The Role of Transient Wetting on Mould Growth on Wooden Claddings (original) (raw)
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HAM and mould growth analysis of a wooden wall
International Journal of Sustainable Built Environment, 2013
The aim of engineers is to design structures, while minimising their energy dependence and create a suitable environment for living. Some of the most important factors for maintaining the indoor environment are temperature and humidity. Unsuitable combinations of heat and moisture (HAM) could indicate a danger of mould growing. The mould's existence influences the reliability and lifespan of a structure. Some materials, for example wood, are very sensitive to mould growth. To analyse a structure for mould growth risk it is necessary to know the values of temperature and relative humidity on the surfaces and inside of structures. There are two possibilities to acquire these quantities; taking measurements at a construction site or in a laboratory, or applying numerical solutions using an accessible programme. One such programme is Wufi, which has been developed especially for HAM analysis. An advantage of measuring at the construction site is the reality, which is not affected by numerical errors. On the other hand, numerical analysis usually needs lower costs and does not demand so much time to simulate long term periods. From the point of view of accuracy, it is suitable to verify the numerical solution with measurements. The aim of this paper is threefold. First, to analyse the risk of mould growth. Second, it presents a verification of numerically calculated data using Wufi 2D against actual measurement data acquired from a real structure, which is presented by a low-energy house located in Oulu/Finland. Third, to prove that the form of low-energy building structures do not increase mould growth risk. After carrying out the verification, the received outcomes are utilised for mould growth analysis. For an expression of reality in the numerical solution, a transient simulation was needed. The received outcomes were then used for mould growth analyses. There is a possibility to predict real mould growth risk inside the structure and on its surfaces, corresponding to the critical relation between temperature and relative humidity, which separates favourable and unfavourable areas for mould growth.
Validation of critical moisture conditions for mould growth on building materials
Building and Environment, 2013
Materials that are stored or used in damp conditions may be subject to mould growth. However, all materials are not equally susceptible; for each specific material, there is a critical moisture level for mould growth. If this is exceeded, there is a risk that mould fungi will develop on the material. This level can be determined in accelerated laboratory tests, at constant temperatures and relative humidity (RH) favourable to mould growth. Within a building however, these parameters are expected to vary from one part of the construction to another, and are seldom constant; there is fluctuation in temperature and RH due to seasonal or shorter-term variations. In this study, test pieces of the same materials tested in a laboratory environment were placed in three outdoor ventilated crawl spaces and three outdoor ventilated attics, where the temperature and RH varied, and mould growth on the test pieces was studied over 2.5 years. Material-specific mould growth curves were produced based on critical moisture levels, as determined in laboratory experiments under constant temperature and RH. When the actual conditions of RH and temperature exceeded these curves, there was mould growth on the test pieces if the time was sufficiently long. The conclusion from the study is that although conditions in laboratory studies are simplified and accelerated, the results serve well to indicate mould growth within a building construction.
Building and Environment, 2009
We report the results of a study to evaluate the growth rate of three species of mould on plasters, finishes and paints typically used in structures with heavy weight building envelopes. The aim was to determine the influence of the chemical composition (in terms of organic fraction of the materials) on the growth rate of moulds. The study was carried out in the following steps: -characterization of materials;inoculation of mould spores (3 species) on 7 types of material (2 plasters, 3 finishes, 2 paints); -growth in a climatic chamber (23 C and 90% RH); -analysis of the mould growth rate using various experimental techniques (fluorescence microscopy analysis, thermogravimetric analysis, etc.). Results show a clear correlation between the organic substances contained in paints, plasters and finishes and the growth rate of the mould. This study is part of a more general research program which addresses the effects on indoor environment air quality based on the European directive 2002/91/EC. This directive specifically indicates that energy consumption in buildings should be limited and sets threshold values for the thermal resistance of the building walls and windows. As a consequence window manufacturers are improving the thermal property of windows by reducing the air permeability, which may increase the indoor and surface relative humidity percentage (RH%) and lead to the development of mould in the indoor environments.
Laboratory study to determine the critical moisture level for mould growth on building materials
International Biodeterioration & Biodegradation, 2012
The susceptibility of building materials to mould growth varies. Some are tolerant to high relative humidity in the ambient air without mould growth occurring, while others are less tolerant, and mould can grow in relative humidity as low as 75%. Within a building, constructions are exposed to different temperatures and relative humidities. To minimise the risk of microbial growth, building materials should be chosen that are tolerant to the expected conditions. In this study, the critical moisture levels for ten building materials with a range of expected critical moisture levels (wood-based materials, gypsum boards and inorganic boards) were evaluated. Samples of the building materials were inoculated with spores from six species of mould fungi (Eurotium herbariorum, Aspergillus versicolor, Penicillium chrysogenum, Aureobasidium pullulans, Cladosporium sphaerospermum, Stachybotrys chartarum) and incubated in test cabinets at specified temperature (10 C and 22 C) and relative humidity conditions (75e95%); growth of mould was analysed weekly for at least 12 weeks. One of the conclusions is that two similar building materials or products may have considerably different resistance to mould growth, and so the results from one type of building material cannot be applied to the other. Also, in order to compare results from different tests, it is important to use the same test method. It is also important to state the temperature at which the critical moisture level applies and how long the material is exposed to the temperature and relative humidity conditions during the test.
