Ceiling insulation

Discussion in 'Builders' Talk' started by Russell74523, Aug 12, 2018.

  1. Russell74523

    Russell74523 New Member

    I’m doing some refurbishment work in my downstairs cloakroom which included repairing a damaged ceiling. The room is part of a front small single storey front extension. There is a flat roof above.

    On removing the old ceiling there appeared to be only half the amount of insulation above the cloakroom. I’m looking to reboard the ceiling but just wanted to check whether I can simply fill the space the the same type of insulation of whether there was a better option whilst the ceiling was down?

    Attached Files:

  2. Wayners

    Wayners Well-Known Member

    I've used that space blanket as less mess and hardly any fibres in the air. Also cheep here . Kingspan type insulation boards would be the best bet although you may want to use the polystyrene sheets as a cheaper option,but not easy to cut neatly..
  3. Russell74523

    Russell74523 New Member

    Thanks, My only concern was that this is a flat roof above and had read about issues with condensation? There doesn’t appear to be any moisture and the it’s probably been this was for about 20+ years.
  4. Wayners

    Wayners Well-Known Member

    Cold plasterboard because of poor or no insulation causes mould on surface board. Last one I done just had a inch of polystyrene bashed to hell and old bits of felt and old rotten wood board bits. Customer was short of cash so I used what I could selvage doubled up and stuck together with a few new sheets of 50mm polystyrene boards. If you can stretch to using plasterboard backed with insulation stuck to the back it's the best job B&Q
    sell... called Gyproc ThermaLine. Here is the one I did last year. I have cleaned up and took picture prior to insulation. Right job! [​IMG]
    Last edited: Aug 12, 2018
  5. sospan

    sospan Well-Known Member

    There are so many options on insulation a lot depends on budget

    It would be quite easy to get some rigid insulation (kingspan, celeotex) etc. and cut that to fit between the joists and leave an air gap above. At the moment that type of insulation can be picked up quite cheap especially slightly damaged boards, which isn't a problem as they will be cut anyway.

    There are a lot of "Rockwool" type batts which are water, mold and rodent resistant again these can be trimmed to fit between the timbers.

    As an additional measure you could fit insulated plasterboard to the ceiling This is simply screwed to the timber. There are lots of versions available but avoid the polystyrene versions whilst being cheap they don't provide much insulation.

    In some of the pictures there looks like water has been getting into some of the joists. I would fix that first before replacing the ceiling. Because there is some damp there, I would spray it with a diluted bleach solution, let it dry and then spray with some timber preservative. Mold, wood worm and rot love damp areas that have been exposed to the air and then sealed back up.
    Wayners likes this.
  6. candoabitofmoststuff

    candoabitofmoststuff Active Member

    Just to possibly confuse things...

    Unless I've misread and misunderstood, there is a flat roof immediately above the ceiling you've taken down... but the pictures appear to show chipboard flooring where the roof should be??

    Now maybe I've got that wrong, but if I haven't, surely chipboard flooring as a roof material can''t be right.. can it??
  7. sospan

    sospan Well-Known Member

    It is the green moisture resistant board which at least is better than than standard chipboard which used to be used a lot for roofs at one point.

    Standard OSB was used a lot - as I discovered on one of my properties a few years ago when I went through the flat roof and landed in the room below quite neatly on the settee
  8. Ben5053

    Ben5053 New Member

    Hi I have the same issue with trying to insulate a concrete outbuilding on the side of my house. Shared flat roof with the neighbours so can't insulate on top. Only 50mm clearance between the concrete roof and the top of the door and windows so no space for a ventilation gap.

    Options I have considered are: the combined insulation plaster board stuck directly to the roof and then painted with a waterproof sealant so the moisture can't get though and condense on the concrete.

    Insulation foam board stuck to the ceiling with sheets of acrylic or other plastic on the top and silliconed at the sides and joints.

    Any help appreciated.
  9. sospan

    sospan Well-Known Member

    You can bond something like Jablite flooring directly onto a concrete roof using adhesive foam. Jablite is quite cheap but much denser so will take a lot of knocks but can be cut easily https://www.selcobw.com/jabfloor-70-floor-insulation-2400-x-1200-x-50mm-bba

    Any gaps between the sheets or on the walls you can fill with expanding foam
  10. egon999

    egon999 Member

    If the insulation is going between the roof joists then its a cold deck roof and will need ventilation, no matter if the insulation is mould resistant.
    You could renew the roof above with a warm deck roof but that would increase your costs quite a bit
    A hallway house solution would be to insulate the void with a decent insulation (Kingspan/celotex perhaps?) forget polystyrene its insulation values aren't much better than quilt, then fit a DPM across the ceiling behind the plasterboard and DONT cut into it for downlighters or whatever.
    Condensation happens when warm air from the room enters the roof construction and gets cold, depositing moisture in the form of condensation. The DPM will help to keep the air from entering the space. Not an ideal solution but its not a massive area and the fully correct solution will be costly
  11. sospan

    sospan Well-Known Member

    Which one are you replying to ?? they are both completely different scenarios :rolleyes:
  12. egon999

    egon999 Member

    hello Sospan
    I was replying to the original post
    I'm saying its a cold deck roof so it needs venting (but it sounds like it hasn't been?)
    1 solution would be to change it to a warm deck roof so no ventilation is needed, but that might be too costly.
    The alternative is to fit a DPM as a moisture barrier and retain it as a cold deck roof still, BUT with a reduced risk of condensation thanks to the moisture barrier.
    As I said not perfect but possibly a cost effective solution that keeps the area warm, limits condensation risk and doesn't cost a fortune
  13. candoabitofmoststuff

    candoabitofmoststuff Active Member

    I'm just surprised it's suitable as a roofing material.
    I'll back out of this now!

  14. sospan

    sospan Well-Known Member

    It was popular about 20 years ago and is still used by a lot of cowboys !

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