Loft contamination by mould in newly constructed property

Newly constructed properties are sometimes far from being contaminants free. Sometimes lack of expertise in a particular area or a simple architectural error can lead to myriad of problems. I have been call to inspect a newly constructed property in the Manchester area which was affected by a significant mould problem in the roof space. This newly build house was spread over three floors and had a party pitched and partly flat roof. The property had cavity wall construction and external rendering. Loft of the property was insulated with loose mineral wool insulation and the roof underside was timber.

Following the completion of the construction the loft of the property has developed a significant condensation problem which resulted in complete mould overgrowth of the loft plywood underside. The property occupants were suffering with respiratory irritations and headaches. The objectives of the investigation were to a) evaluate the extent of mould contamination, b) evaluate the level of airborne mould spores within the habitable areas of the house, c) provide recommendations regarding the best protection measures of the habitable areas.

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To evaluate the level of mould spores in the habitable areas of the property I have collected a number of spore trap and samples to be analysed by optical light microscopy. I have collected samples around the property as well to get a better understanding of the normal environmental background levels. Following the analysis of the samples I have concluded that the ground floor of the property was not affected by the mould growth in the loft. However the first floor samples directly underneath the affected areas showed a significant increase of mould spores. The fungal spores count went from 3000-6000 counts/m3 for outside and ground floor to over 15 000 for the master bedroom. The mould spore samples from the loft area showed concentration of mould spores exceeding 100 000 spores per cubic meter of air. Qualitatively the non-culturable spore trap samples collected in the habitable areas of the property were dominated by Aspergillus/Penicillium spores followed by Alternaria type of spores representing respectively 78% and 6% average distribution in the collected samples on the first floor. The collected background samples were dominated by Cladosporium spores followed by a group of unidentified fungal spores representing respectively 53% and 38% average distribution.

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Quantitative assessment of culturable mould samples shows that at the time of the assessment the overall concentration of viable mould spores in the indoor environment was only marginally less in comparison with the background environmental samples. The overall concentration of viable moulds spore samples indoors ranged between 1020 and 1250 colony forming units per cubic meter. The average background concentration of culturable mould spores in the atmosphere at the time of the assessment was 1380 colony forming units per cubic meter. Qualitatively the indoor viable samples were dominated by Penicillium moulds followed by Cladosporium moulds with minor presence of Yeasts representing respectively 85% and 10% distribution in the samples. The collected background samples were dominated by Penicillium moulds followed by Yeasts representing respectively 88% and 7% distribution in the samples.

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The assessment clearly showed that the loft is the reservoir of mould spores and there is some path that connects the loft and upper floor bedroom which allows for some of the mould spores to contaminate the rooms. The symptoms the occupants were suffering ware in agreements with the widely reported symptoms from mould affected houses.

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Identification of mould colonising the loft showed that the most abundant genera were Penicillium moulds closely followed by Alternaria (alternate, consortiale), Cladosporium and Acremonium strictum. All of these moulds are allergenic in high concentration. In addition to these typical fast growing moulds slow growing macroscopic fungi associated with wood rot were also identified. The presence of macroscopic fungi in suspected areas is a clear indicator of long term water problems and strong fungal rot.

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In the final conclusion of this assessment I have stated that the indoor air quality on the ground floor of the property is unaffected. I have also stated that the indoor air quality on the first floor of the property is significantly degraded. The mould contamination is limited to the loft of the property and exceeds 100 meters squared. Based on the results of moisture mapping, visual observation and microbiological sampling and identification it is my opinion that the most likely reason for adverse health symptoms experienced by some of the occupants, was the continuous exposure to significant concentration of fungal spores and fungal metabolites.

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To prevent continuous exposure of the occupants to the elevated levels of mould spores and to protect the habitable from contamination during the roof reconstruction the following measure were strongly recommended:

1. an air management system within the property should be put in place as soon as practicable and should be maintained for the duration of the roof decontamination. This should include sealing of all opening/apertures and positive pressurisation of the property. The property should be pressurised by filtrated outdoor air free from any fungal contamination and the indoor air pressure should exceed the outdoor by at least 5 pascals. The pressurisation of the property can be archived by the use of inverted negative pressure units (NPU’s) equipped with HEPA filters.

2.all contaminated materials should be removed from the loft areas causing minimal disturbance of the contamination. Clear material transport routes should be established as far as reasonably practicable from the habitable areas.

3.operatives working with the contaminated materials should be protected by disposable coveralls and respiratory protection of at least FFP3 standard.

4.all internal areas of the property should be thoroughly ventilated to remove residual fungal spore contamination. The ventilation can be achieved by during the pressurisation of the property and by management of the air flow within the property.

5.it is recommended to neutralise volatile fungal metabolites by ozone treatment of the property. The treatment should be carried out after the complete physical removal of all contaminated materials from the roof.

By Tomas Gabor

Link through to Sysco - Nationwide specialists in hazard exposure monitoring
Hi, I have been working in my job as an Indoor Air Quality Investigator for a number of years and decided to share my experience with you. You can find lot of related information on my website toxic black mould
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