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Moisture between ceiling slab and airtightness membrane

  • 16-01-2017 9:41pm
    #1
    Rossdarragh1
    Registered Users, Registered Users 2 Posts: 94 ✭✭


    Yesterday my electrician cut a hole in my ceiling (62.5mm slab) to put in recessed lights and noticed there was a lot of moisture trapped between slab and membrane.
    Floors were poured a month ago and place has dried out well since. I haven't yet placed rocwool in the attic. Attic is cold when I go up but I don't think it's well ventilated.
    Anyone got any reason for moisture in this area? Possibly a case of condensation with warm slab meeting cold attic. Rocwool being rolled out might solve this ?

    Just looking at putting slate vents each side of the A roof to gain cross ventilation. Hoping that along with rolling out the rocwool will solve it.


Comments

  • #2
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,145 Mod ✭✭✭✭BryanF


    Correct me if wrong but From previous posts:

    >this was a partially finished house, you bought
    >with no way of achieving a complete air-tightness layer, as the partitions were already in
    >you are managing the build, and haven't employed an arch/Eng to assist you.
    >probably haven't commissioned the hrv unit

    >so to the problem: the builder stuck insulated slabs to the ceiling and put the air-tightness membrane (vapour barrier) on the cold side of the insulation, in the main ceiling areas at least . Vapour barrier is on the Cold side: because the builder hasn't put in the mineral wool yet. So you've trapped warm moist air, on a cold surface where it is condensing.


  • #3
    Rossdarragh1
    Registered Users, Registered Users 2 Posts: 94 ✭✭Rossdarragh1


    BryanF wrote: »
    Correct me if wrong but From previous posts:

    >this was a partially finished house, you bought
    >with no way of achieving a complete air-tightness layer, as the partitions were already in
    >you are managing the build, and haven't employed an arch/Eng to assist you.
    >probably haven't commissioned the hrv unit

    >so to the problem: the builder stuck insulated slabs to the ceiling and put the air-tightness membrane (vapour barrier) on the cold side of the insulation, in the main ceiling areas at least . Vapour barrier is on the Cold side: because the builder hasn't put in the mineral wool yet. So you've trapped warm moist air, on a cold surface where it is condensing.

    - Yes bought partially finished.
    - achieved air tightness of 2.05. Wrapped each compartment and sealed studs.
    - Architect designed internal layout. Know engineers who bounce ideas off.
    - Beam HRV system in and working with air to water heat pump BER provisionally A3

    Yes. Wool not laid out yet as electrician wanted ease of access. Moisture is trapped as membrane couldn't handle amount of moisture in house. Plan to roll out wool even though moisture is trapped in order to stop moisture condensing . Seemingly a common problem when one doesn't lay the mineral wool immediately.


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