Mould in the roof space of a near-new home near Ballarat
A defect investigation in Winter Valley found mould on roof trusses and eaves linings, a cooler drain inside the roof and open valley boards. What causes moisture to collect above the ceiling.
In short: Cold nights, warm interiors and a roof space without enough ventilation create condensation. Add a drain or a valley leak and timber stays damp long enough for mould to grow.
What we found
In December 2025 we investigated a newer house in Winter Valley, on Ballarat's western edge. Traces of mould were on roof truss members and on the eaves lining. Above the ceiling, the evaporative cooler's drain pipe was routed inside the roof space with its roof flashing unsecured, and the tiled valley had side openings that had already let rain in during heavy downpours.
Why roof spaces get wet here
Ballarat winters bring regular frosts and nights near freezing. Warm, moist air from inside a heated house rises into the roof, meets cold framing and the underside of the roof, and condenses. The NCC deals with this through its condensation management provisions, which rely on vapour paths and ventilation being right.
Leaks make it worse
Condensation alone can mark timber. A drain discharging into the roof or a valley that lets in storm water adds far more moisture, often in one place, and that is where staining and mould tend to concentrate.
Is it structural?
Mould on truss timber is reported as a significant item because ongoing moisture can affect durability. It does not mean a roof is about to fail. The fix is to stop the water and improve airflow, then treat or replace affected material as advised.
How an investigation works
We inspect the roof space where access is safe, use a moisture meter and thermal camera to map damp areas, and trace each one to a likely source. The report links each finding to the requirement it falls short of so the builder can act.
If the builder disagrees
Our defect report is aimed at you and your builder. If it becomes a dispute through the Building and Plumbing Commission's dispute resolution service (formerly DBDRV) or VCAT, you will need an expert witness report prepared for that purpose.
Written by our local inspection team from work carried out in Ballarat. Licensed building practitioners, Building & Plumbing Commission registration CDB-U 53425.
