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Bolting doubled up rafters and trimmers?

Discussion in 'Building' started by xdrive, 21 Feb 2021.

  1. xdrive

    xdrive

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    Hi.

    I have made a roof with the velux openings.

    Both trimmers and rafters have been doubled up.

    I have screwed them together and used joist hangers where needed.

    What is purpose of bolting them when the rafters run full span and the trimmers all sit in hangers?

    I have screwed them with normal wood screws.

    I can understand bolting when extending a joist but not in this case.

    Maybe I'm being stupid.

    Please enlighten me.

    Thanks
     
    Last edited: 21 Feb 2021
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  3. catlad

    catlad

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    No need to bolt them together in your case.
     
  4. noseall

    noseall

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    We use 100mm 6's screws staggered up the length. You may have to fix these at a slight angle to prevent the sharp end poking through. If you can get 90mm 6's use them.
     
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  5. xdrive

    xdrive

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    I'm one step ahead I've been using 80mm :)

    So bolts are only necessary for sistering joists or where loads are going to be higher such as trimmers for staircases?
     
  6. noseall

    noseall

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    .
    Bolts are better and more durable as screws are brittle and can snap. I've not seen a grade 6 snap though.
    Yes I'd agree that loads and importance coupled with common sense.
    A doubled up rafter will be connected with roof batten and often with ceiling board and is unlikely to misbehave even without any screws.
     
    Last edited: 22 Feb 2021
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  7. ^woody^

    ^woody^

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    The purpose of any fixing is to transfer the loads equally between each timber so that it acts as a single component.
    How that is done does not really matter as long as the performance is there.

    Sometimes, individual timbers can bow or bend over time and screws may not be good enough to stop that unless there are loads of them.
     
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