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Service life prediction of wooden components – Part 2: Impact of material, exposure and design details
2010 - IRG/WP 10-20440
Dose-response functions permit to estimate the moisture and temperature induced decay potential for any wooden building component and exposure, and thus the service life to be expected. In part 1 of this series dose-response functions were established as a result of double layer field trials carried out at 24 European test sites over up to eight years. Using them makes it no longer necessary to conduct field trials as long as decay actually occurs. They allow determining dose-time functions for a certain construction detail over shortened time periods (2 3 years). Within this paper we present the test set up of different studies aiming on quantifying the impact of material, exposure and design details on the service life to be expected for wooden components. Therefore long-term moisture recordings were applied to different wooden commodities, e. g. fence posts, pickets, decking, and facades. Furthermore, the impact of orientation, distance to the ground, and driving rain load on facade panels was studied. Finally dose-time functions will be recorded for ten different wood species used in horizontal and vertical orientation. First results from the various studies including preliminary service life estimation for various components are also presented.
C Brischke, B Lauenstein, M Bilstein, T Bornemann, A O Rapp

Comparative studies on the moisture performance and durability of wooden facades
2012 - IRG/WP 12-20492
Wooden claddings are traditionally used in many parts of the world. Also modern structures are frequently made from timber and timber engineering panel products. However, wood has to compete with other cladding materials and its durability needs to assure sufficient functional and aesthetic service life. Besides many other factors the durability of a wooden facade is dominated by its moisture performance on the one hand and the occurring moisture loads on the other hand. Within this study continuous wood moisture content measurements were conducted on three different test objects: 1. Combined facade-decking elements made from eleven different wood species relevant for the European market were exposed to the South and to the North in Hannover, Germany. Material-specific moisture performance was evaluated and compared with climatic parameters. 2. Three-years of measurements were carried out on the walls of a timber-made test house at the same test site. Measurements were made in different wood species, at different distances to the ground and in all four compass directions. 3. The effect of different roof overhangs on the moisture load of a wooden facade made from Norway spruce was studied on a test assembly in Tåstrup, Denmark. In addition to the moisture content measurements, wood temperature was recorded daily and relevant weather parameters were collected from meteorological stations nearby. To assess the respective moisture performance of the various materials and construction related parameters, the number of wet days was determined and a performance model was applied to all data sets. Based on a model for above ground decay the expected service life was calculated for different exposures, materials and design details. The highest moisture loads were found on the West facade, which is the weather side in Central Europe, followed by the North facade, where re-drying was inhibited due to limited solar irradiation. Furthermore the splash water zone was clearly identified, where moisture loads were increased and re-drying reduced due to lower wind speeds close to the ground. Finally, the moisture performance of the various timber species differed significantly. Thus, a wide range of service life estimates was deviated from the data sets.
T Bornemann, C Brischke, J-M Lück

Durability of wooden shop-name signage coated with Urushi lacquer and gold leaf attached to the facade of building in Japan
2012 - IRG/WP 12-20493
Wooden shop-name signage plated with gold leaf is one of the characteristics of newly developed westernized commercial buildings appeared after the Great Kanto earthquake of 1923 in Japan. The signage still remains mainly in old districts. The signage with independent letters (Chinese character) shows off the name of the shop with golden colour on the façade of building. The number of these shops sign on the wooden signage has been decreasing quickly during past 2 decades because of the re-development of city or so called “doughnut phenomenon” of city. Before the extinction of all of the wooden signages, we examined 195 signages attached in various types of building to elucidate wood species, manufacturing process, maintenance method, and aboveground dulability of them. Service life of them sign on the facade of shop at 3-4m aboveground seemed to be around 30 years without maintenance, and complete separation of the gold leaf required tens of year. Separation of the gold leaf from the surface of Urushi lacquer progressed gradually for a long time, and the Urushi lacquer layers appeared under the gold leaf for another several decades until all of gold leaf peeled off. After that, it decayed very quickly. The wooden shop-name signage plated with gold leaf has the advantage of appearance and durability, but it would die out in course of time. A traditional use and technology of the wooden signage with gold should be recognized widely at least among people in the wood industry.
K Yamamoto, M Kiguchi

