Conference Agenda

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Session Overview
Session 26: Moisture in buildings and its risks
Thursday, 26/Aug/2021:
4:00pm - 5:30pm

Session Chair: Prof. Thomas Bednar, TU Wien
Location: Room 1 - Room 082, Building: 116

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4:00pm - 4:15pm

Process induced building defects in Norway – development and climate risks

Nora Schjøth Bunkholt1, Lars Gullbrekken1, Berit Time1, Tore Kvande2

1SINTEF, Norway; 2NTNU, Norway

The SINTEF Building Defects Archive is an important source to knowledge on process induced building defects in Norway. This study presents a review of defects investigated by SINTEF in the period 2017–2020, including 175 defect cases registered in 125 reports. The main goal is to understand the primary causes of process induced building defects and which building elements may be considered as risk spots. The review shows that penetration of water is an important cause of damages in building constructions. Almost 3 out of 4 defect cases is related to moisture, caused by moisture sources as precipitation, condensation of humid indoor air or built-in moisture. Defects associated with the building envelope make up more than 70 % of the investigated cases, of which most defects are linked to exterior wall or roof constructions. Regarding roofs, the analysis shows that compact roof structures may be especially vulnerable, as almost 75% of the roof defects concern compact roofs and terraces. The results from the present study has been compared to a review of defects reported in the archive during the 10-year period 1993–2002 (2423 defect cases). The comparison reveals that the share of damages caused by precipitation is almost doubled, while the share of damages caused by humid air from the interior is approximately halved. These findings are supported by two known phenomena: buildings have become more airtight and better ventilated due to stricter building regulations at the same time as precipitation loads increase. The results imply that climate adaptation of buildings is important. As climate change causes more precipitation with higher intensities, the load on buildings increase and a larger focus on risk reduction and protection towards penetration of water from the outside is required.

4:15pm - 4:30pm

Comparison of indoor moisture excess in three different terraced housing projects

Christoph Harreither1,2, Joe Gengler2, Thomas Bednar1

1TU Wien - Vienna University of Technology, Austria, Faculty of Civil Engineering; 2University of Applied Sciences Upper Austria, Wels, School of Engineering

Indoor humidity is a significant boundary condition for the durability of constructions. Indoor absolute humidity depends on factors like external absolute humidity, indoor moisture production and airing. One way to describe indoor humidity is the moisture excess according to ISO 13788. Depending on these parameters the indoor climate can be categorized into humidity classes from 1 to 5.

In this study three neighbourhoods of terraced houses have been investigated. In 15 to 30 houses of each project, indoor temperature and indoor humidity have been measured, inhabitants have been interviewed, and blower door tests have been performed. PSG is a project with about 100 similar, very airtight detached houses constructed in 2009 by using prefabricated wood frames. 30 houses from PSG have been investigated. APW is a project with 26 terraced houses built in 2012, which have mechanical ventilation systems. From this project 15 houses have participated in the study. TES is a low rise high density project with approximately 90 single family houses built in 1974. The results of 20 houses have been analysed.

The measurements show that the moisture excess depends more on the house itself, such as construction type, building equipment etc. than on the user behaviour. It will be shown that most of the houses with mechanical ventilation systems have very low indoor absolute humidity. Furthermore, it will be exposed that houses with poor airtightness have medium indoor absolute humidity and that houses with high air tightness have the highest indoor humidity level although they are detached. Box plots of the moisture excess in the diagram with the humidity classes from ISO 13788 show that the boxes do not overlap. Statistical analysis has been carried out and the data will be used for probabilistic calculations.

4:30pm - 4:45pm

CIB W040: International Surveys of Architecture and Engineering Consultants for Moisture Safety in Buildings

Naomi Morishita-Steffen1, Anssi Laukkarinen2, Thomas Lewis1, Ruut Peuhkuri3, Sabine Wolny1, Juha Vinha2, Thomas Bednar1

1TU Wien, Institute of Material Technology, Building Physics, and Building Ecology, Research Unit of Building Physics; 2Tampere University, Faculty of Built Environment, Civil Engineering, Building Physics; 3Aalborg University Copenhagen, Civil Engineering and Construction Management, BUILD - Department of the Built Environment

