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Solid victorian external wall - earthwool studwall + celotex

Discussion in 'Building' started by danmills, 6 Jan 2015.

  1. danmills

    danmills

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    Hello!

    I own a semi-detached victorian townhouse with basement and loft bedroom and have a few questions on what to do with an uninsulated solid external wall. First thing I did was ditch the aluminum frames and fit new double glazed windows throughout, which is done.

    Loft bedroom was very cold. Fitted last winter with new thermal plaster boarding and about 300mm+ of earthwool. It's snug, the eaves breathe and all is good.

    Mid bedroom has earthwool in the ceiling joists when it was lowered which has also helped keep the loft bedroom warm.

    Living room and stairs have a solid external wall with no cavity. I think they have just been drylined (which has blown) and lining papered over. They are freezing to touch, and you can visibly see the warm/cold draught on the stairwell.

    The basement stair wall is part underground; part above ground (with a window at ground level knee height). This wall has at some point been drylined with a 50mm stud cavity and lining paper/paint on top. I had a nose through the plastic air vent covers and found the cavity was hollow and not insulated - you could see the bare brick beyond. I did a quick temp test of the draught here by temporarily bunging my unused chimney and the wall grille with earthwool and the living room increased by two degrees in 10 minutes. Though they are needed for ventilation, they are the definite sources for the big draughts.

    Because of the existing narrow basement stairway width, I am limited to how much I can insulate this wall. I figured I can just about increase the existing inner leaf by about 25mm which is the depth of the skirting on the current stairs.

    I am trying to limit the amount of mess and time as I have a baby due in just over a month.

    My plan was:

    1) make a series of openings in the top and middle of the existing plasterboard, and ram as much earthwool as I can top to bottom in the current 50mm cavity. Plug it back up.

    2) then form a new extra layer of 25m celotex and thermal plasterboard and fix over the existing plasterboard. Tape edges, lining paper, paint.


    The obvious (but most messy) thing to do would be to rip all the old plasterboard off, fill the existing cavity with membrane backed celotex (foiled side) then new plasterboard, lining paper and paint. Obviously it isn't going to comply with building regs or the celotex web calculator unless I have a much bigger cavity/insulation layer but I simply don't have the space to.

    But would my original idea work ok? Again, it isn't going to meet current building regs, but it's not removing the existing fabric either, so technically it's an improvement and not a new construction.

    Any advice on blinding mistakes regarding thermal bridging and dew point calcs would be most appreciated.

    Thanks! :)
     
  2. jeds

    jeds

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    Don't do it. My advice is rip it off and re-line with a thermal plasterboard. You could get a 70mm board in virtually the same depth which would be a million times better insulation (nearly to regs) and would be a neat and fairly simple job to achieve - if a bit messy. More work yes, but in the long run a much, MUCH better job.
     
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  4. TheVictorian

    TheVictorian

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    As above, do this one properly or you'll have all sorts of problems in the future. Even adding 50mm would be really beneficial.
     
  5. danmills

    danmills

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    Thanks guys - this was my plan B anyway, looks like I will have a busy weekend ahead!

    I'll probably keep the existing studwork and just squeeze 50mm foil backed Celotex and taped joints into the existing gaps; and a 15mm/12.5 celotex/plaster sheet over the top of the 50mm celotex.

    Sound about right?
     
  6. DIYnot Local

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