Conditions Influencing Mould Growth for Effective Prevention of Wood Deterioration Indoors
Applied Sciences
Effective prevention of mould growth indoors is still an important topic considering that mould growth is frequently observed in buildings, it causes serious health hazards and can irreversibly damage infected objects. Several studies have been conducted and mould growth models developed. Despite that, some potentially important aspects such as water damage and spore contamination have received only little attention. The objective of the present study was to investigate the effect of the initial moisture content of wood and spore contamination on mould development indoors. The mould tests were performed in constant temperature (10, 20 and 30 °C) and relative humidity (91% and 97%) conditions. The results show that wetting of wood specimens prior to the test significantly accelerates mould growth at a temperature of 10 °C. For the other temperatures, the effect was insignificant. Similar results were obtained for the test involving dry (conditioned at RH 50%) and conditioned specimen...
Methods for Determining Mold Development and Condensation on the Surface of Building Barriers
Buildings, 2019
The article presents four equivalent methods for checking mold growth on the surface of building barriers and checking water vapor condensation on their surface. Each method applies to two parallel phenomena that may occur on a building barrier. The first method is to calculate and compare temperature factors. In the second method, the characteristic humidity in the room is calculated and compared. The third method is to calculate and compare the characteristic temperatures in the room. The fourth method is based on the calculation and comparison of characteristic water vapor pressures. Three boundary conditions are presented for each method and phenomenon: when a given phenomenon can occur, when it begins or ends, and when it does not occur. The presented methods systematize the approach to the problem of mold development and surface condensation. The presented calculation results relate to the selected building barrier functioning in specific indoor and outdoor climate conditions....
Impact of wind-driven rain on mould growth and indoor climate
2007
In this paper an onset is given to whole building modelling by investigating the impact of wind-driven rain (WDR) on indoor climate and mould growth at interior wall surfaces. The hygrothermal behaviour of a cubic building with solid brick walls is numerically analysed. The simulations demonstrate that the impact of WDR loads on the moisture contents in the walls is much larger near the edge of the walls than at the centre. For the case analysed, WDR causes an increase of indoor relative humidity of up to 51 % and an increase of energy consumptions for heating by 11 % in winter and by 12 % in summer respectively; while a much smaller impact on indoor humidity and a very small impact on energy consumption are seen in spring and autumn. Furthermore the obtained relative humidity and temperature at the interior wall surfaces are combined with isopleths of generalised spore germination time of fungus mould. The results show that WDR loads can have a significant impact on mould growth especially at the edge of the wall.
Houses with mould problems Comparison of two methods for verifying mould growth in buildings
2000
During the last ten years, the adverse health effects in upper respiratory system and irritation symptoms have become increasingly evident in residents living in moisture damaged houses with dampness and mould growth. In the mid of 1995, Finnish environmental health authorities faced the problem with an increasing demand for investigations to verify the microbial growth in suspected buildings and thereby taking appropriate control measures to protect the health of occupants. As an extension of an earlier relatively onerous method for quantification of microbial growth on surfaces, the Food Laboratory in Porvoo developed an applied direct streak method (DSM) aiming at a facilitation of the method verifying the presence of mould growth. The method was established in close collaboration with health inspectors. The DSM was compared to the original culture method (CM) and repeatability and reproducibility were good or very good. The DSM is a semi-quantitative method and enables the health inspectors to take surface samples without breaking the building structures and without being restricted to stiff surfaces. The results can demonstrate that the material is damaged by active viable mould growth. The DSM provides a powerful and useful tool for health inspectors to verify mould growth in buildings and it supports them to make decisions that are needed to protect the health of occupants. The cost of DSM is about one fourth of that of the more elaborate CM. The DSM is being increasingly used in Finland.
Comparison of test methods for mould growth in buildings
2016
The purpose of this work is to compare a range of test methods and kits for assessing whether a building structure is infested by mould fungi. A further purpose of this work is to evaluate whether air-based methods for sampling fungal emissions provide information qualifying decisions concerning renovation needs. This is of importance when hidden surface testing would require destructive measures and subsequent renovation. After identifying available methods on the Danish market for assessing mould growth in dwellings, a case study was conducted to test the usefulness of the methods in four dwellings of different typology and with or without known mould infestations. In each dwelling seven methods were used in parallel. The criteria for choosing the different methods were that they had to be nondestructive, relatively quick and easy, and frequently used by building professionals. The chosen methods measure different aspects relating to mould growth and vary in selectivity and precis...