Fire protection of wooden facades in Norway
2015 - IRG/WP 15-40710
Wood products are experiencing a renaissance as construction material in Europe due to their environmental benefits. In Norwegian building design however, timber has always played an important role but has had its limitations in urban architecture. One of the reasons is a high demand to fire safety in dense house building and multi-story buildings. Though novel construction methods and fire safety design concepts have widened the field of applications during the last years, architects and engineers still face challenges in using wood in buildings that require high fire safety. A critical point of many flame-retardant chemicals in outdoor applications is their poor fixation in wood; they are prone to migration due to moisture changes, which bears the risk of salt crystallization on product surfaces often associated with damage of coatings. Additionally, loss of the chemicals may decrease the fire performance. The draft standard prEN 16755:2014, superseding TS 15912:2012, prescribes the classification requirements for the durability of the reaction-to-fire performance of flame-retardant-treated wood products in humid conditions. The development of the TS 15912 into a European standard is an important but only a first step forward to guide planners to find suitable flame-retardant treated wood products for outdoor applications. The awarenes’ of building planners and the construction industry for choosing appropriate treatments in humid conditions has to be raised; besides, a further development of flame-retardants is desirable, which show a high leaching resistance and, at best, increase the durability against decay and discoloring fungi.
U Hundhausen, K-C Mahnert

Self-Extinguishment Phenomena of Mass Timber in Medium-Scale Compartment Fires
2018 - IRG/WP 18-30729
This paper presents a review of the fire safety risks that mass timber construction may introduce in buildings, with special consideration to medium- and high-rise buildings. These main risks are represented by an effect to the classical fire safety strategy for buildings: (1) Compartmentalisation, to ensure that the fire will not spread farther than the compartment of origin, (2) Preventing vertical flame spread to avoid façade and multi-floor fires. These requirements are essential if an adequate fire strategy has to be achieved. In order to study these newly identified risks in buildings with exposed mass timber (i.e. Cross-Laminated Timber); five medium-scale compartment fire tests were conducted of internal dimensions 0.48 m x 0.48 m x 0.37 m. Two tests had one sidewall and the ceiling of exposed CLT, while the other three were baseline tests (i.e. same geometry and the CLT completely encapsulated). Results consisting of incident radiant heat fluxes onto the compartment walls and the façade area above the window are presented herein. These are the parameters that will determine if self-extinguishment and vertical flame spread will occur. Self-extinguishment of the exposed timber occurred for all the tests with exposed mass timber after the fire consumed all the available fuel on the floor of the compartment. Therefore, after burnout, the heat flux onto the exposed walls was below the critical heat flux for self-extinction. Nevertheless, it was difficult to compare the heat flux data at the time of self-extinguishment with previous outcomes for self-extinguishment conducted on bench-scale testing, as the time scale differences induce a considerable delay before flameout is observed. The heat fluxes into the façade were as much as two times bigger when exposed timber was present.
C Gorska, J P Hidalgo

Long service life or cascading? The environmental impact of maintenance of wood-based materials for building envelope and their recycling options
2018 - IRG/WP 18-50336
A major restraint in choosing bio-based materials (i.e. wood-based) for external use, is the lack of confidence that architects, designers and customers have toward these materials. In particular, the limit state of bio-based materials, which defines the frequency of maintenance operations, might be reached earlier for wood than for other materials (i.e. concrete). On the other hand, resource and energy scarcity together with increasing concern for climate change consequences are raising the demand for competitive bio-based materials in the built environment as substitutes for other energy-intensive materials. Therefore, novel and traditional protective treatments are used to improve the performance of woody materials for outdoor use. Nonetheless, the environmental and economic burden of such treatments is often unknown. The number of LCA (life cycle assessment) studies on the topic is low, with geographically sparse data and non-uniform assessment protocols. This study provides a novel approach to assess the in-service performance, maintenance requirements and end-of-service-life options for over one hundred bio-based materials for façades. The protection techniques of the materials under examination include: chemical modification, thermal treatment, impregnation, hybrid treatments, and surface treatments (bio-film, coating and nanocoating). Natural, untreated wood and composite materials such as wood-plastic composites are included as well. The in-service environmental performance is analysed by considering the amount of material, energy, water and waste that are used and/or produced to maintain one square meter of façade. The options for end-of-service-life include: panel manufacturing, pelletizing, animal bedding, liquefaction, insect conversion, fungal conversion, combustion, incineration, gasification and pyrolysis, anaerobic digestion, fermentation, composting and landfilling. For each material group, the possibility for cascading use is assessed. The overall goal is to increase the confidence in bio-based building materials by tackling environmental issues related to wood modification processes.
M Petrillo, J Sandak, P Grossi, A Kutnar, A