*
Ken,
Does The roof framer’s bible have in it how to size hips and ridges and rafters? I have several old carpentry books (20 to 50 years old), I’ve never seen anything on how to calculate the live load on a hip or a vally rafter.
thanks bill
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Fine Homebuilding's editorial director has some fun news to share.
Featured Video
Highlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
*
question 1, how does one select the right size materal for a hip rafter ?
question 2, how did you calaulate the backing bevels?
been saving my milk bones framing math.
thanks
*
Size the hip one size larger than the rafters that intersent with it. this prevents the bottom of the rafter from hanging down, and possibly splitting.
If you figure the hip rafter from the true total run, it will automatically be dropped, thus eliminating the need to bevel it.
Of course there are some times that it will need to be beveled (I havent run into any yet, and I have a quarter century of erection experience).
Blue
*Blue I have something that may save you some time plywooding the hip roof that you described on another thread. You may allready know it.If I have two 8/12 roofs forming a valley or a hip to figure the plywood angle I do the following: 1. call 48" the diagonal or rafter length.2. figure the run that gives a 48" (sheet of plywood) rafter length.3. this number for the 8/12 is 39 and 15/16--close enough to 40"4. measure the bottom side for sheet going into the valley or hip. Lets call it 20"5. add 40" to the bottom number 20+40= 606. mark the 60" onthe top of the sheet and connect it to the 20"7. For hips subtract
*Daved, If I'm following you correctly, you are describing the plwood cuts for sheating that lies over the hips, or butts into the valleys.I sometimes precut the plywood, primarily to speed up the process when I'm laying the valleys. If I have a flat stack to work off of, I calculate the cut, and cut 3 sheets deep. These precut sheets are then layed, running from the valley outward. I then recut the ply half-on the last rafter that the ply hits. This method of working outward from the valley is twice as fast, and yields less waste.Blue
*Blue,I cut on a roof now more than not and have a pair of special "stand on sawdust and don't die" cheater shoes...What do you do???Sharpened the claw on the Estwing too!JUltralight standing by on high idle for any and all "flying" moments to come...
*Jack,
Joseph FuscoView Image
*Joe,Yuppers...My sharpened Estwing's sole purpose is to, slow my butt from flying prematurely off the roof...yes sir eee...Trying to chose my flight patterns,J
*david, wildwill, others,Let me explain how to calculate the bevel for regular hips and valleys at 90 degree corners when there is only one pitch involved.Suppose the roof pitch is 8/12. Then the slope of the hip or valleys for this roof is 8/16.97Using a framing square, put one of the stair gauges on 8" on the tongue, and the other at 16.97" on the body of the framing square. Place the framing square on a piece of plywood and mark lines on the tongue and body as you would in cutting a set of stair stringers.Next measure the hypotenuse. It should be 18 3/4", which is the length of the hip or valley for 12" of run on a common rafter.Now, change the stair gauge on the body from 16.97" to 18 3/4", while leaving 8" on the tongue. Once again, place the framing square on a piece of plywood and mark the tongue and body as before.Using a "speed square", measure the angle that the line marked on the tongue, makes with the edge of the plywood. You should come up with 23 degrees. That is the backing bevel for an 8/12 hip or valley, top side or bottom.The "backing bevel" will never be greater than 45 degrees in this situation, regardless of how steep the roof may become. The "myth" that the "backing bevel" is equal to the slope of the hip or valley, in other words, is not true. The "backing bevel" will always be less than the slope of a hip or valley for a given roof pitch. For medium and low pitch roofs, it will be reasonably close, but as you go to steeper roof pitches, the difference becomes quite noticeable.For example, if the roof pitch is 12/12, the hip slope is 12/16.97 or about 35 1/4 degrees. The backing bevel is exactly 30 degrees.That's all for now. Don't forget to save up milkbones for the MILKBONE MATH FRAMING CHALLENGE, coming soon.........
*Jack, I have almost always cut on the roof. I don't use any special shoes, I feel most confident with my everyday work boots. I do keep the old ones around till the new ones soften up and grip the osb!I am a kicker nut. Most fast framers put fewer kickers in than I do. I have started putting "t" style kickers at the bottom of roofs. They are haarder to walk on, but they are better for staging materials and tools. After the "t's", I use a stacked 1x3 (bridging stock). These are great for hanging my stapler, and holding usable scraps of ply. I like the 1x kickers better because I can staple them. I place the second 1x, staggered up about 3/4". This is one of my newest and bestest tricks.I once set up an experiment, to find out which was fastest. I was a cut man, for a carpenter sheathing the back side of a garage. I had an carpenter equal, laying the plywood, and cutting it in place alone.He beat us by 15 minutes!It's twice as fast to lay it alone, and cut it in place!I don't sharpen my hammer any more, but I can drive the head through osb easily! Just have to hit it between the joists, or else I'll have a truss repair to do!Blue
*All:Ken's recommendation to buy the Roof Framer's Bible is right on! It covers all the questions I had concerning bevels and miters on irregular pitched hip roofs and a whole lot more, but in a very concise fashion. Also, don't miss the couple pages of formulas in the back of the book.
