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Last Post 04/07/2007 8:01 PM by  okclarryd
Hip roof calculations?????
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drew32
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02/28/2007 12:47 AM

    Ok, I have a question on figuring the squares on a simple hip roof.

    In a pre-test for certification with a carrier there was a question involving a simple hip roof with a 10' extention.

    They wanted to know what the sf of the roof was and what the sf of the north and west slopes was.

    One method is the up and over. You take the length of house x rafter x 2 = total sf. and then take the extention length x the rafter length  and add to that = total sf quick and easy.

    or 40Long x  20Rafter x 2 = 1600 then add 10Long x 10Rafter x 2 = 200 + 1600 = 1800 sf.

    Another method is to break down the roof into 2 trapezoids 2 parallelograms and 2 triangles. (the 3rd triangle will be considered part of the south trapezoid)all the measurements of the individual shapes and add them up. I will call this the individual slope method.

    or 40Long + 18Ridge (top) / 2 x 20Rafter = 580 sf for the north slope. The south is the same.

    Now the triangle is 36Base x 20Rafter / 2 = 360 then the 10Long x 10Rafter parallelograms for the extentions = 100 sf  + 360 = 460 for the west slope. The east is the same.

    Now take the 580 + 460 = 1040 for the north and west or 2080 for the total.

    2.8 squares difference because the test question was an impossible roof.

    With a typical hip, with all slopes having the same pitch. These figures would match perfect and half of the roof would equal to the north and west slopes.

    The problem is that the roof that was drawn on the test could not be made with the given dimentions. There was 18' of ridge on the top of the large hip. The big hip was 40 x 36 with a 20 rafter and the rafter length was the same on all sides. The extention stuck out the south side 10 and had a 10 rafter length. The only way for that to be possible is with a 4' ridge along the top of the big hip(the difference between the long and short sides of a hip = the top ridge (that is basic geometry provided the rafte length is the same on all slopes). But with the "UP AND OVER METHOD" you get 18 squares on this roof. If you figure it using (INDIVIDUAL SLOPE  method you get 20.8 squares. This is the issue. The answer that was given was the 18 sq. But then if you figure up what is needed to cover only the north and west slopes it was deemed that the answer was 10.4 sq. At this point we were told that we are to figure an entire roof using the up and over method and use geometry to get only the 2 slopes.

    That does not  make sense to me. How would you answer the test question.

    Most of the younger guys say the 20.8 is correct with 10.4 for the 2 slopes only. I am a young guy and I agree with this.

    Most of the older guys say it is 18 for the whole roof and that the 10.4 is STILL correct. These guys are my superiors so I do not want to disregard the advice but I feel it is wrong. The class was divided on their opinions but the real question was how to figure the roof on the test. If it was drawn as a perfect roof, either way would work. If it is not a perfect roof , the Individual slope method would be the only accurate one. But the tester may be using the up and over method to figure it and count it wrong on the test. An actual roof would not be an issue. I am only bothered by the fact that the tests may be wrong and I don't want  to miss these questions because of a simple mistake by the one who wrote the test. How should it be figured?

    I like to see what your opinions are on this issue. Sorry the message is so long I was just trying to get all the facts in.

    Thanks and be safe.

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    HuskerCat
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    02/28/2007 1:35 AM

    You have gone back & forth here so much, I am getting confused.

    What is the length?

    What is the width?

    What are the slopes; (should be equal on a normal 20x40 hip)?

    What is the ridge length? This is only important because you have to replace ridge regardless, and ridge will have damage before anything else.

    Your 10' extension may be the issue... is it a gable over the front entry?  What are those dimensions?

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    stevebutler
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    03/03/2007 7:42 PM

    Drew,

    I'm not ashamed to mention carriers (sorry). I have certified with AmFam, Nationwide, Liberty Mutual USAA (failed) @ Farmers over the past year.

    Unfortunately, what you are describing is a problem that presents itself industry wide and not carrier specific. With every certification, the hip roofs are drawn incorrectly. The ridge length is NEVER accurate. A correct ridge length will be the major slope eave length, less the minor slope eave length. When the roof is drawn incorrectly, you are correct in saying that there are (2) possible correct answers for the same roof, depending on how it is calculated.

