack rafters in this type of work
If the roof is a cone instead, cut all of the rafters at 18/12 or 56.3 degrees (plumb cut)
I use 4 layers of 3/4 plywood to form the circular top and bottom plates for this type of work
Good Luck
*Ken, Thanks for replying. To clarify, the roof will be 12 sided, not circular. Also, I will be going with 16/12 pitch, not 18. The commons are easy, but what will the hips and the drop be on a 16/12. I would like to know where you got these numbers from, as well as the math behind them. For instance, I know on a 4 sided roof of 16 pitch, the hips would be 16/17, where did the hip pitch come from in your calculation? I usually just play with the hip to figure the drop, how did you arrive with your figure?Thanks again,Tom
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Don't use a center post. Set up your first four hips with plumb cuts up top. Set up the next four at angles (use a bevel square and a string, primitive but it works). Set the next four the same way and you are done with your hips. Cut 16/17 with 20'' per foot of run. Again take out the masons line, string from center point to center point directly plumb above the outside of the plate to get your hieght above the plate on the commons. I too like to know the math and the theory behind my craft. But, sometimes you just need a sharp rock and a stick. Been there done that and it's still stading there pretty after 12 years .
Peter 20/20
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Tommy,
Okay, we have the following information. We are framing a regular hip roof on a 12 sided polygon, or a dodecagon as it is called. The pitch of the roof,( which is always the pitch of the common and jack rafters), is 16:12
Divide 360 degrees by the number of sides, in this case, 12.
360 degrees divided by 12 equals 30 degrees. Divide this number by 2.
30 degrees divided by 2 equals 15 degrees.
Now, by any method you wish, find the cosine of 15 degrees, which is .9659. ( I use a Texas instruments TI-30X calculator to to this, about $13 ). Next divide 12 by this number. 12 divided by .9659 equals about 12.423 or close to 12 7/16ths, as a fraction. The pitch of the hip then is 16:12 7/16ths. This is essentially the method that Fred Mathews described in an earlier thread.
You can convert this to an angle by dividing 16 by 12.423 which is about 1.2879. Now find the angle that has 1.2879 as its tangent, or 52.17 degrees.
To determine how much to "drop the hip", first find the sine of 15 degrees, which is .2588.
Multiply this by one-half the thickness of the hip rafter, or 3/4 of an inch if you are using 2x stock. Finally, multiply by the roof pitch which is 16/12. The result is .2588 X 3/4 X 16/12 or simply .2588, slightly more than 1/4 of an inch.
That's how much to drop the hips so the edges will plane in.
It's difficult to explain why this works without being able to draw diagrams for you to see. I don't know how to do that yet. Perhaps someone who reads this will give me a clue. I have a scanner, if that is necessary
*
Tommy:
what is the span for the dodecagon,from one side to the other? To get the common rafter length
you can use the Full Lenght Roof Framer writen by
A F Riechers in 1917. I f you really want to keep it simple you can step the rafters off with the framing square,calculate total rise and run for the hips and use the hypotenuse of the right triangle to get your hip lenghts and cuts. A squared + b squared = c squared, c being the hypotenuse or hip , a and b being total rise and run. The twelths scale on the framing square can be very helpfull for this kind of calculation.
With as many members as you have comeing together
at one ridge I would strongly suggest useing a center post to recieve the common rafters,and then nail the hips into the spaces between the commons.
With trigimometry, algebra, geometry or the framing square all being workable solutions for the math the framing square will be by far the simplest means of solving your calculations.
Enjoy brisketbean
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I agree with you Brisketbean on two points. The framing square will be the easiest, and using total rise and total run will greatly speed up the process.
I would use the actual deck as a full scale plan view of the roof:
1)layout the exact center.
2)use a solid, or built up center post that will allow the hips to butt up with out a bevel.
3) draw this block, centering it on the center spot.
4) measure the run of the hip from the edge of the block out to the heel and/or the overhang. This number is your total run (for the hip)
5)calculate the total rise: measure the total run of the COMMON, and multiply by the desired rise. This number is your total rise (note: it has already automatically compensated for the "drop")
6)take these total rise, and total run numbers and divide by 12. The resulting figures are the numbers that you hold on the square to give you the plumb (rise), and level (run) cuts.
7)set your stair gauges, and carefully step off 12 steps. ( note: if you use a different divisor in step 6, then you must step off that amount)
Case closed!
I use this method very regulary in the sub that I frame in. We usually have half an octogon projecting out of the rear of the houses we frame.
Tip: Instead of the step off method, simply calculate the total length using the trusty old pythagorean theory. Total rise squared + total run squared etc.
The center post is a nice visual touch and easy to make. It will speed things up greatly. If the commons will reach the center post (usually they don't on the octogons I frame) be sure to make it large enough to accomodate them.
Good luck,
blue
"Time is the best teacher; Unfortunately it kills all its students."
*Joseph, I looked over your site. You seem to be doing nice work.I got a little bored trying to remember the new abbreviations though. Don't fret though. You know how hard it is to teach an old dog new tricks.I would like to point out one error though. In your haste to tell the world, that they can't manage to find the right plumb cut for a common rafter, you left out some valuable information. This might confuse a novice, but the old dogs around here will simply ignore the advice.I'd like you, to clear things up for me, if possible.You claim that the proper number to hold for an 8/12 plumb cut is 7 5/16. You conviently didn't supply the other number, usually 12. I know that I can hold 7 5/16, as the plumb cut number, but would have to do a quick ratio and proportion calculation to find the level cut number. It would look like this:8 : 12 :: 7 5/16 : ?12 X 7 5/16 divided by 8 = 10.968So, according to you, I should hold 7 5/16 and 10 31/32.It seems silly!I typically hold 16 and 24. The square lays, nicely balanced on the lumber, and I can locate the ends by feel. Thats a good thing for these tired old eyes! I think I'll stick to my OLD, TIRED, AND WRONG methods!I'm anxiously awaiting your reply!Also, keep working on the web page. It has a very good look, starts out nicely, but needs some touch-up. A list of abbreviations and their meanings might be helpful. Blue, grinning in MIRemember: "I took an IQ test and the results were negative."
*
Hey Joe;
Im old enough to remember that song, but am just a middle aged dog not an old dog. After looking at your post regarding "correct" settings on the rafter square I am genuinely confused as to why so many roofs that I have framed happened to come out right. My plumb cuts fit the ridge and my seat cuts fit the plates, my jack rafters line up
perpendicular to the ridge and plates and are 24 " on center unless specified 16 "on center. My hip and valley rafters fit when cut from Reichers
calculations and my roofs plane out properly.
And just to show that the angles are correct,
line up your square on 8/12 and mark and cut the tounge and blade where they are and see if you get a board with a 12" run and a 7 5/16 inch rise.
Since we are kind of simple on the farm we must
be taught with simple methods and the methods I just viewed on your post are far from simple and correct.
Disagreeing in an amiable fashion
brisketbean
*Joe: On your graphic the green line that planes to the center of the ridge and the bottom of the top plate makes no sense to me whatsoever, I must confess I didnt read all of your information on the web page as I havent had a problem laying out a common rafter in 25 years or so. I also have to ask does not the rafter laid out on the square rise 8 inchs for a foot of run?You must be cooking the pitch from either not starting your calculation at same point or running a ridge at a fixed point instead of letting geometry set the level. Your graphic shows no plumb line above the plates , do we assume that you make a single cut on the plate and no birdsmouth on your rafters? As far as the method that you use to calculate and lay out your hips and valleys , I see nothingwrong with it, but it does not have any advantageover the Old Well Used and Succesfull ways employed by fundamentalist framing square advocates. As for the groin ceiling getting two layers of 1/4 inch drywall over plaster, there were two reasons for this 1] about 8000.oo difference in price. 2] there are only two kinds of plaster,plaster that is cracked, and plaster that is going to crack. brisketbean
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Woah settle down there big fella!
