Are my loft joists too skinny?

Discussion in 'Builders' Talk' started by Mohai, Nov 25, 2019.

  1. Mohai

    Mohai New Member

    Hi all,
    I've read most the loft posts here that seem relevant to me.
    I have a house built in 1919 and want to use the attic for storage.
    The first job is to increase the hatch size to install loft ladders as it's currently in between joists.

    I think I've worked out what to do for increasing the hatch size (see below) but I'm not sure on the second part of the job - boarding over the 270mm insulation.
    _____________________________________________________

    Joist size

    The joists are 6" x 1.1" = 150mm x 30mm. Most the forum posts are referring to 4x2s or 3x2s. I've not seen anyone talk about joists at a size similar to mine!

    When it comes to cross battening joists at a 90 degree angle, with 4x2s or 6x2s, would that be too big for these skinny ones to support?
    _____________________________________________________

    Hatch hole increase (pics not to scale!)

    First image:
    Loft 3.png

    Original hatch is between E and F
    I'd screw some timber (G1 and G2) before cutting the red lines.
    Second image:
    Loft 4.png

    What I'd expect after cutting.
    Third image:
    Loft 7.png

    It looks like the general consensus is to double up for where you've cut, in that case the frame would be made up from - G1, F1, G2, F2, H1 and H2
    (these would have to be 6 inches in height to be flush with the current joists? So probably using 6x2s?

    Thanks.
     
  2. rogerk101

    rogerk101 Well-Known Member

    Wherever you've read about doubling up the joists, they meant doubling them for their full length ... not just in the newly created opening. The sleepers should be doubled up in the newly created opening, but the joists need to be doubled from one supported end right the way across to the other supported end.
     
  3. Jitender

    Jitender Well-Known Member

    Post some pictures.

    What is the dimension of G1 and G2.

    It's a lot to do with spans.
     
  4. Mohai

    Mohai New Member

    Ok I didn't know that, cheers.

    So I'd be free to use anything for G1 and G2, maybe 4x2s. After it's all done I'd be removing them anyway.
    Judging by the two responses I really need check the spans then, I've got a couple of photos but that was just from me standing on top of ladders and not in the loft space.
    Been putting it off as it's hard to move about with the insulation being higher than the joists.
    I'll go in tonight and find where they end. Some how they're parallel to the supporting wall in the middle of the house so not sure yet how they join up there.
    I'll attach pictures once I've gone up again.

    Once I've got the full length it will be easier to make an assessment for these joists I presume?

    Thanks for the replies .
     
  5. Mohai

    Mohai New Member

    Hi,

    So I’ve been up and crawled around with my limited amount of planks.
    I’m in a mid terrace house, there’s no supporting wall in the middle Of the house and these joists are 5 metres long between the two neighbours. I found a Piece of paper with the insulation work saying it was 42 square metres.
    I've uploaded a video showing the span of the space.



    (Apologies for the wrong rotation on the last one, it keeps uploading like that!)

    6BCA15E7-B2BD-4961-BA83-FC9D9CC05C00.jpeg

    AF10FE2C-1404-4F3D-A236-B853692A35DF.jpeg
    2D984308-7BB5-400F-B444-B164F5E559D1.jpeg
     
  6. Tony Goddard

    Tony Goddard Active Member

    In terms of the joists taking the load of the boarding, your 6x1 joists are going to be superior to 4x2 or 3x2, the depth of the member is primarily what gives it strength in holding a downward force.
    I would lay 4x2 perpendicular to the existing joists to clear the insulation, then board over that with loft boards. You will be looking at 50Kg / sq meter plus, my loft is based on 4x2's and is jam packed with stuff, boxes of books, a washing machine, an architechts drawing board, a 35mm cinema projector that weighs over 100Kg on it's own and some spare concrete capping stones for the outside wall - all solid as a rock and fatty here can go up there and tinker without so much as a rattle or judder.
     
  7. Mohai

    Mohai New Member

    Hi Tony,

    Thanks a lot for your reply. It really puts it into perspective for me!
    I’ve decided that the 4x2s will be better than using the loft legs seeing as the joists are at very slightly different heights. Using 90 degree joists mean I’d be able to pack any gaps to get the floor level.

    Good to hear the 50kg per square metre, sounds like it's sturdy enough to use as an unofficial study down the line!
    For context here’s the space I’m working on



    I take the pictures and rotate them as they should be, some seem to upload in a stupid orientation!
    A16278EE-6E14-4848-8EBD-7F2314234FD3.jpeg 7F4895DD-DD82-4CB7-A223-CD1AB4C5C99D.jpeg
     
  8. Tony Goddard

    Tony Goddard Active Member

    Your plan is sound, loft legs are carp, they concentrate the weight on points so no good but for light duty storage. Lay the 4x2 upright (so the 4" rising up) that will give you maximum strength - screw it at each crossing but be sure to pack it level before screwing to prevent any risk of cracking the ceiling below when the crews go in - the glaziers plastic packers used in window fitting are great for this.
     
  9. Mohai

    Mohai New Member

    Ah nice one, I wasn't sure on what type of packing to use as none of my previous DIY jobs have needed it.

    Yeah good to hear to use upright as I think there's so much insulation I need the extra 4 inches!
    Is there a recommended gap to space them with, eg stick to 400 (same as ceiling joists) so it makes square holes or just go off whatever loft boarding I get?

    I also didn't know until I opened the instructions on the ladders that you have to add 10mm in the opening to the width and length to put spacers in, apparently the frame can bow or bend if the ladder frame was to be screwed directly into the timber joist frame.

    I'll update this post when I get some more done!
     
  10. Mohai

    Mohai New Member

    Actually I guess the spacing will also depend on the width of the top layer insulation that's already down.
     

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