*My crew normally frames the roof and then has loads the plwood on top with a crane or forklift. The house we are finishing now has a truss roof. There are three different sections. There are 4 valleys(not including crickets and lower roofs. We set the trusses in the middle section first. The tails all needed to be cut and worked on. Because of the tails I snapped a line 12' 1" down from the ridge and ran 4 sheets of plwood. We then set the rest of the trusses with the crane and loaded plywood onto jacks that we placed on the plywooded section.I wish we could still use toeboards when walking the roof. Last June OSHA came by and gave us three citations. We now use ropes and full body harnesses. There had been many accidents in the area before. That is why OSHA came up. Now if I see anyone watching or videotaping my job I immediately find out who they are and what they are doing. There is a maximum height that you are allowed to use roof brackets and 2x6 planks but we are always above that height. The ridge of the house we are finishing is 44'-6".
*Doesn't all the rigging get in your way?Blue
*
thanks ken, sometimes these things come in handy. sounds like your a good teacher to. i'ed still like to see the math for the load on the hip . i've never seen any thing in writing. this is something that has bugged me for years. i got a big pile of milk bones saved up.
*
Blue
The rigging is real tough to work around. At times it seems safer to be off the line. We still use some toe boards but not as many as before. When the work is on the most visible sides of the house the ropes get the most use.
I do like the ropes when we are doing fascia and soffit. Our overhangs are 1'-6" or larger. The fascia is 2x12 cedar with a 2x4 or 2x6 shadow board. The house we are on now has 3' overhangs. The wall jacks that I used on the east coast are to small to use as staging. We build staging going out the window holes . From what I've heard site built staging is the most dangerous staging. I feel better having my guys on the ropes when they are on wooden staging. Up on the roof it is more to follow the rules.
*Daved, my workers comp advisor has told me that the rigging can be more dangerous to use than kickers, and OSHA will accept an alternative "written safety plan" that basically spells out most common sense decisions while working without a harness on roofs.Blue
*KenI finally bought the Roof Framer's Bible. Great book!!. It has the answers to the two questions. I am adding my own angles and miters to it as I figure them for fascia and soffit cuts invovling square tails. I am adding the following:1. The angle and bevel where the dormer fascia returns to the main roof.2. The angle that the dormer soffit hits the main roof.3. I don't miter my valley fascia I butt it, nail from the back and clip the tips with a chisle and saw. The degrees in the bookare right on the money. I am adding the butt cut miters.We just finished a 6/12 with a bunch of dormers. The entire ceiling is vaulted. The roof has a 6 3/4" x 18" glue lam as the ridge in one section and 2 11 7/8 micros in another. The micros are supported by 2- 6 x 12 timber trusses that we built on site.The glue lam ridge runs under the rafters. We ripped a 2x8 down to go on top. We then ripped a 27degree bevel down the edge of the board and nailed it to the glue lam. Instead of the rafters lining up at the ridge they are offset by 1 1/2". I didn't put a plumb cut on the top of the rafter. Instead I left it square. The rafters lap at the ridge and they can be nailed together. Slight imperfections in level and square are never seen at the ridge. The roof went together nicely.
*Ken, Glad to see you teaching roof framing again. I think you just dated yourself, however. I find myself giving copies of the roof framers bible as gifts. 40 % off at Barnes and Noble on the net. I find the more complex roof problems so easy now that I recently offered to frame five sides of a 12/12 octagon dying into an 8/12 instead of the shed roof that was spec'd over a nook. It takes the same time for me now. FHB editors note: Have Ken write an article on roof framing math.Tom
*
I agree with Blue Eyed Devil but only on one point that is that you shouldn't need to bevel the top edge of you hip called "backing the hip" except where the hip runs through a section of roof where the plain is common. Anyways in order to find the degree of turn to a hip use the pitch increments such as 9 pitch to a 12 pitch. Divide 9 by 12 giving you .75 take the inverse tangent of this sum giving you 36.86989765 degrees.This tells the degree that the hip turns toward 12 pitch. Rest of the answers E-mail [email protected]
*What you are trying to do will not work unless you intend to rip one set of rafters to the correct width. When you have rafters of unequal pitch meet at a hip or valley, and assuming you are aligning the tops of the rafters with the top of the hip or valley, the bottoms of the rafters will be at different heights. The two ceiling planes you are trying to create will not intersect the hip or valley at the same height; the true intersection of the two planes will be to one side or the other of the hip or valley.Cy Miller
*
Does anyone have a fast method for figuring the bevel cuts on the bottoms of hips and valleys in enqual pitched roofs?
All most all the roofs I frame have square tails as opposed to plumb cuts. What are someways to determine the tail cut on hips and valleys?