So I missed the statement; "I quit using 17, blah, blah, blah.! Sorry. I am old, I am feeble, and I do make mistakes. I'm willing to learn new things; are you?
But the fact remains, that you are saying, that it is a very common mistake to use 8 and 12 for an 8/12 roof!
That defies logic!
Now quit running off at the mouth like a school kid and explain, unless there is no explanation possible!
All the attacking in the world won't help your math, nor your explanation.
You also didn't disprove my numbers.
So, you still maintain that you are going to hold 7 5/16 and 12, marking the 7 5/16 for the plumb cut? And that is going to correctly give you the 8/12 roof?
If so, I hope you have a healthy stack of wedges!
There's always more than one way to skin a cat!
Sheesh, and I thought you were gonna thank me for pointing out such an obvious error!
Still grinnin' in MI,
Blue
Remember: "I don't suffer from insanity, I enjoy every minute of it."
*Joe, you seem to be very good at diagraming, and html. I'm jealous.However, niceties aside, I have to interject one tidbit. Your numbers have conviently ignored the given 16/12!I don't know how they do it in your part of the world, but here in MI, if they specify a 16/12, I better darn well build a 16/12! Often, maintaining the correct pitch will be critical because usually the roof or soffits of this type of "add-on" is somehow intertwined with pre-fabbed trusses. However, if the entire roof is stick framed, there will usually be more flexibility.You are telling Tommy to build a roof with a IR ( I think thats your term for Unit rise) of 15. How would you like it if you agreed to get paid $16 per square, but received only $15?I'd bet your cipherin' would improve in a hurry!I think I'm begginging to understand your technique, but it needs some tweaking. Please, don't flame me, I'm charred from your last reply. I'd rather indulge in friendly conversation!Happily framin' in MiBlue"I support public edekashun."
*I can see we're going no where with this thread!Have a nice day!BlueFlames gladly accepted at: [email protected]
*I'll bet my best bone that I can figure the height of the ridge out!These are the parameters needed to complete the equation:I need: the pitch (16/12 is given), the span (which I will derive the run, the thickness of the ridge, and the height of the heel.With those numbers, and some additional rules concerning "rounding off", I'm sure everyone, including myself, will correctly figure the height of the ridge!I will put one milk bone on it!A calculatin' framin' fool in MI,Blue"Consciousness: That annoying time between naps."
*Joe,brisketbean,ken,devil, et al.,Thanks so much for your posts, I will take every thing in that I learned here and give it my best shot. I'm going to try and give a description of how it works out for me when I am finished. This turned in to a good discussion on roof framing, which I think would be good sub category for any bulletin board dealing with construction.Thanks again.Tom
*I'll see the raise and raise you one chewy toy!I use a simple $4 dual power with seperate memory recall, and memory clear,Here goes:14' 8 1/2" less 7 3/4 " leaves a span of 14' 0 3/4".calculator time!: 3 / 4 = .75 / 12 =.0625' + 14' =14.0625' / 2 = 7.03125(units) X 16(unit rise) = 112.5" + 9" (heel) = 121.5"The height of a flat ridge will be 121.5" above the plates using a 9" heel and a 16/12 roof!If the ridge is sloped (I'd reccomend that on a 7 3/4" thickness), the upper point will be 5.1666656 higher.The common rafters will be: 16 X 16 m+, 12 X 12 m+. mr sq rt (20) X 7.03125= 140.625" Good night (5 hrs and 8 minutes till the 4 am alarm!)Sleepin' in MI,Blue"He who laughs last thinks slowest."
*
Blue:
I responded to the original post way back when and thought the thread had died.
Imagine my suprise to log on tonight and see the flame war going on!
Joe Fusco-great graphics-but I have to agree w/ blue:You have completely ignored the fact that this is a 16/12 pitch. I'm sure your method works for you well and your work, but I've always believed in the K.I.S.S. rule. When I cut a roof that is 16/12 on the plans (53.13 degree incline angle), you can be damn sure that the pitch will be 16/12. Yours isn't (51.24 dgrees).
At the risk of continuing this thread.........
Fred
*guys.I'm goin'with blue on this one.you all are making a simple job too complicated. we here in MI would just go ahead and build it ( and build it well and tight ,I might add) and be done with it and move on to figgerin' how to trim the darn thing.Steve. framin' and finishing in MI. Remember,He who laughs last gets the last laugh.
*
b Joe's twelve rafter poker...
I raise you all a bag of kitty litter and will even
b throw in the "beast"
if he keeps taking swipes at me at 3 AM so he can go chase the girls in the neighborhood.
b Absolutely no-one
could follow my combo method of doing this roof even if I had an on-site web-cam for my "full scale layout/some math/framing square nearby" methods. I get the job done, it's pretty, it's strong, and thankfully done.
So my bet depends on Ken "father of volleyball" Drake, math wiz, former crew member in charge of all rafter variables and other honorable titles far too numerous to enumerate on at Breaktime.
Well Ken?....I'm putting in your ante if you'll fire up your calculators.
Hardly any thread bears in these woods?
Jack : )
*Joe,Let me begin with some bad news. You owe Mr.Devil a couple of milk bones and AdirondackJack a bag of kitty litter. I quickly checked blue devils calculations using my Construction Master calculator and found them to be accurate.AS you may have noticed by now, several people have posted messages in response to your personal set of roof framing principles. I would encourage you to listen to what they are talking about.To suggest to us that 7 5/16 and 12 are the correct settings on a framing square to cut a 8:12 pitch roof is nonsense. Also, in Tommy's dodecagon, you are encouraging him to use 15 and 12 on the framing square to cut common rafters for a 16:12 roof. This makes no sense whatsoever.I've read the material that you included as a link describing how to cut rafters for a 75' X 32' roof. You are confusing yourself, as well as the rest of us, by your approach to this subject. The double top plate on the walls has nothing to do with the roof. The roof begins on top of the plates, not on the underside. You could remove all of the studs from the wall and replace them with plates all the way to the floor and it would have no effect on the roof. I believe that you are arriving at your conclusions because you are starting at the top of the roof and working back towards the rafter plate. In other words, you are setting the ridge height and then trying to figure out how to cut the rafters.A better approach is to calculate the length of the rafters, cut them with the proper plumb and level cuts and let them locate the ridge height for you. Many times, the ridge board is long and heavy, especially if you wish to double its thickness.You may want to "post up" the ridge board in these situations off of the floor or perhaps from a beam or from the top plate of a conveniently located wall.To find the length of the post from the floor to the bottom of the ridge board try the following. I'll use your roof, 32' X 75', as an example.1) Divide the span by 2. This would be 16 feet.Subtract one-half the thickness of the ridge board, in your example it was doubled, so subtract 1 1/2 inches. The run of the common rafter to the face of the ridge board is then 15 feet 10 1/2 inches.2) Find the RISE for this run for an 8:12 pitch.This would be 10 feet 7 inches3) add the "HAP" ( the plumb measurement above the seat cut at the birdsmouth at the outside of the rafter plate ) to the rise. For a 2X8 rafter with a 3 1/2" seat cut, this would be 6 3/8"4) add the height of the wall that the rafters sit on, for example, 9' 1 1/8" for 104 5/8" precut studs.5) subtract the width of the ridge board, for example, 9 1/4" for a 2X10 ridgeboard.The measurement for the post from the floor to the bottom of the ridge board would then be10'7" + 6 3/8" + 9' 1 1/8" - 9 1/4" = 19' 5 1/4"If you wish to post up directly off the top plate of a convenient wall just subtract the height of the wall from the above calculation. ( if you bevel the top of your doubled ridgeboard to the plane of the roof, add 1" to the above calculation.. 1 1/2" run @ 8:12 = 1" rise)The length of your rafters, plumb cut to plumb cut, along the top edge of the rafter is 19' 0 15/16" for an 8:12 roof pitch. That's about all there is to it.I can assure you that I have a great deal of roof cutting experience under my belt, am well read in the subject, and in addition, I have a 4 year degree in mathematics, which in itself does not necessarily make me a better framer than you or anyone else, but I am well grounded in the math involved. I also have worked shoulder to shoulder along side many other journeymen over the years.AS far as "proving" that this method is valid, what exactly is there to prove? An 8:12 roof is an 8:12 roof whether it's in your backyard or mine.Joe. you seem to be well informed and very knowledgable about many aspects of the building profession, unlike me. I'm only good at a few things.(I have difficulty changing out the batteries in my flashlight. And don't bother asking me to fix the leak under the kitchen sink.)But please stop beating your head against the wall over this subject. No one is going to join you at your roof framing camp this summer. I would go one step further in asking you to remove the related material from your web page until you've had time to reconsider your thinking on this subject. Your information has serious mathematical flaws. It simply is not correct.Would you consider reading the first six chapters of "ROOF FRAMING" by Marshall Gross? There is some good information there about the basics of roof framing for anyone wishing to increase their knowledge of the subject.I hope you understand that my purpose in posting this is to help you and anyone else who happens to read it. So please don't jump into your keyboard and fire back some ugly message to me before you've had a chance to think this over. Sincerely Ken
