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Mould Sampling explained

The ideal situation is for a build to be considered to have “normal mould ecology” – this means that:

1. the moulds found indoors are of the same genre as the moulds found outdoors; and

2. the spore count of those moulds are lower indoors than they are outdoors.

Both moisture/dampness and/or mould in a building can lead to adverse health reactions for the occupants.

The primary focus of a Mould Testing Technician (or Building Biologist) is to identify the source of moisture AND determine how far mould has spread from the original source.

Once the source of moisture has been identified, it is essential to conduct sampling to confirm the type/s of mould/s present (e.g., because different moulds may result in different health effects) and in what areas of the home they are present (i.e., how far it has spread, so as to know the extent of remediation required).

There are various sampling techniques that may be used, each with their own pros and cons. A Mould Testing Technician (or Building Biologist) can advise which sampling method is most appropriate for your individual needs, following consultation with you and visual inspection of the build.

Irrespective of the type of sampling carried out, the results only relate to a ‘snap shot’ in time – in other words, what moulds were or weren’t present, and at what levels they were or weren’t present, at the specific time and in the specific area that the sample was taken.


The Environmental Relative Mouldiness Index (aka “ERMI”) was developed in the US to provide a way to quantify the “relative mould burden” in US homes, by looking at DNA in settled dust.

There are literally millions of mould species, only 10% of which are believed to have been identified by humans. Of that 10%, an ERMI considers the DNA of only 36 species, and a HERTSMI considers the DNA sample of only 5 species, all of which are commonly found in a relatively high concentrations in homes in the US.

The sample is collected either using a vacuum (usually in 2 rooms, such as the bedroom and main living room), or on a swiffer cloth. Due to the fact the sample is limited to a very small area/s of select areas of the build, an ERMI or HERSTMI only provides a ‘snap shot’ of the historical mould load of the build.

Of particular importance is the location that the sample is taken; for example, if a sample is taken from an area of carpet that may have previously been exposed to pet urine, the ERMI score may be far higher than it would if the sample is taken in an uncontaminated area.

An ERMI can be particularly useful for buyers/lessees looking at moving into a new home/premise, particularly if the build is unoccupied.

It can also be a useful tool for clinicians, because the ‘snap shot’ shows the genus and species of the moulds present, which the clinician can then compare to their patient’s individual test results.

A health practitioner, or other individual (e.g., a buyer or lessee), does not need to be versed in mould analysis to interpret the results.

However, both ERMI and HERTSMI have several limitations, such as:

· Homes built in Australia are designed and built differently to homes built in the US, where ERMI samples were designed to be used/taken.

· It is limited to the mould present in the dust collected in only a select few very small area/s – it does not give any indication whether there may be moulds present in other parts of the build.

· It does not assist with identifying moulds that may be present in places other than dust (for example, in the air or on surfaces).

· It does not assist with identifying how far mould spores may have spread – this is part of the primary focus of a Mould Testing Technician, or Building Biologist.

· It does not give any indication what moulds may be present in the air, that may be inhaled by occupants ‑ inhalation is the primary route of exposure.

Importantly, ERMI testing is not recognised by NIOSH when it comes to determining what mould remediation is required, nor can it can be used as a way of testing post-remediation to verify/confirm whether the remediation was successful.

An ERMI or HERTSMI is also a significant more costly sample, as opposed to air or surface sampling (for example).

Given the costs associated, as well as the limitations, ERMI and HERTSMI samples are not, generally, recommended by Building Biologists or Mould Testing Technicians – however, there are exceptions, such as pre-purchase or pre-lease inspections, when a Building Biologist or Mould Testing Technician may prefer this method of sampling.

At Building Biology WA, our preferred laboratory for processing ERMI or HERTSMI samples is MouldLab.

ERMI results are interpreted with reference to the following table:


ERMI Value



Q1 - Less than -4

Low Relative Mouldiness

Further investigation is not needed to determine the sources of the mould.

Q2 -4 to 0

Low-Medium Relative Mouldiness

Further investigation may be needed to determine the sources of the mould if occupants have been reactive, sensitised, genetically predisposed or otherwise immuno-compromised

Q3 0 to 5

Medium-High Relative Mouldiness

Q4 >5 to 20

High Relative Mouldiness

Source and cause of mould should be determined and remediation undertaken, reducing the ERMI to levels below Q2 >20

Very High Relative Mouldiness

Air Sampling

The most common route of exposure to mould is via inhalation AND airborne spores may also settle on contents within a build. Ascertaining what moulds are present in the air can, therefore, be useful in determining the likelihood that occupants in a build are exposed to mould particulates.

