Assessing Your Home for Mould
One of the more difficult situations I see in clinical practice is someone with chronic health symptoms who suspects their home or workplace may be contributing, but there is no obvious mould problem.
There may be no black mould on the walls, no major flood and sometimes no particularly strong musty smell. The building may look completely normal.
Moisture can enter wall cavities through roofs, windows or failed waterproofing, collect beneath flooring, leak slowly from plumbing, develop within subfloors or roof spaces, or occur repeatedly through condensation. A previous water event may also have dried long before someone begins investigating the building.
For this reason, I think it is more useful to ask: has this building experienced abnormal moisture, and is there evidence that this has resulted in microbial growth or contamination?
How can a water-damaged building affect health?
The best-established health effects associated with damp and mould-affected buildings include asthma, allergic rhinitis and other respiratory symptoms. The World Health Organization also recognises that persistent dampness and microbial growth within buildings can adversely affect health and recommends preventing or remediating ongoing dampness rather than trying to define a single ‘safe’ mould concentration (World Health Organization 2009).
However, not everyone I see with suspected mould-related illness presents primarily with respiratory symptoms. A common presentation is a more chronic, multisystem pattern involving fatigue, brain fog, poor concentration or memory, headaches, dizziness, sleep disturbance, sinus symptoms, muscle and joint pain, gastrointestinal symptoms, temperature dysregulation, increased sensitivity to smells or chemicals and reduced exercise tolerance.
This type of chronic multisystem presentation is often described as Chronic Inflammatory Response Syndrome (CIRS), particularly when symptoms have developed or significantly worsened following exposure to a water-damaged building. CIRS describes a persistent inflammatory illness involving symptoms across multiple body systems rather than a simple mould allergy or isolated respiratory reaction (Dooley et al. 2024).
Sometimes the environmental pattern provides another clue. Someone may feel progressively worse while spending time at home, improve when travelling or staying elsewhere, or notice that symptoms began after moving into a particular property, workplace, renovation or water event.
Look for water damage, not just visible mould
One of the first things I recommend is to stop looking exclusively for visible mould and start looking for evidence of moisture or previous water damage.
This may include:
water staining or discolouration on ceilings or walls
bubbling, blistering or peeling paint
swollen skirting boards, cabinetry, particleboard or MDF
warped timber flooring or lifting carpet
recurrent condensation
mould behind furniture or inside wardrobes
damp, earthy or musty odours
staining around skylights, windows or downlights
deterioration around showers or wet areas
evidence of previous leaks beneath sinks or appliances.
Some of these signs can be surprisingly subtle. A bathroom cabinet that has started to swell, a slightly distorted skirting board or an old ceiling stain may tell you more about the history of the building than simply looking for dramatic black mould.
Importantly, water-damaged materials do not need to be wet now. A roof leak may occur only during heavy rain, or a wall cavity may have been repeatedly wet over several winters and be dry when it is finally inspected.
Where could the moisture be coming from?
Common causes include roofing and flashing leaks, blocked gutters, poor drainage, plumbing leaks, failed bathroom or balcony waterproofing, leaking windows, damp subfloors, air-conditioning condensate problems, inadequate ventilation and condensation.
A building does not need to have experienced a dramatic flood. Repeated condensation on cold surfaces or within building assemblies can provide enough moisture to support microbial growth. WHO identifies condensation, visible mould, mould odour and a history of water leakage or penetration as useful indicators of dampness and microbial growth (World Health Organization 2009).
Ultimately, moisture is the key issue. Finding mould without understanding why the building became wet does not solve the problem.
What can you initially check yourself?
Before arranging extensive laboratory testing, it is worth taking a basic history of the property and looking through it systematically.
Use a bright torch and look closely at external walls and corners, skirting boards, wardrobes, windows, beneath sinks, around showers, ceilings below bathrooms, carpet edges and air-conditioning systems.
Think about previous events as well. Has there ever been a roof leak, overflowing gutter, flood, leaking appliance, balcony problem, repeated condensation or visible mould that was simply cleaned and painted over?
