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Housing - Renovation: Cavity Wall Insulation

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  1.  
    • CommentAuthorricho106
    • CommentTimeMay 3rd 2022
     
    Hi

    We are starting our 1960’s bungalow conversion later in the year, currently my bungalow has 70mm cavity with blown insulation. The extension above (stepping brick/block out 15mm each side) and to the side will have 100mm and I am planning to use Celotex Thermaclass 90 cavity wall insulation, I just wondered if there is any more alternatives to look at?

    Another note regarding insulation for the floor, I have planned to have 200mm PIR but it is more cost effective to use 300 EPS 70, has any body got any thoughts on this?

    All help and advice greatly appreciated
    •  
      CommentAuthordjh
    • CommentTimeMay 3rd 2022
     
    Posted By: richo106Another note regarding insulation for the floor, I have planned to have 200mm PIR but it is more cost effective to use 300 EPS 70, has any body got any thoughts on this?
    Personally I would prefer the EPS, as long as you have the extra height available.
  3.  
    Posted By: richo106it is more cost effective


    We also found this, that it was cheaper to have a thicker layer of EPS for the same or better insulation value than PIR. Although were limited by the dig-out depth acheivable (Barn conversion) so we ended up with 150mm EPS in 2 x layers of 75mm
    • CommentAuthortony
    • CommentTimeMay 4th 2022
     
    Re CWI, I would avoid sheet insulation in the cavity, it is very prone to thermal bypass, should be taped, suggest wider cavity with r32 batts which virtually illuminate the possibility of thermal bypass
    • CommentAuthorphiledge
    • CommentTimeMay 4th 2022
     
    As per Tonys concerns.

    The only way I would entertain using partial fill rigid CWI was if I was installing myself. Outer face of internal leaf needs to be dead flat and clean so every sheet sits flush against the masonary and is properly secured and joints sealed. If its not done properly to the BBA cert, its alot of work to remedy defects.
  6.  
    PIR (polyurethane) apparently causes far more carbon emissions in its manufacturing process than some other insulations, including EPS, based on achieving the same insulation value.

    But the cement/lime slab/screed is pretty bad for carbon emissions, IDK if it will ever pay-back its manufacturing emissions, as energy is decarbonised during the early lifetime of the building. If it's feasible to have a suspended timber floor with glass fibre insulation, that will cause much less manufacturing emissions.

    https://www.greenspec.co.uk/building-design/embodied-carbon-of-insulation/
    • CommentAuthorricho106
    • CommentTimeMay 4th 2022
     
    Thanks for all comments, once we expose the void then we will hopefully be able to get 300mm of EPS in

    Regarding PIR cavity wall, the Celotex Thermaclass slots together like big bricks and fits between the brick ties this hopefully alleviate some of the installation concerns.

    Unfortunately we cannot go any wider than 100mm cavity, any other suggestions for the 100mm cavity?

    Thanks again
    • CommentAuthortony
    • CommentTimeMay 4th 2022
     
    Blown in platinum EPS beads
    • CommentAuthorrevor
    • CommentTimeMay 4th 2022
     
    What is your external wall finish that is exposed to the elements? If you are in an exposed situation I would not fill the cavity unless you can install a rain screen to protect the outer skin.
    • CommentAuthorricho106
    • CommentTimeMay 4th 2022
     
    The majority of the external finish will be brick, then one small section will be rendered.

    I will make some enquiries into EPS beads cavity fill

    Regarding the EPS for below the screed is Jabfloor EPS 70 suitable? Or would it be better to use EPS100?
    • CommentAuthortony
    • CommentTimeMay 5th 2022
     
    Jabfloor is fine

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