There have historically been, and still are, problems with water intrusion into new external walls of prefabricated concrete sandwich elements in Sweden to a varying extent. The aim of this study was to obtain documented knowledge and data on driving rain resistance, to provide a basis for improvements and calculations in a common kind of concrete sandwich system with façade components and sealing products. The study included inspections and air pressure difference measurement of façades in the field and driving rain resistance testing of experimental set-ups in a laboratory. Inspection showed that vertical joints between the concrete elements were often significantly too narrow and, at the same time, adhesion loosening of building mastic in these joints was common. TDV-tubes were often incorrectly placed or had a bad incline. Field measurements indicate no pressure equalization, which is also confirmed by lab measurements. Lab results indicated inward leakage at window-wall interface, even without wind pressure, through the TDV-tubes despite a sharp incline, in element joints with a new kind of application of pre-compressed joint sealing tape. The largest leakage flows were of 0.4% of the vertical water flow across a unit width of the façade at the given height. 

There is an increased interest in using Cross-laminated timber (CLT) in construction, but many buildings are erected without weather protection, which poses a risk of moisture impact if wood is exposed to precipitation during construction. The construction industry argues that there are no documented critical moisture levels for CLT and no specific test method. In the study, a laboratory test set-up was developed to study mould growth under realistic and controlled climatic conditions after exposure to distilled water and spore suspension. In the experiments, small test specimens of CLT structures were exposed to distilled water for 1 day or 1 week. During the development of the method it was found that exposed for one day and then given the opportunity for open drying did not give rise to mould growth. On the other hand, growth occurred on surfaces that could not dry immediately, for example at connection points. For specimens exposed for one week, mould growth arose regardless of whether the surfaces could dry immediately or not. The conclusions apply primarily to the climates studied. The methodology needs to be further developed, with other scenarios being studied, and calibrated against samples exposed to outdoor air, dust, dirt and rainwater. 

The current distribution and population structure of many species were, to a large extent, shaped by cycles of isolation in glacial refugia and subsequent population expansions. Isolation in and postglacial expansion through heterogeneous environments led to either neutral or adaptive divergence. Norway spruce is no exception, and its current distribution is the consequence of a constant interplay between evolutionary and demographic processes. We investigated population differentiation and adaptation of Norway spruce for juvenile growth, diameter of the stem, wood density, and tracheid traits at breast height. Data from 4461 phenotyped and genotyped Norway spruce from 396 half-sib families in two progeny tests were used to test for divergent selection in the framework of QST vs. FST. We show that the macroscopic resultant trait (stem diameter), unlike its microscopic components (tracheid dimensions) and juvenile growth, was under divergent selection that predated the Last Glacial Maximum. Altogether, the current variation in these phenotypic traits in Norway spruce is better explained by local adaptation to ancestral environments than to current ones, where populations were partly preadapted, mainly through growth-related traits. © 2022 The Authors. 

