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Article

Application of Environmental and Biological Frequency Indicators to Assess the Serpula lacrymans Fungus in Wooden Dwellings

by
Rodrigo Espinoza Maldonado
1,2,
Ariel Bobadilla
1 and
Carlos Rubio-Bellido
2,*
1
Centre for Research in Construction Technologies, University of Bío-Bío, Collao Avenue #1202, Concepción 4030000, Chile
2
Department of Architectural Construction II, University of Seville, 41004 Sevilla, Spain
*
Author to whom correspondence should be addressed.
Buildings 2024, 14(3), 589; https://doi.org/10.3390/buildings14030589
Submission received: 9 January 2024 / Revised: 15 February 2024 / Accepted: 16 February 2024 / Published: 22 February 2024
(This article belongs to the Section Building Energy, Physics, Environment, and Systems)
Browse Figures
Versions Notes

Abstract

:
High moisture content, low ventilation levels, and changes in the hygrothermal design of wooden dwellings could generate environmental conditions favorable for developing the rot fungus Serpula lacrymans, which is known as the most destructive fungus of its kind. The purpose of this research was to develop an experimental methodology to determine the conditions of the appearance of the fungus S. lacrymans, through in situ measurement of biological and environmental frequency indicators for wooden dwellings in South Central Chile. The referential standards for the appearance of the fungus were determined based on specialized literature and measurements of dwellings with and without deterioration. The frequency indicators for the appearance of the fungus defined and studied were as follows: frequency of air temperature FATs (%), frequency of relative humidity FRMs (%), frequency of ventilation rate FVRs (%), and rot fungus spore concentrations (CFU/pp). The methodology was validated by being measured in various enclosures and spaces under the floor in wooden dwellings in the cities of Valdivia and Temuco. The results confirmed the strong relationship between environmental relative humidity frequencies, ventilation levels, and spore concentration regarding the appearance of the fungus, where the growth dynamics cannot be separately explained without a previous analysis of the variables. In general, the dwellings most affected by the presence of the fungus had the greatest moisture levels, lower ventilation levels, and greater spore concentration. This study is the basis to diagnose the phenomena of the appearance of the rot fungus in wooden dwellings in climates favorable for its development.

