Six months after moving into their new home, Tara and Rob noticed dark patches appearing on the ceilings of those rooms that had been heated during the recent winter. The staining was particularly noticeable around the downlights. While there was no odour in the home, they were concerned that the discolouration may have been due to mould growth. As they had received one professional opinion that the staining was due to mould and another stating that it was due to thermal tracking, Building Wellness was asked to conduct surface mould sampling to determine whether or not mould proliferation was present in the discoloured areas.

Test results

Laboratory analysis of the surface samples found that there was no proliferation of mould in the indoor environment. The presence of mould was barely detectable on either the stained or unstained ceiling surfaces. 

Outcomes

As mould proliferation was not associated with the stained areas, the discolouration was thought to be due to thermal tracking, which occurs when airborne dust and dirt particles stick to surfaces that have become wet due to condensation of moisture from the air.

As warm air can hold more moisture than cool air, condensation may occur when warm air hits a cooler surface. In cooler weather, an uninsulated ceiling surface will be cooler than the same surface that is insulated. When heated indoor air contacts the uninsulated surfaces, it will cool, thereby giving up some of it's moisture as condensation on the cool surface.

Tara and Rob were advised to ensure that ceiling insulation was correctly installed and to find, then eliminate, major sources of dust/dirt/soot in the home. To ensure that the heating and air conditioning unit was not injecting dust into the indoor environment, they were also advised to have the system inspected and serviced by a HVAC professional.