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carpenters, gable roof experts, truss support Q's

Discussion in 'The Lounge' started by R72K5, Feb 5, 2005.

  1. R72K5

    R72K5 Banned

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    ok ive got a roof i need to put in purlins or whatever you call the pieces you run in triangle layout to help support or brace between ceiling joists and roof rafters

    i need ot know the best angle to put these in at in order to provide best roof weight support and anti-spreading of tops of walls

    exactly like this:
    http://www.carsondunlop.com/OBS/imagesreports/truss.gif

    i guess the ceiling joists and collar ties are what prevents spread,


    and i think that colllar ties are never used when vertical braces are used ?

    except for king posts,.

    right ?

    when to use what ?


    thanks
     
    Last edited: Feb 5, 2005
  2. sapper

    sapper 1/2 ton status GMOTM Winner

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    On a simple truss system like that we use a couple different pitch's. Usually for a 8-10 ft building a 4/12 is nice and around 12-15 ft a 5/12 will look good. I like the 5/12 which is 18 degress, you can use just one center post instead of the webbing in the pictures. If you spend a hour or so making up a jig on ply wood with 2x4 blocks to fit the components you can knock out all of the truss' you need in less than half a day and it cuts down on time arivation and varaition. A coupkle tools to get are a rafter square and a sliding t bevel, makes transfering angles real simle. Jope this helps a little
     
  3. Stickseler

    Stickseler 3/4 ton status

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    Exactly what (and why) are you trying to acomplish?

    Ceiling Joist are exactly that Ceiling..unless they clear span ext. bearing to ext. bearing they dont help wit wall spread and then you need a collar tie. These go in the middle or lower 1/3 of the roof perpendicular to the walls to prevent spreading of the walls and flattening of the roof.

    If your talking about increasing roof load ability it depends on how the the roof is built and the ceiling is built and what kinds of material and spans are used and wether or not you have a structual ridge or not. I would advise against putting a King post in if you dont have bearing directly underneath it to transfer the load to the foundation.

    Get more info like material spacing and spans and I can take a (not to be held liable) guess as to what will work. :grin:
     

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