In the recent FH there is an article about framing a hip roof. I hope the readers realize that most of these articles are about technique and don’t address structural issues. Being an architect in the Gulf Coast area with high wind speeds, we are always keenly aware of framing issues. I noticed the author likes to have the hip at the same depth as the rafter. Most codes requires the hip to be at least one size deeper, however framers I talk to don’t realize that a hip is really a sloped beam with tapered tributary area of dead and live loads. In sizing a hip correctly a framer has two choices, size the hip as a beam from the wall plate to the ridge, or add a beam in the ceiling joists with a sub column up to the hip to reduce the span. For example in our area the max. hip span using a # 2 pine, 2 x 12 hip on a 7/12 pitch is 13.4 ft, or 9′ 6″ from each corner. So the room can’t be wider then 19′ using a 2 x12 hip with a 7/12 roof pitch. Pitch does effect the hip size. If the hip was in a horizontal plane, it would be considered a diagonal beam, tilt the beam and it becomes a hip, still supporting vertical loads.
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Ford Motor Company slashes prices for some F-150 Lightning models to stimulate demand for electric vehicles (EVs).
Featured Video
How to Install Exterior Window TrimHighlights
"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
Here in So. Cal. the structural framing members are spec'd by the structural engineer or architect of record, the framer has no say in choosing lumber sizes. BTW, I missed that article. Which issue is it in?
"...never charged nothing for his preaching, and it was worth it, too" - Mark Twain
The most current issue.
Do not agree with your theory because rafters butting a ridge have opposing forces, rafters butting a hip do not oppose or canel out the opposite force due to the angle they join into the hip. Having ceiling joists and attic floor will keep the hold the lateral forces and keep the walls from spreading open, but will not contribute to the load carrying capacity of the hip.
How come messages get deleted by admin authority? Are there swear words in it that we shouldn't see?
I deleted my first response because I did not have the time to respond to comments.
If a hipped roof has a ceiling that ties all rafter ends firmly, a hip cannot sag.
In order for a rafter to move down, it must also move out.
I suppose the devil in this is the connections - rafter to plate- cj to rafter-rafter to hip, but if all is good, the hip could be a 1x8.
Dream on.
Where have you been all my life!
;)
We recently had a thread here with the inquirer asking about removing a post from under his hip. He asked the same Q three different ways and I told him three different times that he needed a qualified pro on site to evaluate load paths. I'm sure he still didn't really hear me.
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
From what I understand is that your talking about a hip with ceiling joists, not a cathedral hip.
I'm a framer and I don't design what size anything is, the Architects or Engineers do. I've never post under hips, I post under valleys. Mostly the hips are designed one size bigger than the rafters, sometimes even two sizes bigger.
I've framed many hips before that were the same size as the rafters when the hip was framed with a clipped ceiling and sheetrocked. We just double them up. Sometimes the rafters are 2x10's and the hips will be specked out as double 1-3/4"x9-1/2" lvl's.
Acutally hips and valleys carry the same load, there is no difference, whether the rafters are sloped up to the hip or down to a valley, the contributing roof area is the same and the dead and live loads are still the same.
I think this is a good example of an area where carpenters and engineers don't see eye to eye. Engineers simplify data to get to a solvable problem. Carpenters see what's worked in the past.
Hips and valleys are calculated the same way based on tributary area projected onto a horizontal plane, but you have to admit there is some buttressing effect in a hip situation with ceiling joists/rafter ties, as opposed to a valley.
"Carpenters see what's worked in the past."
I look at it more like Carpenters see what they've gotten away with in the past.
Production is not the application of tools to material, but of logic to work.
I'll give ya that!
I look at it more like Carpenters see what they've gotten away with in the past.
They get away with it because it works!
Most of the stuff nowadays is way overengineered.
blueOur Skytrak is for sale. It has 500 hrs on it. We want 50k (you pay the freight) and we'll finance it. Drop me an email; it's a good buy.
Especially when it comes to a conventional stick framed roof system. Recently did a house that had a simple hip roof on the garage. Rafters were to be 2x12 #1 on 12'' centers. The hips were 5-1/8 x 18'' glu-lams.We were to use lower pockets at the corners so that the seat cut was minimized on the glu-lams. The span was only 40'. I suggested to the builder that we 86 that wet dream and go with trusses. The cost savings was substantial. Sometimes I believe that the up and coming engineers just don't have any concept of some of the time tested methods of roof construction. And you know, construction these days is less about building something, than avoiding litigation.