1. Introduction

Moisture in dwellings could be caused by several sources: external ones, such as accidental installations, rainfalls, snow melting or frost, underground water, surface current waters, and construction water derived from wet processes inside materials, and internal ones, such as the effect of condensation, which is strengthened by building occupancy [1]. Moreover, high relative moisture content inside dwellings could generate favorable environmental conditions and nutritive substrates for the appearance of different species of fungi, mold, and bacterial proliferation or corrosion [2]. However, the formation of these microorganisms also depends on other environmental physical parameters, such as material moisture content, enclosure ventilation, thermal insulation, an appropriate design of the layers of the perimeter envelope, and biodeterioration treatments [3,4,5,6].
To reduce risks, the hygrothermal design should limit the heat transit and vapor mass through the various layers of the envelope, a phenomenon known as HAM transport [7]. Designers should consider certain physical criteria or rules to define and organise layers, as well as to define minimum thicknesses. The properties of thermal conductivity, the permeability to the passage of water vapor, and the moisture absorption of each layer should be considered according to their location and function in the enclosure to reduce condensation, i.e., a phenomenon that affects energy performance, indoor environment quality, and the durability of all buildings, to acceptable limits [8,9].
In buildings including wood as structural or non-structural elements, efforts should be made to ensure that the temperature field, moisture content, and vapor pressure among layers do not coincide for a critical period within the hygrothermal conditions required by the fungus to start its destructive process. These conditions should be verified by the project professional in the design phase to make corrections, if necessary, to obtain and certify an appropriate bio-hygrothermal design [10]. However, poor designs could lead to a high risk of fungi growth, thus affecting building’s performance and occupants’ wellbeing [11,12].
Changes in the moisture of the lignocellulosic materials of a building, such as structures, cladding, floors, and unprotected plates, could favor both fungi growth [13] and the appearance of xylophagous insects [14] that affect the structure of these elements [15].
Biodeterioration is caused by the presence of microorganisms, such as bacteria and fungi, and is visible when materials change [16]. However, some basidiomycete fungi, which cause the brown or cubic rot, are among the most aggressive xylophages in buildings [17,18]. These fungi significantly damage the internal structure of wood, thus causing great mechanical resistance loss, which becomes important in structures supporting a building [19,20].
Within this category, the most important and harmful brown rot fungi in wooden buildings are Serpula lacrymans, Coniophora puteana, Antrodia vaillantii, and Lentinus lepideus, which can quickly degrade cellulose and hemicellulose and modify the lignin structurally [21]. In white rot, basidiomycetes and some ascomycetes feed on the three polymers of the wood cell wall, although structural loss is slower than with brown rot. Wood acquires a “whitish” colour due to both lignin degradation and the intact cellulose not used by these fungi. The representative fungi species are Trametes versicolor, T. hirsute, and Schizophyllum commune. On the other hand, the ascomycetes responsible for white rot (i.e., Chaetomium globosum, Monodictys putredinis, Hypocrea muroiana, Cryphonectria parasitica, and Fusarium oxysporum), whose hyphae are developed in the lumen and inside the secondary cell wall, mainly degrade cellulose, thus changing the structure of the lignin and softening the lignocellulosic material [20,21,22].
In a study conducted in Austria, wood-destroying fungi were found more often in old buildings (530/82.1%) than in new buildings (115/17.9%). The Serpula lacrymans fungus was found 351 times (88.4%) in old buildings, mainly in flats and cellar rooms. Its close relative S. himantioides was isolated twice, on a rotten floor of spruce wood in a farmhouse and on spruce flooring in a multistory building [23].
In the last decades, the total number of appearances of basidiomycete in buildings in Europe (Czech Republic, Poland, Germany (old East and West), Belgium, France, Norway, Denmark, Finland, Latvia, Estonia, Romania, and Albania) mainly corresponded to S. lacrymans and C. puteana, except in Norway, where Antrodia was the most frequent genus [24,25].
S. lacrymans is the most aggressive rot fungus (the first out of 10) in wooden buildings worldwide, followed by Coniophora puteana, Trametes versicolor, and Donkioporia expansa [26,27]. Economically, this is the most important fungus, which is considered as the cancer of buildings, causing damage costs of around USD 36 million annually in France [28,29], and around USD 2.2 million weekly in the United Kingdom [30]. The solution in these cases is invasive [31] and includes the opening of suspicious areas to detect the area affected. This is generally carried out when the fungus is widely developed, i.e., when there is a visual proof [32].
The great development of the S. lacrymans fungus mainly affects the mechanical capacity of dwellings by weakening their structural components [33]. This fungus develops much better in coniferous woods or wood-based products with a moisture content of about 20%, with temperatures between 5 and 26 °C, and with a wide range of environmental moisture [34,35].
The biological growth dynamics of the fungus varies and depends on several concomitant factors, such as temperature, lighting, ventilation, moisture excess, and the substrate on which the colonization process is settled and starts [36].
S. lacrymans and other rot fungi require environmental moisture around 90% for at least 20% of the time to start their development and colonization, together with wood and other lignocellulosic material with moisture content levels greater than 20% and lower than saturation moisture content levels [37], with optimal values found by German experiments to be between 30% and 40% [38,39]. Most authors have indicated the temperature range between 5 and 35 °C [40], with optimal growth values between 21 °C and 22 °C [41].
In 2004 onward in Chile, the Universidad Austral de Chile identified the first appearance of the Serpula lacrymans fungus in some dwellings in Temuco and Puerto Montt [42]. In 2018, the Housing and Urban Planning Service (SERVIU) in Los Ríos Region identified isolated cases of dwellings affected. There were also some isolated cases in Concepción, in the Biobío Region. Between 2019 and 2020, the Ministry of Housing and Urbanism of Chile (MINVU) recorded 17 cases of dwellings affected to a lesser or greater extent by this fungus in the city of Valdivia: 1 in Paillaco, 1 in the Union, 12 in Temuco, and 3 in Padre Las Casas, thus affecting the populations of Teniente Merino in Valdivia and of both Millaray and Las Quilas in Temuco, as well as others in various areas of these and other regions [43]. The problems were mainly found in ventilated floors and in the joints between walls and floors, consistent with the advance of the mycelial growth from the natural ground [44]. Figure 1 shows the damage and progress of the fungus under the floor, on the floor and in the walls of four dwellings in the city of Valdivia.
In the last two decades, attacks of this fungus in Chile have been increasingly reported. Its appearance has been strongly related to the erroneous implementation of measures to reduce thermal transmission and air tightness of buildings in energy improvement [45]. Within this scenario, the Supreme Decree Number 255 of the Ministry of Housing and Urbanism of Chile, corresponding to the Familiar Heritage Protection Programme, was created. Among other goals, it aims to thermically renovate the existing dwellings through grants given by the State to provide inhabitants with greater comfort [46].
To avoid the risk of the appearance of the fungus S. lacrymans and other rot fungi with similar germination conditions, calculation tools or simulation software are required that allow us to define appropriate bio-hygrothermal designs, and which link the critical parameters of germination with the environmental conditions of the homes and construction elements of the envelope. However, design alterations over the years create favorable conditions for the rot fungus to develop. In this case, it is necessary to define the causes of the appearance of the fungus, with the aim of determining solutions for the improvement and remediation of the attacked homes. For this, it is necessary to use validated experimental methodologies, which can directly or indirectly account for the development of the rot fungus.
This study aims to develop an experimental methodology based on the measurement of hygrothermal and biological frequency indicators to verify the appearance of the Serpula lacrymans fungus in wooden homes in South Central Chile. The critical standards for the appearance of the fungus are defined, and they are validated with measurements carried out in situ in wooden dwellings in Valdivia and Temuco.