    The correct mathmatical way to calculate the roof area is by using the geometric shapes of all slopes, however, the industry accepted practice for calculating the roof area is "up & over". I was fortunate enough to have set in on a 3 day certification for AmFam. In the seminar, AmFam states that "up & over" is correct when calculating a full replacement. Nationwide wants geometric shapes calculated on partial slopes & "up & over" calculated on the full replacement. Even when 2 slopes which clearly make up 50% of the roof area exceeds 50% of the correct "full replacement" answer. (i.e. 10.4 vs. 18 sq.)

    I failed the USAA exam because I used the correct geometric calculation during the roof diagram portion. What I find unfortunate is that most carriers hand you an exam, stating that an adjuster with 3 years experience should know how to calculate, without telling you which method they prefer. More dissapointing is that the adjusters taking the test have figured out that the tests are incorrect, providing (2) possible correct answers and the ones making the tests can't figure this out.

    I realize that this discussion opens me up to dispute from other adjusters. So before you respond, draw a simple hip roof. 36' X 40', with a ridge length of 22' and a rafter length of 20' (all 4 sides) Now, calculate the sq. on one minor & 1 major slope. (10.2sq.). We ALL know that this is equal to 50% of the entire roof area. Now, calculate the roof as a full replacement "up & over" (40X20X2) = 16sq.. The reason 50% of the roof area does not equal 50% of the full replacement value is because the ridge length is not correct.

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    Brent_Young
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    03/04/2007 12:04 AM

    The up and over method always has a bit of extra sq ft but in this example, you have the up and over as 1800sf and the breakdown method as 2080 sf. I guess you have to consider this as a custom roof and use the breakdown per slope method.

    "Up and over", "perimeter times steepness" are estimating tools and "slope breakdown" is EXACT, which should be used for custom roofs.

    Do not forget you are also being tested on your ability to follow the directions of the test? DID IT SAY "USE THE UP AND OVER METHOD"?

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    CATdawg
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    03/04/2007 10:32 AM
    >>draw a simple hip roof. 36' X 40', with a ridge length of 22' and a rafter length of 20' (all 4 sides) Now, calculate the sq. on one minor & 1 major slope. (10.2sq.).<<

          I got 9.8 sq.: 

                               Minor slope: 1/2 x  (height x width of right triangle) x 2   =  1/2 x 20 x 18 x 2   =  360

                               Major slope: 1/2 x (ridge length + eave length) x rafter length   =  1/2 x (22 + 40) x 20  =  31 x 20  =  620

                               360 + 620 = 980 = 9.8 sq. 

         Interestingly, for the 36' x 40' perimeter with 20' rafters on all 4 slopes to be true, the top ridge would have to be 4 feet. The pitch would be 5 3/4" in 12". With the correct ridge dimension (4'), the "geometric" and "up-and-over" methods agree (1600 sq. ft).

         For the 22' ridge to be true with 20' rafters,  the perimeter would be 36' x 58'. Once again, both calculating methods reach the same number: 2320 sq. ft.

         It would be possible to build a roof 36' x 40' with 20' rafters on the two main slopes and a 22' ridge. But the two smaller slopes would need a longest rafter  
    length of 12.52 feet .
         QUIZ:  What is the pitch of the two smaller slopes?  What is the total amount of ridge shingles? What is the deviation between the two calculating methods?
    Lee Norwood, aka "CATdawg"
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    stevebutler
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    03/04/2007 10:51 AM
    Oops, 9.8 is correct, I was on the wrong diagram..... Anyway, you are correct on all counts. The ridge must be 4' if the rafters are 20' and the perimeter would be 36X48 with a 22' ridge. My point is that we as adjusters understand that the example I gave is an impossible roof and being so, would net (2) correct answers on a certification test. Since the test developers to not seem to know this, why do the carriers refuse to tell you which method they are looking for when giving the exams ? Would it not be easier if the test developer would just use a proportionatlely correct roof for testing ?
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    CATdawg
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    03/04/2007 11:22 AM

     
     Posted By steve butler on 03/04/2007 9:51 AM
     ...why do the carriers refuse to tell you which method they are looking for when giving the exams ? Would it not be easier if the test developer would just use a proportionatlely correct roof for testing ?

