Replies

1. 
   Piffin | Sep 28, 2007 05:12pm | #1

   Could you explain what it is you are looking for?

   'design' to me would be if you want a scrolled shape on exposed ends, but you set this idea or word in opposition to the concept of engineering, then you say what size you are using, which is a large part of what engineering is.

   supposing that what you are really looking for is engineering, that is covered in tables for typical dimension lumber, but may not be instantly available for larger ones like you are specing.

   I would be very surpised to find any engineer anyplace that would OK rafters that size that could span 24 feet.
   However, it is possible that what you mean is that the building is 24' wide and the span from the structural ridge ( which would need engineering as well) to the loading wall is only 12'.

   ????

   so - please clarify wheather you are looking for free engineering or for design advise.

   And if engineering - then be more specific what the spans, pitch and location is. You also need to know what your local codes require for live loads - to carry snow or to resist wind. Some spouthern areas might still be only 15#/sf while some mountain areas are running 70-120#

    

    

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1. 
   Donnelly | Sep 28, 2007 05:20pm | #3

   Thanks for the message.  I did mean that the building is 24' wide with 12 foot walls and a loft floor, essentially making it 1 1/2 story. I was thinking 10/12 pitch, sheathed in 11/4" pine T&G.

   I live in Canada so there will be some snow load.  I was thinking of a kingpost-type design with a collar-tie at 8' above the loft floor.

1. 
   mike_maines | Sep 28, 2007 05:32pm | #4

   You say "loft"...does that cover all or only part of the second floor? 

   A collar tie 8' above the loft floor will do almost nothing for you.

   Canada's a big place...any idea what kind of snow load you have?

   Do you plan to have any insulation in the roof or will the rafters be exposed?

   With a king post and the bottom chord spanning 24', you are getting into custom territory...a couple hundred bucks spent on an engineer will be worth it. 

2. 
   CapnMac | Sep 28, 2007 06:37pm | #5

   I was thinking of a kingpost-type design

   So, what you really need is a practiced timber truss designer.

   A kingpost truss puts a center member right dead center of your "loft" space, which will divide the space you want to have into two spaces.

   So. I'm thinking you really need some form of queen truss, instead.

   But, I'm jsut words on the internet, and in Texas at that--as timber truss designers go, I'm only a hack architect.

   Could read this:  http://www.timber.org.au/resources/Revised%20Datafile%20SS7%2072dpi.pdfOccupational hazard of my occupation not being around (sorry Bubba)

1. 
   Piffin | Sep 28, 2007 06:56pm | #6

   yep - sounding more like custom timber truss 

    

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2. 
   Piffin | Sep 28, 2007 05:18pm | #2

   Another important point for engineering this roof is what species and grade of lumber these are.

   It sounds like you already have them, but I can get free engineering from the yard where I buy my lumber, they have the software that will run the numbers so I can compare between different products.

   Anytime it is a unique situation, I hire an engineer.

    

    

   Welcome to the
   Taunton University of Knowledge FHB Campus at Breaktime.
    where ...
   Excellence is its own reward!