2. Methodology

For this study, the frequency indicators of temperature and relative moisture were applied [32], as well as of ventilation and spore concentrations defined by exhaustively analyzing the environmental and biological variables from actual measurements. Temperature, relative moisture, ventilation, and spore concentrations of rot fungi were simultaneously measured in living rooms, main bedrooms, and spaces under the floor in wooden dwellings in the cities of Temuco and Valdivia, where the presence of Serpula lacrymans was reported [42]. A total of three dwellings affected by this fungus were studied in the two cities, as well as one control dwelling with no damage for comparison. The methodology is included below.

2.1. Definition of the Frequency Indicators

For quantitative measurements, dwelling performance measures were compared with the standards, which were defined for a normal state or condition according to both the Referential Standard IICRC S520 [47] and the existing literature that set limits for the variables of temperature and relative moisture for the appearance of molds and rot fungi [32,37]. The standard reference of the ventilation frequency was calculated under the criterion of new air ventilation rates to limit relative moisture levels up to 70%, according to the following dilution ventilation rate:
Q = M v   /   3 .   ( W i − W e )
The equation of dilution ventilation is as follows:
n = 3.6   Q e   /   V
Air changes per hour
where:
  • Qe: extraction volume, l/s;
  • Wi: absolute moisture of the place at an air temperature of 19 °C and 70% of relative moisture, g/m3;
  • We: absolute moisture of the locality with the mean temperature and absolute moisture in July, g/m3;
  • n: volume air changes in the place per hour, 1/h;
  • V: volume of the place, m3.
The maximum spore concentration thresholds for the attack of the fungus were defined according to the collection of spores in the environment of the dwellings not affected by the rot fungi.
The environmental frequencies of relative moisture (FRMs), air temperature (FATs), and ventilation rate (FVRs) were analyzed for a weekly measurement period. Referential standards or relative moisture thresholds in the time were defined for the mold activation (≥70%) as the first barrier and for S. lacrymans (≥90%). Temperature ranges between 5 °C and 35 °C were defined for the appearance of the rot fungus, as well as ventilation rates lower than 1.8 (1/h) in the living rooms and (1.5) 1/h in bedrooms and spaces under the floor. Likewise, the minimum spore concentration standard was established in 52 units that form colonies per Petri plate, which were measured for a maximum of 4 h (Table 1).

2.2. Dwellings

A total of 18 dwellings belonging to the room set Teniente Merino in the city of Valdivia and to the room set Las Quilas and Millaray in the city of Temuco were studied because the Agricultural and Livestock Service (SAG) of Chile identified the presence of the Serpula lacrymans fungus in all of them.
The dwellings were built between the 1960s and 1970s in a semi-detached floor with a surface area of 60 m2, with both ventilated floors in the dry places and concrete floors in bathrooms and kitchens. The original dwelling was structured on radiata pine wood and raulí floor beams. The original indoor and outdoor claddings were wooden boarding. The dwellings of Valdivia maintained the system of ventilated floors, whereas the dwellings in Temuco replaced their structure of ventilated floors with concrete floors (Figure 2).
Figure 2 shows the dwellings used for study.
Some changes were made in the dwellings with the passage of time by owners themselves and by the grants given for the thermal improvement of the envelope elements (windows, walls, ceilings, and ventilated floors). The main changes in the original design were as follows: adjacent increases, replacement of wooden flooring with a thermal sandwich floor solution, obstructed small windows, construction of sheds in courtyards, and replacement of ventilated floors with concrete floors, among others. Out of the 18 dwellings, 6 units were experimentally evaluated, 3 in Valdivia (Dwellings No. 1, 2, and 3) and 3 in Temuco (Dwellings No. 5, 6, and 8). Likewise, the witness dwellings of No. 4 in Valdivia and No. 7 in Temuco were also included because there was no presence of the S. lacrymans fungus (Table 2).

