In recent years, metagenomic analysis using next-generation sequencing has made it easier to study microbial communities in buildings. This study investigates the structure and diversity of eukaryotic and bacterial communities in microbial samples collected from various Japanese residential types, ranging from traditional to modern houses.

Microbial sampling was conducted over multiple years during summer and winter in living rooms and bedrooms, targeting various surfaces. Simultaneously, indoor environmental parameters such as temperature, relative humidity, and carbon dioxide concentration were measured. Additionally, residents provided information on housing characteristics and living habits, including building age, presence of pets, and HVAC system usage.

Previous studies have suggested a link between microbial communities in floor dust and asthma. Condensation inside air conditioning units may promote mold growth. Given that human inhale approximately 15 m³ of air daily, this study focuses on microbial communities in indoor and outdoor air, floor surfaces, and areas surrounding air conditioning units.

The results showed that modern houses had a higher relative abundance of human-associated bacteria on floors. Acinetobacter, commonly found in moist environments, was frequently detected in both indoor air and floors of modern residences. In traditional houses, especially in earthen-floored areas, halophilic Halococcus was identified. Additionally, Paracoccus, prevalent in air conditioning units, was also abundant in indoor air, suggesting that air conditioning systems influence indoor microbial communities.

Nowadays, people spend a considerable amount of their time indoors. Therefore, indoor physical, chemical, and biological environments are cru-cial for human health. While modern homes offer improved insulation, air-tightness, and air-conditioning systems to create thermal comfort and in-door air quality, recent studies suggest that promoting microbial diversi-ty—rather than strict sterilization—may benefit health. This study investi-gated the relationship between environmental factors—such as temperature, humidity, and ventilation—and microbial community structures in 28 homes across Japan. Air samples were collected from bedrooms, living rooms, and outdoor areas, and microbial communities were analyzed using 16S and 18S rRNA gene amplicon sequencing. PERMANOVA revealed significant differences between outdoor and indoor air, but not between liv-ing rooms and bedrooms. The influence of location was more limited for eukaryotic communities than for bacterial ones. NMDS and PCoA plots showed that outdoor air formed a distinct cluster, while indoor air samples overlapped. Seasonal variation significantly affected both bacterial and eu-karyotic communities, though the effect was weaker for bacteria. Among environmental factors, the air change rate (ACR) was strongly negatively correlated with the similarity between indoor and outdoor eukaryotic communities. In addition, air temperature and relative humidity appeared to influence eukaryotic community structures. These findings highlight the importance of considering not only short-term environmental conditions but also long-term structural and ventilation-related factors when evaluat-ing indoor air quality and its microbiological composition.

In modern society, much time is spent indoors. Controlling indoor air quality is an important factor for human health. Recent studies have shown that the alpha diversity of microbial communities is related to the risk of allergies and asthma in occupants. It is possible that human health benefits from living in harmony with a diverse microbial community rather than overcontrolling it. Therefore, the micro-bial diversity index can serve as an indicator of whether the indoor microbial en-vironment is healthy for humans. Our previous studies showed that the quantita-tive and qualitative structures of indoor eukaryotic and bacterial communities are related to temperature, relative humidity, and airtightness. It is assumed that a similar relationship exists for the diversity index and that it is possible to control the diversity index using indoor environmental factors. However, the quantitative relationship between these factors and microbial community diversity remains unclear . In this study, the indoor thermal environments of houses were char-acterized from indoor environmental measurements obtained from several houses in urban and rural areas of Japan using statistical analysis. In addition, the impact of these results on the diversity index (Shannon index) of eukaryotic and bacterial communities in indoor and outdoor air was evaluated. The results indicated that bacterial and eukaryotic community diversity indices were related to temperature and absolute humidity, especially in detached houses during winter. These findings may inform the development of indoor environmental control strategies aimed at promoting healthier microbial exposure for occupants.

Wood-brick heritage buildings, iconic cultural structures across East Asia with timber frames and masonry foundations, are increasingly subject to adaptive reuse. However, the impacts of different usage patterns on their hygrothermal environments remain insufficiently understood. This study investigated two heritage buildings in the Forbidden City in Beijing: one adaptively reused as an office and the other unoccupied. Through a year-long monitoring of indoor temperatures, relative humidity, and surface temperatures, the study analyzed the deterioration risks of condensation and mold growth, as well as human thermal comfort, to optimize environmental regulation strategies. Results re-veal that office-related activities significantly altered the indoor hygrothermal environments. The combined operation of radiator heating and air-conditioner (AC) narrowed the annual indoor temperature ranges by about 50% and ex-panded relative humidity ranges by about 30%. This alteration improved ther-mal comfort for over 80% of the winter and summer hours, and mitigated con-densation and microbial initiation risks in transitional seasons. Nevertheless, the intermittent AC operation increased daily temperature fluctuations by 1.3 to 2.3 times, enhancing the risks of condensation on floors and wall bottoms during the cooling period and thermal stress between interior and exterior wall surfaces. To ensure sustainable conservation and utilization of heritage build-ings, this study recommends elevating summer AC set-points by 2–3°C, adding climate buffers at entrances, and equipping unoccupied buildings with envi-ronmental sensors to guide transitional-season ventilation decisions. These da-ta-driven strategies reconcile preservation needs with adaptive reuse, providing transferable solutions for wood-brick heritage buildings.

Damage, failures and functional defects in buildings create huge costs for the property owners and insurance companies as well as the entire society. The cost of inefficient use of resources and direct and indirect measures to repair and fix damage, failures and functional defects in Swedish buildings was 2016 expected to be between 5,9 and 7,3 € billion per year. Approximately 70 % of those costs were linked to free water, moisture or other indoor environment problems.

This study intends to present a literature review which aims to inventory the area of studies which investigate damages and causes of damages in buildings. Previous studies (Mundt-Petersen et al. 2023A Mundt-Petersen et al. 2023B and Wallentén et al. 2023) indicate possible gaps and intermingling in the area for parameters such as:

- Technical aspects of causes of damage (such as damaged membranes or pipes) compared to qualitative aspects (such as bad motivation or stress) and financial aspects cause damage.

- What actors cause the damage

- Damage compared to the cause of the damage

- In what part of the building process the cause of the damage occur such as the design process, construction process, management and maintenance or renovation and rebuilding compared to when the damage occurs.

Based on the literature, the paper also intends to give examples of different types of damages and causes of damages and how those could be categorized which may be of interest in the on-going work develop the standard ISO/FDIS 22185-XX which dealing with damage.

References

Mundt-Petersen, Wallentén, Joelsson, Kläth, 2023A, Distribution and location of damages in Swedish buildings, J. Phys.: Conf. Ser. 2654 012014, 13th Nordic Symposium on Building Physics, Aalborg, Denmark 2023, doi:10.1088/1742-6596/2654/1/012014

Mundt-Petersen, Wallentén, Edskär, Joelsson, 2023B, Causes of Damages in Swedish Buildings, DBMC 2023, Beijing, Kina, https://www.scipedia.com/public/Olof_Mundt-Petersen_et_al_2023a

Wallentén, Mundt-Petersen, Joelsson, Kläth, 2023, Damaged Swedish Buildings, DBMC 2023, Beijing, Kina, https://www.scipedia.com/public/Wallenten_et_al_2023a

ISO/FDIS 22185-1 – Diagnosing moisture damage in buildings and implementing countermeasures – Part 1: Principles, nomenclature and moisture transport mechanisms

ISO/FDIS 22185-2 – Diagnosing moisture damage in buildings and implementing countermeasures – Part 2: Assessment of conditions