I suggested to the builder that we 86 that wet dream....
LOL.... atta boy. At least they specified dropping the hip pockets. I see the same type of crap all the time. 2x10 rafters with a 16" or 18" LVL hip. They scratch their head and try to figure out what we did wrong when they see the corner dropped to keep the the HAP consistant and not end up with the heel of the seat a foot inside the wall.View Image
This post is just too good to pass up. There are so many levels upon which the responses are variously both true and false. It often boils down to numbers.
Some thoughts and observations:
IF the spans are not too great and IF the rafters and ceiling joists can be anchored together well enough, sure, structural hip ridges can "work" without much up-sizing. I think that a problem is that these days, for custom framing, the roofs are BIG. That alone causes some of the structural complexities.
I get a kick out of the argument regarding "how we have always done it" or "what has worked in the past" and others along those lines. Just looking at the sizes of the houses these days (that is, houses that are big enough and unique enough that they require engineering input) I find that the problem is that all of the same details and structural features that might have been present in the past are not always present now. Yes, there is much value in understanding how things are done in the field but really, ask a bunch of different framers how they do something and why, and you will get a bunch of different answers.
The whole notion of what "works" means, can also be very interesting to debate. Some want to use it to mean that a structure merely stands up with no noticeable problem. This may disregard and consideration for long term effects. I see plenty of 1950's ranch roofs that were stick framed and are sagging now. Sure, that's 50 years of service but who wants to be responsible for "fixing" it now? Others fail to recognize that the code required design load probably doesn't occur (maybe) ever. The code still requires that the structure be designed to the prescribed load. If an engineer says they designed something to the code requirements, they had better have designed it to the full code requirements.
I like to use an analogy (always dangerous but...) If the code says you are supposed to stand 10 feet away from the cliff and you instead stand 5 feet away, you still haven't fallen off the cliff but, you are not in compliance with the code. Now, who is to say you can't stand 3 feet or 2 feet away from the cliff? One person might be willing to take more risk than another but it is important to appreciate where the legal (code) requirement for the design is.
"Over-engineered" is such a vague term. Unless you have reviewed the calculations, assumptions etc. such a characterization is meaningless.
With all that said, I must say that I still find it very helpful to understand how framers "want" to frame something or what their thoughts are about a particular framing issue. I'm an engineer but I couldn't do my job well without understanding the challenges of the framers. There are often several different ways to solve a framing problem (from the engineering stand-point). My experience is that different framers like to do things different ways. Just like engineers, we're all people. Often I can tailor my engineering solutions to the preferences of a builder. It helps me to know what those preferences are. If they are not conducive to a correct (engineering-wise) solution, I can use that information to highlight why I am calling for something and why not something else. It just seems to go better when I can speak directly to the particulars.
Just my 2 cents
They scratch their head and try to figure out what we did wrong when they see the corner dropped to keep the the HAP consistant and not end up with the heel of the seat a foot inside the wall.
I would accuse you of doing it wrong too Diesel.
I wouldn't advocate ending up with the seat cut a foot inside the wall either. I would advocate using the hip as the standard sized heel and building up the 2x10's to match it. That's how we do it here in D-town.
blueOur Skytrak is for sale. It has 500 hrs on it. We want 50k (you pay the freight) and we'll finance it. Drop me an email; it's a good buy.
I would accuse you of doing it wrong too Diesel.
Yeah that seems to be a hobby of yours.
You read my post wrong Blue. I said that we drop the corner to AVOID having a seat cut where the heel is inside of the plate line.View Image
You read my post wrong Blue. I said that we drop the corner to AVOID having a seat cut where the heel is inside of the plate line.
I didn't read it wrong. If you were framing a house in D-Town, you wouldn't be droppin the corner and you wouldn't have a seat cut inside the plate. I'm just trying to point out a regional difference. I have no interest in busting anyone's chops.
blueOur Skytrak is for sale. It has 500 hrs on it. We want 50k (you pay the freight) and we'll finance it. Drop me an email; it's a good buy.
Blue, what exactly do you mean by building up the 2x10's to match a 14" to 18" LVL hip? Do you do a full seat cut on the hip and add plates until the top of the 2x10 planes in with the top of the hip?