2.3. Monitoring and Determinations

Measurements were simultaneously conducted for the two cities between 4 and 10 November. Environmental variables, such as air temperature, relative moisture, ventilation rates, and spore concentrations, were measured in the living rooms and main bedrooms. These variables were also measured under the ventilated floor in the 4 dwellings in Valdivia.
Variables, such as indoor climate, relative moisture, air temperature, and CO2 concentrations, were measured every 10 min for 7 days. A digital sensor kit (HOBO UX120-006M made by ONSET COMPUTER CORP., Bourne, MA, USA) with 4 channels for data acquisition was used to measure environmental relative moisture in percentage (%), air temperatures in Celsius degrees (°C), and CO2 concentrations in parts per million (ppm). Outdoor climate, environmental relative moisture (%), and air temperature (°C) were determined by using two weather stations (Davis 6163 Vantage Pro 2 Plus made by DAVIS INSTRUMENTS, Hayward, CA, USA) simultaneously installed in each city.
Natural ventilation was determined according to the fall in dilution concentrations of the CO2 levels measured in each place, according to the calculation principles set by the ASTM E741 standard [48] by the optional regression method and given by the following dilution equation:
At = ln C(0) − ln C(t)
Ventilation equation due to CO2 fall, where:
  • At: air change rate (1/h);
  • ln C(0): initial CO2 concentration, (ppm);
  • ln C(t): CO2 concentration in the time t1, (ppm).
Spore concentration in the air was indirectly determined by collecting spores of the rot fungus because of rainfall in Petri capsules. These capsules were located under the floor and inside the four dwellings in Valdivia. The biological load was collected for 4 h in each plate, and it was then put in a benlate/agar/malt extract growth (BEMA). Concentration was determined by directly counting the colony forming units per Petri plate (CFU/pp). Species were identified by increasing the ITS region of the ribosomal DNA with BLAST, a computer tool.

3. Results

3.1. Frequency of Air Temperature FATs (%)

The maximum and minimum temperatures were 27.6 °C and 11.1 °C, respectively, for the dwellings in Valdivia, and 27.8 °C and 10.9 °C, respectively, for the dwellings in Temuco (Table 3). All the temperature frequencies in the living rooms, bedrooms, and spaces under the floor during the weekly period were always between 5 °C and 35 °C, which is considered beneficial for fungus development according to the standard on the temperature frequencies defined for the appearance of the fungus (Table 4). The lowest outdoor temperature in Temuco was 5.4 °C, and 5.8 °C in Valdivia, greater than the lower range of 5 °C. However, for the climate of these localities, lower temperatures could be occasionally found in winter.

3.2. Frequency of Relative Moisture FRMs

As for the measurements under the floor in the city of Valdivia, Dwelling 2, which was the most affected by the active presence of the fungus, maintained moisture frequencies of 100% of the weekly period at about 90% of the threshold for the appearance of the fungus. This frequency was about 90% for 55% of the time in Dwelling 1, with a lower presence of fungi than Dwelling 2. In Dwelling 3, with the lowest presence of fungi, the relative moisture frequency under the floor never exceeded 90%, maintaining an average of 82%. In Dwelling 4 (witness), with no fungi, relative moisture frequency did not exceed 90%, and the average relative moisture frequency was 85% (Figure 3).
In the living rooms and bedrooms, no dwelling exceeded 90% of relative moisture during 20% of the time, according to the relative moisture frequencies defined for the appearance of the fungus (Table 4). This phenomenon could be explained mainly because of the spring measurement period, when outdoor relative moisture was greater than 90% in particular cases, and dwellings recorded high ventilation rates. However, slightly greater relative humidity levels are expected for winter by comparing the local meteorology with that during the weeks of the study (Table 3).
The frequency of 70% during 5% of the time for the appearance of mold was exceeded in the living room of Dwelling 2, and in the bedrooms of Dwellings 1, 2, and 3 in Valdivia (Table 4). There was no mold, but there was fungi after their visual inspection. This could be related to the periodic cleaning works made by users to make them disappear, as well as to the substrate colonization, an antagonist behaviour of rot fungi [49].

3.3. Frequency of Weekly Ventilation Rate FVRs (%)

In all the living rooms, minimum ventilation frequencies were met 50% of the week as an average for no appearance of the fungus, and 48% of the time in bedrooms. However, Dwelling 4 (witness) in Valdivia was ventilated at lower rates (Table 4) because it has thermally improved one of the walls, which in turn improves the standards on air hermeticism.
As for the ventilation frequency under the floor, Dwelling 4 (witness) met the minimum ventilation standard only 11% of the time, whereas Dwellings 1, 2, and 3 never exceeded the minimum ventilation threshold, concordant with the visual observations in which the fungus was in all these dwellings (Table 4). Figure 3 represents ventilation behaviour under the floor in the city of Valdivia.