*Joe, I went back and forth yesterday 4 times between this thread and your site. You state that 8:12 rise @16' run = 10'8", I agree. But in your calculation for a common rafter you use a height of 10'6" saying that's what the plans specify, I don't see how this is an 8:12. My top of ridge @ center would be equal to the rise plus HAP. I agree with Ken, the Marshall Gross book is exceptionally good, like you he is figuring everything with a simple calculator except his 8:12 is being laid out 8:12. Question, would the diagonal side of a triangle window that I ordered 6 weeks before the job started(with an 8:12) be parallel with your rafter? I know it would on Ken's roof.Not flaming enjoy your web site and the pics of your craftsmanship. FredAn aside, worked with a guy named Willie Fuscoback in western PA,hell of a nice guy and great concrete finisher he could bullfloat better than most guys could trowel. Any relations back there
*Good evening again Joe.I'm going to take a shot at your question, but I'll admit that I'm not quite sure what you mean. I think the different terminology has me a bit confused. The "ridge high" comment threw me.You are correct to say that if the ridge is fixed at 121, and the heel is adjusted to 7" that the angle, or more correctly, the ratio will not be 16:12.In my neck of the woods, the desighner can specify the slope, or the ridge height, but if he wants to specify both, his numbers better jive!I said earlier in a post that I was kinda figurin' your method out. Here's my guess. You are putting a higher value on ridge height, and sacrificing slope ratios. Your figures probably work out (I never really ran them). The mistake, however, is caliing a 7 5/16:12 a 8:12. It might make sense to you, but for all the others, it would be too confusing, since their methods are slightly different.If you drop two inches off the heel, and want to retain the 16:12 slope, the new ridge height will be 119". If you want the ridge fixed at 121", you can't have a 16:12 without adjusting the heel back to 9".Hope this helps, I've no interest in outsmartin' anyone!blueHey, you owe me a chewy toy!wanna go double or nothing on a tougher question?
*Joe, This post answers my question regarding your site info based on my 7:17 post. Looks like your book has the same worn cover as mine. regards fred
*Joe, I agree! Wish more people in the trades had the zeal for thier work as demonstrated here.Recently did an independent inspection on a big house (12,000 sq.ft.)here in NVA prior to owner signing off on framing draw. 5 pages of obvious framing flaws,and quality issues (ie. windows in a bay area that were visually out of level to each other by 1/2")that would of filled a book. Custom home, I don't think so. Wonder if the building industry is going the way of the auto industry of the 70's.Sure have seen some Pinto & Vegas out there lately. Any relation to the Mr Fusco I mentioned. fred
*Joe,Since I put in Ken's ante it's time to hand over the pot.I had no clue what you were doing with your roof pitch yak till I think Ken enlightened us all that you may be setting ridge height first and working things back down to the wall tops next.And like Ken pointed out, why are you drawing top plates with lines all over the place? I can't figure it out at all. Everytime I do a roof frame I draw out a little of it just to know what it looks like and for ordering material etc, but never draw lines where you do.My hats still off to you though and hold you in the highest of respect. And bet what you do works perfectly as I get a feeling your work rates right up with the best. So keep up the good work and if you want since you like challenges I'm open to you trying again to explain your methods and drawings especially the strange drawings.Not trying to charcoal...just a warming flame,Jack : )
*Sean,b Help! I think we need a dedicated search engine for "Stick framing a 12 sided roof."Trying to be brief for a change,Jack : )
*Fantastic Ken,You've out done your self as far as making yourself understandable and I know enough not to doubt your math or roof framing ability. Been there, can't match you.I think this is the first time I have actually been able to follow a written discussion of roof framing math (even one of yours) as my methods just aren't by "the book."If we can get Joe to concede I'll split the pot with you and Devil. OK, who wants the end that bites and who wants the end with the fluffy tail?Jack : )
*Any owners of b Solidbuilderfollowing this thread?I always wanted to buy that program since it seems to advertise the ability to automatically do all the work needed to build the roof in this topic.Post your Solidbuilder output here and or better yet send me the program and I'll attempt it myself.CAD for CAT,Jack : )PS- Really is a "nice kitty kitty kitty".....
*
Joe:
I have only had one job where ridge hieght was
critical enough to cause me to have to lower ridge below the given pitch of the roof on the plans. It also was for building code as per Sullivans Island S. C. fire code. It seems thier fire fighting equipment would only reach 38' and thier code only allowed that to the peak of the ridge. The pitch was an 8/12 and I had to drop to an 7,3/4"/ 12 to bring it into compliance with
code. As far as I am concerened thats nose bleed territory that high off of the ground anyway and
should be left for the birds and clouds to habitate.
Early on in my former framing career I found that too much emphasis on setting the ridge at a given hieght,staight and level could get you in trouble in a lot of situations. In our area most
houses are framed on a slab and that is not a level or flat surface in most cases, in fact they seem to rarely be any too close to square. I once worked for a "framer" a short period of time and
found him to be as ignorant about the trade as anyone I had ever worked with before. To my suprise I learned something from him. I have learned tidbits from some very unlikely sources
so I try to keep a somewhat open mind in most areas of life. I started the day after they had laid out the walls on this little one offset ranch house, we raised the walls ,plumbed and lined them to a point and started to nail the joists and rafters. The guy just started grumbling about his jackrafters never would line up on the hips and he just couldnt figure out why not. Come to find out the way he squares his slab is he pops a chaulk line for the longest exterior wall on the house, in a 35 mile an hour wind, with
up and down in the slab and what have you, and then he lays his out of square by an 1/8 of an inch beat up twisted alluminum framing square on the slab lining up the blade with the chaulk line, he sets the square on the slab and stretchs the chaulk line to line up with the tounge of the square and the other 50 feet or so of slab, pops the line and presto its square. He then proceeds
to pull all of his lateral measurements off of these two wrong lines and wonders why it dosent work when you get to the roof.
I always square my slab or deck in about the same manner as most "carpenters" do with 6 8 10 or multiples there of and avoid most problems
in the roof framing. With the quality of workmanship and materials we see these days its
getting more and more difficult all of the time to build theoretically correct structures. The
floating ridge can be a true lifesaver in some applications, and although not level it will still be geometrically correct. As a pup I tried to raise a couple of roofs with a set ridge height, and did not want to waver untill it snapped what the problem was. Having, what I later found out in life to be a fault or shortcoming, a spirit of perfectionism, I had a very difficult time dealing with anything less than perfect and learned to adapt a little slower than most. There are still a lot of things that
have to be perfect in every way shape and form,
but there are battles that arent worth fighting
as well.
Still learning and breathing
brisketbean
*
Joe,
That be the drawing.
Hopefully Ken learns how to post graphics as well as you do cause I just don't think you know how to draw a drawing that most of us could understand.
