This paper deals with the experimental investigation of hygrothermal behavior of wooden-frame building envelope. The experiment was based on in-situ monitoring of a full size experimental monozone house built at the University of Lorraine. Variations in temperature and relative humidity inside and outside the envelope were logged simultaneously with local meteorological data. Results showed the high coupling between temperature and relative humidity variations within the envelope materials. An overall hygrothermal response of the wall highlighted an interesting hygrothermal dynamic behavior of the envelope which may contribute to mitigate variations of relative humidity inside the building. Nevertheless, relative humidity evolves within a range of values that can lead to mold growth at a certain position which may alter wooden envelope life.
Timber and timber products are renewable materials that, due to their durability and strength properties, meet the requirements of the construction industry, are widely used in buildings. An analysis of the scientific literature has shown that there is a lack of detailed research that fully investigates the influence of the rate of increase of the moisture content of the timber on the mechanical and, especially, the strength properties of the LVL panels. Upon immersion into water of the bottom of the specimen, the water starts rising quite quickly at the edge of the specimen, and the first six hours are the most critical. The levels of water rise inside the LVL specimen were less significant than at the edges. It was found that water significantly affects the bending strength of the panels, which, when the strength of the wet panel compared to the strength of the dry panel, decreases to 45% after one soak cycle and almost to 52% after two soak cycles. The tensile strength of the wet specimens is ~40% less than that of the dry specimens. The strength of the panels that were dried back to their initial state was found to be sufficient again, different from the initial strength only within the error limits; the strength properties of the building structure will not be affected.
Dimensional behavior of nail-laminated timber-concrete composite caused by changes in ambient air, and correlation among temperature, relative humidity, and strain
A timber-concrete composite (TCC) slab composed of nail-laminated timber (NLT) and topping concrete (TC) was developed for flooring applications. The NLT was laminated alternately with lumber and plywood. To investigate the dimensional behavior of the TCC slab, the temperature, relative humidity (RH), and dimensional changes of the slab exposed to outdoor air were monitored for 205 days. Temperature change was directly transmitted to both components, and RH change was gradually transmitted to the NLT. Concrete pouring caused a sharp increase in NLT width, which was the laminating direction of the nails. This resulted from swelling of the wood because of the moisture in the concrete mixture and loosening of the nail lamination. The member composition for the nail-laminating system, fastener type, and concrete volume help to secure the dimensional stability of the NLT. Cracks in the TC caused width deformation, which was recovered by drying shrinkage of the TC. Correlation analysis among temperature, RH, and strain indicated that dimensional changes in NLT correlated strongly with RH, while those in TC correlated strongly with temperature. The correlation between longitudinal strain in the TC and strain in the three directions of the NLT was attributed to the notches designed for mechanical connection.
As the height of mass timber buildings continues to grow, a new set of design and detailing challenges arises, creating the need for new engineering solutions to achieve optimal building construction and performance. One necessary detailing consideration is vertical movement, which includes column shrinkage, joint settlement, and creep. The main concerns are the impact of deformations on vertical mechanical systems, exterior enclosures, and interior partitions, as well as differential vertical movement of timber framing systems relative to other building features such as concrete core walls and exterior façades.
Current environmental crisis calls for sustainable solutions in the building industry. One of the possible solutions is to incorporate timber-framed constructions into designs. Among other benefits, these structures are well established in many countries, originating in traditional building systems. This paper focuses on experimental timber-frame walls. Different wall assemblies vary in thermal insulation materials and their combinations. We investigated ten experimental wall structures that have been exposed to natural external boundary conditions since 2015. The emphasis was on their state in terms of visual deterioration, mass moisture content, and thermal conductivity coefficient. We detected several issues, including defects caused by inappropriate realization, causing local moisture increase. Material settlement in loose-fill thermal insulation was another issue. Concerning was a significant change in the thermal conductivity of wood fiber insulation, where the current value almost doubled in one case compared to the design value determined by the producer.
The differences of physical and mechanical properties of different laminations, such as softwood, hardwood or other structural composite lumber, in hybrid cross-laminated timber (HCLT), lead to their dimensional stability and bonding performance more complex than generic cross-laminated timber (CLT). In this paper, the spruce-pine-fir (SPF) dimension lumber and construction oriented strand board (COSB) were employed to fabricate HCLT. The effects of four configurations and three adhesives on the dimensional stability and bonding performance of CLT and HCLT were evaluated in term of the water absorption (WA), thickness swelling (TS), block shear strength (BSS), wood failure percentage (WFP) and rate of delamination (RD). The results showed that with the increase of the COSB laminations, the WA of HCLT specimens decreased, and the values of TS, BBS and WFP increased. The configuration had a significant influence on the dimensional stability, BBS and WFP of the specimen. The adhesive had a significant influence on the dimensional stability and some bonding performances of the specimen. The phenol resorcinol formaldehyde (PRF) specimens had the lowest average RD value compared with the one-component polyurethane (PUR) and emulsion polymer isocyanate (EPI) specimens. Failures were prone to occur in the middle of the thickness of COSB lamination during block shear and delamination tests. The outcome of this paper could help the engineering application of HLCT.
