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waterloocabin23
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# Posted: 1 Apr 2021 10:35am
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I'm planning a 16 by 24 cabin with a gable roof. Would like a 12/12 exterior pitch. Want a cathedral ceiling with no rafter ties. What is the maximum interior pitch with scissor trusses? I have seen some online that look steep inside - example Knottypinecabins.ca
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Nate R
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# Posted: 1 Apr 2021 11:27am
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Not sure on maximum, might depend on your snow load.
I got a quote a few years ago for 16' wide scissor trusses, 12/12 outside and 6/12 inside. Certainly looks like you could do at least 8/12 with that, but maybe even 10..... I just had asked for 6 in my quote.
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Brettny
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# Posted: 2 Apr 2021 08:16am
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Call the truss builder. They should have all the snow calculations and everything you need right there.
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ICC
Member
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# Posted: 2 Apr 2021 10:42am
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As brettny said, ask the truss company.
Scissors trusses are an engineering compromise. Unlike a standard truss with a full width bottom chord, a scissors truss does develop an outward horizontal force where the truss is attached to the wall tops. The amount of movement under load can be designed to be less or more. The snow load is one factor that needs to be designed for. Reducing the pitch of the interior makes it easier to reduce the outward force. Using larger wood components (2x8 instead of a 2x4 for example) in the main exterior pitch members helps.
I prefer to keep that outward movement under maximum design load down to 1/2". The first design out of the engineering software will usually have more than that but be cheaper than a better design.
Also ask the truss designer about how much insulation space they are having in the area where the outer and inner planes meet at the eve. A raised heel design will lift the truss to provide plenty of room for good insulation and venting. Talk about insulation and venting if needed now before the truss is designed, built and installed.
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