Comparative surveys of design consultants in Austria, Denmark, and Finland were conducted to determine the current knowledge level and problems experienced with moisture damage during design and construction. The studies are part of the needs' analyses of five stakeholder groups for the CIB W040 research roadmap. The surveys aim to realign research efforts with stakeholder needs to ensure moisture safety in buildings. Survey results show that a third of construction projects in the last five years were affected by moisture problems, even though practitioners applied multiple measures to prevent moisture damage in all three countries at least some of the time. Approximately 20 % of the moisture damage was caused by water installations. In each country, preventing moisture damage was important; the means to address moisture problems varied with no one solution dominating in any country. Design and construction guidelines were more helpful than the building code requirements. Information about moisture safety is available, but dedicated time and budget are required to implement better moisture safety during the design and construction phases. A quantitative goal resulting from the current survey is to raise the percentages of moisture safety measures being taken systematically while reducing the lack of available instruments. However, the usefulness of selected measures and instruments needed will be strongly case-specific. Accordingly, given their pronounced difference in nature, subtopics such as reasons for problems due to leaky water installations should be analysed in greater detail. For this purpose, other methods than an online survey may be more effective. The survey results can be used to refine future research work and the development of smart tools to prevent moisture damage in the design, construction, and occupancy phases.

4:45pm - 5:00pm

Damage risk assessment of building materials with moisture hysteresis

Michele Libralato1, Alessandra De Angelis1, Paola D'Agaro1, Giovanni Cortella1, Menghao Qin2, Carsten Rode2

1Polytechnic Department of Engineering and Architecture, University of Udine, Italy; 2Department of Civil Engineering, Technical University of Denmark, Denmark

Heat and Moisture Transfer (HMT) simulations of building envelopes are used for the assessment of moisture related damage risks. HMT simulations are commonly performed accepting the hypothesis of not considering the moisture hysteresis of materials.

This hypothesis allows among the others one simplification: when a porous material is in hygroscopic equilibrium with the air in the environment and in its pores, one value of Relative Humidity (RH) corresponds to a unique value of Moisture Content (MC), and the other way around.

Although the majority of the commercial simulation tools are based on this assumption, they can be used to consider hysteresis using the mean sorption curve or calculating the upper and lower bound of the MC values with hysteresis performing two simulations, one with the desorption isotherm (upper bound) of the materials and one with the adsorption isotherm (lower bound).

For the definition of damage prediction models, sometimes hysteresis is not considered, and RH values are used to calculate the damage entity of materials, even if it depends on MC. This is frequently the case of wood decay and corrosion of metal inclusions.

This contribution will present some simulations and risk assessments to show that defining the damage models as functions of RH does not allow to take in account the influence of moisture hysteresis of materials. The results of HMT simulations (using the software MATCH, which considers moisture hysteresis) on wooden walls are presented, showing the hysteresis effect on the MC-RH plane, and a wood decay risk analysis will be performed using the 20% MC rule. Considering MC and RH as two independent variables could allow to perform risk assessments with moisture hysteresis effects, also when the upper and lower bound approach is used.

5:00pm - 5:15pm

Pore-scale investigation of dynamic effects on the moisture retention curve during spontaneous imbibition

Michele Bianchi Janetti1,2, Hans Janssen2

1University of Innsbruck, Austria; 2KU Leuven, Belgium

The moisture retention curve is often assumed to be independent of the process dynamics, i.e., of the drying/wetting rate. Experimental outcomes and pore-scale simulations put however this assumption into question. It has been shown that dynamic effects might significantly affect the moisture retention curve, which presents different behaviours, depending on whether it is determined under transient or steady-state conditions. However, while dynamic effects of the drainage process have been widely studied, the data concerning spontaneous imbibition are still quite limited. In particular, a lack of knowledge about building materials is present, the majority of prior studies addressing soils’ behaviour.

This study aims at reducing this lack of knowledge by investigating spontaneous imbibition in porous materials via a pore network approach. The liquid flow in the network is described via the Hagen-Poiseuille equation, while a percolation algorithm controls the dynamics of liquid-gas interfaces through the network junctions. Dynamic moisture retention curves are determined by linking the average capillary pressure to the moisture content in the representative element of volume (REV). The dynamic effects are quantified via a dynamic storage coefficient, which put into correlation the deviation between dynamic and static capillary pressure with the local saturation rate.

It is generally assumed that the steady-state/dynamic capillary pressure deviation is proportional to the saturation rate. In this study we are going to verify whether this assumption holds for spontaneous imbibition. Randomly generated networks are generated with porosity and pore volume density of real building materials. The model sensitivity on physical and numerical parameters (contact angle, porosity, time step) is estimated. It is shown that, in order to obtain representative results, the dimension of the REV and its location inside the domain have to be properly chosen. The results represent a major step forward to the characterization of dynamic effects in building materials.

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