Take your drawing and draw in the rafter with all its dimensions and show us the pitch etc. As you always say, I challenge you to make it understandable.
Sincerely wishing I knew how to add "colors" so I could "warm" this up,
jack : )
*
Joe- Of course if ridge ht is specified per your example, the geometry works out to not be 16/12. And I don't know where the 7 and change # even came from. But it seemed you didn't answer blue's question. On the jobs I've been on, ridge ht is rarely specified, and if it is, then the slope is rarely specified. Its a rare set of plans (IMO) which gives wall ht, ridge ht and slope and gets it all right. Love the discussion though-I'd thought it died.
*
Hi Joe,
It's me, your old buddy, Ken.
First, thanks for the reply, even tho I had to remove some dry skin after reading it. I can take the heat though.
I must admit that when I visited your Web Site the other day, I really didn't spend a lot of time going through every little calculation that you made, but I did notice some things that I felt could not be mathematically correct.
I printed out all of the information from your Web Site this morning and have it in front of me for reference while I'm typing this. After the comments I made about it, I feel an obligation to follow up on what I was talking about.
The first six items are pretty much standard stuff, although, in modern times, very few framers make a distinction between the terms "roof slope" and "roof pitch". They are interchangeable terms, it's just a matter of personal preference as to which you care to use. If you've ever gone to the library and dug up some of the old writings on roof framing you may be aware that at one point in time, pitch meant something completely different. An 8:12 roof was called a "1/3 pitch roof". A 6:12 roof was referred to as a "1/4 pitch roof". I guess you can see that all they were doing was putting the "unit rise" over 24 instead of 12 and then reducing the fraction. As time went on, these ideas "fell from grace" so that today we very rarely hear roof pitch used in this way. Thank God for that. Never made much sense in the first place. (Having any fun yet Joe?))
My only concern about your thoughts on "roof rise" is this: After you determine that the "rise" for 16' of run @ an 8:12 pitch is 128", which I agree is correct, do you simply put the top of the unbeveled ridge board at 128" above the "roof deck" as you call it? If you changed your mind and decided to use a single ridge board or perhaps a tripled ridge board, would you set the tops of all three at 128". From what I see in your calculations and your later discussion on "Actual Roof Rise", apparently you would set all three at 128".
If you do, when you later calculate what you refer to as the "actual roof slope angle" you're going to come up with three different answers.
As far as "rafter plate thickness" goes, I can't for the life of me understand why it is that you would want to include the thickness of the rafter plate in your calculations. You're introducing another variable to deal with that is totally unnecessary. Where did you get this idea from in the first place? I'm curious to know. Along with this you refer to the bottom side of the double top plate as the "roof deck". Never heard of such a thing. Do other framers working in your area refer to the top of the wall studs, which would be the underside of the plates as the "roof deck level"?
Let's take a look at some of these calculations now. To calculate the Common Rafter Length, you use 16' - 1 1/2" = 190 1/2" as the run, and because of your method you end up with an "actual roof rise" of 117 3/4". Fine. I can live with it.
Next you plug these numbers into the Pythagorean
Theorem and find that the common rafters are
223 15/16". Still going good, I'm with you.
It's now time to cut the rafters. Because of your crazy ideas, even though you used 8:12 to calculate the "rise", the roof is not going to be an 8:12 roof anymore. You now must start all over again and recalculate the roof pitch. This is an exercise that you will always be able to look forward to, because instead of doing it like the rest of us, that is, start from the top of the rafter plate and work up, ADDING the H.A.P., you have decided to start at the bottom of the plates and work down, SUBTRACTING the H.A.P.
You now take the rise of the common rafter, 117.75", and divide it by the run of the common rafter, 190.5", and then multiply it by 12 to get 7.417. So your new roof pitch is 7.417/12 or very close to 7 7/16:12 Still with you Joe.
There really isn't anything "wrong" with what you're doing, except perhaps taking the time to do about ten times as much math as necessary, but that's your choice.
Let's get on to the last section where you show us how to calculate the length of the hip rafters and how to determine the plumb cut. This is where I have some real problems with your calculations.
Once again you call upon Pythagorus to determine the "actual run of the hip rafter".
You find out through the formula and the numbers that you plugged into it that the actual run of the hip rafter is 166 1/2 inches.
How could that possibly be? The run of the common rafters is 190 1/2 inches. The actual run of the hip rafter has to be much larger as always. In fact, the actual run of the hip rafter is
1.4142( 190.5" ) or about or about 269.4 inches.
Quite a bit different than 166 1/2". Your mistake here is that you used the "rise", 117.75", in the formula instead of the run, 190.5".
Next, to calculate the length of the hip rafter, you plug two new numbers into the formula, both of which are once again incorrect. The first number, instead of 166.52", should have been 269.4".
The second number, instead of the run, 190.5", should have been the rise, 117.75".
If you now recalculate, using the numbers that I suggest, you'll arrive at an answer of 294", or
24' 6" for the hip rafter length, about 41 inches longer than yours.
Let's check it out using your Construction Master IV calculator which you say you use in the field these days.
1) Enter 7 5/16" for the pitch
2) Enter 190 1/2" as the run of the common rafter
3) Press diag to find the length of the common rafters. Mine comes up with 223 1/16"
4) Press Hip/V to find the length of the hip rafter. I get 293 3/8"
The answers we are getting are just slightly different from what we found above, because we are using 7 5/16" as pitch which is slightly different than the pitch that we found to be 7.417:12.
Now for our last calculation. The "inch rise" or "actual roof slope angle" of the hip, as you call it.
First let me say this. For those of us who frame
roofs in a more traditional way, there wouldn't be any need to do a calculation in the first place.
If we know that the pitch of the roof is
7 5/16: 12, We would simply set the stair gauges at 7 5/16" on the "tongue" and 17" on the "blade" or "body" of the framing square.
But this time tested method doesn't seem to work for you, so once again, you're off to make another series of needless calculations so that you can express the hip slope in the form, ?:12
If you insist on doing this, the proper method would be to divide the "rise" of the hip rafter, 117.75", by the "run" of the hip rafter, 269.4", and then as you did correctly for the common rafter, multiply by 12.
117.75 / 269.4 x 12 = 5.245. So, expreesed as a ratio, we know know the hip slope is
5.245:12 or very nearly 5 1/4:12
If you set your stair gauges at 5 1/4" on the tongue and 12" on the body, and then draw a plumb line on a 2x4, you will find that this line is identical to the line you would draw using 7 5/16" on the tongue and 17" on the body, something we knew all along.
Once again Joe, in your Web Site, you use two incorrect numbers in your calculation and arrive at 10 1/2:12 as the hip slope, exactly twice the unit rise that it actually has. That would make the hip rafters have a steeper pitch than the commons if it were correct. It isn't.
According to an earlier message that you posted, I guess this means that we can now be friends.
I'm looking forward to that as well as to exchanging our ideas as time goes by.
It's obvious that you are very talented, I respect you for that. I'm really impressed with your drawings and overall knowledge of computer use. I would like to have included a few diagrams along with this but am waiting for Sean to simplify the process as he claims will happen soon.
Ken
*Joe,Explain why you involve the walls top plates in your drawings and calculations?Jack : )
*
THERE IS NO WAY ANY OF YOU CAN BE RUNNING A FULL TIME BUISNESS BUILDING CUSTOM HOMES AND SPEND THIS MUCH TIME ARGUEING ABOUT ALL THE DIFFERENT WAYS TO FRAME A ROOF CORRECTLY. IT SOUNDS LIKE I KNOW WHO TO CALL IF I EVER NEED A PAPER HOUSE FRAMED.BUT US FRAMERS WHO ACTUALLY FRAME HOUSES EVERY DAY WOULD SIMPLY BREAK OUT OUR BLUEBOOK THAT CAME WITH OUR SPEED SQUARE AND BUILD IT. THE FIRST TIME I BUILD IT MIGHT TAKE A LITTLE WHILE, BUT I WILL FINISH IT LONG BEFORE YOU HAVE ALL YOUR MEASUREMENTS FIGURED OUT USEING YOUR PFDHNXNIUH THEORY. GET REAL, JUST BUILD IT!!!.
