Die Feuchte ist ein zentrales Thema in der Baubranche, das meist negativ besetzt ist, da Schäden und mangelnde Hygiene mit ihr in Verbindung gebracht werden. Der Bauschadenbericht des VHV von 2022/23 [1] zeigt, dass Schäden aufgrund von Feuchte zu den häufigsten und teuersten Bauschäden gehören und das, obwohl die DIN 108-3 dies schon seit den 80er-Jahren verhindern soll. Eine Erklärung könnten die Auswirkungen unserer Anstrengungen zu Energieeinsparung und zur Reduktion der CO2-Emissionen im Bausektor sein.
Eine andere Erklärung ist sicher auch im Zeitdruck bei der Gebäudeerrichtung zu sehen. Letzteres führt zu größeren Problemen mit der Rohbaufeuchte, während die wünschenswerten Maßnahmen zur Steigerung der Energieeffizienz mit größeren Temperaturunterschieden und einer besseren Luftdichtheit der Gebäudehülle einhergehen, was gleichzeitig die Raumluftfeuchte und die Gefahr von Tauwasserbildung erhöht.

Moisture damage plays a key role for the durability of buildings and for the health and comfort of occupants.
Various numerical models were proposed for engineers and architects to evaluate the hygrothermal condition
before constructing in China. Although the physical discipline is universal, the complexity and variety of climates
and building components make the moisture-related problems as well as the development and application of
hygrothermal models distinctive in China. This paper is a comprehensive survey of the state-of-the-art in China to
promote future advancement and academic communication between China and abroad. It investigated hygrothermal
white-box models in China including modeling and input parameters. The paper presents that the assumptions
of available models limit the application of hygrothermal white-box models in some situations. It also
shows that there is a shortage of suitable indoor and outdoor climate databases. To sum up, the following items
are necessary to establish hygrothermal simulation in building practice: models working with separate driving
potentials for liquid and vapour transport; hygrothermal reference years as outdoor climate data; indoor climate
data, either measured occupants’ behavior or derived from building operation setpoints influenced by outdoor
climate.

If condensation occurs on non-hygroscopic surfaces of insulated wall constructions, droplet runoff may
happen if the amount of condensate exceeds certain limits. Depending on the situation this phenomenon may
help to dry the wall, but it may also result in material degradation by water accumulating at the bottom where
drainage is not intended. The limits for interstitial condensation amounts on non-hygroscopic materials
calculated by the dew-point method in European standards differ with values up to 500 g/m². However, it is
questionable whether these limits are based on rigorous experiments and whether they are suitable to evaluate
hygrothermal simulation results. Therefore, a laboratory test method has been developed to determine the
amount of condensate required for water to run off from vertical surfaces or interfaces of insulated assemblies.
For this test 14 fibrous insulation materials (9 x mineral wool, 3 x wood fibre, 2 x cellulose) and 4 types of
condensation planes (hydrophilic, hydrophobic, smooth, or rough surface) were examined. The results proved
to be much lower than in the above-mentioned standards. Mostly, they ranged between 100 and 200 g/m².
Furthermore, by correlating the acceptable amount of condensate with the hygrothermal properties of the
insulation materials, a simple formula was derived to estimate the material specific limit value, using its moisture
equilibrium at 80 % RH. Finally, by comparing the test results with hygrothermal simulation results, it can be
concluded that the water content in the critical one-centimetre-thick layer of the assembly, referred to in
DIN4108-3 (2018), is appropriate to assess the probability of condensate runoff.

Damage to buildings is usually caused by water or moisture.
The causes can be manifold: 1.1 million insured cases of
damage caused by mains water per year alongside damages
due to construction moisture or inadequate measures to protect
against moisture. Heavy rain, flooding, condensation, rising
damp in walls are further causes of damage to technical installations,
e.g. heating, ventilation, power supply, or to furniture,
machinery and manufacturing equipment. Sometimes even
people and animals are affected. Consequential damage can
be, for example, hidden mold growth, frost damage, structural
problems, unpleasant odors, or restrictions of use.

Shading of the roof surface directly influences the thermal conditions and thus also the hygrothermal behaviour of the roof construction. Especially in the case of wooden flat roofs, shading can lead to a reduction in drying and therefore taking in account the effects of shading is essential for a moisture-safe design of such roofs. In this paper, possibilities to account for different shading situations in hygrothermal simulations are shown and their influence on the roof structure are discussed.

In recent years, insulating materials made from renewable natural materials have gained in importance – mainly due to advantages in sustainability and carbon footprint. However, the moisture content limits specified in standards and guidelines for such materials are mostly quite low, which considerably restricts their range of application. In order to enable reliable and broader use in the various areas of the building envelope, robust limits are required that relate not only to the combination of temperature and humidity but also to the duration of their exposure. After all, microbial growth in the exterior climate is possible in most regions, at least temporarily. Therefore, a transient assessment can best evaluate how a construction must be designed to safely avoid damage. In this contribution both new limit curves and a transient decay prediction model, based on durability tests of natural fibre materials in the laboratory are proposed. First evaluations by field tests have already been performed.

To reduce CO2 emissions and save grey energy, natural materials like wood and
wooden materials are becoming more and more important. However, these products are
particularly sensitive to moisture, as they can be attacked by mould or decay fungi. In contrast
to mould growth, which typically is associated with visual impairment and health problems, the
growth of decay fungi may result in structural defects which clearly must be excluded. Up to
now it is mostly assumed that wooden materials are more sensitive to such attack than solid
wood. Therefore, different wood fibre insulation materials were inoculated with decay fungi and
exposed to different climates to determine the requirements for the decay process and to compare
them with the requirements of decay by the same fungi of solid wood. The results prove that
some natural fibre materials are equally or even more resistant to decay fungi than solid wood,
while others are less. The resistant products can therefore be assessed like solid wood – for which
already temperature dependent thresholds and in part also transient decay prediction models are
available. Maybe even specific higher moisture levels can be acceptable. However, the results
also suggest a differentiated view on natural fibre insulations, as they have a very different
susceptibility to wood decay. Uniform and significantly lower limits than for solid wood are not
justified.