Microbial Growth Inside Insulated External Walls as an Indoor Air Biocontamination Source

Abstract

The association between moisture-related microbial growth (mesophilic fungi and bacteria) within insulated exterior walls and microbial concentrations in the indoor air was studied. The studied apartment buildings with precast concrete external walls were situated in a subarctic zone. Actinomycetes in the insulation layer were found to have increased concentrations in the indoor air. The moisture content of the indoor air significantly affected all measurable airborne concentrations.Concrete sandwich facade panels have been commonly used in building frameworks in northern Europe since the 1960s. These panels consist of two reinforced concrete panels enclosing a layer of mineral wool thermal insulation (rock or fiberglass wool), essential in the subarctic climate. Mold growth has been reported on the internal concrete core, initiated by the condensation of indoor humidity due to serious panel cracks (3). In a previous study (16) it was shown that microbial growth is found infrequently in the insulation layer in structures of this type in Finland, but such growth is increased if the external wall is in poor condition. Microbial growth within the exterior walls has seldom been considered a risk factor for indoor air quality (10). Compared to microbial growth on internal structures, the envelope does not necessarily have similar direct contact with the indoor air. However, if the supply airflow drifts through a contaminated wall structure, it may affect the quality of the indoor air. In the present study, we evaluated whether indoor air quality may be influenced by microbial contamination in the insulation layer of precast concrete external walls.Test buildings and insulation samples. We studied 50 inhabited apartment buildings, 2 to 38 years in age, with precast concrete sandwich panels as their framework structure. The buildings were situated in the southern coastal area of Finland, in the Turku region (60°50ЈN, 22°05ЈE to 60°39ЈN 22°40ЈE) and in Salo (60°39ЈN, 23°12ЈE). Prior to sampling, the condition of the exterior walls was monitored visually by using five parameters (Table 1) with a three-step scale (bad, moderate, good). Insulation samples from the external wall were taken from the whole depth of the insulation layer through boreholes from the outside. The sampled sites of the panel were (i) the central upper edge, (ii) the upper corner, (iii) the side edge of the panel, (iv) below the window, (v) the lower edge, and (vi) the central area. A total of 364 concrete panels were sampled. For the microbiological analysis, a subsample of the insulation sample was suspended in peptone water (1.0 g of peptone, 0.85 g of NaCl, and 0.02% Tween 80 detergent in 1 liter of deionized water), and the concentrations were determined by dilution plating (14) . Fungal colonies were counted after 7 days, and bacteria were counted after 10 days of incubation (at 25°C). The results are expressed as CFU per gram of insulation material. The fungal genera were identified microscopically, and bacteria were classified as actinomycet...

Quantitative PCR analysis of fungal DNA in Swedish day care centers and comparison with building characteristics and allergen levels

“…Other studies have indicated that wooden materials offer more favorable conditions for fungal growth than other building materials (Meklin et al., 2003; Pietarinen et al., 2008). Water condensation can be particularly problematic inside the structure of walls (Burge, 2002; Pessi et al., 2002), and moisture and mold problems in Swedish buildings may be more frequently located inside the building construction in floors and walls (Bornehag et al., 2001; Roussel et al., 2008). One limitation of our data is that we have no information about the type of wall construction, only the external material.…”

Building upon current knowledge and techniques of indoor microbiology to construct the next era of theory into microorganisms, health, and the built environment

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Winter Time Concentrations and Size Distribution of Bioaerosols in Different Residential Settings in the UK

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