I en tidigare genomförd SBUF studie (ID:13651) pekades det på att problem förekommer med vatteninträngning i ytterväggar bestående av betongsandwichelement. Historiskt sett har det förekommit vatteninträngning och även idag uppmärksammas problem med vatteninträngning i nya ytterväggar i varierande utsträckning, med prefabricerade betongsandwichelement. Det finns ingen entydig bild över omfattningen men däremot att det finns problem. Denna studie är en fortsättning av SBUF 13818. SBUF projekt 13818 visade på flera väsentliga avvikelser vid besiktningar och vid laboratorieförsök av fasader med betongsandwichväggar. Det finns ett behov i branschen av att klargöra utformningen av pålitliga lösningar och tätningar. Därför har nu nästa delsteg varit att studera tryckskillnad över verkliga fasader för att få klarhet i om verkliga fasader har en tryckutjämnande funktion och samtidigt få en avstämning om tidigare labbförsök var realistiska. Dessutom dra nytta av den kunskap som finns genom en litteraturinventering. Generellt sett visade utförda fältmätningar exempelvis på betydande tryckskillnader över fasad, 30-40 Pa undertryck i vägg mot ute, även vid relativt låga vindhastigheter på 5-8 m/s. Uppmätta fasader/väggar, var fogade med fogmassa och bottningslist samt TDV-rör/öppningar i fogkryss. Fasaderna kan därför inte anses ha en tryckutjämnande funktion (jämnställning av tryck). Fasader med aktuella TDV-öppningar har förmodligen otillräckligt med öppningar. Detta överensstämmer med de tidigare labbförsöken. Observera att i dessa fältmätningar så har enbart lufttrycksdifferensen över fasad och vägg samt vindhastighet och vindriktning mätts. Fasadernas regntäthet med mera har inte omfattats av dessa fältmätningar. I den internationella litteraturen förespråkas tvåstegstätning med dränering vilket inte förefaller vara så vanligt i Sverige idag. Eventuellt kan tvåstegstätade lösningar med dränering ha blivit misskrediterade i Sverige på grund av olika fel eller brister i utförande. Genomgående framhålls i den nationella och internationella litteraturen att tvåstegstätning ska vara en mer pålitlig och tätare metod än enstegstätning, om tätningar utförs korrekt. Inför fortsatt forskning kan konstateras att det finns ett behov av en guide med goda tätningsprinciper för dagens olika konstruktioner, lösningar och material med dokumenterade egenskaper, funktion och hållbarhet.

There have historically been, and still are, problems with water intrusion into new external walls of prefabricated concrete sandwich elements in Sweden to a varying extent. However, it has been unclear exactly what the causes are. It appears as if there is an application of single line of defence in sealing of joints in walls, which are known to be problematic. The aim of this study was to obtain documented knowledge and data on driving rain resistance, to provide a basis for improvements and calculations in a common kind of concrete sandwich system with façade components and sealing products, and to grade the driving rain resistance of various sealing principles. The study included inspections of concrete sandwich walls in the field and driving rain resistance testing of experimental set-ups in a laboratory. By scaling down concrete elements in the experimental set-up, it was possible to study multi-storey façades and made by experienced producers and contractors. Intentional defects were also created in an extra experiment based on inspection results. Inspection results showed that, in all buildings, vertical joints between the concrete elements were often significantly too narrow and, at the same time, adhesion loosening of building mastic in these joints was common. In general, the joints were equipped with small openings of tubes for depressurization, drainage and ventilation. However, they were often incorrectly placed or had a bad incline. Lab results for intact concrete sandwich walls indicated inward leakage at window-wall interface, even without wind pressure, through the tubes despite a sharp incline, in element joints with a new kind of application of pre-compressed joint sealing tape. The largest leakage flows were of 0.4% of the vertical water flow cross a unit width of the façade at the given height. To our knowledge, there does not appear to be a performance report on the current solutions, which in itself is a major uncertainty, i.e. the right conditions did not exist to avoid inward leakage.

This study examines how cross-laminated timber (CLT) constructions, including joints, connections and attachment points, are affected by precipitation during construction. The case studies are based on moisture content measurements and material sampling as well as microbiological analysis during the structure’s construction stage. The study does not include remediation control. The field measurements show microbiological growth in all buildings and almost all floor structures that were investigated. Of a total of 200 measuring points analysed, half had mould growth and around a third had moderate or extensive growth. The moisture content measurements for one of the locations with the largest percentage of elevated or high moisture content was at the top of the floor structure in the bottom gap between timbers in the CLT top layer. This is one example of several materials or construction components where there is limited possibility of dry out. Based on the outcome, it would appear difficult, or impossible, to avoid the appearance of microbial growth during construction with CLT without weather protection. Previous studies indicate that microbiological analysis of CLT is extremely rare in both laboratory and field studies, which implies that there are obvious shortcomings in the scientific work. The fact that mould growth is often invisible needs to be disseminated, especially in practical studies. However, there seems to be a good level of awareness in the literature that theoretical studies often conduct mould growth risk evaluations. There do not appear to be any moisture safety assembly methods or solutions for CLT construction that do not have weather protection or a declaration of the critical moisture conditions for CLT products. © The Author(s) 2021.

