Prevent mould in wardrobes - air gap vs insulate exterior wall

Discussion in 'Builders' Talk' started by MxHx2022, Jan 3, 2024.

  1. MxHx2022

    MxHx2022 Member

    hello! I'm due to install fitted wardrobes on an outside wall and want to take measures to limit the occurrence of mould. I can spare 10cm or so of room depth and but am having trouble deciding between battening the wall out so to create air flow behind them or, stripping the plaster off, adding the likes of 10cm cellotex and re-plastering. House was built in 2011 and is cavity insulated. There will be underfloor heating under the wardrobes but only used in the winter months. The design of the doors have air grilles in them to aid airflow.

    Does anyone have any experience of this? Which of the 2 will be most effective in preventing mould?

    Much appreciated.
  2. Mark DM

    Mark DM Screwfix Select

    Could you leave the wardrobe backs open and then there would be no cavity that may need to be ventilated. I have constructed several built in wardrobes at my own place ( including against outside walls) and for customers over the years and had no issues.
  3. MxHx2022

    MxHx2022 Member

    I guess that’s not a bad shout. Thank you.
  4. iwcourse

    iwcourse New Member

    I agree with this, usually we do this method every time I get built in wardrobes. Great resource!
  5. Mr Rusty

    Mr Rusty Screwfix Select

    There are two factors in play. One is the temperature gradient between inside and outside and the other is ventilation/air movement. A fitted wardrobe in itself is insulation - it is between the warm fairly humid room air and the freezing temperature outside. Any internal insulation will move the dew point of that temperature gradient inwards. The dew point of ambient air (say 20-22 degrees and 50-60% humidity) is around 12-13 degrees. If the room air hits a surface at the dewpoint temperature it condenses. In a room where there is a fitted wardrobe on an outside wall, the wall is protected from room heating, so is colder - the insulation provided by the wardrobe has moved the dewpoint inwards so instead of being inside the wall where it would be if the wardrobe wasn't there, it is closer or even on the wall surface.

    If any of that room air is moving passed the condense, as it is only at 50-60% humidity, it has the capacity to evaporate any condensation away - hence the reason ventilation is so important - there can be an equilibrium where the evaporation is equal to teh rate of condensation - as long as the rate of evaporation can be greater, the moving air has a drying effect - the faster that evaporating air is replenished the faster the drying (hence drying clothes on a windy day is better than a still day). In a situation where there is no air movement, the condensation occurs but doesn't evaporate - the still air immediately above the liquid water becomes 100% saturated because it can't move away and the liquid condense persists.

    Liquid water = mould

    So the answer to the question is 1) yes, insulate an exterior wall if you can - it will move the dew point inwards, but hopefully behind the wall surface where the room air can't get to it and condense. The idea is that the insulated surface is above the dew point because it is in better contact with the room air and hence warmer 2) Try and get air movement in to the room - open the windows in the day time. Ventilation is the no1 remedy for condensation and damp.

    If all else fails, use a dehumidifier to lower the humidity of the room, which has the effect of lowering the dew point, hopefully below the surface temperature of the surface of the external wall behind the wardrobe.
    Last edited: Jun 13, 2024
    Alan22 likes this.
  6. koolpc

    koolpc Super Member

    Had this issue once. We decided to line the wall behind the wardrobe with insulation paper. Worked a treat for us...
  7. Alan22

    Alan22 Screwfix Select

    I don't think you can get a better explanation than Mr Rusty's, damp/condensation comes from a difference in temperature, warm wardrobe/cold wall.

    I pulled 2 fitted wardrobes out of a room that had been built into alcoves either side of the door, one was fine, the other was black with mould behind, when I took the plasterboard off the black side to replace I found a fireplace with an open chimney behind, it was freezing behind and the wardrobe had a thick plywood back creating a dew point between the ply and the wall, insulated it and it was fine.
    Mr Rusty likes this.
  8. Astramax

    Astramax Super Member

    Lined several fitted wardrobe interior of external walls for clients (and my own) over several years using WallRock Thermal mould ever has appeared.
    koolpc likes this.
  9. Derevonian

    Derevonian New Member

    Make sure you have warm air from your underfloor heating gets into the wardrobe. (Easily done by the good wardrobe design) If the wardrobe doors have vents the temperature inside the wardrobe and air circulation will prevent any condensation.

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