scholarly journals Validation of critical moisture conditions for mould growth on building materials

2013 ◽  
Vol 62 ◽  
pp. 201-209 ◽  
Author(s):  
Pernilla Johansson ◽  
Thomas Svensson ◽  
Annika Ekstrand-Tobin
Keyword(s):  
Building Materials ◽  
Mould Growth ◽  
Critical Moisture ◽  
Moisture Conditions

Laboratory study to determine the critical moisture level for mould growth on building materials

2012 ◽  
Vol 73 ◽  
pp. 23-32 ◽  
Author(s):  
Pernilla Johansson ◽  
Annika Ekstrand-Tobin ◽  
Thomas Svensson ◽  
Gunilla Bok
Keyword(s):  
Laboratory Study ◽  
Building Materials ◽  
Moisture Level ◽  
Mould Growth ◽  
Critical Moisture

Risk for Mould Growth on Hemp-Lime at Different Relative Humidity

2022 ◽  
Author(s):  
Sanne Johansson ◽  
Kristin Balksten ◽  
Paulien Brigitte Strandberg-de Bruijn
Keyword(s):  
Relative Humidity ◽  
Building Materials ◽  
Microbial Growth ◽  
Mould Growth ◽  
European Climate ◽  
Northern European ◽  
Critical Relative Humidity ◽  
Different Temperatures ◽  
Critical Moisture ◽  
Hemp Shiv

Microbial growth often thrives in humid conditions, at high relative humidity. Moulds are complex organisms; many types of mould are able to survive strong variations in humidity and temperature, such as those on building façades. For some building materials a critical relative humidity is determined, which functions as a theoretical threshold; at this (or lower) relative humidity microbial growth will likely not occur. Hemp-lime is a building material that consists of hemp shiv (the woody core parts of the hemp stem) and building lime. It is a material that can be used for walls, and even though it has been used for more than 20 years, thusfar little is known about its critical moisture levels for microbial growth. The aim of this research was therefore to determine at what relative humidity microbial growth occurs on carbonated hemp-lime material, and to study if there is a protective influence of a carbonated lime binder on the hemp shiv. The objective was to study microbial growth on hemp shiv, hemp-lime and on hemp with a thin layer of lime at three relative humidity (75 %, 85 % and 95 %) and at two different temperatures (15°C and 23°C); conditions that could occur naturally in a hemp-lime façade exposed to high rain loads in a northern European climate. Hemp shiv seems to have a relatively low resistance to microbial growth, similar to that of wood. However, because the hemp is protected by lime it can withstand much higher relative humidity without microbial growth occurring on the material. The critical moisture level for hemp-lime seemed to occur between 75 and 85 % RH, while the material was completely without microbial growth at 75 % RH. The lime had a protective effect on the hemp and acted as a mould inhibitor, both over time and with varying temperature and humidity.

scholarly journals Threshold values for mould growth: Critical moisture level of 21 different building materials

2020 ◽  
Vol 172 ◽  
pp. 20002
Author(s):  
Pernilla Johansson ◽  
Lukas Lång ◽  
Gunilla Bok ◽  
Carl-Magnus Capener
Keyword(s):  
Building Materials ◽  
Field Studies ◽  
Test Method ◽  
Moisture Level ◽  
Mould Growth ◽  
Specific Product ◽  
Material Choice ◽  
Critical Moisture ◽  
Four Levels ◽  
Specific Material

The susceptibility for mould growth varies among different building materials. One way to describe the susceptibility is the lowest RH at which mould can grow on a specific material, the critical moisture level (RHcrit). Determining RHcrit for materials provide the basis for material choice in designs where moisture and temperature conditions are known. In this study, RHcrit of 21different products were determined according to SIS-TS 41:2014/SPMet 4927. This test method is developed based on the results of a variety of laboratory studies and validated by field studies. Test specimens were inoculated with a suspension containing spores from six different mould fungi and were then incubated in moisture chambers at four levels of RH at 22 °C. After 12 weeks specimens were analysed for mould growth. RHcrit was determined based on the lowest RH at which mould grew on the specimens. RHcrit varied among different products, even between product belonging to a similar group of material, for example, calcium silicate boards or gypsum boards. The results show, and confirm, previous findings that it is not possible to estimate RHcrit for a specific product based on material group. Instead, each product must be tested.

