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Thread: purlins

  1. #1
    Join Date
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    Default purlins

    Hello to all, this is my first post (new member). i am a new inspector down in Houston,Tx. My question is in regards to purlin requirements. I have inspected a few homes where purlin boards/support appeared to be missing! What is the code requirement for purlin installation? I know the size recommendation i.e. rafters. Do all roof structures need purlin support? Please see photo!

    Thanks
    Steve

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  2. #2

    Default Re: purlins

    Welcome Steve,

    This will partially answer your question: http://www.inspectionnews.net/home_i...e-purlins.html

    Added rafter support (e.g. purlins) is only required if the rafters can not span the entire distance on their own, kind of like determining whether another beam is needed for proper deck support.


  3. #3
    Ron Bibler's Avatar
    Ron Bibler Guest

    Default Re: purlins

    Steve always look at a roof from the out side and the inside.... 99% of older roof will have some kind of a dip in the roof line at one point or another.

    If you can see a dip in the roof you should point that out in your report.

    Best

    Ron


  4. #4
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    Default Re: purlins

    Quote Originally Posted by steve mcgown View Post
    Hello to all, this is my first post (new member). i am a new inspector down in Houston,Tx. My question is in regards to purlin requirements. I have inspected a few homes where purlin boards/support appeared to be missing! What is the code requirement for purlin installation? I know the size recommendation i.e. rafters. Do all roof structures need purlin support? Please see photo!

    Thanks
    Steve
    I would not expect to see a purlin with what you have in the picture.

    Scott Patterson, ACI
    Spring Hill, TN
    www.traceinspections.com

  5. #5
    Ted Menelly's Avatar
    Ted Menelly Guest

    Default Re: purlins

    Quote Originally Posted by steve mcgown View Post
    Hello to all, this is my first post (new member). i am a new inspector down in Houston,Tx. My question is in regards to purlin requirements. I have inspected a few homes where purlin boards/support appeared to be missing! What is the code requirement for purlin installation? I know the size recommendation i.e. rafters. Do all roof structures need purlin support? Please see photo!

    Thanks
    Steve
    A way to lock it in as far as possibly needing purlins and supports is after you walk the roof. If you are bouncing up and down as you walk there is way to much give and it should not move like that. Or if you step from one rafter to another on the roof and there is excess sag to the one you step to then that will tell you something as well.

    By the looks of that attic I would say that the 2x6 rafter is a minimum of 12 to 16 feet long. 12 feet is a pushing it to have acceptable deflection. 16 feet is way to far. High winds coming up through the eves and the roof bouncing in the wind could easily pull that roof of in a sustained higher wind. Wlaking on them over 12 feet long is stretching it as far as cracking one. It is not always something in a book that tells you to write something up. Just explain the condition you found while inspecting.


  6. #6
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    Default Re: purlins

    Quote Originally Posted by steve mcgown View Post
    Do all roof structures need purlin support?
    Thanks
    Steve
    Simple answer, no.

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  7. #7
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    Default Re: purlins

    Quote Originally Posted by Ted Menelly View Post
    A way to lock it in as far as possibly needing purlins and supports is after you walk the roof. If you are bouncing up and down as you walk there is way to much give and it should not move like that. Or if you step from one rafter to another on the roof and there is excess sag to the one you step to then that will tell you something as well.

    By the looks of that attic I would say that the 2x6 rafter is a minimum of 12 to 16 feet long. 12 feet is a pushing it to have acceptable deflection. 16 feet is way to far. High winds coming up through the eves and the roof bouncing in the wind could easily pull that roof of in a sustained higher wind. Wlaking on them over 12 feet long is stretching it as far as cracking one. It is not always something in a book that tells you to write something up. Just explain the condition you found while inspecting.
    I think you're confusing length and rafter span, Ted.

    Here's a clickable link to the American Wood Council's joist & rafter Maximum Span Calculator (its set to default with #2 SYP but you're free to change any of the settings and values): Maximum Span Calculator for Joists & Rafters

    Last edited by H.G. Watson, Sr.; 01-12-2011 at 04:28 PM.

  8. #8
    Ted Menelly's Avatar
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    Default Re: purlins

    Quote Originally Posted by H.G. Watson, Sr. View Post
    I think you're confusing length and rafter span, Ted.
    From the top plate to the ridge seems as though it would be stretching the span a bit for a 2x6....or from top plate to ridge that rafter length seems a little on the long end for adequate support without undo deflection

    Kinda goes hand in hand...I know, I know...proper terminology.

    In any case bounce on the roof. If you have lots of bounce..no good. If rafter cracks or breaks, no good. A lot of sag when stepping directly on the rafter, no good. The roof should feel nice and stiff. I doubt it does as it is.

    If in fact it is a least 12 feet and I do believe it is that or more, it needs support seeing how it is a 2x6


  9. #9
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    Default Re: purlins

    Ted, rafter spans are determined horizontally.


  10. #10
    Join Date
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    Default Re: purlins

    Quote Originally Posted by H.G. Watson, Sr. View Post
    Ted, rafter spans are determined horizontally.
    I'm impressed HG, you said that without calling him an idiot! Been "working" with Brian on your anger management issues?


  11. #11
    Ted Menelly's Avatar
    Ted Menelly Guest

    Default Re: purlins

    Quote Originally Posted by Benjamin Thompson View Post
    I'm impressed HG, you said that without calling him an idiot! Been "working" with Brian on your anger management issues?

    HG is just a stickler on terminology. Yeah he is right but anything crossing an open area, trench ditch, top plate to ridge, one side of the river or another, spans that void, expanse, whatever but also has a particular length to it. I know why he is saying it and I also Know HG.

    Use the term that fits the item one is referring to.

    I got it HG


  12. #12
    Join Date
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    Default Re: purlins

    He's absolutely right, span of a rafter is not measured ridge to wall, but I'm surprised HG called it out so civilly! I was commenting on his change of attitude, not his correction. Nothing wrong with correcting a mis-statement if it is done politely.


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