     

    Steve, I too am constantly amazed at the number of lapses of logic encountered in everyday life. I was recently asked by a vendor to submit an ID photo "1in. x 1.375 in .JPG format". This is a nonsensical spec...but the same request was sent to hundreds (thousands?) of people. I'm confident that the photo submissions  were of  many different sizes, since  digital photo files are measured in pixels, not inches. Indeed, we all later received slightly different instructions, which were still difficult to implement (and very expensive: Kinko's 2 x 2 passport photo $12.99, scanned to disk another $6.99, plus time and gasoline). To add to your above rhetorical questions, shouldn't those attempting to impose something like this on others be required to do it themselves first to see if it will work? Why make what should be a simple process for an experienced adjuster, capturing and resizing a photo of oneself (say, 300 x 300 pixels), an expensive and confusing ordeal?

    The fanciful or paranoid might be led to believe that management concocts these adventures in la-la land to evaluate how individuals react to certain situations. 

    A likelier explanation would be corporate inertia in the case of a faulty test question ("It's already on the disk, just print it out" or somesuch). My photo ID example is more probably due to some person or persons being assigned a project above their competency and not getting adequate guidance.

    >GULP<  Now I'll be branded as a troublemaker!     Oops! Off subject!

     
    Lee Norwood, aka "CATdawg"
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    Medulus
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    03/31/2007 12:28 AM

    I admit I had a bit of trouble understanding the first post in this thread.  Now I know why I didn't do better in the USAA test.  I passed it, but just barely.  It wasn't because I didn't know how to measure a roof.  It was because of an error in the test and the lack of explanation.  And it explains why the vendor was at a loss to even explain how one might pass it. 

    I hope someone is paying attention.  In the real world the up and over method is going to produce the same area or more than the geometric shape method, and the using the area of the geometric shapes is always going to be exact where the up and over is approximate, but close.  No roof in the physical world is going to give you such divergent dimensions using the two different methods.

    I hope someone who designs tests is paying attention.  Maybe we catadjusters are a little smarter than the bean counters give us credit for.

    Steve Ebner CPCU AIC AMIM

    "With great power comes great responsibility." (Stanley Martin Lieber, Amazing Fantasy # 15 August 1962)
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    HuskerCat
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    03/31/2007 2:17 AM

    Steven--

    You scared me there for a moment, with your self-doubts....but then you came through as you always do!

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    LarryW
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    03/31/2007 8:29 AM
    A hip roof has the exact same square footage as a gable roof covering the same structure as long as the pitch remains the same.
    No one is absolutely worthless, at the very least you can serve as a bad example.
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    RandyC
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    03/31/2007 9:33 AM
    Notwithstanding theoretical roofs with dimensions that don't match,  I keep hearing about the existence of roofs which figure differently  "up and over" vs. "geometric shape".  Since I can't know what I don't know, I have to allow for the possibility of things outside my experience.
    Could someone give an example of one of these much talked about exceptions? Thank you Randy Cox
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    RandyC
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    03/31/2007 10:19 AM

    ROFL Every time I try to edit my reply, I get one more box.  I'm going to quit before I have the entire web site boxed in.

    RandyC

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    StormSupport
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    03/31/2007 10:25 AM

    HAhahahahahahahha Randy!

    I thought that was some kind of test for the roof calculations!!! 

    Do the right thing, ALWAYS
    ~Meg~
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    stevebutler
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    03/31/2007 11:52 AM

    Randy, on 3/3, in the begining of this thread, I gave such an example. In fact, the example came directly from a recent Nationwide certification I attended.

    The example was as follows:

    a simple hip roof. 36' X 40', with a ridge length of 22' and a rafter length of 20' (all 4 sides)

     

    I understand Larry's logic that a hip roof with the same pitch on all slopes will net the same calculation with either method. What is being missed is that the examples given on the certification tests are IMPOSSIBLE roofs. There is NO logical way to build a roof of the size I just gave you... By using an impossible roof diagram, there will always be (2) correct answers. (1) using geometric shapes & another using "up & over". The test administrators do not tell you which method they want, they are assuming that as an adjuster, you know how to calculate a roof.
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    RandyC
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    03/31/2007 3:10 PM

    I've been drawing pictures of this roof all morning trying to unravel its mystery, but all I've got is a headache.  I got a 36 x 40 with a 22" ridge drawn, but it was hip on one end only.  I don't know what it  is on the other end.