*Andy,Yes there is, they got up early and go to bed late.D.C.
*
Gentlemen,
Thanks again for all you wonderful insights. I wonder, can sean tell us if this is the longest thread to date? I feel responsible. Back to the original post:
Which of the cited texts is the best, and most inclusive reference for roof framing?
And, Who can deliver the most accurate and concise method of framing the 12 sided roof including a description of the math involved. I have studied these posts and suffice it to say that the water is a bit murky. I have a room that measures 14-11-1/2 from o.s. framing to o.s. framing from accross the 12 sided room. The pitch is 16/12 with 4" of brick on exteriors and 12" overhangs, 2x8 rafters.
Once more,
Tom
*
Andy;
In softer tones I must ask, are you serious about useing the little blue book that comes with the speed square to calculate roof with? I throw
those away or give them to a laborer that seems to have a little interest in learning something. Have you ever heard of The Full Length Roof Framer writtren by A F Riechers ? Its a pocket sized book that gives you all of the lengths for any sized roof of any pitch from 1/2 to 24/12 and also gives you all of the correct bevels for side cuts ,valley shingles etc etc. Its a great resource for about
12 bucks.
Although some of the posts got off of the subject at hand, there was a multitude of good information
available for anyone with an interest in improving thier skills, if they had the fortitude to wade through the rest, and to discern the useable information from the fluff. Also when you consider
your methods critically, you often can find ways to improve them, and thats what I thought this forum was intended for.
brisketbean
*
Joe,
Perfect example that your earlier posts and pictures are whacked as far as "roof deck plane" being shown at top of studs, bottom of plates.
I think it best to work examples that are more common or explain particulars such as building off a roof deck.
I have built off a roof deck for the same reason your drawing details.
And the roof plan we are all working on in this thread along with all the talk of supporting the ridge off the floor if setting ridge first only makes sense if one assumes no roof deck.
And I repeat, if no one including you normally set roof deck plane at stud top height, why confuse the heck out of any and all that might wander up and down this huge thread?
Learning how to "warm up" my posts,
Jack : )
*Andy,Whoa there Gorilla boy.For me this is my slow period; time to post, do proposals for seasonal tennis business, ski, and make you jealous cause you're out there driving nails till your blue in the face.And about the little book, you might be the first person to build a roof from it....How bout a Saranac there buddy, chill.The secret 2x tosser,Jack : )Ps- What I'm sayin is "we're pretty friendly here, no need to bite your way in the door.
*Now that's funny!It's already been spelled out seven different ways!It's up to you to take the techniques, and plug inyour own numbers!You have still left out several variables:center post? , frieze, fascia, header height, reveal etc.?The basic math equation is posted, hashed, & re-hashed. Do you know how to figure simple roofs, mathmatically speaking?Maybe your quesions should be more specific.Your going to start a thread that'll smoke this machine!Blue"Which came first? The woman or the department store?"
*
Tommy,
"Except the Lord build the house, they labor in vain that build it.....for by wisdom a house is built, and by understanding it is established; And by knowledge the rooms are filled with precious and pleasant riches.
Psa. 127 and Pro. 4:3,4
What you need is the "Roof Framer’s Bible by Barry D Mussell.
You can get it from M.E.I. Publishing, PO Box 2065 Stockbridge, Georgia 30281
Sorry I don’t have the telephone number however I have seen the add in the back of FHB, in most of the latest issues. Perhaps you can order it Fed Ex or some such way. Page 204 and 211 will explain very concisely and briefly all that you will need to know to frame any turret style polygon dodecagon and there is 20 times the cost of the book in information for framing "bastard hips" that you will use sometime, if you continue your framing career.
The opening verses are quoted just before the table of contents and certainly seem fitting given the wisdom that has been conveyed to you via the previous posts. Just remember wisdom is the application of knowledge, this book will give you the knowldge, its up to you to apply to your situation. My thanks to Joe and Ken all others who have labored intensely to convey a very interesting subject matter in the spirit of helping someone who is in need.
FWIW page 20 shows hip rafter backing with illustration of dropping the hip, this is done by cutting the birdsmouth deeper by the amount of hip drop, doesn’t make the jacks shorter if it is placed on same layout. If someone likes to back edges that is just as good but I don’t see any reason that it would be better. Or more accurate. Let us know if it makes more than a "philosophical" differance.
I just love these little quotes from regular users, but I’m fresh out of new ones.
Montana Mike
*
Joe, you seem like a worthy adversary, I'm in the process of conjuring up a problem that you will not be able to solve!
In the meantime, you conjure up a problem that I cannot solve.
I'll post my query as a new topic tomorrow!
I'm betting two bones (milk, fat free please) and one chewy toy!
Blue
May the nerdier carpenter win!
*Andy, I can frame these roofs so fast, because I know how to figure them, that I do have time to argue theory.And...I can figure the roof faster than you can find the right page on your book.And, don't don't be braggin' about them slow squares, the ones that single handedly lowered the overall intelligence level of the new recruits in the last 20 years!Andy, it's not nice to holler at guys that have taken the time to learn something that you have chosen to ignore! Your acting like what you do, is beyond what the others can do.I've employed many a framer (for short durations only) that also carried around a chip on their shoulder because their peers had a broader intellectual base. Knock that chip off yours, and pick up the books that will also give you the theoretical tools of your trade. Knowledge is power!I frame large (3000+) custom homes in a sub with four other crews. They are all bluebook and slow square framers. They (the other crews) stand up many walls unfinished because they don't know how to "theoretically" figure the trim, porch, soffit, etc. Then they climb ladders, scaffolds, and dangle like billy goats, all because they didn't take the time to understand the theoretical formula's that govern the construction process. I laugh all the way to the bank!And you know what the funniest part of it is?It's all very simple stuff!blue, theoretically framin' faster than slow squarers...any time!"Pride is what we have. Vanity is what others have."
*Andy, I'm on an extended break from framing because of an injury that occured on the job. ( My feet only fell 7 feet, but my head fell 13 feet).I'm undoubtedly spending more time in "Breaktime" than I normally would because of all the free time on my hands, but I would like to inform you that I already have one mother, and don't need another.Instead of ragging on us the next time you return home after a hard day at work, feeling frustrated because you got caught off guard in the porta-potty and had to sacrifice a few pages of your prized blue book, why don't you just do what any other normal human being would do in this situation. Beat the kids, kick the dog. The last time I checked our Constitution, it still was permissible for an adult in this country to decide what he would, or would not, like to do with his or her free time.I've got to go now, my good buddy Joe is waiting for me to post some information on "dropping the hip". If you hear from him this evening let him know that I'm getting some stuff together, and will post it soon.
*Tommy,It's Wednesday evening.Have you started framing the roof yet?If not, when will you start?I have some information for you if you would like, if you haven"t begun yet. Let me know soon.I have Roof Framer's Bible, mentioned above. The information in it about dodecagon framing is good, but there is not much of it. I will explain if you respond. I'll check to see in the morning.
