Expand existing loft hatch

Discussion in 'Carpenters' Talk' started by jamime, Jan 18, 2019.

  1. jamime

    jamime New Member

    I'm expanding my existing loft hatch to install a Keylite KYL07 loft hatch & ladder.
    The roof joist on left of image is 65mm wide.
    The ceiling joists are 50mm wide.

    The new hole will be 1000mmx700mm and I will be widening the hole in the image up, down and to the left. So keeping the ceiling joist on the right.

    My plan is to use 100x47 c16 treated timber for all new wood work. There will be two new joists on the top and bottom of the opening (red) and one on each sides to attach the lining.

    What is the best fixings to use? I will be putting a PSE lining around the opening so the finish needs to be flush.

    I read on DIY doctor Number 8 4 inch which I think translates to approx M5 screws.
    I've also read recommendation on using coach screws with a timber connector.
    There are also joist hangers and L brackets, but not sure how these would cope with double width joists.

  2. Jord86

    Jord86 Well-Known Member

    Number twelve (pozi 3) Wurth 100mm screws is what I would use, fit your doubled up trimmers as singles first as you can get a good fixing through and into the ceiling joists through the trimmer, then screw the second one to the first. I would look to double up the side ceiling joists that are taking the trimmers and hatch if possible, just a length spanning over the upstairs walls would be OK, doesn't have to go to wallplates. You can get double and triple width joist hangers. Support the joists you are cutting before you trim them. PSE lining can be pinned on, so that's irrelevant really.
  3. jamime

    jamime New Member

    Thanks @Jord86 I couldnt find the wurth ones on screwfix but I did find GoldScrew PZ M6x100

    The ceiling joists at the bottom of the image I can double up. At the top of the image the nearest wall is the external one so I would have to run it to the wall plate. Is this what you would do, or is it overkill?
    I've put an image below, ceiling joist is in purple, roof joist is in blue.

    The new stringers going from left to right, would you terminate the trimmers before the roof joist (option 1) or connect it to the roof joist (option 2).
    I've included another image so you can see the roof structure.

  4. Jord86

    Jord86 Well-Known Member

    Why do you need to cut the one side, the joist centres are roughly 400mm/16" centres aren't they? Why can't you turn the trap the other way and limit the cutting of ceiling joists?
  5. jamime

    jamime New Member

    Staircase newel post is in the way, wouldn't be able to extend the ladder :( In the orientation I have suggested the ladder would extend onto the landing, rotating it would mean it would end on the stairs if the newel wasn't in the way
  6. jamime

    jamime New Member

    @Jord86 what do you think attach stringer to roof joist or stop short?
  7. Jord86

    Jord86 Well-Known Member

    Your roof joist is part of an A frame/King post/Queen post/can't tell from your picture truss, yes you need to connect the trimmers to this. Your first photo didn't give this detail, you need the trimmers to connect to it otherwise it's all floating and you'll be in shitt street. Use joist hangers. Double up the ceiling joist the trimmers are going into on the right hand side of the photo if you can, screw a new 4x2 or whatever the timber is alongside.

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