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  1. #1
    Join Date
    Feb 2008
    Location
    Toronto, Ontario Canada
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    21

    Default Irregular/Bastard Hip Roofing Help

    Greetings;

    Just joined today, after reading numerous threads about irregular hip roofs.
    Incredible just how much everyone knows! Great forum.

    Anyway, I am a professional renovator (Jack of all trades, master of none) who's trying to frame out an irregular hip roof on an addition to my own house. Although I have intermediate carpentry/math skills, I cannot figure out just how to finish the roof. I have searched the internet and read books, but can't find an answer that completely solves all the variables involved.

    For all you master carpenters out there - and Joe Bartok's - here is my problem which I would REALLY like a STRAIGHTFORWARD answer to (I am about to eliminate the hip and continue the gable to the end, which of course will not blend well with my house.)

    Situation:
    -gabled extension perpendicular from the house, pitch is 3.5/12 to match house. The rafters and ridge are up for this section. The theoretical ridge height is 40.8 inches and my major run is 139.875 inches.
    -the roof ends with a hip that is supposed to be 6/12 per drawings. (minor)
    -using a construction master calculator and scientific (trig) calculator, I have figured out all the math (I think!). Haven't had to do this much math in 20 years!
    -PROBLEM: I can't seem to find a way to match up the soffits/facia between the two pitches. My desired soffit overhang is 12", the sheathing angles are obviously different between 2 pitches
    (ie. after following my calculations, info on the net, the facia on the 6/12 rafter tails are about 3.5 inches lower than the 3.5/12 major roof pitch.

    Can anyone help? My wife is about to kill me, what with all my wining and time spent on this problem. Been going thru a lot of beer too.

    Thanks, Renovator4

  2. #2
    Join Date
    Jan 2006
    Location
    Houston,Texas
    Posts
    644

    Default Re: Irregular/Bastard Hip Roofing Help

    Renovator,

    If you want to keep equal overhangs, raise the plate for the 6/12 side and shift the hips accordingly.

  3. #3
    Join Date
    Jun 2004
    Location
    Port Orchard, WA
    Posts
    2,636

    Default Re: Irregular/Bastard Hip Roofing Help

    Can you post some pictures of what you've got going? That usually helps, plus it makes explaining much easier.

    Another reason for pictures and/or drawings is that when people search the threads later, they will understand how to solve the problem much more quickly. . . . . . and possibly with less beer :-)

    Tim

  4. #4
    Join Date
    Jun 2004
    Location
    Caldwell, NJ
    Posts
    3,153

    Default Re: Irregular/Bastard Hip Roofing Help

    Quote Originally Posted by renovator4 View Post
    Greetings;

    Just joined today, after reading numerous threads about irregular hip roofs.
    Incredible just how much everyone knows! Great forum.

    Anyway, I am a professional renovator (Jack of all trades, master of none) who's trying to frame out an irregular hip roof on an addition to my own house. Although I have intermediate carpentry/math skills, I cannot figure out just how to finish the roof. I have searched the internet and read books, but can't find an answer that completely solves all the variables involved.

    For all you master carpenters out there - and Joe Bartok's - here is my problem which I would REALLY like a STRAIGHTFORWARD answer to (I am about to eliminate the hip and continue the gable to the end, which of course will not blend well with my house.)

    Situation:
    -gabled extension perpendicular from the house, pitch is 3.5/12 to match house. The rafters and ridge are up for this section. The theoretical ridge height is 40.8 inches and my major run is 139.875 inches.
    -the roof ends with a hip that is supposed to be 6/12 per drawings. (minor)
    -using a construction master calculator and scientific (trig) calculator, I have figured out all the math (I think!). Haven't had to do this much math in 20 years!
    -PROBLEM: I can't seem to find a way to match up the soffits/facia between the two pitches. My desired soffit overhang is 12", the sheathing angles are obviously different between 2 pitches
    (ie. after following my calculations, info on the net, the facia on the 6/12 rafter tails are about 3.5 inches lower than the 3.5/12 major roof pitch.

    Can anyone help? My wife is about to kill me, what with all my wining and time spent on this problem. Been going thru a lot of beer too.

    Thanks, Renovator4
    Assuming your 139.875" run is with 1/2 the ridge thickness deduction, your total run including the 12" overhang is 151.875" for the 3.5/12 side.

    That will give you a total run including the 12" overhang of 88.59375" giving you the run to the plate of 76.59375".

    The hip will offset to the 6/12 side 8-9/16" and you raise the plate on the 6/12 side 2.5".

    Your 40.8" for a theoretical ridge height doesn't include the H.A.P. cut of the rafter. That would have to be added on to get to the top of the ridge.
    Joe Carola

  5. #5
    Join Date
    Feb 2008
    Location
    Toronto, Ontario Canada
    Posts
    21

    Default Re: Irregular/Bastard Hip Roofing Help

    Hi KPatrix & Tim;

    Thanks for replying. I can't provide pictures, as my wife has the digital camera and is out of town.

