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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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Housing - Renovation: Which type of cavity wall insulation?

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  1.  
    • CommentAuthorrhamdu
    • CommentTimeJan 15th 2022
     
    We have the choice of bonded bead or mineral fibre insulation for cavity walls.

    Later we may want to cut through the walls for doors or windows or a possible extension. I'm thinking the bonded beads are more likely to stay in place when we do this.

    What would people recommend?

    By the way, additional wall insulation may be added later, internally or externally. But I can't see how this would affect our choice.
  2.  
    Bonded beads - I think most people are using graphite EPS now, but check - lambda 0.031-0.033W/mK vs c 0.038 for white beads.

    If you insulate (Edit: I wrote *externally*) (should say *internally*) you need to get a condensation risk analysis - too much IWI and you could potentially get interstitial condensation on the inner skin between CWI and IWI. Probably wise to get risk analysis for EWI too, but less critical I suspect.

    *Thanks FT for the later advice to edit!!. I thought I had admitted my sins sufficiently!
    • CommentAuthortony
    • CommentTimeJan 15th 2022
     
    Beads no question about it.
    • CommentAuthorrhamdu
    • CommentTimeJan 16th 2022
     
    Thanks guys. Beads it is then. I've been quoted for the job, using some which I'm pretty sure are the graphite type.

    Posted By: Nick ParsonsIf you insulate externally you need to get a condensation risk analysis - too much IWI and you could potentially get interstitial condensation on the inner skin between CWI and IWI. Probably wise to get risk analysis for EWI too, but less critical I suspect.


    "Externally" a typo for internally I assume. Condensation is indeed a worry. When I've done IWI in the past I have used a vapour barrier. On the current project - a detached chalet bungalow - EWI is an attractive option.
  5.  
    Yes,

    Typo!
    • CommentAuthorrevor
    • CommentTimeJan 19th 2022
     
    If going down route of polystyrene in cavity make sure you have no cables in there. The PVC cover on the cables is attacked by PS.
    • CommentAuthorrhamdu
    • CommentTimeJan 26th 2022
     
    Posted By: revorIf going down route of polystyrene in cavity make sure you have no cables in there. The PVC cover on the cables is attacked by PS.


    Always a good reminder. Not a problem this time since we will be rewiring.
    • CommentAuthorjms452
    • CommentTimeFeb 19th 2022
     
    Beads flow better and don't sag either - get the graphite ones!
    • CommentAuthorrevor
    • CommentTimeFeb 19th 2022
     
    Are you in an exposed area if so I would reconsider filling the cavity and have a proper survey. Our first house 50 years ago we did cavity insulate, foam injection we had then. It worked really well we had no issue but we were in a sheltered spot. Our second house a late Victorian semi had 2" cavities and we did not fill them as there was a lot of mortar bridging the cavity. Our current house we externally insulated the original stone building and put 100 mm of insulation in a 150 mm cavity maintaining a barrier to weather and allowing air circulation, Where I live now is an exposed area considerable number of houses have damp issues and had to have the insulation removed. The installation companies have disappeared off course. When we were building I mentioned I had seen a build going up where they were filling the cavity post construction, to my BCO and he told me whilst it was an approved method he warned me off doing it as he had seen so many problems associated with full fill cavity.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 19th 2022 edited
     
    Posted By: Nick ParsonsYes,

    Typo!
    Go back and correct it now, or you'll be tweeted and condemned forever!
  11.  
    Thanks FT: Sins admitted. Please don't condemn me! On the other hand I am so un-wedded to Twitter that...
    • CommentAuthorJeff B
    • CommentTimeFeb 19th 2022
     
    We had Rockwool fibres blown into our cavity walls in our previous house and in 25 years there we had no damp problems despite living in a pretty wet area (Gwent valleys). Maybe we were just lucky?

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