>> what exactly do you mean by building up the 2x10's to match a 14" to 18" LVL hip? Do you do a full seat cut on the hip and add plates until the top of the 2x10 planes in with the top of the hip? <<Whether you a frame a hip with a cathedral ceiling or level ceiling the top of the hips have to be flush with the tops of the jack rafters and the bottom of the hip will be sticking down lower than the bottom of the jack rafters and you can fir down the bottom of the jack rafters if it's cathedral.On a Cathedral ceiling the HAP cut on the hip planes in at the top of the HAP cut of the common rafters. You don't have to drop the outside corner; you can cut the seatcut on a 2x4 wall 5" following the 45° angle of the corner and plumb a line down and cut those lines on a 45° cheek cut in both directions. That would make the inside of the hips tight to the inside or the corner.You can't do this if you have a flat ceiling because the hip would be sticking down lower than the bottom of the finished ceiling.
Joe Carola
On a Cathedral ceiling the HAP cut on the hip planes in at the top of the HAP cut of the common rafters. You don't have to drop the outside corner; you can cut the seatcut on a 2x4 wall 5" following the 45° angle of the corner and plumb a line down and cut those lines on a 45° cheek cut in both directions. That would make the inside of the hips tight to the inside or the corner.
BTDT.
The problem here is that the hip has been reduced to the equivalent strength of the rafter stock , unless you find a way to have the dropped portion contribute to bearing._______________________________________________________________
I'm diagonally parked in a parallel universe
>> The problem here is that the hip has been reduced to the equivalent strength of the rafter stock , unless you find a way to have the dropped portion contribute to bearing. <<
Heck,I disagree with that, because I only do that when it's a cathedral ceiling and never had a hip fail.Better yet, when it's a flat ceiling I've cut every single hip level cut straight through flush with the bottom of the ceiling joists with 12-16" of level cuts on every single hip roof before and they're all still standing.Everyone including you has had to have done this before, there's no way around it with a level ceiling.I’ve asked every Architect and Engineer about this very topic and they all say it's alright.I know most of my work is still standing and I don't see any sagging in any roofs that I've framed because I still live in the same area where I've framed house and additions that I still see 23 years later.So if I get accused of saying that I've been doing it this way for 23 years and it's still works, then I'm guilty.I also frame the way every plan is designed by an Architect or Engineer and I change with the times like they do. So who's right and who's wrong? Where do you draw the line.Me as a framer, I get the plans and follow them to the exact design. If I see something unusual, I will question it.I just framed an addition for the first time with rafters and floor joists 24" centers and I questioned it and the Architect said it was fine.I still didn't like the fact that the 2x12 floor joists 14' span were 24" centers and questioned it again. Both Architect and GC told me to frame it that way and I did after they said it wasn't a mistake.Joe Carola
Edited 10/22/2006 11:29 pm ET by Framer
Joe, there is a lot of redundancy built into common design aspects of roof framing. That is why we can say - "that's how I've always done it, and it's still there".
This doesn't mean that there is no effect on a beam or a timber based upon how it encounters a bearing surface. You wouldn't notch a floor joist halfway up and hang it from the rim, it would reduce the strength of the joist by half. These timbers are meant to bear on their bottom surface, giving the strength of the entire member. This would be equivalent to using 2 x 6 joists for a span that required 2 x 12's.
Now, I'm not saying that notching a hip beam at the corner as you described is an automatic recipe for failure, I am saying that it does have an effect on the strength of the beam as opposed to a full seat cut which engages the full depth of the beam. When this difference is crucial, I much prefer to frame the corner to allow for full bearing along the bottom of the hip.
As to flat ceilings, yes, I have had to cut them level with the plane of the ceiling - however, there are ways to support such hips when utilizing a framed flat ceiling.
There are many ways to deal with the issues we are discussing and they should be considered in the design phase. A double member hip would be one way. Dropping the corner would be another.
One concern not yet mentioned about the dynamics of hip performance is the need for the hip design to resist rotation. Even if the walls that the rafters and jack rafters bear on are correctly braced by some design to resist spreading, the jack rafters and any load on them can rotate downward if there is a failure of the hip beam.
By the way, I am using the terms 'beams' and 'timbers' here in the structural sense, even if it might be a 2 x 6 hip on a porch, or a 2 x 4 ceiling joist.