    It's a pretty simple situation. The gabled roof is 3.5/12 with a hip that is supposed to be 6/12. I just finished trying to raise my plate in order for the rafters on both pitches to have the same soffit/facia height. Now the 6/12 irregular rafters won't meet the hip.

    Quick question - towards which part of the roof is my hip supposed to swing towards now? I had it angled to the lower pitch major roof 3.5/12. If it's supposed to be on the side of the 6/12, how do I handle it once I've raised my HAP using 2, 2x6's and a 1/2 ply? (3.5" to give me equal facia heights).
    This is the root of the problem I'm having.

    Thanks - hope it's not snowing where you are in the States! (this is why there's beer involved - it's snowing on me and well, I am Canadian :)

    Renovator4

  6. #6
    Join Date
    Feb 2008
    Location
    Toronto, Ontario Canada
    Posts
    21

    Default Re: Irregular/Bastard Hip Roofing Help

    Why didn't I join this sooner?!!!!

    Thanks, Joe. I apologize, but the major run (for 3.5/12 roof) was 139.875" on center, so less 1/2 the thickness of the 2x8 would equal 139.125".

    By raising the plate on the 6/12 hip, how does this affect where my hip is placed and the angles involved?

    Cheers,

    Greg aka "Renovator4" (should have picked a better handle)

  7. #7
    Join Date
    Jun 2004
    Location
    Caldwell, NJ
    Posts
    3,153

    Default Re: Irregular/Bastard Hip Roofing Help

    Here's a quick drawing to get you started using a 2x for a ridge.
    Attached Images Attached Images
    Last edited by Joe Carola; 02-26-2008 at 03:56 PM.
    Joe Carola

  8. #8
    Join Date
    Mar 2005
    Location
    Sol III
    Posts
    1,935

    Default Re: Irregular/Bastard Hip Roofing Help

    Quote Originally Posted by renovator4 View Post
    -the roof ends with a hip that is supposed to be 6/12 per drawings. (minor)
    Quote Originally Posted by renovator4 View Post
    By raising the plate on the 6/12 hip, how does this affect where my hip is placed and the angles involved?
    Not to be picky, but I hope the “6/12” Hip is a typo and this means the slope of the roof. One roof slope is already 3.5/12 and a Hip rafter is less than either of the two roof slopes (14.14057° or a hair under 3 1/32 over 12 for your 3.5/12 and 6/12 combination of slopes).


    Quote Originally Posted by renovator4 View Post
    Quick question - towards which part of the roof is my hip supposed to swing towards now
    There is no “swing”, that would be a Radial Shift. There are times when this is appropriate but (if I'm reading your post correctly) this is not what is happening here.

    The adjustment is made laterally: Parallel Shift. Here’s another link to some example Valley Soffit Overhang Calculations … think of the Valley as an “upside down” Hip to help visualise which way the rafter is being shifted/raised.
    Last edited by Joe Bartok; 02-26-2008 at 04:04 PM.
    "I cannot teach anyone anything; I can only make them think." - Socrates

  9. #9
    Join Date
    Feb 2008
    Location
    Toronto, Ontario Canada
    Posts
    21

    Default Re: Irregular/Bastard Hip Roofing Help

    Hi Joe;

    Sorry about the typo about the hip being 6/12. Fingers getting cold :)

    So, if I raise my plate on the 6/12 side of the roof (hip side of the roof) up 2.5", then ADD the birdsmouth cut required to correctly seat onto a 2x6 plate (ie, 5.5" wide) AND have my hip rafter placed 8-9/16" (center of hip rafter?) on the 6/12 side this should all tie together?

    I already have my plate raised 3.5" on the 6/12 (hip) side by the way. Scary.

    Man, I feel like I'm being a pain in the @#$@, but really need this done.
    Thanks for your help!

    G - Renovator4

  10. #10
    Join Date
    Jun 2004
    Location
    Staten Island, NY
    Posts
    534

    Default Re: Irregular/Bastard Hip Roofing Help

    R4,

    I seem to see this the opposite of how Joe C sees it. I have the steep side to the back of the hip, since you said that the "gable" was equal to the main house pitch of 3.5/12. If that's the case you'll need to extend the ridge as well by 5".

    Also since no one has told you how to get this numbers. . .

    The plate rise is just the difference in pitches for any 12" overhang. If your overhang is less than of greater than 12" you would need to multiply your overhang by the (difference of pitches)/12 to get the plate rise.

    To get the hip offset just divide the plate rise by the ratio of the smaller pitch 2.5" / ((3.5)/(12)) = 8.57" or 8-9/16"

    To find the ridge extension it's just a matter of dividing the plate rise by the steep pitch ratio (2.5") / ((6)/(12)) = 5"

    The last thing is the hip shortening which is just the hypotenuse of a triangle with a 8-9/16" run and a 5" rise or 9-15/16"L
    Last edited by Joe Fusco; 02-26-2008 at 06:19 PM.