scholarly journals Current building strategies in Greenland

2020 ◽  
Vol 172 ◽  
pp. 19004
Author(s):  
Eva B. Møller ◽  
Tove Lading
Keyword(s):  
Organic Material ◽  
Building Materials ◽  
Test Site ◽  
Building Construction ◽  
Mould Growth ◽  
Good Test ◽  
Short Period ◽  
Harsh Climate ◽  
Building Designs

Most buildings in Greenland are built within the last 70 years. Within this relatively short period, the building styles have often changed; from small wooden houses in the 50ties to also encompass more industrialised buildings in the 70ties, and later more diverse technics. This paper describes the major tendencies in building construction of today. Apart from an extreme climate, one of the challenges in Greenland is the lack of building materials; almost everything has to be imported. Greenland is an island-operated community, with no interlinking road grid between towns and settlements. Therefore, everything must be transported by ship or plane. Furthermore, severe mould growth is a big problem. Consequently, three building strategies are currently prevailing. 1) In-situ concrete gables and partitioning walls, and facades with wooden studs. 2) Focus on non-organic material and therefore concrete structures with exterior insulation. 3) Strategies focussing on the process e.g. mainly using prefabricated elements. The paper describes the pro and cons for the different strategies seen in a Greenlandic context. The harsh climate makes Greenland a good test site for assessing new building designs. Furthermore, assessment of sustainability might be very different in Greenland from countries where resources and transportation is very different.

scholarly journals Exterior Wood-Frame Walls—Wind–Vapour Barrier Ratio in Denmark

Buildings ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 428
Author(s):  
Martin Morelli ◽  
Torben Valdbjørn Rasmussen ◽  
Marcus Therkelsen
Keyword(s):  
Building Materials ◽  
Frame Structure ◽  
Diffusion Resistance ◽  
Mould Growth ◽  
Climate Data ◽  
Safe Side ◽  
Air Tightness ◽  
Wood Frame ◽  
And Diffusion ◽  
Exterior Wood

Wood-frame walls in cold climates are traditional constructed with a vapour barrier that also constitutes the air-tightness layer. Polyethylene foil as a vapour barrier is likely used; however, other building materials can be used to obtain correspondingly sufficient properties. 1D hygrothermal simulations were conducted for a wood-frame structure to investigate the wind–vapour barrier ratio, and if the vapour barrier of polyethylene foil could be omitted and replaced by other materials. The results were postprocessed using the VTT mould model. The results showed how wood-frame walls can be designed with respect to internal humidity class and diffusion resistance divided into three categories: no risk for mould growth, needs further investigation, and is not performing well as the risk for mould growth is present. For internal humidity classes 1–3, the ratio between wind and vapour barrier must be about 1:5, and 1:10 for classes 4 and 5 to be on the safe side. Simulations were performed for the climate of Lund, Sweden, which were used to simulate climate in Denmark too. Nevertheless, the results are related to climate data and, thus, the location.

scholarly journals Predicting mould growth on building materials- the PJ-model

2020 ◽  
Vol 172 ◽  
pp. 20001
Author(s):  
Pernilla Johansson ◽  
Thomas Svensson
Keyword(s):  
Building Materials ◽  
Dynamic Models ◽  
Technical Specification ◽  
Field Studies ◽  
Moisture Level ◽  
Mould Growth ◽  
Limit Values ◽  
Ongoing Work ◽  
Previous Round ◽  
Development And Validation

Mould growth in buildings is a complex process, affected by moisture and temperature, the properties of the building material as well as characteristics of the mould fungi. The complexity poses challenges when assessing the risk of mould growth in buildings. Mathematical models are often used to predict whether mould will grow in a part of building with expected RH and temperature conditions. The models can be described as static or dynamic. In a previous round-robin study, comparing results from models with observations from field studies, the outcome of the dynamic models evaluated depended on the user of the model. Also, the models often underestimated the risk of mould growth. A better agreement was found for static models, especially for the PJ-model. It is a part of a standardised technical specification (SIS-TS 41:2014) and has not previously been described as a model. The critical moisture level (RHcrit), determined by tests according to the method, is used as input. Thus, the subjectivity in the predictions is reduced. RHcrit is the lowest moisture level at which mould can grow and is temperature-dependent. The PJ-model provides an equation to estimate RHcrit at typical temperatures in buildings. If RH in a building section exceeds the limit values at the current temperature, growth is predicted. This paper describes the PJ-model version 1.0, some of the extensive work performed during the development and validation of the model and the ongoing work to refine the model to include considering transient conditions and measurement uncertainties.

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