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how do I calculate roof slope for carport

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  1. #1
    DNL
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    Default how do I calculate roof slope for carport

    GDay all

    I am about to build my skillion roof carport which is 7m along the lenght of the house and 5.5m across the driveway. In the plans the maximum roof slope is 5 degrees.

    So how do I calculate the fall across the 5.5m.

    I seem to recall a builder telling me there needed to be a 20mm drop for every metre of roof length. This would mean the roof fall is 110mm. But I would like to know how it is calculated so I don't exceed the 5 degree slope.

    cheers and any advice - formulas and explanations greatly appreciated.
    Dave

  2. #2
    Old Chippy - 4K Club Member
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    Default

    Go to this site - sure to be a calculator for what you want:
    http://www.blocklayer.com/Roof/

  3. #3
    Apprentice (new member)
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    5 degrees works out to 88 mm rise per metre run so the rise over 5500mm is 484 mm

  4. #4
    Senior Member
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    Don't forget there is also a minimum drop for different roofing iron

  5. #5
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    I think if you read your plans you will find it say minimum fall. For custom orb the minimum is 5 degrees and for trimdeck it is 2 degrees minimum

  6. #6
    DNL
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    cheers fellas

    WACanetoad....I found detail on the Lysagth web site which indicates trimdeck has a minimum 2 degree slope or 1:30 fall. On 5.5 metre this comes out to 183mm fall. My rear verandah was 1:50 and it floods off. Its not trimdeck but similar with a larger profile. I think I might adjust to 1:50 as this is a 110mm fall and will work just as well.

    regards and thanks for responses.
    Dave


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