I've done just what you described, I just wanted to point out that there is an effect, and caution the inexperienced not to start hacking away at structural framing members._______________________________________________________________
I'm diagonally parked in a parallel universe
>> You wouldn't notch a floor joist halfway up and hang it from the rim, it would reduce the strength of the joist by half. These timbers are meant to bear on their bottom surface, giving the strength of the entire member. This would be equivalent to using 2 x 6 joists for a span that required 2 x 12's. <<Heck,A floor joist I would never do that to, plus it would never pass code. I don't believe a floor acts the same way as a hip does. A floor joist is laying flat. A hip is a single member running 45° rising upward with jack rafters nailed into them holding the hip up. The birdsmouth can be notched out the way it's always been notched out and still stand.It's obviously true because we keep framing them this way and they're still standing. I've done a million additions on old homes and the hips are cut the same way with no failures. Why? Because there's no structural damage done by doing this. It's been proven a million times with all the houses with the hips cut that way without any problems.>> Now, I'm not saying that notching a hip beam at the corner as you described is an automatic recipe for failure; I am saying that it does have an effect on the strength of the beam as opposed to a full seat cut which engages the full depth of the beam.
When this difference is crucial, I much prefer to frame the corner to allow for full bearing along the bottom of the hip. <<You cut the wall down because that's the way you've always done it and to you think that the way I do it or anyone else does can weaken it, when it doesn't weaken it.I cut many single hips before and seen many single hips before on all the old homes that I tie into with a long level seatcut and no structural damage has been done.
Joe Carola
Better yet, when it's a flat ceiling I've cut every single hip level cut straight through flush with the bottom of the ceiling joists with 12-16" of level cuts on every single hip roof before and they're all still standing
If it's a flat ceiling, it's normally very easy to fully support that "overcut" hip by inserting a perpindicular beam, buried in the ceiling, to carry the hip. That option isn't available in most cathedral ceilings but I did have to do it on a big custom a couple years ago. It took a little creative framing to make it look good, but in the end, it looked great.
blueOur Skytrak is for sale. It has 500 hrs on it. We want 50k (you pay the freight) and we'll finance it. Drop me an email; it's a good buy.
Here's a shot of a Bay Roof I framed four years ago where the double valley was 2-2x10's and the main hip was a single 2x10's and the rafters were 2x8's and it was cathedral inside. The Bay hips were single 2x10's.The GC later on firred the bottom of the jack rafters down.Here are some pictures. The inside shot of the hiip and valley isn't that clear but you can see how I knotch out the valley and hip instead of dropping the plate.
Joe Carola
Wow, that's quite a roof. I know the tops have to plane in, I guess I was asking whether it was better to drop the plate or add extra plates, and if you really have a big difference in size (say 2x10 rafters and a 16" or 18" hip) then what is the efficient way to furr the rafters down.
I suppose most of the time there is not that big a difference between the height of the hip and of the rafter, so the answers you showed would work.
I framed a roof one time that was a wrap around the corner of the house and a new gable roof addition on the other side of the house and there was a hip and valley and they were both cathedral. The rafters were 2x8's and the hip was a double 1-3/4" x 11-7/8" lvl and valleys were double 1-3/4" x 18" lvl's. The valley was holding up the shed rafter on one side and hold up the valley rafters for a new gable roof on the other side.It was on the plans with the bottoms exposed and just sheetrocked or you can dress them up with oak or mahogany or any type of wood that you want.If they were 16" or 18" hip or valley, then you can frame false rafters underneath later on if it's called for or in the budget.Joe Carola
Edited 10/22/2006 11:40 am ET by Framer
Joe,Nice frame up. What are the dark spots on the cripple jacks in the last pic? We send anything that looks like possible mildew back.Chuck Slive, work, build, ...better with wood
Thanks Steve. The dark spots aren't mildew. I wouldn't use mildew wood either. Maybe just the light.Joe Carola
Joe,You mentioned " cathedral hips". I gues you would stap the bottoms of the jacks to match the hips.What is your method for insulating the roof and maintain ventilation? I have seen the styrofoam inserts. How do you get the air flow past the hip? Kind of off topic but , you seem to be very good at what you do.Chuck Slive, work, build, ...better with wood
This has been a fairly interesting thread. I really enjoyed the pictures of the the bay valley framing done by Framer. Very nice work and a joy to look at. But these arguments are the same ones I have been listening to, in one form or another, for the last 32 years that I have been a framing contractor. Codes do change, and I have adapted to the changes as I have gone along. In my defense, not one of the conventional roofs I have framed has ever failed and I certainly don't expect any such failure to ever occur. Some of my frustration comes from looking at houses that are over 200 years old in our country and a couple that are over 500 years old in Europe that have roofs that were framed using techniques that I still use today and knowing that the materials used would never pass muster with a structural engineer today. How they managed without the engineered lumber of today must be considered a modern miracle by many who post here. I am looking forward to retirement from the field and hoping that those that follow fight the good fight, but I will bet that the arguments between architects, structural engineers and the guys in the field will continue unabated. And in the end, maybe it will produce a better product.
