A house that smells musty, worse after rain or when it has been shut up, but shows no mould anywhere you look, often has growth in the spaces nobody lives in: under the floor or in the roof cavity. Treating it means getting into the cavity, cleaning the affected timbers, removing damp debris and fixing the airflow or drainage that keeps it wet. The work is quoted and carried out by an independent local contractor engaged through Illawarra Mould Removal.
Why Illawarra subfloors and roof voids get mould
Many older homes through the northern suburbs and coastal villages are raised-floor weatherboard or double brick on sloping blocks. Their subfloors were built to breathe through perimeter vents, and decades of garden beds, paving and extensions often cover them. Add stormwater running under the house after heavy rain and you get damp soil, still air and cold timber. NSW Health’s mould factsheet makes the same link, noting that poor subfloor ventilation worsens damp and that weep holes and vents at the base of a home should be kept uncovered. Our subfloor ventilation guide covers the options.
Roof voids fail differently: small flashing leaks that never reach the ceiling, exhaust fans ducted into the cavity instead of outside, and condensation under the roofing on cold, clear nights, which also affects newer, tightly sealed homes.
What the service involves
- Physical entry. Someone gets into the subfloor or roof void, not a torch through a vent, and maps growth on bearers, joists, flooring undersides, rafters and sarking.
- Moisture profiling. Timber moisture, soil dampness, drainage paths and cavity humidity, plus any active leak.
- Cleaning timbers in place. Structural timber with surface mould is HEPA-vacuumed and treated, not ripped out. Timber showing decay or structural concern is referred to a licensed builder.
- Removing what holds damp. Mould-affected insulation, stored items, builders’ off-cuts and leaf litter are bagged and removed.
- Fixing airflow and water. Clearing or reinstating blocked vents, mechanical ventilation where passive airflow cannot cope, ducting exhaust fans outside, and referral to a licensed plumber or drainage contractor where water gets under the house.
- Follow-up readings to confirm the cavity is drying, with a written summary.
When to get it looked at
- A persistent musty or earthy smell with no visible mould; our guide to a musty smell in the house helps narrow down where it comes from
- Cupping, lifting or springy floorboards
- Mould that keeps appearing at skirting level or low on walls; rising damp versus condensation explains how to tell the two apart
- Ceiling mould that returns after treatment, suggesting the cavity above feeds it; see bathroom and ceiling mould removal
- A building or pre-purchase report that flagged subfloor damp
If you want answers in writing before committing to treatment, a standalone mould inspection covers both cavities.
How the job runs
- Describe the problem through the quote form. For hidden cavities, photos help less than the smell pattern, the age and construction of the house, and your suburb.
- Site inspection. Cavity work is never priced sight unseen. The inspection establishes access, extent and cause, then produces an itemised scope.
- Access. Clearance under older homes on sloping blocks can be very low at one side. Where there is no workable entry, a licensed builder can cut an access hatch, priced before anything proceeds.
- Asbestos screen. SafeWork NSW advises that homes built before the late 1980s may contain asbestos. Suspect material stops the job: asbestos must be removed by a licensed asbestos removalist, and friable asbestos needs a Class A licence.
- Treatment: timbers cleaned, debris and affected insulation removed, vents cleared, waste disposed of through licensed channels.
- Ventilation and drainage works. Mechanical ventilation wiring needs a licensed electrician; drainage repairs need a licensed plumber. Treating timber while water still runs under the house is wasted money.
- Re-check with follow-up moisture readings and a written record.
What drives the cost
Access matters most: a subfloor you can crawl through comfortably costs far less to work in than one that must be done in sections at minimal clearance. After that, the area affected, how much insulation and debris comes out, whether mechanical ventilation is needed, and what the moisture source turns out to be. No figures are published here; the mould removal cost guide explains the drivers.
Frequently asked questions
How do I know it is subfloor mould if I cannot see anything?
Mostly by smell: musty and earthy, strongest near floor level, after rain or when the house has been closed up. Cupping boards and skirting-level mould are the visual signs; only a physical inspection with moisture readings confirms it.
Is the white fluffy growth on the timbers under my house mould?
It may be mould or it may be a timber-decay fungus, which is a different problem and can be structural. The inspection distinguishes the two, and anything structural goes to a licensed builder.
Will treating the roof void fix the mould on my ceilings?
If the cavity is the source, through a leak, condensation under the roofing or a fan venting into it, yes. That is why ceiling and roof void work are often quoted together.
Will the musty smell go away after treatment?
Once growth is treated, damp material removed and the cavity drying, the odour fades as airflow does its work. If it persists, something is still wet, which is what the follow-up readings are for.
Get the hidden problem found
Use the Get a Free Quote form: give your suburb, the age of the house and where the smell is worst, and an inspection can be arranged that gives you answers in writing.
quote form