Ceiling framing location visible on the ceiling

Cause

Condensation forms on the ceiling along the lines of the cold bridges formed by the framing in an insulated roof space - mould growth is the result of regular condensation 

Repair

  • to remove mould/mildew, wash the ceiling with a fungicidal wash to kill the mould. Repaint with a quality paint that includes a fungicide

  • check the existing ceiling insulation and fix any gaps in the cover. Where necessary, install additional insulation over the existing insulation and framing. If insulation is in extremely poor condition, remove it completely and replace with new

  • ensure there is good ventilation in the house. Opening windows for at least 10 minutes every day can make a difference

  • mould only grows where there is high humidity, so reduce indoor moisture levels:

    • avoid the use of unflued gas heaters inside

    • avoid drying clothes inside

    • install a rangehood over the cooktop and vent the cooking steam outside

    • install an exhaust vent near the shower in the bathroom and vent the steam outside, or install a shower dome above the shower

Cause

Condensation forming on areas of ceiling where there is no framing in an uninsulated ceiling 

Repair

  • to remove mould/mildew, wash the ceiling with a fungicidal wash to kill the mould. Repaint with a quality paint that includes a fungicide

  • insulate the ceiling space. Where there are recessed downlights in the ceiling, consult the drawings and details in NZS 4246:2016 Energy Efficiency – Installing bulk thermal insulation in residential buildings.

  • ensure there is good ventilation in the house. Opening windows for at least 10 minutes every day can make a difference

  • mould only grows where there is high humidity, so reduce indoor moisture levels:

    • avoid the use of unflued gas heaters inside

    • avoid drying clothes inside

    • install a rangehood over the cooktop and vent the cooking steam outside

    • install an exhaust vent near the shower in the bathroom and vent the steam outside, or install a shower dome above the shower