A basic humidity meter can provide additional information if humidity is repeatedly elevated or condensation is common.
If you are already unwell, I would avoid pulling up carpet, opening wall cavities or disturbing suspicious materials yourself. Hidden contamination can release considerably more dust and fungal particulate once disturbed.
What about ERMI testing?
ERMI, or the Environmental Relative Moldiness Index, uses quantitative PCR to measure DNA from 36 selected mould species in settled household dust.
One potential advantage is that settled dust can reflect contamination accumulated over a longer period than a short air sample and can provide species-level information. For this reason, ERMI can sometimes be a useful screening tool where there are ongoing concerns but little obvious visible mould.
Australian research examining 76 water-damaged homes in south-eastern Australia found that many of the mould species included in ERMI occurred at comparable concentrations to matched US homes, suggesting that the test can provide useful information in Australian buildings (Rossini et al. 2017).
However, I would not use ERMI alone to determine whether a home is safe or unsafe. The US Environmental Protection Agency describes ERMI as a research tool and notes that it has not been validated for routine non-research use (US EPA 2026).
An ERMI result cannot tell you where water is entering the building, which room contains the source, whether mould is actively growing now or how extensive the water damage is. Results can also be influenced by sampling location, cleaning practices, flooring and historical contamination.
So if an ERMI is concerning, the more useful question is: where is the water damage that could explain it?
When to consider a building biologist
If symptoms are significant, the building history is suspicious or initial testing raises concerns, a comprehensive assessment by an appropriately trained building biologist or indoor environmental professional can be very useful.
A proper inspection should go beyond looking for visible mould. It may include:
review of previous leaks, renovations and water events
internal and external visual inspection
moisture mapping of walls, ceilings and flooring
thermal imaging to identify areas requiring further investigation
assessment of humidity and condensation risk
inspection of accessible roof spaces and subfloors
assessment of air-conditioning, ventilation and condensate drainage.
The important point is that no one instrument gives the answer. Thermal imaging, for example, does not directly detect mould; it identifies temperature differences that may indicate an area worth investigating with moisture measurements.
This broader approach is important because assessment of water-damaged buildings is fundamentally about identifying moisture, affected building materials and the likely source, rather than simply collecting mould samples (NIOSH 2018).
What can laboratory testing show?
Laboratory testing becomes most useful when it is targeted towards a specific question and interpreted alongside the building history, visual inspection and moisture assessment (Australian College of Environmental Studies 2023).
Air sampling can identify fungal structures present in the air during the sampling period and compare different rooms or indoor and outdoor air. Its main limitation is that it is only a snapshot. Hidden mould may not be releasing significant numbers of spores at the time of sampling.
NIOSH cautions that short-term spore counts or culture results cannot be interpreted as health-risk thresholds and notes that detailed visual inspection and evidence of dampness or musty odour can be more reliable for identifying building moisture problems (NIOSH 2025).
Surface sampling, such as tape lifts or swabs, can provide information about fungal structures on a suspicious material. Culture sampling can identify organisms capable of growing under laboratory conditions, while dust PCR testing, including ERMI, measures fungal DNA accumulated within dust.
Where there is a strong suspicion of contamination inside a wall or ceiling cavity, targeted cavity investigation may sometimes be required.
The useful information comes from bringing these findings together with the building history and moisture assessment rather than treating any single result as definitive.
Finding the source is the important part
Imagine someone has an elevated ERMI but no obvious visible mould.
An assessment identifies abnormal moisture around a bedroom window. Thermal imaging shows an anomaly extending down the wall and moisture measurements confirm that part of the wall is affected. Further investigation identifies failed flashing that has allowed rain into the cavity, and targeted sampling confirms fungal growth in the affected materials.
The situation has moved from:
‘My ERMI is high.’
to:
‘Water is entering through this part of the building, this wall cavity is affected and these materials require remediation.’
That is much more actionable.