"not one of the conventional roofs I have framed has ever failed and I certainly don't expect any such failure to ever occur."
That doesn't mean they never will. It only means they haven't yet.
"Some of my frustration comes from looking at houses that are over 200 years old in our country and a couple that are over 500 years old in Europe that have roofs that were framed using techniques that I still use today..."
Two thing here that I would point out - First, houses are a lot bigger now than they used to be. What works on a small house may not work on a biger one.
Second - Houses that were wel built 200 years ago still exist, but the ones that were just slapped together are gone. So what's left from 100 years ago is likely the best of the best. And many of those were post and beam, not stick framed.
"How they managed without the engineered lumber of today must be considered a modern miracle by many who post here. "
Inflamatory, meaningless BS like that is hardly helpful.
I knew a girl so ugly, they use her in prisons to cure sex offenders. [Rodney Dangerfield]
Interesting response. I view these boards as a place for those of us who make a living in construction to post their opinions as part of the give and take of any spirited discussion. Depending on the subject at hand, some will agree with my position on any given topic and some will not. No need to call anyone's opinion meaningless BS, it is after all, just an opinion.
I thought it was funny =)"...never charged nothing for his preaching, and it was worth it, too" - Mark Twain
Adding plates would be one way, but I wouldn't suggest that in our cold climates because it creates cold spots in the wall at the ceiling.
We normally add heel blocks and if the ceiling needs to be flush (cathedrals, studios, etc), then we have to furr down the ceiling by some method.
blueOur Skytrak is for sale. It has 500 hrs on it. We want 50k (you pay the freight) and we'll finance it. Drop me an email; it's a good buy.
I should have know better than to ask if you added extra plates--I know you hate to use extra wood!
I have yet to see a set of structural specs not get upgraded a step beyond what either the architect or framer expects to be sufficient. It's almost to the point of silliness.
I've started warning clients up front that calling an engineer for a small question is not just the $500 review fee, but the chance that he'll want everything connected to it to be upsized two steps beyond code.
Most recently a 3' wide set of stairs spanning 9' was spect'ed to require 4 (!) 14" lvls for stringers.
We have a set of plans for a simple roof with two medium sized dormers that has lvls in places that can't physically be built. Apparently to fit the problem into the engineer's computer program he screwwed the pooch.
Other designs we see often have lvls dropping into living space as if the client won't notice 1-1/2' projections in an otherwise smooth design. Give me a break.
Engineers and architects are over designing to avoid litigation instead of what makes sense for a particular building.
Beer was created so carpenters wouldn't rule the world.
What you call overdesign, I call good sensible design. When it bounces to much to crack the drywall, when it deflects to cause openigs to be trapazoidal it was not a sensible practical design was it? As engineers and architects should go out into the field to see how things are built in the real world with real people and are required to maintain continueing education units for their licenses, framers should also be required to see defective poor work practices out in the field for continueing education. There are consequences when structures fail. The framer may be last one to ever get affected by litigation.
What you call overdesign, I call good sensible design. When it bounces to much to crack the drywall, when it deflects to cause openigs to be trapazoidal it was not a sensible practical design was it?
I'm in favor of structrual practices that hold up over the lifetime of the building. That's a high standard, but isn't the same as spec'ing 24" footers automatically when 16" will adequately support the same structure. That isn't four 14" lvls for a 9' run of stairs.
What I'm not in favor of are architects reusing designs well suited to the structural requirements of commerical structures on residential applications to save time. It bloats budgets and doesn't help the homeowner. In fact paying for a grossly overbuilt structure takes money away from other worthwhile uses that would extend the life of the building as a whole.
As engineers and architects should go out into the field to see how things are built in the real world with real people and are required to maintain continueing education units for their licenses, framers should also be required to see defective poor work practices out in the field for continueing education.
Unfortunately, many framers don't give a crappola and won't be around for the long-haul anyway. There just aren't many elderly framers.
For those of us who remodel we don't have to make a special trip to the field, we work with older structures daily and can come close to guessing the types of problems associated with the various ages of buildings in our area.
We see what 1, 10 or 100 years of use and abuse does to foundations, walls, floors, stairs, and whatnot. A signficant portion of our time upfront on any job is spent accurately measuring how plumb, level and square a structure is room by room.
When was the last time an architect or engineer actually measured the deflection of a structural element in use? We do it all the time.
If you are designing a floor for L/480 deflection then design it for that and not L/1440.
