Insulating a Concrete Flat In

Discussion in 'Builders' Talk' started by senjers, Jan 18, 2021.

  1. senjers

    senjers New Member


    I have a flat roof structure attached to my house which was a small Police station office many years ago. The structure joins to my neighbour who has an identical layout. The police station was split in half when the houses were sold.

    It is currently my home office. It is a brick cavity wall with a concrete (I assume block and beam) roof and wet plastered ceiling.

    There is no insulation at all and is very cold and chills the whole side of the house.

    I was wondering if anyone has any ideas for insulating this room.

    I have considered:

    1. A cold roof with kingspan but worried about interstitial condensation complications with ventilation, vapour barrier.

    2. Hot roof not really sure how to do this, just dot and dab the insulation on the existing ceiling?

    3. Inverted roof. Insulation looks expensive but very easy. Will need to get neighbour involved.

    Any pointers would be greatly appreciated as the doesn't seem much info on a concrete flat roof.

    Thanks in advance.
  2. Severntrent

    Severntrent Screwfix Select

  3. senjers

    senjers New Member

  4. Bob Rathbone

    Bob Rathbone Screwfix Select

    I would advise that you fix 38 x 25mm tilers lath to the concrete at 600mm centres, fill the space between with 25mm polystyrene board, fit a vapour barrier and board over. Do the same with the walls and keep the vapour barrier continuous right down to the floor.
  5. senjers

    senjers New Member

    Thank you
  6. senjers

    senjers New Member

    New boarding on the walls is probably more work than I was anticipating.
  7. koolpc

    koolpc Super Member

    Hello, hello, hello! What we here then!
    nigel willson likes this.
  8. rogerk101

    rogerk101 Screwfix Select

    The original poster hasn't specified how much height he is willing/able to remove so we can't advise on insulation thickness. However much he can lose, it's always better to use PIR insulation boards like Kingspan KoolTherm rather than ploystyrene of rockwool as the insulation effect per millimetre of thickness is dramatically superior. 25mm of polystyrene would barely make a difference to heat loss, but 200mm or Kingspan would mean you could probably heat the room with a candle!
  9. senjers

    senjers New Member

    Ceiling height is 8 ft. I could live with 200mm or a bit more height reduction. Thanks
  10. jcswright

    jcswright New Member

    Is it like a link-detached house then senjers? I've been thinking about an inverted roof over the garages between us and the neighbours but I can't see how to avoid the cold bridging at the edge of the flat roof where it joins the main (2-storey) house. Any ideas?
  11. jcswright

    jcswright New Member

    I have to ask - what does this mean?! I haven't seen it anywhere else...
  12. Astramax

    Astramax Super Member

    Don't worry about koolpc....every village has one!
  13. Frutbunn

    Frutbunn Active Member

    Evenin' all.
  14. Severntrent

    Severntrent Screwfix Select

    Good ole Dixon
  15. koolpc

    koolpc Super Member

    You must be a youngster....Google it
  16. Frutbunn

    Frutbunn Active Member

    People of a certain age will know!
  17. Frutbunn

    Frutbunn Active Member

    They revived Dixon for Radio 4 back in 2004.
    The show I should add not Jack Warner!
  18. Jord86

    Jord86 Screwfix Select

    You certainly couldn't unless you are Warwick Davies, maximum you would want to lose before the room starts to feel like a hobbits den is about three inches, so 2x2 on the ceiling filled in between with celotex then covered with insulated plasterboard will be the best for your scenario.
  19. jcswright

    jcswright New Member

    Ha - I get it now :)
    koolpc likes this.

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