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Housing - Renovation: Wide Cavity Wall Insulation Options

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  1.  
    • CommentAuthorTriassic
    • CommentTimeOct 3rd 2015 edited
     
    My neighbour has a bungalow constructed around a steel frame with a steel truss roof. The exterior is rendered blockwork and timber stud work and plaster board to the inner leaf. The cavity is 150mm wide and is devoid of insulation. Last year he had a few companies to look at installing insulation and none are willing to take on the job, a couple have said the steel frame is a problem.

    What options does he have?
    • CommentAuthorDarylP
    • CommentTimeOct 3rd 2015
     
    EWI?
    • CommentAuthorgravelld
    • CommentTimeOct 3rd 2015
     
    Is the steel on the warm side of where the insulation would be? Is it exposed to the cavity?
    • CommentAuthorTriassic
    • CommentTimeOct 3rd 2015
     
    It's exposed within the cavity, I think this is why the insulation companies are shying away from the job. If the steel is inside the cavity, what's the problem and the solution?
  5.  
    Other option would be to strip out the inner lining and install rigid insulation board in the cavity, leaving a 50mm or so ventilation gap between the outer skin and the insulation. That's what I've been doing here.
    • CommentAuthorgyrogear
    • CommentTimeOct 3rd 2015 edited
     
    For starters, how about blowing loose polystyrene beads into the cavity.

    https://www.youtube.com/watch?v=iMOTvNmva1s

    gg
    • CommentAuthortony
    • CommentTimeOct 3rd 2015
     
    I would DIY polystyrene beads and don't tell anyone.
  8.  
    I think the problem is that some ventilation of the steel is necessary to evaporate away any condensation that forms. This is not just moisture from the inside, steel will also attract condensation from the air outside in some weather conditions.

    If you completely fill the cavity, it may not dry out quickly enough.
    • CommentAuthorgravelld
    • CommentTimeOct 3rd 2015
     
    That's why I asked if the steel was on the internal side of the cavity (I.e. the warm side)
  10.  
    Usually it would be inside the cavity with mechanical fixings to both the inner and outer skin and so not clearly warm or cold side.
    • CommentAuthorgravelld
    • CommentTimeOct 3rd 2015
     
    Even if you did EWI wouldn't you also either need to fill the cavity or continue over the roof too to avoid the cavity acting like a surrounding chimney and sucking out the heat?
    • CommentAuthoratomicbisf
    • CommentTimeOct 3rd 2015 edited
     
    Posted By: gravelldEven if you did EWI wouldn't you also either need to fill the cavity or continue over the roof too to avoid the cavity acting like a surrounding chimney and sucking out the heat?


    Logically yes but I'm not sure whether this is actually done in practise. Many people, including many who should know better, treat any wall that is unsuitable for CWI as 'solid wall', and forget that this sort of wall actually has more of a cavity than most!
    • CommentAuthortony
    • CommentTimeOct 3rd 2015
     
    Polystyrene beads would make things warmer and even if (which is unlikely) condensation did form it would breathe away through the beads as there will be a temperature gradient from in the home to outside, this acts as a transport mechanism for moisture in the same direction.
    • CommentAuthorgyrogear
    • CommentTimeOct 4th 2015 edited
     
    What is an unknown known, is the treatment of the steel structure inside the heated volume.
    For fire protection, it needs two layers of plasterboard. For insulation, it probably needs 30 mm XPS under the plasterboard. This ought to prevent it forming a thermal bridge.

    gg
  15.  
    Is the effect of blown insulation on this steel frame any different to the steel cavity wall ties in old cavity walls?
    • CommentAuthorringi
    • CommentTimeOct 4th 2015
     
    Posted By: PeterStarckIs the effect of blown insulation on this steel frame any different to the steel cavity wall ties in old cavity walls?


    Yes if one cavity wall tie fails it is not the end of the world!

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