FAQ – Why is my ceiling mouldy?

Mouldy ceilings worry people.

However, not all mouldy ceilings are caused by leaking roofs. Most mouldy ceilings have nothing to do with roof leaks.

This ceiling is mouldy due to a roof leak

 

If you have an ugly mould area in an isolated area of your ceiling – along with brown staining, then you probably have a roof leak.

The brown staining is the fine dust on your ceiling that has been dissolved by the rain water and is leaching through the plaster. The mould is because the ceiling is damp (usually due to the ceiling insulation getting soaked by the roof leak).

If this is the case with your ceiling, then you should contact me to check out your roof.

However, I am asked to inspect a lot of mouldy ceilings that has nothing to do with a leak.

If the whole ceiling is covered by a fine layer of mould, then it is probably not a roof leak. If there are patches of fine mould around the cornices with no brown staining – then it is just a damp room. Not a roof leak.

Dampness on a ceiling is a good attraction for mould growth. In the winter time, ceilings are prone to dampness because room heating and the presence of our warm bodies send warm moist air upwards. This moist air hits the cold ceiling (more pronounced on ceilings that are not insulated) and forms condensation. When mould spores are around, they migrate to the moist environment and thrive. Very quickly, they multiply and soon you have a fine coating of mould all over your ceiling.

Some rooms are more prone to dampness. Bathrooms and bedrooms are the worst because they are more private and are often closed and unventilated.

The solution to damp rooms causing mould growth on ceilings is to make sure that you have good ceiling insulation. The insulation keeps the ceiling warmer in the wintertime and there will be less condensation. The room needs to be ventilated. And it is very important to kill off the mould effectively, remove it and apply a good quality ceiling paint.  I do not do any of these things – so find a good ceiling insulator and a good painter…

8 Responses to "FAQ – Why is my ceiling mouldy?"
  1. Hi mate.. i have recently had my house re roofed and i still get mould on my ceiling above the stairs.. he said it is because the insulation in the floorboards in the roof havent got enough room to breathe is this real or are they trying to pull a fast 1 because they messed up the roof and dont want to do it again for free? I got quoted 5k off them to do the roof which i thought was a bit cheap because others quoted 10k now im regretting my decision.. hope you can help.. kindest regards

    • Hi Phil,

      I am not sure about the ‘breathing’ but…
      All I know is that in my experience, most mouldy ceilings are caused by no (or very little) ceiling insulation directly above the mould areas. If the ceiling is insulated, it does not get cold and cause warm air to collect (condense) – and attract mould.

      From an insulation perspective, insulation relies on trapped air to provide its insulating properties. It is not good practice to compress the insulation from its expanded state, or to have the roof element touching the insulation – as these will reduce the R rating. This may be what the ‘breathing ‘ relates to.

      Hope this helps.

      Jack

  2. We have a flat roof with some sort of straw in the roofing. Due to rusting and roof sagging we have a large mouldy area 1m2 size on interior ceiling. How do we best eliminate the mould? We have just replaced the roof.

    • Hi Tracey,
      I am not a mould expert. And I have no experience in eliminating mould.
      I have seen mould caused by lack of ceiling insulation.
      I have seen mould appear for no apparent reasons (that I can think of).
      There may be a mould expert that you can find?

      Jack

  3. I own a single story house with A framed rooftop. The ceiling in the bathroom and one of the bedroom create mold along the edge of the cieling of the exterior wall above windows in both rooms. The mold happens in the summer and I the winter , the attic received new rake in insulation and the house has new fanfold and tyvec with new vinyl siding. This is the second time. Unsure, I am going to replace the gutter next. Any ideas let me know

  4. Hi

    I am on the middle floor of a three story apartment block. I have mould covering my lounge, dining room and hallway but not bedrooms or bathrooms. The mould is fist size and in a grid pattern every 30cm approx. There is a young man in the apartment above me that runs his air conditioning at what seems below zero, apparently 24 hrs. We have been experiencing extreme humidity in Cairns. I have not been running my air conditioner but have fans on 24 hours in lounge/dining and main bedroom and balcony double doors off lounge room are never closed.

    I am the owner of the unit and understand it must be from condensation but do not understand why it is happening now ( the man has been in his unit for 2 yrs) and could it be ongoing if not addressed and just cleaned?

    Hope you can shed some light.

    Regards

    Karen

    • Hi Karen,
      I think you have identified the culprit!
      It is your upstairs apartment that is making your ceiling cool.
      There will be condensation because of the humidity in Cairns and also because you do not use your air conditioner to de-humidify your apartment.
      You probably just need to clean your ceiling with anti-mound solution and have your air conditioning turned on. You will not get condensation if you cut down the humidity in your apartment.

      Hope this helps.

      Jack

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