3.4. Spore Concentration CFU/pp

As for the spore concentration under the floor, Dwellings 1, 2, and 3 presented fungus concentrations of 124, 85, and 102 CFU/pp, respectively. These values were compared between 318%, 63%, and 96%, respectively, greater than the 52 CFU/pp established as the threshold for the appearance of the rot fungus (Figure 4). The greater number of spores in these dwellings coincided with both the damage and presence level of Serpula lacrymans under the floor.
As for the concentrations in the living rooms and bedrooms, there were values between 22 CFU/pp and 190 CFU/pp. The witness dwelling in Valdivia presented a concentration of 18 CFU/pp, and the dwelling in Temuco presented a concentration of 36 CFU/pp, which were values lower than the limit established for the appearance of the fungus (Table 4).
Out of the 64 mycelia isolated in the growth medium BEMA, 43 were white rot fungus, and the remaining were deuteromycetes and ascomycetes. Unlike Pottier et al. [46], the results did not show any proof of the growth of S. lacrymans during the study period. However, other white rot species were identified by the similarity percentage between the isolated fungus of the dwellings and that of the database of the National Centre for Biotechnology Information, NCBI (Table 5). The inability of the methodology to show the presence of this fungus could be due to the high growth rates observed in the mycelia of white rot fungi, thus preventing the growth of S. lacrymans by substrate capture. However, the presence of the white rot fungus showed the existence of an environment favorable for both its growth and the growth of other rot fungi.

4. Discussion

Frequencies have been usually studied at a laboratory scale to characterize fungi species and in predictive tools to define hygrothermal designs for the non-appearance of molds, as reported by Sedlbauer and Viitanen [50]. On the other hand, the prediction and studies of rot fungi have estimated the useful life of wooden structures regarding the risk and the influence of the fungus decomposition, in which variables, such as moisture in wood and the surface temperature, have been used to establish the conditions of how fungi and xylophagous microorganisms should be attacked [51].
This study has shown the environmental frequency conditions generated under the floor, where moisture behaviour was not influenced by outdoor conditions and relative moisture frequencies exceeded the growth thresholds of the fungus, as occurs with ventilation, which was lower than the minimum thresholds. A prototype dwelling and a wall section with a closed lower chamber were built under controlled laboratory conditions, and passive and mechanical ventilation treatments provided good results to control the vegetative growth of the fungus, for ventilation speeds from 0.2 m/s to 0.3 m/s, without defining ventilation thresholds [44]. Consequently, ventilation thresholds and frequencies could be studied as inhibiting mechanisms of the growth of the fungus.
The national and international literature is consistent regarding the modifications in the hygrothermal design. Many changes affect the air permeability and the natural ventilation capacity of the envelopes, thus increasing environmental moisture in spaces. Moreover, the permeability for the passage of water vapor of envelopes is sometimes influenced, thus increasing the risk of surface water and interstitial condensation and favoring the proliferation of fungi and microorganisms [52]. Intervention or changes in the architectural constructive design, both in new and existing dwellings, implies paying more attention to the hygrothermal design of wooden dwellings capable of being attacked by the rot fungus. Envelopes, and in particular ventilation, should be determined not just by the needs of human breathing, as defined by the NCh3309 Chilean standard [53] or by other international standards, but by the need to maintain moisture levels that do not exceed the limits to avoid mold as precursor organism growth of the rot fungus (first control) [54,55]. As for ventilation, not all of the dwellings meet the frequency standards, so the hermeticism of the envelope should be reduced and a hybrid ventilation system should be provided to ensure the control of indoor moisture in spaces.
As for spore concentrations, Burge et al. [56] stated that Petri plates with growth media should be used to develop existing colonies in the environment, but the growth medium could also favor the development of some taxa more than others, and even the same species could suffer self-inhibition processes in terms of germination or self-growth, thus being one of the reasons why the presence of Serpula lacrymans was not identified. However, this technique could be a good option to identify the mycoflora in potential environments for the rot fungi growth. According to Pottier et al. [46], the Serpula lacrymans fungus favors other white rot fungi, coincident with the molecular identification of the measurements of the study and including other species not recorded by this author, such as Bjerkandera adusta, Peniophora lycii, Phanerochaete sórdida, Stereum hirsutum, Sterum illidens, Trametes ochracea, and Trametes versicolor.
One of the limitations of the study was the measurement period. The ground was evaluated in spring, but the best conditions for the fungus growth take place in winter, when the frequencies of temperatures and relative moisture are more critical, with low temperatures and high relative moisture. These conditions were not possible for this study due to the availability of access. According to Jenning et al. [25], under field conditions, most sporophores (which play a role in the development of the mycelium) are produced in spring and autumn, and the case study was in spring. However, the fructification (fruitful body) could take place in winter and, to a lesser extent, in summer, according to the predominant temperatures, so this study could be applied to observe the development of the mycelium of the fungus even in spring if environmental conditions are met for its growth.
Finally, in all the case studies, the S. lacrymans fungus originally appeared in the natural floor, concordant with the study by Findlay et al. [57], so criteria should be established for hygrothermal designs, as well as critical constructive points of solutions of ventilated floor and joints of floors with walls.