Remediation should begin with the moisture source
Once the source and extent of the problem have been identified, the first step is correcting the water or moisture issue. Depending on the cause, this may require a plumber, roofer, builder, waterproofing specialist, drainage contractor or HVAC technician.
For more significant contamination, professional remediation may involve containment, HEPA filtration or negative air control, removal of damaged porous materials, detailed cleaning of materials that can remain and management of affected contents.
The goal is not simply to kill mould.
Painting over a water-damaged wall, spraying an antimicrobial product or fogging a property does not replace correcting the moisture source and physically addressing contaminated materials. Professional remediation guidance focuses on source correction, appropriate removal and cleaning, and post-remediation verification (IICRC 2024).
For significant water damage, I generally prefer the environmental assessor to provide a written scope of works identifying the moisture source, affected areas, materials requiring removal or cleaning, containment requirements and how the work should be checked afterwards.
Where possible, I also prefer the assessor to be independent from the company performing the remediation.
Checking the building afterwards
Post-remediation verification may include confirming that the moisture source has been corrected, checking that remaining materials are dry, visually assessing cleanliness and, where appropriate, repeating targeted environmental sampling.
The aim is not to prove that there are no mould spores anywhere in the building. Mould is naturally present in indoor and outdoor environments.
The aim is to establish that the abnormal moisture source and associated contamination have been properly addressed.
Putting the pieces together
If you are experiencing chronic multisystem symptoms and suspect that your home or workplace may be contributing, the absence of obvious visible mould does not necessarily rule out a water-damaged environment.
The most useful approach is usually progressive:
health and exposure history → signs of water damage → moisture assessment → targeted environmental testing → locating the source → remediation → verification
ERMI and other laboratory tests can contribute useful information, but they are only part of the investigation.
Ultimately, the goal is not simply to prove that mould exists.
It is to identify whether there is a meaningful moisture problem, determine where it is, understand what has been affected and develop a clear plan to correct it.
Resources
Australasian Society of Building Biologists (ASBB) – Provides information on building biology and environmental health, including certified assessors. ASBB website
Institute of Inspection, Cleaning and Restoration Certification (IICRC) – Provides standards and certification relating to water damage restoration and mould remediation. IICRC website
References
Australian College of Environmental Studies (2023) Mould testing manual, version 2, Australian College of Environmental Studies, Warrandyte, Victoria. Australian College of Environmental Studies
Dooley M, Vukelic A and Jim L (2024) ‘Chronic inflammatory response syndrome: a review of the evidence of clinical efficacy of treatment’, Annals of Medicine & Surgery, 86(12):7248–7254. https://doi.org/10.1097/MS9.0000000000002718
IICRC (Institute of Inspection, Cleaning and Restoration Certification) (2024) ANSI/IICRC S520-2024: Standard for professional mold remediation, 4th edn, IICRC, Las Vegas, NV. ANSI/IICRC S520-2024
NIOSH (National Institute for Occupational Safety and Health) (2018) Dampness and mold assessment tool for general buildings – form & instructions, DHHS (NIOSH) Publication No. 2019-115, Centers for Disease Control and Prevention, Morgantown, WV. https://doi.org/10.26616/NIOSHPUB2019115
NIOSH (National Institute for Occupational Safety and Health) (2025) ‘Mold, testing, and remediation’, Centers for Disease Control and Prevention, accessed 5 September 2026. NIOSH Mold, Testing, and Remediation
Rossini G, Neil V, Lark D, Wymer L and Vesper S (2017) ‘Comparison of mold populations in water-damaged homes in Australia and the United States’, Fungal Genomics & Biology, 7:1–7. https://doi.org/10.4172/2165-8056.1000152
US EPA (United States Environmental Protection Agency) (2026) ‘Environmental Relative Moldiness Index (ERMI)’, US EPA, updated 6 July 2026, accessed 5 September 2026. US EPA ERMI information
World Health Organization (2009) WHO guidelines for indoor air quality: dampness and mould, WHO Regional Office for Europe, Copenhagen, accessed 5 September 2026. WHO guidelines
This article provides general educational information and is not intended to replace individual health or environmental assessment.