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Rafter specification help

  • 08-05-2008 11:01am
    #1
    NovaGSi
    Closed Accounts Posts: 254 ✭✭


    Good afternoon,

    what size rafter should I use for a span of 4m. The roof is a vaulted (I think that is what it is called) type, there are no trusses.

    Cheers,
    Mick


Comments

  • #2
    sydthebeat
    Subscribers Posts: 42,171 ✭✭✭✭sydthebeat


    is it 4 m between wall plate and ridgeboard???

    do we assume no intermediate support...

    To be on the safe side id go with 44 x 175 C16 at 400 c/c..... you may get away with C14, but id stick with C16....


  • #3
    NovaGSi
    Closed Accounts Posts: 254 ✭✭NovaGSi


    Yes, 4m between wall plate and ridegboard.

    Yes, no intermediate support.

    How can I be sure that the timber is C16?

    Thanks for the quick response

    Cheers,
    Mick


  • #4
    sydthebeat
    Subscribers Posts: 42,171 ✭✭✭✭sydthebeat


    it should be stamped C16 mick.... It should also be stamped with an IS 444 mark.. this is proof of the certification of the timber... it may also be stamped GS, SS, NS or RS... if its C16 Spruce it will probably be stamped NS, which means 'normal structural' strength grade.


  • #5
    jjahbss
    Closed Accounts Posts: 5 ✭jjahbss


    If your putting in a vaulted ceiling, you might need a ridge beam rather than a ridge board. Your biggest problem will be the threat of roof spread rather than the rafters deflecting. With the vaulted ceiling you will not be triangulating the roof and it is likely to spread as a result if an adequate ridge beam is not used. How long is your ridge, and is it running from a load bearing wall into a load bearing gable? It is likely that you will need an RSJ to act as your ridge beam to eliminate the threat of spread.


  • #6
    muffler
    Registered Users, Registered Users 2 Posts: 46,553 ✭✭✭✭muffler


    Rafter/wallplate detailing would be more than important than the ridge


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  • #7
    Mellor
    Registered Users, Registered Users 2 Posts: 39,902 ✭✭✭✭Mellor


    I'd fit a collar


  • #8
    sinnerboy
    Closed Accounts Posts: 5,433 ✭✭✭sinnerboy


    jjahbss wrote: »
    If your putting in a vaulted ceiling, you might need a ridge beam rather than a ridge board. Your biggest problem will be the threat of roof spread rather than the rafters deflecting. With the vaulted ceiling you will not be triangulating the roof and it is likely to spread as a result if an adequate ridge beam is not used. How long is your ridge, and is it running from a load bearing wall into a load bearing gable? It is likely that you will need an RSJ to act as your ridge beam to eliminate the threat of spread.

    100% agree

    also - use 225 x 50 rafters - not for structural reasons , but to maximise space for insulation

    see here

    http://www.boards.ie/vbulletin/showthread.php?t=2055291606


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