Loft Insulation Advice

Discussion in 'Eco Talk' started by Paul2978, Sep 16, 2020 at 8:51 AM.

  1. Paul2978

    Paul2978 New Member


    Taking down my old larve and plaster ceilings - (what fun!)

    Can anyone suggest the best options for the insulation.

    Id like to fully board the loft its very high and so has lots of space, also its been a haven for all types of birds / rodents over the years so I dont want it to be a mass of 3 layers of loft insulation, but id also like to have decent insulation. The joist are around 12cm in width.

    So that would only give me the option of the 100mm (10cm) normal glass insulation. I could go with Insulation Board and they would be between the plasterboard and the loft boarding.

    Can anyone give me any advice on a good solution?

    Also what thickness if I went for Kingspan thermal boards?

    Many thanks
  2. Hans_25

    Hans_25 Screwfix Select

    You could do what I did, which is time consuming but effective and makes the entire loft space a clean and dry storage area.
    - Put 100mm glass insulation in between the joists, Knauf Earthwool is nice stuff, not itchy. Then board over.
    - Put another set of PIR/Celotex like insulation in between the roof rafters, leaving 50mm air gap behind. I put 70mm deep. Cover over with airtec double or similar, acts as a Vapour Control Layer.
  3. Paul2978

    Paul2978 New Member

    can i squeeze 200mm into the space do you think so its thicker?
  4. Hans_25

    Hans_25 Screwfix Select

    No point squeezing 200mm into the space of 120mm. If you "raise" the floor so there's 200mm of space, then by all means.
  5. HandyHeath

    HandyHeath New Member

    No, if you have 120mm to fill don't use any thicker then that. Don't compress the insulation, it isn't designed to be compressed and actually works better when it's not compressed.
  6. Paul2978

    Paul2978 New Member

    @Hans_25 what width Celotex did you use?

    " leaving 50mm air gap behind. I put 70mm deep"

    Was it 70 mm or 50 + 20mm
  7. Hans_25

    Hans_25 Screwfix Select

    It was big sheets 8' x 4' x 70mm thick and they all had to be individually cut to size and shape. Took a long time, over 100 pieces to cut in all.

    My rafters are 3" x 2", I added 2" x 2" treated timbers to give around 120mm depth, then fitted 70mm thick insulation with 50mm air gap behind using battens to ensure the right gap.
  8. hippy mickey

    hippy mickey New Member

    Hi Paul, I went with loft legs too increase my loft insulation with roll insulation and bordered over the top. however on a side note I should of done the 1st floor ceiling lights first :( as I am now about to unscrew loft boards to relocate ceiling lights in 2 bedrooms. If you have spot lights you need protection and air gaps look on elc forum for info. Good luck

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