*David, it looks like every one has passed on your question. I think the wording has everyone confused, and they just don't want to get started.Additionally, you have not included any specific examples. This leads those of us who know to have to type out the entire theory and technique for roof framing.Your nonclementure, tells me that you have enough knowledge to be dangerous, but I'll give you a hint anyways.First, you are using the term bevel incorrectly. I think you are trying to figure the plumb cuts, and the level cuts.To find the level cut, at the bottom of a hip, you need to know the ratio of the rise and run.You probably already know that the unit rise of either of the roofs, will work. You can't just add them and divide by two either!One way that I roughly figure the cuts are: measure the total rise of the hip, and divide by twelve. That is one number that you hold on your framing square. What?!!!! You only have a speed square?Class dismissd!Blue
*Blue I'll cLarify my question and maybe you can help me with my problem.The valley formed by the intersection of two 6/12 roofs is a 6/17(if they are perpendicular to each other). The plumb cut is 19.45 degrees the seat cut is 70.55 degrees the valley is at a 45 to the two roofs. Many of the roofs that I frame are also the vaulted ceiling of the room below. Ceiling joist are rarely used. I rip a bevel on the underside of the valleys and hips to make hanging sheetrock and wood ceilings easier. The bevel on the 6/17 valley would be 19.45 degrees.The smallest valleys or hips I see are 2-2x12. They increase in size to 4 micros, glulams and steel. The snow loads are large. Strapping a ceiling is unheard of. It is faster for me to install a triple or quad member valley when the bottoms are beveled. When I am framing these roofs I rarely layout for the hip and valley jacks. I figure them by using the distance from the center of the hip at the wall top plate and calling that the run(this works because a 45 degree triangle is formed). To install the hip jack we nail it to the wall and where it plans into the underside of the hip is where it goes. The bevel makes installation easier. If a have a 6/12 roof and a 9/12 roof intersecting the valley formed will be about a 5/12 ( 22.59 degrees plumb cut and 67.41 seat cut). The bevels of the plumb cuts of the valley and valley jacks will be 33 degrees and 57 degrees depending on which side of the valley they fall. I now need to rip the underside of the valley. How do I determine the bevel? The bevel is different on each side of the bottom of the valley.
*Daved, the last time I beveled was over ten years ago, so I might not be the best guy for your problem.I do think, however, that the two angles that you mentioned:33, and 57 degrees will be the correct answer for the bevel too. If not, they will be a factor.Blue
*daved,Pick up a copy of Roof Framer's Bible by Barry Mussell (1996) Both of your questions are answered in it, for just about any combination of roof pitches you would run into.If you have further questions about the formulas involved in arriving at these values, post another message in this thread.
*Thanks for the tip Ken. Sounds like the Roof Framers Bible is a reference book that has tables. I will pick up the book but I would also like to know the formulas for answering both questions.
*Ken, Does The roof framer's bible have in it how to size hips and ridges and rafters? I have several old carpentry books (20 to 50 years old), I've never seen anything on how to calculate the live load on a hip or a vally rafter.thanks bill
*wildwill,I have never seen any stats on the live load for hip or valley rafters.
*
Joseph FuscoView Image
*daved,I've had a long day. I'll get back to you this weekend about the two topics that you mention, but for openers, the backing bevel for a single pitch roof, ( at 90 degree corners ) on the hip or valley rafters is NOT the slope of the hips or valleys for that roof. This "myth" has persisted for about 150 years because the correct backing bevel for typical "medium" pitched roofs ( 4/12 to 8/12), is very close to the slope or angle of the hip or valley.For example, for a 6/12 pitch roof, the slope of the hip or valley is 6/16.97, or 19.47 degrees. The correct backing bevel on the hips or valleys, ( top or bottom) is 18.43 degrees. Only a difference of 1 degree, but as the roof becomes steeper, the difference between the slope of the hip or valley and the backing bevel becomes more pronounced.For example, if the roof pitch is 12/12, the slope of the hip or valley is 35.26 degrees, but the backing bevel is exactly 30 degrees, a difference of about 5 degrees.Let's get a little steeper...( ok with you Jack?)Suppose the roof pitch is 24/12. Then the slope of the hip/valleys is 24/16.97 or 54.74 degrees. The correct backing bevel in this case is 39.23 degrees, a "slight" difference of about 15 1/2 degrees ( can see it from my house). The backing bevel at a 90 degree corner, for a single pitch roof, can never be greater than 45 degrees. This should be comforting to you, since you would always be able to cut the backing bevels on hip and valley rafters ( top or bottom) with a typical circular saw that does not bevel beyond 45 degrees.Final summary:For typical single pitch roofs ( at 90 degree corners), the backing bevel for hips/valleys, is NOT the pitch, slope, or angle of the hip/valley. Also, the backing bevel in this situation can never be greater than 45 degrees.MORE TO COME..........................Blue Eyed Devil....Joe......don't eat all your remaing milkbones, the MILKBONE MATH FRAMING CHALLENGE is coming soon.