It simply makes sense to build the entire house with it's long-term health in mind, not simply overbuilding parts of it taking away resources from other parts.
Beer was created so carpenters wouldn't rule the world.
I think my hips exceeded calculated structural load capacity, long ago.
Never mind that kink in my slinky
*grin*
Beer was created so carpenters wouldn't rule the world.
Measuring that structural element's deflection already in use is too late. And as the room above fills with party goers the deflection increases but the member should not fail. You also don't want the drywall to continue cracking after every birthbay bash held upstairs.
YOu must've come across that one industrial architect/engineer who designed he first foundation wall with enough reinforcing to create concrete wall in an empty lock. I've seen his work. However, I can't believe you think all architects are like that, I certainly don't think that all builders are architect/engineer wannabees who never saw it all the way through. I respect the guys out in the field who wan to ask why and share there experience, I don't respect the guy in the field who uses the "gut feeling experience" to design every structural element.
Did you bother to ask the architect if the 24" footers were because of poor soil conditions established with soil borings? Typically, you'll see the architect's telephone number on the title block. Use that funny little cellphone attached to your hip and call the architect and ask the question. It could be he has a good reason. If not, then call him an idiot. I've seen those builders who just form the footings and pour the concrete just because they can walk in the excavation for the foundation on dirt that covers soft landfill.
Did you bother to ask the architect if the 24" footers were because of poor soil conditions established with soil borings? Typically, you'll see the architect's telephone number on the title block. Use that funny little cellphone attached to your hip and call the architect and ask the question. It could be he has a good reason. If not, then call him an idiot.
I'm not calling architects idiots as I realize there are pressures driving many of the overly cautious designs.
I've seen those builders who just form the footings and pour the concrete just because they can walk in the excavation for the foundation on dirt that covers soft landfill.
?
We've all seen builders who shouldn't be allowed to pick up a hammer, let alone a trowel.
Beer was created so carpenters wouldn't rule the world.
Yes we have.
You're right about avoiding litigation. However, code requirements are code requirements, architectural and engineering licenses bring on very serious responsibilities. The 30 year old carpenter that works out of his trunk and boasts he's got 25 years of experience and in his gut knows how it can be done with 2x12s instead of (2)14"LVLs will never produce any calculations to justify his point of sizing structural members.
"They get away with it because it works!"
They get away with it because it works MOST of the time.
The BS about "We've always done it that way only goes just so far. You can drive down the road with your eyes closed for 10 seconds and probably get away with it most of the time. But that doesn't mean you can KEEP driving down the road with your eyes closed.
I agree some stuff is over-engineered. But many of the changes that have come about have been good things.
Impossible: Something that nobody can do until somebody does it.
Right on!
Acutally hips and valleys carry the same load, there is no difference, whether the rafters are sloped up to the hip or down to a valley, the contributing roof area is the same and the dead and live loads are still the same.
From your engineering point of view, perhaps you are right.
Of course, I've seen some blatantly stupid blunders by engineers.....so, I tend to believe things that I've actually experienced in the field too. My field experience tells me that the hips are supported by the opposing members of the roof, while the valleys tend to want to sag under the weight of their intersecting members.
blueOur Skytrak is for sale. It has 500 hrs on it. We want 50k (you pay the freight) and we'll finance it. Drop me an email; it's a good buy.
>> Acutally hips and valleys carry the same load, there is no difference, whether the rafters are sloped up to the hip or down to a valley, the contributing roof area is the same and the dead and live loads are still the same. <<They can also be framed as catheddral without supporting them.Joe Carola
Acutally hips and valleys carry the same load, there is no difference, whether the rafters are sloped up to the hip or down to a valley, the contributing roof area is the same and the dead and live loads are still the same.
This is a good article about the subject http://www.jlconline.com/cgi-bin/jlconline.storefront/4541519c0003c8b427177f0000010569/Product/View/9405stra
Excellent article, amazing how structural engineers all have a different view of the stresses involved.
"In sizing a hip correctly a framer has two choices, size the hip as a beam from the wall plate to the ridge, or add a beam in the ceiling joists with a sub column up to the hip to reduce the span."
First, framers do not size anything. Second, there are lots of ways to size hips.
I prefer to design each roof surface as a diaphram. The hips are then sized to support the edge loads - not the surface loading.
Others use FEMs to size all the components.
Everyone, including me, gets the wrong answer. Those who follow prescriptive codes are by law sufficient. Those who are allowed to do engineering and do so are also by law sufficient.