The overall objective of this study is to provide information to building design practitioners that will help to improve accuracy of hygrothermal models and enable them to better use these models to predict the durability and thermal performance of wood-based building envelopes. To achieve this, hygrothermal models using WUFI Pro software are validated with experimental data obtained from five wood-frame wall assemblies, with different insulation and vapour control strategies, exposed to the climatic conditions of Vancouver from October 2018 to May 2020. This exercise provides a set of model input parameters that the practitioner can use to assess similar structures exposed to similar environmental conditions. Sensitivity analysis is conducted on the model input parameters to establish which are the most important in obtaining a good fit to experimental measurements, and therefore accurate prediction of assembly performance. There is also discussion on limitations of the hygrothermal model.
Understanding moisture behavior in cross-laminated timber (CLT) is critical to the widespread use of CLT in construction in the United States. Currently, very little data exist on the long-term impact of moisture on CLT in real structures. The objective of this research was to collect data regarding the long-term moisture variation in the CLT panels at the University of Arkansas student residential building, named Adohi Hall. The climate of Northwest Arkansas is different from those of previously monitored buildings, mostly located in the Pacific Northwest. Comparatively, Northwest Arkansas has a warmer climate with higher average annual precipitation. Moisture sensors were installed in 45 locations throughout the building to provide a comprehensive evaluation of the building. Results indicate that for the interior floors of the building, i.e., not the roof, CLT panels have not encountered moisture intrusions. At the roof level, moisture intrusions during construction were trapped in the CLT panels by waterproofing. This trapped moisture resulted in slower drying to below acceptable levels of moisture.
Mass timber has seen increased use as a building material for low and mid-rise construction in recent decades. The durability of mass timber elements has not been fully examined and the effects of wood destroying organisms on this these materials merits attention. The effectiveness of currently labeled soil termiticides and passively applied biocides at post-construction or as remedial agents needs to be evaluated for mass timber used in structures, particularly in areas with elevated risk of termite attack. The ability of soil insecticidal drenches or spray-on insecticide/fungicide treatments for protecting mass timber in service was assessed with a modified AWPA Standard E21 above-ground test using three ply Douglas-fir or southern pine cross-laminated timber as well as Douglas-fir mass plywood panels. Samples of each material (305 x 102 x 102 mm) were installed in an above ground protected test at the Harrison Experimental Forest (HEF) (Saucier, Mississippi) in September, 2019. Six replicates of five treatments including soil termiticide, no treatment, spray-on borate at initiation, borate rods and remedial treatment, using spray on borate of attacked material after two years, were tested. Samples were left undisturbed for two years and then examined and rated. Near surface moisture content increased to levels approaching the fiber saturation point over the two-year non-disturbance period. Untreated control samples were attacked by both decay fungi and termites. Samples treated with borates at test initiation showed limited decay or termite attack. Soil termiticide treated plots showed no sign of termite attack, but some samples had heavy decay compared to non-soil termiticide treated plots.
Nowadays, advanced hygrothermal simulation tools are available and they are widely used to predict moisture-related risks in building components, such as mold growth and increased conductive heat losses. This paper takes advantage of these capabilities to analyze moisture-related risks in the innovative wood-based retrofit solutions, developed in the ongoing H2020 “e-SAFE” project. In particular, simulations carried out through the Delphin software for the warm Mediterranean climate of Catania (Italy) allowed assessing the effectiveness of several insulating materials used in the wall assembly and the moisture-related performance determined by adopting either a waterproof membrane or a vapor barrier in convenient positions. The results show that the solutions with highly permeable and highly moisture-capacitive insulation (e.g., wood fiber) are mold free, but at the expense of increased heat losses by up to 12%, compared to dry materials). In some circumstances, foam glass or extruded polyurethane could be preferable, due to their high resistance to mold growth and their flat sorption curve. The vapor-open waterproof membrane applied to the outer side of the insulation is suggested, while a vapor barrier on the outer side of the existing wall worsens mold-related issues.
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