*Tommy,My computer went down this morning so I'm at a friend's house to send this. If you reply, it may be a few days before I return anything, as I'm pretty sure that the CPU is going off to the hospital.In your last post you sounded like all the information that we posted left you a little confused. I've never actually framed a dodecagon but sat down and worked a plan for you to do so.As usual, there are many different ways to skin a cat, this is just one way. But it is straight forward and easy to understand.I'm using the following information that you provided:roof pitch 16:12 Span 14'11 1/2"Start by cutting two sets of common rafters. (I'm not going to use a centerpost.)The run for calculating the first set, ( set 1 )will be half the span or 7'5 3/4" The rafter length will be 12' 5 9/16" You will just butt these first rafters to each other as there will be no ridgeboard or centerpost.The second set, ( set 2 ) will run at right angles to the first set so shorten the run 3/4 of an inch.run = 7'5" rafter length = 12'4 5/16"The first set of rafters go at 12 o'clock and 6 o'clock. The second set at 3 o'clock and 9o'clock. Lay them out at the center of each of the plates, naturally. Put these four rafters up, nailing them well and accurately.Use an appropriate HAP. If the plates are 2x4, I would just make the seat cut 3 1/2" and then see what the HAP turns out to be and stick with it for the entire roof. Make a little template. I'm sure you know what I mean. I think if you do this you'll find out that it comes out to be 7 3/8" on a 2x8 rafter.By the way it's a little late for this, since I'm sure that you already have the walls in place, but the plate length of each of your 12 walls should have turned out to be 48 1/8" I'm sure you are very close to that. If you are off a little, don't fret, these polygon roofs tend to be a little forgiving anyway. For future reference, if you ever have to frame another dodecagon, to get the length of each side, just multiply the span by .268, so in this example, 14' 11 1/2" x .268 = 48 1/8"The number .268, by the way, is the tangent of 15 degrees.When cutting rafters with a framing square, we usually put the rise on the tongue, and the run on the body. In this case, because of the steep slope, put 16 on the body and 12 on the tongue and of course use the body for the plumb cut.Next, cut and install 4 identical hip rafters.Cut them just as you normally would for a hip roof built on a rectangle. The common rafters has divided the roof into four sections at this point.Locate the hip corner that is at the center of each section, (the middle one). The hip rafters at these corners will be make 45 degree angles with the common rafters that you have up. Use 16 once again on the body for the plumb cut but change the stair gauge on the tongue to 12 7/16" for the level cut. Make a double cheek cut at the top of the hip rafters setting your saw to 45 degrees, just as you would in a typical "square" roof situation. The length from the top point to the top of the Hap measurement, measured along the top of the rafter "should be"12' 5 11/16" , but if you like, just measure each one. Drop the hips 1/4" so that the top edges will plane in with the common and jack rafters. Now nail these in place just as you normally would, making sure the edges of the hips plane with the edges of the commons that you have in place.You are going to find the next step a little unusual, but I can assure you that it will work fine for you. Rip some header blocks to be used for installing the 8 remaining hip rafters.Start with a nice straight 2x4 about 10 feet long. Lay it flat on the horses and rip it from one end to the other at a 30 degree bevel. Measure over 2 7/8" and make another rip for the entire length of the 2x4 at 15 degrees this time, keeping the same surface up so that you end up with a long point to long point measurement of 2 7/8". Now cut 8 pieces about 12" long from this. Make your cuts are square at both ends.Between each common rafter and adjacent hip rafter, nail in one of the blocks, using a torpedo level to check to see if they are plumb. MAKE SURE THAT THE 30 DEGREE BEVELED SIDE IS AGAINST THE COMMON, AND THAT THE 15 DEGREE BEVELED SIDE IS AGAINST THE HIP. Step back and take a look at what you just created with these blocks, a "centerpost" of sorts, in the shape of a dodecagon that has incorporated 4 of the hips and 4 of the commons into it. It's now time to put in the 8 remaining hip rafters. Draw a plumb line using your framing square, set the saw table to bevel at 15 degrees and cut along the plumb line. The SHORT POINT of this bevel, will hit the blocks that you just installed at the point that the block meets the common rafter.. So just measure each one and cut and install them. Four of them will have to have the short point of the bevel cut on one side of the hip at the top and the remaining 4 will have the short point of the bevel cut on the oppositeside. Drop all of these hips in the same manner as the first four. Nail them in.The last step is to cut and install some jack rafters. If you are framing at 24" O.C., since your plates are only about 48" long, you could get away with just one rafter right down the middle between each set of hip rafters. If so, cut 8 header blocks from a 2x12 at any convenient length say 10 inches, from the long point of a 15 degree bevel to the long point of a 15 degree bevel. Lay out for a ( shortened ) common rafter at dead center on each one. Layout for this common on the center of each plate as well. Measure, cut and install these shortened commons. Don't forget to move the stair gauges back to 16" and 12". If instead you are framing for 16" on center, cut the blocks in the same way but make the length 17 1/2 inches instead. When you install the jack rafters to these blocks they will then be 16" O.C.The length of the rafter tails for 12 inches of overhang will be 20" for the commons or jacks, and 20 1/4" for the hips. Set the plumb cut ahead 3/16" and bevel at 15 degrees to make the fascia cuts on the hips.The plywood cut should turn out to be only 7 11/16" if this is of any interest to you.Good luck Tom, and no matter which method you use, take a few pictures. Maybe you could scan them and send me a copy later on. I'd like to see how it comes out.
*Joe,You're so close....Last night I drove home from Vball with no taillights....Lots of snowbank ramming mashed trailer wires.Too much snow on the courts,Jack : )
*Joe,Such simple beauty is the base of all good things to come....Nice graphicb So draw some more of these "other" roof systems you keep diverting your self away to, "b accidentally" de-simplifyingan already seemingly difficult subject of semi-complex roof framing...In easier "speak'"....b Elaborate.Me likes your drawings,Jack : )
*Joe,How about both ends of the "nice" kitty kitty?Still really interested in an example of when you have had to figure a roof from stud tops verses wall top, or deck top.And any other obscure starting point that I can't think of yet since you have inferred that there may be many.I bet "one fully clawed cat" that in your early days you started at stud tops accidently in search of a starting point and have just made it work ever since....Just guessing...Possibly Hallucinating,jack : )
*Joe,Seventh round bell is sounding and.....Joe's ducking..fast on his feet...drawing..posting..the fangs still remain with the cat.Will it go round and round and round?...It's anyones best guess...could go either way..Yes I saw the perfect prior graphic drawn my way. b Thank you...It answers one question in a series.As per my prior post 26.1.1.2.1.2.1 (please reread) I do not know of any reason to refer to "top of studs" as a reference point in doing roof design calculations or graphics. You're not answering my b explain other qwest for enlightenment.You're the "challenge Man." Take ten paces, turn and shoot.All in friendly fun and learning...ready for round eight of your ducking my jibes,Jack : )
*b Sean...FIRE !!!He bit my ear off!....Thats it, it's all over...he's gone over the edge this time.OK you don't understand my questions....I don't understand your graphic in post #14.If noone can explain either you or I to the other, we better call it a draw and move on.How bout we smokem peace pipe,Jack : )
*b Who said Ducting....who said ducking..... as in avoiding by either turning on me with "Joe's barbecue web cam" or better yet adding confusion to confusion to confusion.....b Ducting?......Where are you going with that Joe?Any scitsophrenia in the family tree?Concerned fellow "poster child,"Jack : )
*Hey JoeI was just gonna suggest you role up a big fat one, fire it up, and blow out the flame thrower but I guess yer already there. Done like dinner!! LOL-Pat
*b Smokin Joe,Skitsophrenia...sometimes caused by searching the entire planet for it's spelling....Buy Amazon Stock...They have the best fuzzy logic search engine on the net....Great free spellchecker!Toasted,Jack : )
*
Ken:
With posts like your last one a guy wont even have to know how to spell carpenter, to be able to
frame a dodecagon. Excellent job of describing
the process, and the technique for building your
centerpost with a combination of rafters has to have more structural integrity than any system
with a single member centerpost. The tangent of 15 degrees to multiply for a side is great, I use
the tangent of 22 1/2 degrees to get a side for
an octagon, it sure beats the old hunt and peck method. I believe you could also take the circumference from the circle formed by the outside points of the plates and divide by 12
to arrive at the same measurement. Where can a guy find a tangent table for all pollygons, or what is the mathematical formula to arrive at the tangent for any given bevel?
