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Insulated plasterboard over insulated plasterboard

  • 06-01-2023 10:50pm
    Registered Users Posts: 8

    Our front room is insulated but doesn't seem to retain heat very well. The previous owner put 62.5 mm insulated plasterboard on the external wall. The PVC windows in the house are double glazed and at least 20 years old. We hope to replace them at some stage in the future.

    A neighbour recently put 92.5 mm insulated plasterboard on all his external walls. My question is could I put more insulated plasterboard over the existing insulated plasterboard in that room? Thanks.


  • Registered Users Posts: 2,755 ✭✭✭MicktheMan

    You could but likely it won't make much of a difference to heat retention, just make your room smaller.

  • Registered Users Posts: 8 Spokane

    Losing another inch or two wouldn't bother me too much, Mick.

    There is no fireplace or draughts in the room.

    The window takes up about 45% of the external wall. The wall has an approximate U Value of 0.4. The window has an approximate U Value of 2.8.

    A new window would have a U Value of about 1.2.

    Would I be better off just replacing the window?

  • Registered Users Posts: 606 ✭✭✭Whatwicklow

    Fixing will be problematic, they will need to go through both slabs with sufficient bite into the batton / stud.

    a long fixing will encourage movement, movement will encourage cracks.

  • Subscribers Posts: 39,821 ✭✭✭✭sydthebeat

    Yes, and insulating the jambs, head and Cill if possible

  • Registered Users Posts: 984 ✭✭✭Still stihl waters 3

    Does the ceiling have an insulated board? And maybe someone could answer this but I thought you couldn't put more than half the thickness of the the cavity on the internal wall due to dew point or something like that

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  • Registered Users Posts: 8 Spokane

    Hi, SSW3.

    No, the ceiling hasn't got an insulated board but I have thought about using a 52.5 board for that purpose. It's a 2 storey house and there's a bedroom overhead.

    Unfortunately, the house was built with cavity blocks. If it was a cavity wall, I presume the previous owner would have pumped the cavity with bead instead of using insulated plasterboard.

  • Registered Users Posts: 1,013 ✭✭✭TimHorton

    Go for it , On North facing bedroom I added 100 MM Insulation to on External Wall / 25 MM on Window Reveals (removed Windows Board) , Moved Radiator and 2 Sockets - Sealing all Gaps. I then added an unbroken Vapour Control Layer (Green) , Followed by 3x2 Battens at 400 MM Centres and finally a layer of 12.5 MM Foiled back plasterboard - Taped and Jointed and then redecorated - Its gone from cold uninviting room to lovely and warm...(gets 5 degrees warmer than before) Plan doing the same with adjoing Bedroom that has an ensuite.

  • Registered Users Posts: 984 ✭✭✭Still stihl waters 3

    If its only the 1 room I'd do the ceiling with a 92 mm insulated board, doing the walls again seems pointless, I'd check the room for draughts around skirtings, plugs and windows

  • Registered Users Posts: 8 Spokane

    Does anyone know if I could put external insulation on walls that already have insulated plasterboard on them.

    As I stated earlier, it's a cavity block house, not cavity wall.

    Good idea/bad idea.......?

  • Registered Users Posts: 1,013 ✭✭✭TimHorton

    Sure according to some on here External is the Holy Grail...

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