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The performance of porous and hygroscopic building materials is closely connected to its sorption properties and ability to get wet. Weight, mechanical, acoustic, and thermal properties as well as the resistance to discoloring and decay causing organisms are affected by moisture. For various reasons and purposes it is therefore recommendable to monitor the moisture content of building components continuously. The most common and most easily applicable methods are electrical resistance measurements. They can be applied to wood and wood-based materials as well as to mineral products such as mortar and brick. However, resistivity measurements require material specific characteristics and a temperature compensation since both parameters have a significant effect on electrical conductivity. This study aimed on developing a model to determine the moisture content at any temperature for different building materials such as native and modified wood as well as untreated and hydrophobized mortar. Therefore, the electrical resistance was measured with a data logging device in the giga ohm range to obtain values at low moisture contents. The model enables measurements at a wide range of moisture contents and suited with an acceptably high accuracy by using the appropriate resistance characteristic for each building material.

Wood is frequently used for claddings and decking where it is exposed to moisture and various biotic agents limiting its serviceability. In-situ moisture monitoring can help to determine the moisture-induced risk for decay and might therefore serve as faster alternative to traditional durability testing, which usually requires exposure for many years. This study aimed on determining the moisture-induced risk for decay of differently severe exposed wooden components, i.e. combined facade-decking elements and horizontal double layer set ups mimicking poorly designed terrace decks made from twelve different wood species and thermally modified wood. The huge variation of moisture-induced risk for decay of timber used above ground became evident. Dosage as well as service life estimates differed in dependence of wood species, design detailing, and decay type to be expected. An exposure dose was utilized for alternative durability classification of timber in less severe exposure conditions such as for cladding applications and compared with common durability classification based on decay assessment. Differences in durability between the various wood species and materials became apparent in the horizontal double layer and met fairly well the expectations based on durability classification according to the European standard EN 350 and previous findings from above ground field tests. Combined facade-decking elements were found to be useful for moisture content (MC) monitoring of wood in less severe exposure situations such as facades and freely ventilated decking, but not for correlation between moisture induced risk and fungal decay, since the latter occurred exclusively at water trapping contact faces. Nevertheless, the use of MC and temperature recordings combined with a dosimeter-based decay model might allow for an alternative time-saving way to estimate and classify wood durability.

Reed ( Phragmites australis (Cav.) Trin. ex Steud.) has been used for thatching roofs since centuries in many regions around the globe. Reed is a renewable resource and provides excellent thermal insulation properties. It is an appealing and very traditional material with known performance when applied as house roofing. However, during recent years an alarmingly high number of prematurely failing roofs were observed in different European countries, but the reason for drastically reduced service lives of thatched roofs is not understood, yet. This study aims therefore on comparative and comprehensive resistance tests to white, brown, and soft rot causing fungi to be performed with reed of different origin. Furthermore, thermal modification of reed was applied as potential environmental friendly technique to improve the durability of reed. Untreated reed of different origin as well as thermally modified reed (TMR) was found to be susceptible to white, brown, and soft rot decay. The latter caused most severe damage to the reed samples, i.e. >40% mass loss, and should therefore be addressed for future studies more in detail. The resistance of reed against the various decay fungi differed slightly between origins and culm sections. Thermal modification significantly improved the durability of reed. Mass loss caused by fungi was reduced by up to 80% at highest treatment intensity. However, the required treatment intensity did not become evident from the results yet. This should be determined in more detailed experiments including further target properties such as water exclusion efficacy, color, brittleness, and further strength properties to assure processing of the material for thatch.

Several factors such as local climate, design details, exposure conditions and coatings have an indirect effect on decay in outdoor conditions. Besides all these factors, in particular the wood temperature and moisture content (MC) directly impact on the fungus and its ability to metabolize and degrade wood cell wall substance over time. Therefore the significant role of MC has been addressed in a wide range of field experiments and approaches to establish decay models. However, all these approaches have one crucial aspect in common, i.e. the need for defining a minimum threshold for wood MC that is necessary for the onset of decay and its subsequent progression. The aim of this study was therefore to examine the moisture requirements of different brown and white rot causing basidiomycetes for growth and decay of a wider range of European-grown wood species including moderately durable, durable and even very durable species. Remarkably, the majority of the material/fungus combinations under test it was observed that the minimum MC for fungal decay was more or less distinct below fiber saturation, whereby the highest deviations from MC threshold to FSP were found for beech and Scots pine sapwood, i.e. the wood species with the lowest inherent resistance.

Service life planning and performance classification are key issues in the building sector. Well-functioning ‘performance models’ are absolutely essential to predict the service life and functionality of buildings, building assets, and building products over time. Different types of performance models have been established for various building materials, but cannot necessarily transferred to wood-based materials, primarily due to their organic character. For performance modelling of wood products biological agents need to be considered, such as wood disfiguring and degrading organisms. Different approaches to adequately reflect the influence of biotic and abiotic factors on the performance of wood have been reviewed and evaluated with respect to their usability in the building trade. We found that efforts in developing performance models for both fungal decay and mould growth have been intensified in recent years. A high heterogeneity among the numerous attempts became visible, different strategies have been followed, and were roughly distinguished according to the respective objectives, governing variables (e.g. mass loss, strength loss, remaining strength, decay ratings, service life, aesthetic appearance, etc.), data sources and the resulting level of accuracy. A framework of how exposure, dimension, design details, and the material-intrinsic ability to take up and release water can be linked to model the moisture risk in wood products is in principal available. Methods and models have the potential to get implemented not only in design guidelines, but also in European and international standards. In particular, various dosimeter models could serve as reliable tools to quantify the effects of different construction details.