Keep doing what your doing, heal well and be blessed, as you are a blessing to thoses who wish to improve thier skills.
brisketbean
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Brisketbean,
Thank God somebody besides this once disciple of Kens' (The Granfather of Volleyball) has discovered the "wise old broken man" is full of mathematical wisdom beyond most.
Ken,
I always worried about you on my sites though I didn't doubt your ability to be safe but I gotta ask you, What The H*ll Happened Buddy? Thank god for all the beach ball, it must have toughened you up for your fall. Thirteen feet's a big one.
Ken, start a thread on all the trig numbers you like to keep handy on the jobsite.
Wintering through the "land of black flys,"
Jack : )
Sean...WE made it to 100!
*Brisketbean, the correct formula for calculating the degrees for polygons would follow the same ratio/calculation that you use for the simplest polygon; the square!There are a total of 360 degrees in a square, triangle, pentagon, hexagon, etc.The side cuts for rafters on a square or rectangle is calculated by using this ratio:360 degrees divided by (4 (sides) x 2 rafters at each corner) or:360 divided by (4 x 2) or:360 divided by 8 = 45the dodegran would look like this360 divided by 24 = 15The sidecuts on a dodecagon is 15 degrees. I would like to throw in my 2 cents concerning the built up center post.You claim that it is "more structually sound", but I'm not sure what makes it stronger.I am however, aware that the installation without a post, is very tricky. It is very hard to properly nail the beasts when they all come together too close. Planning the installation sequence is essential, but eventually, there will not be very much room for your fasteners, or your hammer. The nailing angle is often suspect!I've never done a dodeagon, but have done many, many octogons. The center nailing post speeds things up significantly without sacrificing structural integrity. The center post functions the same as a ridge in typical roof framing. Does framing a roof without a ridge seem structurally sounder to you?blue, posting in windy MI"I'm not as think as you drunk I am."
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Hey, Tom
I know what your going through I to am a framing carpenter, and I have had similar problems something that helped me was a book I got at the libary. I do not remember the exact name, but the book is from Fine Homebuilding and it has old articles on tough roof framing. The drawings and pictures may help.
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brisketbean,
You are absolutely correct about finding the side of an octagon by multiplying the span of the octagon by the tangent of 22 1/2 degrees, which is = .4142
This is by far the simplest way to determine the length of each side although there are many other ways of doing it.
As far as your suggestion about finding the circumference of a circle that passes through the outside corners of the octagon and then dividing by the number of sides of the octagon to get the answer,
I tried it for two examples and it resulted in answers that were sort of close, but not accurate.
Let me demonstrate. Suppose we have an octagon with a span of 20 feet. Then the length of each side of the octagon would be .4142 x 20feet = 8' 3 7/16"
Now let's try this using your other method. I wish I could include a diagram along with this but still don't know how.
Anyway. if you were to draw a circle through the outside corners of the octagon, you could determine the radius of the circle that you mention by the calculation 10 feet x secant 22 1/2 degrees
which would be 10 feet x 1.0824 = 10 feet 9 7/8"
Once you know the radius of a circle, to find the circumference, mulyiply by 2 and then multiply by 3.1416 which we call " pi "
In this example, 10' 9 7/8" x 2 x 3.1416 = 68' 1/8"
If we divide this by the number of sides, or 8, we get
8 feet 6 inches, to the nearest 1/16 of an inch, or about about 2 9/16" too big.
I also tried it for Tommy's now World Famous dodecagon, and this time the answer was only about 1/2" too large.
My guess is, that as the number of sides increases, you will get a closer approximation but at best it will always be slightly too large.
Chances are that the only polygons that any of us will frame during our lifetimes ( other than a square which is just a four sided polygon ) will have either 6,8,10, or 12 sides.
The easiest way to get the angle that you need to take the tangent of is simply to divide the number of sides of the polygon into 180. That's all there is to it.
For example, for a octagon, 180/8 = 22.5 degrees
and for Tommy's W.F. dodecagon, 180/12 = 15 degrees.
brisketbean, the easiest way to fine the tangent for these numbers is to push a button.
Get yourself a reasonably cheap scientific calculator that has trig functions on it, that is, sin, cos, and tan. I would strongly recommend the Texas Instrument TI-30x. Battery or solar models are available. It is well laid out and has large keys. ( about $13)
Now, just press 22.5 and then press tan, and you will see .414213562. You only need the first 4 digits after the decimal.
In the future, I'll undoubtedly be posting some other stuff that may require you to know values such as these, and it sounds to me that you certainly are interested in knowing how to do these things, so ask your sweety to but you one for Valentine's Day.
In the meantime, here are the tangents for the polygons that have 6,8 10 and 12 sides.
6 sided polygon or Hexagon. tan30 degrees = .5774
8 sided polygon or Octagon. tan22.5 deg = .4142
10 sided polygon or Decagon. tan18 deg = .3249
12 sided polygon or Dodecagon tan 15 deg = .2679
Don't forget whoever is reading this that my computer is in the hospital for about 3 weeks so unless I get into a friends house, as I am today, I won't be posting as much.
*Tommy,How is your "World Famous" dodecagon coming along?Just a few quick comments on the rather lengthy treatise that I posted. The reason that I suggested that you rip the blocks for the hips to exactly 2 7/8" is because at this measurement, if you nail them in as I suggested, it will "force" the centerlines of all of the hips to meet at the centerpoint of the top of the roof. Just make sure that the hip rafters are nailed tightly up against the common rafters as I described and that the edge of the hip planes in with the edge of the common.Also, when you insert the 2 7/8 blocks, plane the top edge in with the common rafter. When it hits the hip, you'll find that it will hit about 1/2 inch below the edge of the hip. This doesn't make any difference to you, just ignore it. It's not supposed to plane in with the hip since the edge of the common and the edge of the hip are actually in two different roof surfaces.A final comment about inserting two jack rafters in each roof section instead of just one down the middle. I would put two jacks in each section. It will make the fascia work way easier. I think you know what I mean.
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Congratulations gentleman,on your obvious experience and expertise.May we have your permission to refer the DIY crowd to this thread when next we read "homebuilding isn't rocket science" ?(although I suspect a good deal of what rocket scientists do isn't rocket science)Anyway, I am impressed.My hat is off to you all.
*brisketbean:look at my response way at the beginning of this now very long thread. I derived the formula for your "tangent" for an n-sided polygon.Fred
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Ken, I have a few questions.
I do not know trig, and maybe it's time to learn. I would be able to punch the tangent in to find the lengths of the sides on the recommended TI-30X. I'm on my way to get one, I like the large numbers idea.
My question: Why do you divide the number of sides into 180 degrees instead of 360? Obviuosly, the number would be twice as large, but...
Is that a postualate? Theorm?
I mentioned earlier in another post that I often frame an octogon roof, or more correctly, five sides of the octogn. Your method for finding the sides will come in handy!
I do the roof slightly different, of coarse there are many different ways, and I won't for one second tell you that my way is the only way. I'm just throwing it out here for funsies!
The roofs are 10 : 12, with 12" overhangs past brick (usually). The spans are about 12'. I have to double frame the roof (one set carrys the roof, and the lower set provides extra room for insulation.
Of course, the pine must reach the windows and doorwall in an orderly fashion. Usually a 1x10 frieze and a 1x6 fascia will do fine.
I install the overhang before I begin the roof. A few temporary braces hold the soffit level.
Heres the main difference: I install the hips first. Then, I install two jacks in each section. usually this is plenty enough to satisfy the 24" oc requirements.
I think on the dodeagon, I would do the same, installing all the hips first, to a built up center post. I like the idea of square cuts. Since the wall length would be 48" in tommy's situation, only two jacks per wall would be required. Basically I'd be eliminating the centered commons, the same as I do on the octogon.
The reason that I like to eliminate the centered common, is because of the busy-ness that occcurs at, or near the center post, or the mini headers that you described.
I too have employed the mini header method. It works fine, but I have found the other method a bit easier. It uses about the same board footage, and is very forgiving. In Tommy's roof, each jack would be roughly 72".