    Instead of freeing my spirit, I've boxed myself in.    I'm still stuck on the arithmetic of the co-insurance example at the NFIP seminar.

    Randy Cox

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    host
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    03/31/2007 4:50 PM
    Randy I removed the boxes. It was making me dizzy. I'm looking into the problem with the quotes.
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    Buford Gonzales
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    03/31/2007 5:34 PM
    What came first, the Adjuster or the Adjuster Exam. I believe the exam begot the Adjuster and the Exam saw that it was good. And the Exam saw that the Adjuster was lonely so the Exam begot the Bad Faith Settlement and saw that the Bad Faith Settlement would lead to work. And the exam saw that that was good. The Exam then saw that it was to simple to be an Adjuster so the exam begot the Erroneous Question with no proper answer. And the Exam saw that this was good. And the Erroneous Question was asked and the Educated Adjuster got it wrong and the Dim Bulb from LA LA Land passed the exam and all was good. Fear not Brave Adjuster for you have answered the question correctly and the Dim Bulbs will feel justified in his passing of the Bad Faith Exam for the Bad Faith Insurance Carrier in the Land of Nod. And that is the way of the World.

    Next Week, Poncho and Cisco save Planet Earth from the Unethical Insurance Carrier with the obscene Profits
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    HuskerCat
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    03/31/2007 7:55 PM
    Posted By Larry Wright on 03/31/2007 8:29 AM
    A hip roof has the exact same square footage as a gable roof covering the same structure as long as the pitch remains the same.
    True, but the answer will be different. 


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    LarryW
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    03/31/2007 11:48 PM
    With the example given, the short side slopes would have to be on a steeper pitch than the long side slopes. This is why the parallelogram/triangle calculations yield a higher result than the length X width calculations. Is it possible that the test did not say all slopes were of equal pitch?
    No one is absolutely worthless, at the very least you can serve as a bad example.
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    rickhans
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    04/07/2007 4:54 PM

    Although this is different, it reminds me of an argument I had with a teacher in a graduate computer science course I took after getting my math degree.  The answer to a test question had to be either a 0 or a 1. I put down a 0 and slashed the zero using what was the industry standard at the time for denoting a 0 vs. the letter O.  0 was the correct answer but he marked it as wrong, using the argument that if the answer would have been "1", then I would have claimed that I had simply corrected the answer to be a 1 thinking he would be dumb enough to accept it. He also claimed that  the alpha letter O was to be slashed, not a zero even though every printer and most terminals at the time had a slashed zero.

    I dislike test makers who can't make accurate questions.  In my opinion, the example given above does not have 2 correct answers as some say.  The only correct answer would be that the drawing is wrong and could not be replicated in actual construction therefore is a trick question.  Since either the pitch is incorrect or the measurements given were incorrect, neither answer could be considered the "correct" answer without knowing  which  part  or the drawing was true.  In calculating a roof, there can never be more than one "correct" answer  which is the answer that gives the true amount of shingles needed to cover the roof.

    I have fought this battle in the past on some of my children's tests when an answer was marked wrong by the teacher but the question inself was faulty, or as in one instance, the teacher was unqualified to be teaching the course and could not answer the questions herself correctly.  It used to be that some teachers would allow for "throw away" questions, meaning that x number of questions answered "wrong" would be discarded before scoring to allow for faulty questions. 

    As to the last comment about a hip vs. gable, the square footage will be the same if the roof is a "true" hip with all 4 hip rafters meeting at the ridge, which means there is only one true and correct answer.  I personally calculate the different geometric shapes when it is other than a true hip in order to get the true number of squares.  I don't believe in doing approximations by rule of thumb.  I created a spreadsheet to enter all of the measurements, although on a real complex roof I sometimes use a calculater while on the roof to be sure I don't miss a measurement.

    In real life, however, the pitch sometimes does change on a roof.  I rebuilt one roof that a tornado tore off that turned out to be complex because the owner had us put a partial 2nd story on the house first.  The only way to tie the original roof in was to twist it, having a different pitch on each rafter.

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