5. Conclusions

This study has defined an experimental methodology and the critical frequency indicators for the appearance of the rot fungus S. lacrymans in wooden dwellings. The study was based on the comparative measurement between affected dwellings and control dwellings, which have never been attacked by the fungus. These had the same characteristics and were in the same environment as the damaged dwellings. The main environmental and biological frequency indicators for the appearance of the fungus defined and studied were as follows: frequency of air temperature FATs (%), frequency of relative moisture FRMs (%), frequency of ventilation rate FVRs (%), and rot fungus spore concentrations (CFU/pp).
This study has also verified the frequencies of the growth of the fungus with a real wooden dwelling that could be used to establish hygrothermal solution measures in the case of existing dwellings and/or dwellings with problems of fungi, as well as bases or criteria for the hygrothermal design of new dwellings through a practical and non-invasive methodology. Moreover, the environmental and biological comparative behaviour under the floor was observed in dwellings with the development of the active mycelium of the fungus, as well as in another dwelling without its presence but with the same characteristics and in the same environment. As a result, Dwelling 4 (witness) in Valdivia never exceeded the critical threshold of 90% of relative moisture during the 20% of the time indicated by the literature in which the mycelium of the fungus starts its development.
The results under the floor showed that Dwellings 1 and 2, which were the most affected by the active presence of the fungus, had moisture frequencies greater than 90% for a period of 55% and 100% of the time, respectively, and their ventilation levels never exceeded the minimum threshold of 1.5 (1/h) for the non-appearance of the fungus. On the other hand, Dwelling 3, with the presence of the fungus, but to a lesser extent than in the other two dwellings, never exceeded the threshold of 90%, showing an average relative moisture of 82%, and its ventilation levels never exceeded the threshold of 1.5 (1/h). In Dwelling 4 (witness) without the presence of fungi, moisture did not exceed 90%, and the average was 84%, a little bit greater than Dwelling 3, which presented fungi in lower amounts. However, its ventilation frequencies exceeded the minimum threshold of 1.5 (1/h) during 11% of the time, thus indicating that ventilation plays an important role in the inhibition of the fungus. S. lacrymans coexists with moisture lower than 90% and ventilation frequencies lower than 100% of the time, a complex dynamic yet to be explained in the existing literature.
As for the spore concentration of rot fungi under the floor, Dwellings 1, 2, and 3 with the active presence of S. lacrymans showed spore concentrations of 124 CFU/pp, 85 CFU/pp, and 102 CFU/pp, respectively, greater than the maximum threshold of 52 CFU/pp defined by the witness Dwelling 4.
These results showed the strong relationship between environmental relative moisture, ventilation levels, and spore concentration regarding the appearance of the fungus, so the growth dynamics cannot be explained separately without a previous analysis of the set of variables of environmental frequency and spore concentrations under the floor for the appearance of the fungus.
The relationship between relative moisture and ventilation should be studied in situ. Likewise, cases should be measured and studied in winter to adjust the frequencies and thresholds according to the comparative measurement of the most critical period.
Further research lines could be the application of this methodology to establish the causes in dwellings affected by rot fungi, and maybe the establishment of solutions and hygrothermal improvement. In addition, new lines related to the development of predictive treatments could also be addressed by using the environmental frequencies and spore concentrations defined in this study.

