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Replace Suspended Floor Sill Plate

Discussion in 'Building' started by primetime, 5 Jul 2018.

  1. primetime

    primetime

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    Hi All,

    My kitchen floor is bouncy so pulled a few boards and I have quite a bit of moisture and rot. It looks like some floor boards where replaced at some time but nothing was done about airflow so the problem has come back under my ownership. I've been excavating a lot of debris and soil, re-routing pipes buried in concrete and getting sufficient airflow in and around the joists. It's already drying out nicely.
    What's left of the sill plate looks to be supported on loose bricks on a soil base with no damp proofing. If I rebuild to the same spec it's likely I could have more damp and rot in the years to come. Is resting the sill plate on bricks which are resting on soil accepted practice? I'm looking for suggestions for a more robust method of supporting the joists when I get around to replacing them.

    Cheers.
    sill.jpg
     
  2. blup

    blup

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    The crucial thing is damp proofing the sleeper walls, and checking the ends of the joists won't rot by contact with the main wall which will be under the dpc.

    Blup
     
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  3. John D v2.0

    John D v2.0

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    Yes we had similar and lots of muck bridging the gap to the wall, clean it out and lever it up slightly if you can take the weight off the floor, and slide a step of dpc underneath the timber and maybe against the wall. In time with ventilation the wood should dry and won't continue to take on water.
    Where it was rotten and easy to replace the timber and bricks we did that, but there were places where we couldn't.
     
  4. blup

    blup

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    I used concrete block laid flat when rebuilding a sleeper wall, with polythene dpc between the floor and the underside of the bottom block. That was more stable than using bricks, and any gap at the top was filled with timber cut/planed to size.

    Blup
     
  5. primetime

    primetime

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    Thanks for the replies. I was nervous about replacing rotting wood with new wood that will go the same way. The wall was injected before I moved in, this had the affect of slowing down the appearance of damp on the wall but the rot continued merrily underneath. With excavation, ventilation and DPM I'm coming around to getting some more wood (so to speak...)

    Next question is minimum joist size. Can I replace like for like? Going any deeper might require more excavation to eliminate choking of air flow.
     
  6. John D v2.0

    John D v2.0

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    Yes we replaced 4 by 2 with 96x45 or whatever it is. The size is mainly for deflection/bounce and your house certainly won't be in danger. I think we used c24 because that's what wickes had
     
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  8. bobasd

    bobasd

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    you need through ventilation from that outside wall to the opposit outside wall.post photos showing the outside of the walls at ground level on both walls. you need a few more airbricks maybe and to clear the existing ones.

    youl need to examinejoist ends on both sides of the room and at any knee wall in the middle of the joist span.
    you can cut the joist ends off and remove the plate.
    then cut pockets in the wall for bolt-on joist pieces to sit.
    the joist bolt-on ends are wrapped in dpc material caps.

    you have rising dampin the wall.the plaster needs knockin off back to brick at least 300mm above any damp signs.and rendered with sand and lime render.
    just below the red plugs ther seems to be a wood packing piece - if it is wood then remove it an any other wood in or on the lower wall.
     
  9. primetime

    primetime

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    There is one clear airbrick on the outside of the wall with the photo (it's a short wall before solid concrete floor). The other end of the joists is the party wall under the kitchen cabinets - have broken out some pipes buried in concrete but haven't got the sill plate yet to look at its condition. I've knocked a brick out from under the disused chimney to create cross flow - it seems to be drawing up nicely and everything is drying out.

    It looks like some sistering has been done previously so am going to replace any joists that have rot and cut back the sill plates to good material and replace. Had planned on using the sill pates instead of cutting pockets. I will line the underside of the sill plate with dpm.

    The piece that looks like wood under the plugs is a white brick.

    Something like jabfloor insulation will go between joists whilst I'm at it.

    I'm looking to remove most of that orange wall - taking knocking back to brick 300mm to the extreme!

    I've pointed the camera across the room and the dwarf wall could do with re-building to allow airflow. The good news is that most of the rest of the joists look in good condition from what I can see.

    Will get some more photos up soon.
     
  10. bobasd

    bobasd

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    if the orange wall is going then youve opened up a whole new ball game. what do you intend to do after the wall is gone?
     
  11. primetime

    primetime

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    Enjoy a bit more space and look for somewhere else to hang things. Floorwise, the joists run through underneath probably just short of where I took the first photo. The floor will continue where the wall was.
     
  12. bobasd

    bobasd

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    so its not an outside wall?
    if the joists run through the wall then you dont need the plate although its useful for firmly fixing the jists in a level position.
    perhaps a photo showin where the suspended floor ends and the solid floor begins?
     
  13. primetime

    primetime

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    Hope this is a bit clearer. Air brick outside. Looking at adding another where I have circled. There is one to the right as well. The orange wall is behind the air brick you can see.
    air brick outside.jpg
    Below is where the air brick lines up in the kitchen. The air path effectively telescopes but I can't get a telescopic air brick in because there isn't a cavity. The joists start running through to the next room on the left.
    air brick location inside.jpg
    Below picture is further under the floor. Looks in ok condition (joist could do with having support directly under it)
    dwarf.jpg
     
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