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  1. #1
    Join Date
    Mar 2007
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    Tampa, Fl
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    155

    Default Angle of Purlins

    Are these purlins angled too much? What's the rule of thumb? Looks like a post-fire retrofit due to the paint/charred rafters.

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  2. #2
    Brandon Chew's Avatar
    Brandon Chew Guest

    Default Re: Angle of Purlins

    The purlin (the board running perpendicular to the rafters) needs to be sized no less than the required minimum size of the rafters they support. The one in your photo may be too small. It should also be installed with its edge bearing against the rafters, not flat as in the pic.

    The braces can be 2x4s, must go from the purlin to a bearing wall, can't be more than 4 ft on center, if longer than 8 feet they need to be braced, and the angle between the brace and the ceiling joists must not be less than 45 degrees.

    Refer to IRC 802.5.1


  3. #3
    Jon Randolph's Avatar
    Jon Randolph Guest

    Default Re: Angle of Purlins

    I call them out if they are not close to perpindicular with the rafter.


  4. #4
    Join Date
    Mar 2007
    Location
    Healdsburg, CA
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    1,741

    Default Re: Angle of Purlins

    No rule of thumb, but code complying:
    IRC-R802.5.1 Purlins: Installation of purlins to reduce the span of rafters is permitted as shown in Figure R802.5.1. Purlins shall be sized no less than the required size of the rafters that they support. Purlins shall be continuous and shall be supported by 2-inch by 4-inch braces installed to bearing walls at a slope not less than 45degrees from the horizontal. The braces shall be spaced not more than 4feet on center and the unbraced length of braces shall not exceed 8 feet.

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  5. #5
    Join Date
    Mar 2007
    Location
    Ormond Beach, Florida
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    25,314

    Default Re: Angle of Purlins

    Unless the UBC says something different than the IRC, I've corrected that drawing.

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  6. #6
    Join Date
    Mar 2007
    Location
    Healdsburg, CA
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    1,741

    Default Re: Angle of Purlins

    Caught redhanded! The 2x6 purlin brace is history in the CBC 2007.

    Jerry McCarthy
    Building Code/ Construction Consultant

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