One other factor in my roofs: usually the heel is quite large resulting in no seat cut. I usually have to add a heel block.
Anyways Ken, I'm looking forward to some carpentry related trig lessons. Hope your hd is going to be okay. If this thread is archived, start a new post.
Blue, a framin fool in MI
"I love cats...they taste just like chicken."
*Blue,I would frame this 12-sider starting with hips too....seems obvious really but since I rely more on self discovery. I often trip onto alternative not in "the book" methods. Lets see what Ken has to say...he's open to ideas.I also like the "no center" method....b the kiss rule applies to both ideas.b had chicken tonight....strange...tasted like cat?Jack : )
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Blue;
I hope you got your handles on up there in your winter wonderland, yall need to wear them about 8 months out of the year? I call it a wonderland because I wonder what posseses people to live in an ice box, It gets cold here in Amarillo, but it dosent stay that way for long. We should be about 60 degrees or better tommorow, I love it. We got the heat turned on in one of our projects about two weeks ago and this house still had flys alive in it.
As to the ridge having any structural value with opposing rafters and decking, as far as I can tell its a zero. I have worked on houses 250 plus years old, without ridges and cant see any problems in not having a ridge. I guess it would be similar to raising a trussed roof to frame one without a ridge,
and I hate to use trusses.
I like Kens method because he starts with the commons, wich is the best way to determine the true center of the roof and I think the nailing angles you get from being able to nail his vertical bridge blocks are impossible to surpass with this many rafters coming together in such a small area. I
am a converted centerpost advocate , that will admit the nailing possibilities diminish each time you add a set of rafters. The initial few rafters can be joined very strongly nailed to each other instead of to a member that has a means of moving independently
of the rafters, but after the first few sets are in place the integrity of the structure is established.
After all of these members come together the difference in strength is moot as we all know that
it is a very strong structure with this many members.
Stay warm till the spring thaw,
toasty in texas
brisketbean
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Brisketbean,
I agree 100% with your point about the structural integrity of these type of structures. It's always difficult to get a nail gun in to some of these places when framing these type of structures. On the otherhand, it simply isn't necessary to nail the poop out of these rafters.
As you point out, once the first two opposing pairs of common rafters are in place, and especially after the first four hip rafters are added, and everything is well nailed, this baby ain't goin' nowhere.
When the blocks are added and the next 8 hip rafters are framed in, you would hardly have to nail these rafters at all, as long as they fit properly. Where could they possibly go? You could always add a bunch of collar ties to strengthen the structure, if you were in doubt.
Finally, once the roof is sheathed with plywood or whatever, this thing is bulletproof.
One quick observation about centerposts.
In my last post I discussed how to find the length of the side of a polygon. In a dodecagon, for example, 180 degrees/12 = 15 degrees.
Tangent 15 degrees = .268
Finally .268, times the span, 14'11 1/2" = 48 1/8"
If you wish to build a centerpost, it is nothing more than a small dodecagon itself. For example, consider the one than Joe submitted in one of his great drawings. ( How does he do that? )
His centerpost was to have a "span", if you will, of 7 3/4". Therefore, the length of each side would be 7 3/4" x .268 = 2.07" or just slightly larger than 2 1/16"
The point I would like to make, is that if I were going to use a centerpost, I would want each side of it to be 1 1/2", the thickness of the rafters.
If you wished to know how big the centerpost would turn out to be, its "span", just divide the length of the side by .268 instead,
1 1/2"/.268 = 5.6" or a little under 5 5/8"
That's all for now, I'm at yet another friend's house while my computer is in the hospital.
By the way, Brisketbean, I live down in San Antonio. Isn't it a little cold up there?
Got to go now, some of my friends are waiting for me down at the swimming pool. Ken
*Joe's World,Joe, are you a Golden Gloves Champion?OK....finials and 4x4's...your roof framing center is the way to go.However, I think Ken is working with the generally given specs Tommy's post started with.Is it possible for you to turn off the defensive barbecue act?You assume we can read your mind, no?Well maybe we can, so now I'm gonna run and grab my Oil well fire fighting suit!@Jack : )
*Thats funny Jack! Maybe I better find mine too.Joe does seem to over-react to criticism. I think he likes confrontation.Joe, take it easy, we're all here because we're interested in other's techniques, and we're willing to share some of our experiences with others. Try to make it easy on us to share!Blue, hoping he's left out of the 'que!"Always remember you're unique, just like everyone else."
*The info regarding the centerpost dimensions is helpful, especially if you intended to use one. Joe's rebuttal makes sense (leaving a bit more room etc.) but...The one problem that I had with your small rips is the same problem that I have with Joe's center post: too many nails converging on such small pieces, especially along the grain. I see splitsville coming!Joe's "hollow" center post will also have too many nails penetrating such a small piece, especially when he finishes face nailing into the finial.Your blocking would work fine Ken, but I think I would slide down the roof about a foot, thus creating slightly larger pieces to work with. I have built octogons using this method and I agree that the structure is very tight indeed after the blocks are wedged into place.If I was going to use Joe's method, I would eliminate the center post frame, and simply laminate the finial, and then cut the bevels. I'd be willing to sacrifice the ability to nail and get by with a one inch build up on all sides of a 4x4 finial. Or I'd probably bevel a 6x6. Decisions, decisions!I'm leaning toward a 6x6, except that there's usually none around. I certainly don't intend to hop in my van and drive forty miles to get one though!After reading all this, I think I'd laminate a center post approx 12" long using 3)1 3/4" microlams. The numbers would work out and all hips would be the same length. I think that falls into the kiss category!The question of a center post certainly is a matter of choice. I don't think that either is significantly stronger, quicker or aesthetically affected either way. The lack of nailing certainly wouldn't be much of a factor on these small spans. I've got a dozen balancing now in MI and there seems to be no problems to date.Now, if Joe will just leave me off the spit...Blue, standing 'em up on MI"Give me ambiguity or give me something else."
*Joe,If b the trees think b the bear sh*t in b the woods, then to b the forest,....it did.Jack b Rabbiting out of here b Quick!
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Tommy;
As I showed a couple of apprentices today, one
who isnt a mathematical wizard can solve problems
like framing your dodecagon with little more than the use of a good rafter square. Once the rise and run is determined, a carpenter can take a 2 foot long board and his framing square, provided
he has fairly good vision, lay it on this board lining up the feet and inches of rise on the tongue and the feet and inches of the run on the blade, useing the twelvth scale, mark the two points and bevels on the scap piece of wood and from this get the rafter length and the cuts. The cuts are the two bevels marked on the scrap and the length of the rafter can be obtained by lining the twelvth scale on the edge of the board and reading the feet and inch measurement from point to point.
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Right on Brisket!
These roofs are not so complicated!
Your method will work for 99% of most roofs. I probably wouldn't want to use it, to cut 6 x 16" prefab exposed gluelam beams, but then again, I've never had to.
Math is great, but there are other ways!
By the way, who is that Tommy fella that you're referring too?
Blue, hoping they'll archive this soon!
I'M SICK OF LOADING THIS THREAD!
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I am currently framing a large custom with a detail that I have not framed before. I have exactly one half of a 12 sided room attached to the main house at the first floor level such that half of one segment runs into a corner parallel to the side wall. This "turret", will have a first floor porch roof (about 8' wide) and a second floor eave (maybe 2' wide) around its perimeter. A kneewall about 5'high will pierce the intersecting gable roof plane such that a 12 sided 18/12 pitch roof (or cone) will sit mostly above the gable roof. I know there are some bright minds out there that can give me some guidance on how to frame this monster that would eliminate some expensive head scratching. If anyone can point out the pitfalls or maybe suggest a reference book, I would greatly appreciate it. By the way, isn't a 12 sided object called a dodecagon?
Anxious,
Tom
how bout a construction master calculator, a hip from each of the twelve sides equal in length, then jacked in ????