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Advice on floor structure

Discussion in 'Wood / Woodwork / Carpentry' started by Mike Hickson, 30 Aug 2019.

  1. Mike Hickson

    Mike Hickson

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    Hi,

    I am new to this forum and would be grateful for some advice. I am undertaking a full restoration of an 18th C stone cottage and would like advice on strengthening an area of existing floor.

    The floor is First Floor covering 25m2 with hallway below and landing/bedroom above. Due to height restraints, it has been constructed using 100mm by 50mm timber joists spanning 2.7m (a bit undersized). At one end, the joists bear onto the inner stone wall, and on the other, sit on a ledger plate bolted to the stone wall. In theory, the floor structure is "existing" and I could possibly just leave it, but in practice I want to improve it.

    Ideally I would like to double up the joists and use flitch plates to compensate for the lack of depth in the joists, but I am struggling with how best to attach the joists (including constructed flitch beams) to the wall end. I could just keep the existing ledger plate arrangement and bear the joists onto that, but i would prefer to replace the ledger and hang the joists off it. I am not sure if this would defeat the idea of the flitch beams, and how I would hang them from the ledger. Im struggling to find suitable hangars.

    Thanks very much in advance, any help greatly appreciated
     
  2. Notch7

    Notch7

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    100 x 50 joist ends will easily take a floor load.

    So you dont need the sister joists or flitch plates to have end support.

    If your wall plate is cream crackered then that needs dealing with.

    Do you not have the room to fit 120 x 50? -I think that would get to your 2.7m span
     
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  4. Mike Hickson

    Mike Hickson

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    Thanks for the reply. Unfortunately not. I am installing a staircase in this space and only just (by mm) have the height clearance to meet Building Regs for this. The existing floor is quite springy and not especially well constructed. As you say, I will probably replace the wall plate anyway. It is currently 100mm by 50mm as well, bolted to the stone wall and doesnt look like it is man enough (although possibly is?). I would prefer to hang the joists from the wall plate rather then bear them on top of it as this will make it much neater overall.
     
  5. JobAndKnock

    JobAndKnock

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    I've done a number of floor repairs where a rolled steel angle section (L-profile) was drilled and resin anchored into the wall. A thin timber ledger (pad) was then fixed onto the horizontal steel projection and the joists end-notched and sat atop the timber pad. The joists were "blocked" (i.e. solid strutted) at the angle plate to prevent movement. To reduce springiness you could add additional rows of solid strutting into the floor structure, at say 400 to 600mm centres (making a lattice) as opposed to the traditional 1/2 or 1/3 of the floor width. Your solid strutting should be te same thickness and at least 80% as deep as the joists to be effective. If notching to sit on a ledger the notches must not exceed 1/3 of the depth of the joists, otherwise you'll weaken them, although you could presumably reduce the thickness of the pad to as little as 12mm (plywood) if needs be. Using a glued and screwed sheet material (on 150mm centres) for flooring above this (either plywood or chipboard) will make for a more rigid floor than you'd ever get from a conventional planked floor
     
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