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Housing - Renovation: Cavity Wall Insulations

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    1960's seafront detached house has just been surveyed and there is no cavity wall insulation in the original (main part of the house but there are wool bats in the extension.

    I have been quoted £2010 for 109m2 (£18.44m2) which I thought seems reasonable and they are going to see if we can qualify under Eco4 or similar which would be great

    The product they propose is Superbead Graphite which appears to have a lambda of 0.032

    The cavity is 80mm - what sort of U values would this product yield? Standard brick internal and external skin with render external and render/skim internal?

    Questions:

    - Is this a must before we even consider EWI?
    - Is this suitable for a seafront property (installer said yes)
    - Should we do this before or after we install new windows? We may adjust a few openings but imagine as it will be bonded there won't be fallout like the old loose fill material
    - Price okay? I think it is decent and not something we could set up ourselves (compressor, spray, materials, labour)
  2.  
    The cavity is 80mm - what sort of U values would this product yield? Standard brick internal and external skin with render external and render/skim internal?

    Round about 0.3W/m2K - maybe slightly better

    Questions:

    - Is this a must before we even consider EWI?

    In my view (and that of many others, yes. If you have a rare, completely air-tight cavity then maybe not, but I would not have taken the risk.

    - Is this suitable for a seafront property (installer said yes)

    Certainly more suitable than mineral wool, but ask what exposure region they have 'modelled' you in.

    - Should we do this before or after we install new windows? We may adjust a few openings but imagine as it will be bonded there won't be fallout like the old loose fill material

    After, I think. The bonding was not that good on mine.

    - Price okay? I think it is decent and not something we could set up ourselves (compressor, spray, materials, labour)

    Seems about pro rata compared with mine.
  3.  
    Okay, we will have a look at some opening changes in the next few weeks, but I think the price sounds good.

    The question is whether EWI is then necessary or are there better steps to take
  4.  
    Depends what you mean by necessary and how much the enabling works and insulation will cost. Remember that in an older (originally un-filled) cavity wall you effectively have a solid wall at every opening. OTOH EWI is a hell of an expensive way to sort that is you are satisfied with something in the area of 0.3. I would do it, but then I regard the investment as *very* long term.
    • CommentAuthorwookey
    • CommentTimeAug 18th 2024
     
    You can cut out the thermal bridge at the reveals to remove the 'solid wall round windows' problem. On a 60s building the walls are probably not tied together here by the bricks (vertical DPC in place - so you are 'just' making that DPC wider and insulative).
    And 80m of insulation so U=0.3 isn't _bad_, but of course EWI too is much better. Is it already rendered (for seafront protection?) so it'll look just the same afterwards?
  6.  
    Are you saying to remove windows and cut out the front to back bricks? Just to remove a thermal bridge?

    It seems a lot of time and manpower to make marginal gains, unless of course we were looking to renew every window and frame at this point too which we'd rather do as and when they require replacement or change.

    How would one detail the gap of the front to back bricks are removed? It'll then need re rendering and skimming internally - again all this effort and extra works to chase an arbitrary number?
  7.  
    ''Are you saying to remove windows and cut out the front to back bricks? Just to remove a thermal bridge?''

    I'm not. I am talking about 'cloaking' the thermal bridge - i.e. IWI to the solid brick area. Something like 12mm PIR adhered to 9mm plasterboard or Spacetherm WL (10mm aerogel bonded to 3mm Magnesium oxide board).
    •  
      CommentAuthordjh
    • CommentTimeAug 19th 2024
     
    Posted By: VictorianecoAre you saying to remove windows and cut out the front to back bricks? Just to remove a thermal bridge?
    Wookey didn't tell you to do anything. He just stated what he has already done. Perhaps your priorities are different to his. That's no reason to disrespect them.
  9.  
    How far into the room would the insulated reveals need to go? The bridge would be more than just the reveals surely?

    Would it be okay to just EWI the front elevation of the property (for now)? I guess you would need to return the side elevations by at least 1lm?
    • CommentAuthorwookey
    • CommentTimeAug 28th 2024
     
    Posted By: VictorianecoAre you saying to remove windows and cut out the front to back bricks? Just to remove a thermal bridge?


    I could cut out the bricks without removing the windows. Obviously it depends how/where your windows are set in the brickwork but it's quite common for them to be in the outer leaf.

    I cut out the thermal bridge _and_ added 25mm PUR in the reveal. And yes it's a lot of faff and mess. But the details around windows make a surprising difference. Not sure I ever actually modelled the psi-value for this but it definitely improves the junction.

    A decade or so later we got new 3G windows which were moved back in-line with the insulation to further reduce the psi. They would have been somewhat compromised had the thermal bridge remained in place.
  11.  
    So if we are to fit new windows we would try to fit them at the cavity gap?

    If not, locate them on the outer face and then EWI up to them?

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