An air sample is collected with the use of a pump, that sucks air into a cassette and traps spores on a plate.

The aim is to have “normal mould ecology” – in other words, ideally, we want there to be less mould inside than there is outside (Kemp & Kemp, 2010). In order to identify whether a build has ‘normal mould ecology, a minimum of 3 air samples are required to be taken – a sample taken outdoors, a sample taken indoors in a room that is not suspected to be contaminated with mould and a sample in a room where mould is suspected to be present.

Depending on the size of the build and the extent of the mould suspected to be present, additional air samples may be required – a Building Biologist or Mould Testing Technician will only be able to give an indication of the number of samples that are required after undertaking a visual inspection of the build.

Where build materials and/or contents may have settled mould spores on them, they are considered to be Condition 2. Generally speaking, Condition 2 contents can usually (but not always) be cleaned/remediated/restored to Condition 1 (i.e., normal mould ecology). While a Building Biologist or Mould Testing Technician has an understanding of mould remediation, we are not IICRC approved mould remediators and are, consequently, unable to assist with the remediation process; we are, however, happy to provide some general guidance as to the steps that may assist with restoring contents, where possible.

Air sample results are interpreted with reference to the following table:

Hygiene Rating

Total Indoor Concentration in a Passively Ventilated Building

Low Less than ½ the outdoor air

Normal Less than the outdoor air

Elevated More than the outdoor air, but less than 1,000 spores/m3

High More than 1,000 spores/m3, but less than 2,500 spores/m3

Extremely High More than 5,000 spores/m3

At Building Biology WA, our preferred laboratory for processing air samples is AEML in Melbourne (we may occasionally also use Symbiotic Labs).

Surface Sampling

Following visual inspection, a tape/lift or swab sample may be taken if your Building Biologist or Mould Testing Technician considers suspects visible marks/stains/spots may possibly be mould.

Where build materials and/or contents have visible mould on them, they are considered to be Condition 3. Condition 3 items may be able to be cleaned/remediated/restored, depending on whether the materials/contents are porous, semi-porous or non-porous.

Surface sample results are interpreted with reference to the following table:

Hygiene Rating

Surface Fungal Spore Limit


Less than 50 spores/cm2

Normal Fungal Ecology

50 to 500 spores/cm2


500 to 1,000 spores/cm 2 + prevailing species*


More than 1,000 spores/cm2 + dominant species + propagules**

Extreme Contamination

More than 5,000 spores/cm2 + dominant species + propagules** + confluent spores

At Building Biology WA, our preferred laboratory for processing surface samples is AEML (we may occasionally also use Symbiotic Labs).

How much will sampling cost?

Each individual sample is processed by the laboratory and charged separately; the more samples that are taken, the higher the laboratory costs will be. Until such time as visual inspection has been undertaken, in person, it is impossible to say what sampling will be most appropriate, or how many samples may be required.

The costs also differ depending on the preferred lab. While our preferred lab is based in the eastern states, there is a lab here in WA that can process samples more urgently, if required. The costs associated with urgent processing (locally) are significantly higher, however this is an option available to our clients if they require their results back urgently.

Different sampling methods also attract different laboratory charges. For example, the laboratory costs associated with processing a single ERMI/HERTSMI sample are significantly more than the laboratory costs associated with processing a single air/surface sample.

A Building Biologist or Mould Testing Technician is qualified to interpret the laboratory results, giving consideration to health.

Do I need to get my home checked again at a later date, once sampling has been done?

Once an initial audit has been undertaken and the lab results received, a Building Biologist (or Mould Testing Technician) can provide recommendations as to what (if any) remediation is required.

If remediation is required, it is recommended that post-remediation sampling be carried out after the remediation steps have been carried out, to verify/confirm that the remediation has been successful and that the build has returned to normal mould ecology.

What about commercial testing and insurance?

Building Biology WA provides sampling services for remediation and commercial cleaning companies. Often for insurance purposes pre remediation sampling to determine contamination and spread and post remediation verification sampling to determine the effectiveness of the remediation and determine in normal mould ecology has been achieved is required. Building Biology WA can provide these services as well as professional advice and a scope of works for remediation if requested. Building Biology WA can also provide reports for the purpose of litigation.



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