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Doubling rafters for new velux

Discussion in 'Building' started by keilo, 31 Mar 2012.

  1. keilo

    keilo

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    Hello,

    I have a mid terrace house which has one purlin on front and one on the rear. I wish to install a couple of veluxs, and am planning to re-enforce the existing rafters for trimming around the new velux.
    Now this is all above the purlin, but do i need to continue re-enforcing the rafters below the perlin, i.e. into the eaves area? or is above the purling, and fixing into the purlin adequate?

    Thanks
     
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  3. ^woody^

    ^woody^

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    Just between the purlin and ridge
     
  4. keilo

    keilo

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    Cheers Woody! :D
     
  5. Alphadock

    Alphadock

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    How did you get the new rafters behind the purlin? Is this possible without removing the roof covering?
     
  6. RNReindeer

    RNReindeer

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    With a fair bit of fiddling and wriggling.
    It might be easier to turn the sister rafter through 90degrees to fiddle it in, so you have more space/room for fiddling, then twist it back to it's correct oientation when it's properly located.
    There's usually sufficient flex in the lathe to allow it to be rotated, but maybe not right alongside the original rafter initially.
     
  7. Alphadock

    Alphadock

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    Thanks RNreindeer,
    However the issue is the length not the depth of the rafter.
    The only option I can see is splicing, but this would have to be mid span, not over a structural member.
    Do you know if there is an exceptable way to do this?
     
  8. RNReindeer

    RNReindeer

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    Maybe it will fit in lower down the roof, then you can slide it up to the correct position.
    Don't forget it only has to be just long enough, between the two purlins or the purlin and ridge, so you can often get it in on an angle at first. If at the end of the day, you still can't get it in, then you're going to have to remove some of the roof covering when you're installing the velux, and position the sister rafter then.
     
  9. Alphadock

    Alphadock

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    Between lower and upper purlin is the longest span, so sliding up from elsewhere isn't possible.
    It may just work on the diagonal but the rafters are at 330 centres so might not quite be enough!
    Removing the roof covering is what I'm trying to avoid.
    Do you know about splicing the rafter?
     
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  11. RNReindeer

    RNReindeer

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    No, sorry. Ask on the roofing forum.
     
  12. jeds

    jeds

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    What size Velux are you fitting? If you are only cutting out one rafter I doubt you would need to double up.
     
  13. Alphadock

    Alphadock

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    2 rafters per window
     
  14. jeds

    jeds

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    Still might be worth working it out. The Velux isn't the issue - it weighs about the same or less than the roof it replaces. The issue is transferring load from the cut rafters to the side rafters. Calculate the load for the area between the cut rafters and divide by two. Find the load table for that particular load per metre and check your existing rafters. If the spans are short (which they usually are when divided by purlins) I'd bet your existing rafters will be within the allowable span.
     
  15. Alphadock

    Alphadock

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    Thanks John,
    How do I find the weight of tiles and close board?
    And where can I find the load rating table? I've only seen span tables before, no mention of the actual weight that they can carry.
     
  16. theprinceofdarkness

    theprinceofdarkness

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    The strength of a 4" X 1" plank is 1/2 that of a 4" X 2" but a lot easier to twiddle from flat to upright. Just use two of them and really surprise the roofers here, use glue as well !!
    Frank :)
     
  17. DIYnot Local

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