Various procedures are used for testing the durability of wood and wood based materials for decades. Generally they can be divided in field and laboratory tests, whereby lab tests allow more defined and reproducible conditions and benefit from shorter test durations. However, while laboratory test results are hardly transferable to real life situations, field tests ensure more realistic conditions. For instance natural weathering and detoxification of biocidal compounds through so called “non-target-organisms” is assured only under outdoor field exposure. Due to these dissimilarities a diverse and in some cases also unrealistic classification of wood durability can be obtained when testing a material exclusively under laboratory conditions. This study will exemplarily focus on English oak (Quercus robur L.), which is classified as ‘durable’ according to the European Standard EN 350-2 (1994) . Results from several laboratory and field test studies showed an enormously high variation of its durability between ‘very durable’ (Durability class (DC) 1, EN 350-1 (1994) ) to ‘not durable’ (DC 5). Therefore this study aimed on a comparative evaluation of the durability of English oak in laboratory and field tests using standard specimens, but also full-size components under in-service conditions. The test results showed only little variation in durability of different oak origins. However it was indicated that a transferability of results determined in laboratory decay tests with pure cultures to the performance of a certain material in outdoor exposure is possible only to a limited extend.

The durability of wood in ground contact is influenced by various factors such as substrate quality, climate and micro flora of the soil, which should consequently be considered for service life prediction of wooden components used in ground. In particular the impact of horticultural soil management and melioration measures demand consideration. Therefore this study aimed on comparing the impact of different soil substrates on the performance, service life, and finally durability of different European grown wood species. Specimens of Scots pine sapwood (Pinus sylvestris L.), Norway spruce (Picea abies Karst.), Douglas fir (Pseudotsuga menziesii Franco), European beech (Fagus sylvatica L.), and English oak (Quercus robur L.) were exposed to six different soil substrates: field soil, fertilized field soil, a turf – field soil mix, bark mulch covered field soil, silica sand, and gravel. Furthermore specimens were partly embedded in concrete. Mini stake specimens (8 × 20 × 200 mm³) and standard stake specimens (25 × 50 × 500 mm³) were exposed in parallel at the field test site in Hannover-Herrenhausen, Germany, to allow also for identifying effects of the specimen size and volume. After 4.5 years of exposure the decay rates differed significantly between field soil containing substrates and those containing no natural soil substance. In general decay proceeded slowest in concrete followed by sand and gravel. The effect of adding turf, fertilizer and bark mulch to the field soil was negligibly small. Concrete embedding as protective measure performed well during the first 2–3 years, but showed increasing decay rates afterwards. In comparison, the decay process was often similar between substrates, once decay has started. In all soil substrates decay was dominated by soft rot followed by white rot. The average lifetime of the mini stake specimens was remarkably shorter compared to the standard specimens indicating a potential to shorten test durations. However, the use of mini stakes involved practical problems and led to some extent to an underestimation of wood durability. The meaning of different soils and specimen types, independent of other site influences, for service life prediction and durability assessment of wood is discussed and the need for further studies on this topic is highlighted.

Premature failure of timber construction can have dramatic consequences, at worst threat to human life or physical condition. Timber components might perform unexpectedly poor due to insufficient protection by misuse, design, low work execution level, or due to low resistance of the material in use. However, information about the material resistance of prematurely failed structures is usually lacking. Therefore this study aimed on developing a method to display the relationship between damages occurring on structures in service and the resistance against wood-destroying fungi of the material used. Drilling cores taken from wooden structures were found to have the ability to serve as specimens in laboratory decay test when compared to standard specimens. Therefore, drilling cores were sampled from different components of six timber bridges in Hannover, Germany, made from English oak (Quercus robur L.). The cores were submitted to the white rot fungus Trametes versicolor and to soft rot fungi in terrestrial microcosms. The determined mass losses due to fungal decay were compared with the level of damage of the studied bridge components. The results indicated that the material-inherent resistance was responsible for damages rather than poor details of the construction. The methodological approach might be used to provide further knowledge about the relationship of timber in service and under ideal laboratory test conditions.

Moisture has an important influence on fungal decay and therefore on the service life of wooden building components. The applicability of a long-term moisture recording system with glued electrodes was investigated on two different building objects: a cladding with different roof overhangs in Taastrup, Denmark, and a pedestrian timber bridge in Essing, Germany. Results after 2–4 years of in situ measurements are presented in this paper. The measurement system was found to be applicable and provided plausible data on both objects. For measurements on the Essing bridge, the measurement system was modified by means of using electrodes containing wooden substitute dowels to avoid the gluing at site under adverse circumstances. Moisture differences depending on the roof overhang and the distance to ground were identified and quantified within the cladding in Taastrup. Differently severe moisture conditions were observed for different building components of the Essing bridge, as well as weakening points of the construction in terms of moisture accumulation. Besides valuable information about variable moisture conditions within the examined objects, the use of automated moisture recordings provides an early warning system against increased decay hazards.