  11. #11
    Join Date
    Sep 2005
    Location
    Washington, DC
    Posts
    4,685

    Default Re: Irregular/Bastard Hip Roofing Help

    With several replies, this may or may not help...

    Your 6/12 rafters will be 2 1/2" higher than the 3.5/12 rafters, at exactly the point where they meet the outside face of whatever they will bear on. If you were to draw a plumb line at the outside face of the bearing plate, to the top of the rafters, if that plumb line is 12" from the outside face of the fascia, measured horizontally, the 6/12 rafters will be 2 1/2" higher at that point.

    You can add 2 2x's to your plate for that side, and reduce the HAP 1/2".

    There's a lot more to it...

    Does that make sense?

    Tom

    The hip will swing toward the steeper roof, btw.
    1) Unconsciously Incompetent: He knows not, and knows not that he knows not. He is a fool. Shun him.
    2) Consciously Incompetent: He knows not, and knows that he knows not. He is simple. Teach him.
    3) Unconsciously Competent: He knows, and knows not that he knows. He is asleep. Wake him.
    4) Consciously Competent: He knows, and knows that he knows. He is wise. Follow him.

    May we all endeavor to progress from not knowing that we know not, to knowing that we know.

  12. #12
    Join Date
    Feb 2008
    Location
    Toronto, Ontario Canada
    Posts
    21

    Default Re: Irregular/Bastard Hip Roofing Help

    Thanks, Team "Joe"!

    Yes, Joe F., I was a little confused by Joe C's interpretation, but given that I didn't supply any pictures or drawings, I don't hold any blame.

    Thank you for actually showing me how those numbers are derived. Refreshing! I did, actually, keep my ridge long on purpose, since I first attached the common rafter on the 6/12 minor pitch to the ridge beam after raising the plate. If I used the numbers from the construction master calculations, I would have cut the ridge too short. These are things that I believe people should know (I haven't turned up a lot of info on raising the plate...)

    One last question for today. If I raise the plate accordingly on the 6/12 side, and the hips are placed here as well (8-9/16" in from each corner), do I assume that the hip rafters are NOT raised and are indeed placed on the original top plate of the wall? Also, I am using a cheek cut at the top of the hip rafters of 30.26 degrees. Once I put up the 2x8 hip rafter (just to see how things are going) I cannot see how, given that angle, they land on the 6/12 side of the roof (especially 8-9/16" in!).

    Would you please explain?

    Once I get this figured out and constructed, I will post a summary on all the steps involved so anyone else - anywhere - can do it.

    Until then, please stay posted! Thanks for everything thus far.

    G- Renovator4

  13. #13
    Join Date
    Jun 2004
    Location
    Staten Island, NY
    Posts
    534

    Default Re: Irregular/Bastard Hip Roofing Help

    R4,

    The answer is. . . it depends. The plates are raised to keep the HAPS the same on all the members. If you want to cut all the HAPS the same then the hip sits on the raised plate. If you use an oversized hip and decrease it's HAP by 2-1/2" then no it doesn't.

    The plumb cut on the hip is like a 3/12 (14.15°) and not 30° so you'll need to recut it.

  14. #14
    Join Date
    Sep 2005
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    Washington, DC
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    4,685

    Default Re: Irregular/Bastard Hip Roofing Help

    I find out the hip's plumb-line length, which is dependent on how big the hip is, and both pitches. Take 2/3 of that, and that's what I try to make the HIP'S HAP. Since it sits on the wall with the raised plate, I'll compare that "ideal" HIP HAP to the 6/12 rafter's HAP. Then adjust the raised plate accordingly right where the hip sits. Sometimes that will mean only 1 2x plate under the hip, instead of 2.

    This is not the easiest thing to explain in just words.

    Tom
    1) Unconsciously Incompetent: He knows not, and knows not that he knows not. He is a fool. Shun him.
    2) Consciously Incompetent: He knows not, and knows that he knows not. He is simple. Teach him.
    3) Unconsciously Competent: He knows, and knows not that he knows. He is asleep. Wake him.
    4) Consciously Competent: He knows, and knows that he knows. He is wise. Follow him.

    May we all endeavor to progress from not knowing that we know not, to knowing that we know.

  15. #15
    Join Date
    Feb 2008
    Location
    Toronto, Ontario Canada
    Posts
    21

    Default Re: Irregular/Bastard Hip Roofing Help

    Thanks, Tom!

    You are confirming what I am beginning to think - that framing out an irregular hip is a mixture of calculations/formulas and versatile carpentry.
    (kind of like Einstein with a wormdrive :)

    Just to note Joe's mention of the plumb cut. I agree it's supposed to be around 14.14 degrees. What I meant was the cheek cut on the 6/12 side of the hip rafter. I thought it was supposed to be 30.26, but I can't see how that will make it land almost 9" in from the outer corner on the 6/12 side top plate....I guess I'll try it out in the morning.

    Signing off for now - I will check back in/bug you all tomorrow!
    Thanks again everyone, have a great evening!

    Renovator4

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