Polystyrene thickness vs 300mm Glass Wool

Discussion in 'Eco Talk' started by IanMKnight, Dec 7, 2019.

  1. IanMKnight

    IanMKnight Member

    So i want to board for storage boxes some of my loft (about 12m sq) but it has been insulated with the required 300mm of glass wool horror. Hence i was going to use these loft stilt things and board onto them.

    However, after a bit of investigation i find that most of the loft has already been boarded with TnG (obviously many year ago) and the new glass wool just put on top of it.

    So I was thinking of pushing the glass wool to the sides and then put polystyrene sheeting over the existing TnG boards and then put the stuff to be stored on the polystyrene. So question is; how thick a polystyrene sheeting/boards should i use?
    Many thanks ik
     
  2. rogerk101

    rogerk101 Screwfix Select

    Which polystyrene? Expanded or extruded? If expanded, I would probably use 200mm thick. If extruded, probably around 150mm.
     
  3. carldurrant

    carldurrant New Member

    I have 300mm of wool all over my loft, but down the centre for requires access, I have 150mm of wool between the joists and 50mm PIR board sat on the joists with hardboard over the top to allow me to crawl through.

    Building control was happy with this.

    Typically rule of thumb - PIR (celotex ) is roughly twice as efficient as wool. Polystyrene sits fairly in the middle - e.g. 50mm PIR = 75mm for = 100mm mineral wool
     

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