Lately, a new technical solution, pre-compressed joint sealing tapes in precast concrete sandwich panel facades, has been introduced in Sweden. Although the consequences of performance failure can go far beyond the component, affecting the building, the introduction has gained little attention in terms of risk assessment in the literature and in industry. Instead, reference cases are used as verification without formal evaluation, potentially leading to serial failure. The aim of this paper was to provide guidance on how a design–build contractor should handle this new technical solution. A risk assessment framework using a design–build contractor’s perspective was applied to the case. The framework addresses new technical solutions or adaption to new conditions (e.g., climate change) with the aim of preventing serial failures. Moisture conditions within the joints were simulated using present and future climates, and probabilities of failure were assessed using the Monte Carlo method. The results of the study included identified risks of failure associated with the solution and factors influencing the probability of failure. A main issue was the exposure of the facade to driving rain but also run-off areas and imperfections in the application of the joint sealing tape. Future climate changes affect performance negatively. In conclusion, the new technical solution might be possible to use if draining potential is ensured in all detailed designs and a set of recommendations, including full-scale testing, is provided for the design–build contractor. © 2021 by the authors.

There is a need of upgrading the old building stock with respect to the thermal insulation of the building envelope and specifically the façades. There are several systems on the market, and some are quite new and innovative. To bring down the cost some of the systems many are based on prefabricated moisture tight insulated units. This means that in case there is moisture tight barrier on the interior side, two moisture tight barriers surround the wall structure. The leakage of driving rain into the structure then represents a major threat to the durability of these systems. This paper investigates the pressure build up in water rivulets running down a façade acting together with the wind pressure. A driving rain leakage potential is introduced. Using real weather data years and Monte Carlo Simulations, the mean and standard deviation of the annual leakage through small hole is estimated. The examples show that the leakage can reach a level 0-0.5 liter/year for a hole with a diameter of 1-2 mm, and 0.5-3 liter/year for a diameter of 3-4 mm.

In current practices crawl spaces are typically ventilated with outdoor air. This leads very often to high relative humidity especially in the beginning of the summer, which can be problematic if the excess humidity cannot be ventilated efficiently enough. This paper introduces a crawl space concept where the crawl space is highly insulated and traditional ventilation openings are replaced by minimal mechanical exhaust ventilation set by pressure difference with the aim to prevent potential pollutants to penetrate indoors through the base floor. The concept that has been developed based on the simulation study is tested in this study with field measurements in four single family houses. Continuous measurements of relative humidity and temperature in crawl spaces and outdoor air were running more than one year in each building. The results revealed that all the crawl spaces had very low relative humidity, mostly below 75% and for very short periods close to 80% even though some of the buildings were new and construction phase moisture was drying out. The results revealed that the crawl space concept studied provided an ultimate moisture safety and can be recommended for all buildings with wooden floor. © The Authors

This project aims to expand understanding of how cross-laminated timber (CLT) constructions, including joints, connections and attachment points, are impacted by precipitation during construction. The project's case studies have been based on measurements of moisture contents and material sampling as well as microbiological analysis during the construction stage of the structure. The study does not include control of remediation. A literature review and interviews with seven individuals also were conducted. The results are based on two case studies with a total of four buildings. The field measurements show microbiological growth in all buildings and essentially on all investigated floor structures. Of a total of 200 analysed measuring points, half had some growth and about a third had moderate or extensive growth. Based on the outcome, it seems difficult or impossible to avoid the appearance of microbial growth during construction with CLT without weather protection. The literature review shows that microbiological analysis of CLT is extremely rare in both laboratory and field studies, which indicates that there are obvious shortcomings in the scientific work in practical studies. However, there seems to be good awareness in the literature that theoretical studies often conduct mould growth risk evaluations. In the survey, half of those interviewed believed that remediation was needed only in the case of growth visible to the naked eye. There appear to be no moisture safety assembly methods or solutions for CLT construction without weather protection or declaration of the critical moisture conditions for CLT products. As a result, it is recommended that weather protection is used, preferably complete weather protection. © The Authors.