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Insulating garage ceiling

Discussion in 'Building' started by Humph, 26 Jan 2015.

  1. Humph

    Humph

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    I'm in the process of insulating a garage/play room and looking for the best way to insulate the flat roof. I was originally going to pack it full with rockwool and board over with plasterboard but I've read a few write ups regarding air flow and condensation. My joists are 150mm so i'm now thinking about using an 100mm insulating board that sits directly on top of plasterboard leaving a 50mm gap from ceiling to allow it to breath.
    Do this sound right ???
    Once room is fully insulated we will be adding heating so I guess I need to take this into account as well.
     
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  3. Burnerman

    Burnerman

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    That will give you an infill of 4" Kingspan slab insulation, so that's about right!
    Cut the slabs so they fit tight between the rafters.
    John :)
     
  4. Humph

    Humph

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    Hi, thanks for quick reply.

    Should I treat walls the same ?? leaving a slight gap for air flow or do I pack them tight. I have two single brick walls which I intend to stud, insulate and board
     
  5. Burnerman

    Burnerman

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    Internal walls, that's just fine, and if any outer walls are cavity type then that should be fine too.
    Any suspected damp ingress through the wall needs a vapour barrier of course.
    What's the floor like.....concrete with a vapour barrier below?
    John :)
     
  6. tony1851

    tony1851

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    Back to the ceiling: don't forget the polythene vapour barrier before you apply the plasterboard.
    And make sure that 50mm gap can be vented. Are there vents on opposite sides to encourage airflow?
     
  7. Humph

    Humph

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    Floor is concrete, not sure about vapour barrier. I have built a stud frame on top and laid in 100mm rockwool at 600mm gaps and finished with chipboard flooring. Then covered with moisture sheet and the thin insulating boards and laid laminate flooring.
    This room is a fairly new build. Our original garage sit's at the back of our property with the driveway coming up the side of house. We have extended the garage forward to the front on house so now having a double length garage. The drive was dug out and filled with concrete. When looking at room from outside the wall to left is main house and the new single brick wall to the right is built right up against my neighbours house wall so not sure how I would vent ceiling.
     
  8. robby71

    robby71

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    i fitted Kingspan to my garage roof fixed to 2x1 battons and taped along the seams with duck tape - looks neat and felt warmer afterwards

    [​IMG]

    I also fitted some insulation foil to the metal doors

    [​IMG]
     
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