Author Contributions

Conceptualization, R.E.M. and C.R.-B.; methodology, R.E.M. and A.B.; validation, C.R.-B. and A.B.; analysis, R.E.M., A.B. and C.R.-B.; investigation, R.E.M., A.B. and C.R.-B.; writing—original draft preparation, R.E.M. and C.R.-B.; writing—review and editing, R.E.M. and C.R.-B.; visualization, R.E.M.; supervision, C.R.-B. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Ministry of Housing and Urbanism of Chile (Exempt Resolution N° 9545), and executed by the Construction Technology Research Center from the University of Bío-Bío.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author, [C.R.-B.], upon reasonable request.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Buildings 14 00589 g001
Figure 1. Picture (a) shows a wooden plank flooring with visible damage; (b) fungi can be seen at the joint of the slotted plywood plate of a wall with floating floor; (c) degradation of an original wooden floor; (d) deterioration in the joint of the slotted plywood wall and the newly constructed structural plywood floor; (e) fruiting bodies under the floor and outdoor cladding; (f) presence of active mycelium under the floor.
Figure 1. Picture (a) shows a wooden plank flooring with visible damage; (b) fungi can be seen at the joint of the slotted plywood plate of a wall with floating floor; (c) degradation of an original wooden floor; (d) deterioration in the joint of the slotted plywood wall and the newly constructed structural plywood floor; (e) fruiting bodies under the floor and outdoor cladding; (f) presence of active mycelium under the floor.
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Figure 2. Pictures from (a–d) correspond to the dwellings in Temuco, and pictures from (e–h) correspond to the dwellings in Valdivia. Dwellings (d,g) correspond to witness dwellings, with no damage.
Figure 2. Pictures from (a–d) correspond to the dwellings in Temuco, and pictures from (e–h) correspond to the dwellings in Valdivia. Dwellings (d,g) correspond to witness dwellings, with no damage.
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Buildings 14 00589 g003
Figure 3. Behaviour of the environmental variables under the floor.
Figure 3. Behaviour of the environmental variables under the floor.
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Figure 4. Environmental frequency and spore concentration under the floor in Valdivia.
Figure 4. Environmental frequency and spore concentration under the floor in Valdivia.
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Table 1. Environmental and biological frequencies for the appearance of fungi.
Table 1. Environmental and biological frequencies for the appearance of fungi.
Performance IndicatorsReferential Standard
Frequency of weekly relative moisture
FRMs (%) mold		≥5% weekly time about 70%
Frequency of weekly relative moisture
FRMs (%) Serpulla fungus		≥20% weekly time about 90%
Frequency of weekly air temperature
FATs (%) mold and Serpula		100% weekly time within the range (5–35 °C)
Frequency of weekly ventilation rate
FVRs (%) mold and Serpula		0% weekly time lower than 1.8 (1/h) in living rooms, and 1.5 (1/h) in bedrooms and spaces under the floor
Rot fungus spore concentration≥52 (CFU/pp) measured for 4 h as maximum
Table 2. Changes in the dwellings.
Table 2. Changes in the dwellings.
ItemAddressLocalityCityChanges
(1)Lago Malleco #560Tte. MerinoValdiviaIncrease, obstructed small windows, replacement of ventilated floor with thermal sandwich floor
(2)Lago Malleco #570Tte. MerinoValdiviaIncrease, obstructed small windows, replacement of ventilated floor with thermal sandwich floor
(3)Lago Villarrica #2780Tte. MerinoValdiviaShed, obstructed small windows, replacement of ventilated floor with thermal sandwich floor
(4)Lago Llanquihue #3030Tte. MerinoValdiviaShed, thermal improvement in wall, no changes in the floor
(5)Los Aromos #0184Las QuilasTemucoReplacement of ventilated floor with concrete floor
(6)Los Helechos #1450Las QuilasTemucoIncrease, replacement of ventilated floor with concrete floor
(7)Los Notros #1463Las QuilasTemucoShed, replacement of ventilated floor with concrete floor
(8)Palihue #968.MillarayTemucoNo significant changes
(4) Witness dwelling in Valdivia. (7) Witness dwelling in Temuco.
Table 3. Summary of the measurement of indoor and outdoor environmental variables between 4 November 2019 and 10 November 2019.
Table 3. Summary of the measurement of indoor and outdoor environmental variables between 4 November 2019 and 10 November 2019.
CityDwellingSpaceMaximum Temperature
(°C)		Minimum Temperature
(°C)		Average Temperature
(°C)		Maximum Relative Moisture (%)Minimum Relative Moisture (%)Average Relative Moisture
(%)		Maximum Ventilation (1/h)Minimum Ventilation (1/h)Average Ventilation (1/h)
Valdivia1Under the floor18.611.914.096.966.988.80.70.00.0
Living room25.511.418.073.346.758.510.00.01.6
Bedroom23.511.116.193.055.881.23.10.00.3
2Under the floor16.712.214.293.390.191.70.90.00.1
Living room24.215.119.472.254.562.99.00.01.2
Bedroom23.514.118.770.549.360.18.80.00.6
3Under the floor18.913.815.685.876.781.80.90.00.1
Living room25.816.220.558.039.647.99.50.01.4
Bedroom17.912.915.395.076.089.73.40.00.2
4
(witness)		Under the floor16.614.215.488.778.583.52.30.00.4
Living room25.614.119.282.349.263.89.80.00.5
Bedroom27.613.219.982.543.761.98.70.00.7
Outdoor30.75.815.792.130.463.8---
Temuco1Living room26.110.917.075.945.562.512.10.00.8
Bedroom27.212.718.266.243.257.78.00.00.4
2Living room21.314.017.369.354.963.01.30.00.1
Bedroom27.814.720.073.258.364.42.10.00.1
3 (witness)Living room26.714.319.476.549.959.51.10.00.1
Bedroom27.613.519.375.145.359.11.50.00.1
4Living room25.514.119.167.044.154.70.60.00.0
Bedroom25.014.919.263.546.255.58.00.01.1
Outdoor28.85.415.886.935.963.6---
Table 4. Results of the frequency measurements in the wooden dwellings in Temuco and Valdivia for the appearance of the S. lacrymans rot fungus. Period between 4 November 2019 and 10 November 2019.
Table 4. Results of the frequency measurements in the wooden dwellings in Temuco and Valdivia for the appearance of the S. lacrymans rot fungus. Period between 4 November 2019 and 10 November 2019.
PerformanceDwellings in ValdiviaDwellings in Temuco
Dw. 1Dw. 2Dw. 3Dw. 4 (witness)Dw. 1Dw. 2Dw. 3 (witness)Dw. 4Referential Standard
Frequency of the weekly air relative humidity FRMs
FRMs living room 70 (%)446086100≥5% time greater than 70%
FRMs bedroom 70 (%)8252100130100≥5% time greater than 70%
FRMs living room 90 (%)00000000≥20% time greater than 90%
FRMs bedroom 90 (%)4306100000≥20% time greater than 90%
FRMs under the floor 90 (%)5510000----≥20% time greater than 90%
Frequency of the weekly air temperature FATs
FATs living room (%)100100100100100100100100100% of time between 5 °C and 35 °C
FATs bedroom (%)100100100100100100100100100% of time between 5 °C and 35 °C
FATs under the floor (%)100100100100-----
Frequency of weekly ventilation rate FVRs
FVRs living room (%)3949416975100100100≤0% time lower than 1.8 (1/h)
FVRs bedroom (%)95799865879810049≤0% time lower than 1.5 (1/h)
FVRs under the floor (%)10010010089----≤0% time lower than 1.5 (1/h)
Spore concentration
Concentration in living room (CFU/pp)18346-18190433628≥52 (CFU/pp)
Concentration in bedroom (CFU/pp)904322-6732--≥52 (CFU/pp)
Concentration under the floor (CFU/pp)1248510252----≥52 (CFU/pp)
Table 5. Identification of rot fungi through PCR.
Table 5. Identification of rot fungi through PCR.
Coincidence of Percentage of the NCBI Database
ValdiviaTemuco
SpeciesTypeTotal of
Isolated		12341234
Lago Malleco #560Lago Malleco #570Lago Villarrica #2780Lago Llanquihue #3030 (Witness)Los Aromos #0184Los Helechos #1450Los Notros #1463
(Witness)		Palihue #968
Bjerkandera adustaWhite12100%-100%100%100%--100%
Peniophora lyciiWhite4100%--99.9%-99.8%99.8%-
Phanerochaete sordidaWhite1199.2%99.0%-99.1%99.1%99.1%-100%
Stereum hirsutumWhite8100%99.9%99.9%100%----
Sterum illidensWhite299.6%---99.5%---
Trametes ochraceaWhite3---100%--100%-
Trametes versicolorWhite3100%---99.4%---
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Espinoza Maldonado, R.; Bobadilla, A.; Rubio-Bellido, C. Application of Environmental and Biological Frequency Indicators to Assess the Serpula lacrymans Fungus in Wooden Dwellings. Buildings 2024, 14, 589. https://doi.org/10.3390/buildings14030589

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Espinoza Maldonado R, Bobadilla A, Rubio-Bellido C. Application of Environmental and Biological Frequency Indicators to Assess the Serpula lacrymans Fungus in Wooden Dwellings. Buildings. 2024; 14(3):589. https://doi.org/10.3390/buildings14030589

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Espinoza Maldonado, Rodrigo, Ariel Bobadilla, and Carlos Rubio-Bellido. 2024. "Application of Environmental and Biological Frequency Indicators to Assess the Serpula lacrymans Fungus in Wooden Dwellings" Buildings 14, no. 3: 589. https://doi.org/10.3390/buildings14030589

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