Wetting circumstances, expected moisture content, and drying performance of CLT end-grain edges based on field measurements and laboratory analysis

To reduce the carbon impact of new buildings, wood is seeing increased use as a structural material. Cross-laminated timber (CLT) and glue-laminated wood (glulam) elements allow the construction of multi-storey buildings. However, wood is vulnerable to moisture, especially when naked wood is exposed to weather during the construction process. This paper presents the moisture strategy employed during the construction of a four-storey CLT/glulam building in Trondheim, Norway. The building was constructed without the use of a weather-protective tent, requiring alternative protective measures. The construction of the main structure was scheduled to be as short as possible. Local protective measures were employed to protect the structure from rain and free water was removed after rain events. The project was closely supervised by the client, with particular care for moisture control. Moisture was regularly measured at 50 points throughout the building. No wooden surfaces were encapsulated until a wood moisture content below 15 weight-% was measured. The performance of the moisture strategy was evaluated using measurements of wood moisture, indoor climate, airtightness, and visual inspections. The wood moisture content quickly decreased as the building envelope was assembled, indicating that drying was well facilitated. In the first year after construction, gaps between the flooring and baseboards were observed, suggesting that the wooden elements have experienced some shrinkage. The moisture safety strategy is deemed to have been generally successful. The overall experiences were important in the development of new recommendations in the SINTEF Building Research Design Guides for CLT structures.

Section: Discussionmentioning

confidence: 99%

Moisture safety strategy for construction of CLT structures in a coastal Nordic climate

Time,

Andenæs,

Karlsen

et al. 2023

“…2 Period shortened to be comparable with other construction projects. 3 Sensors only calibrated before installation. 4 Affected by heating during measurement.…”

Section: Hygrothermal Conditions Outside and Inside The Weather Prote...mentioning

confidence: 99%

“…Olsson [1] indicated that more than half the samples taken at the site exposed to precipitation had elevated levels of mould growth. In two studies [2] [3], wetting of end-grain is identified as crucial even for short exposure, enhanced by low drying out capacity in construction details. This is similar to the findings in [4], where mould growth is found even after a short exposure period (1 day) for floor-wall connections (where connections per se involve delayed drying out).…”

Section: Introductionmentioning

confidence: 99%

Weather protection at the construction site: work environment and conditions for moisture and mould growth on massive timber

Bolmsvik,

Eriksson,

Tengberg

et al. 2023

During the last decade, the use of timber (especially massive timber) has increased worldwide, mainly driven by anticipated environmental benefits. However, there is debate on how to handle the susceptibility against microbial growth for wooden constructions, especially during the construction phase. Sometimes full weather protection is used to avoid exposing the wooden material to outdoor conditions, but oftentimes the structures are fully exposed to precipitation. In an earlier study, one construction site using a full weather protection was studied, and the results showed promising results on the improved hygrothermal conditions and reduced risk of mould growth. Moreover, the site contractor also indicated improved work environment and productivity, however, this was not included in that study. This present study aims to investigate the effects of using full weather protection during construction in seven different construction projects to follow-up and broaden the earlier single project study. The studied aspects include the hygrothermal conditions, potential of mould growth, and influence on the work environment. Temperature and relative humidity were measured and analysed. Samples of cross-laminated timber (CLT) were analysed using a microscope, and the results are compared to theoretical mould growth potential. This is measured both inside the weather protection and outside at the seven construction projects. Furthermore, a work environment questionnaire is distributed to workers at the sites to collect the perceived work environment using a full weather protection. The results of the study partly confirm the conclusions from the earlier study, i.e., reducing the risk of mould growth and causing a slightly warmer and dryer conditions than outside. In addition, the results indicate an improved work environment. The majority of the interviewees wishes a weather protection in their next project regarding the work environment.

“…Beside interior insulation, the improved material characterization could be of help to research targeting structures where timber has a significant role. For example, the wider spread of cross-laminated timber (CLT) structures has introduced issues such as of dryout of rain absorbed during erection [7] and the difficulties in modelling such cases.…”

Section: Introductionmentioning

confidence: 99%

Capillary condensation redistribution (CCR) test: measurement results of 5 materials and comparison to modelling

Klõšeiko,

Valk,

Põldaru

et al. 2023

To improve the accuracy of hygrothermal modelling, a capillary condensation redistribution (CCR) has been proposed to help distribute the share of vapour and liquid conductivity functions based on a wider experimental dataset. This paper aims to provide further data by presenting the CCR test measurement results of 2 calcium silicate (CaSi) boards, 2 aerated autoclaved concrete (AAC) boards and spruce (the latter both perpendicular and parallel to the grain). A variation of the CCR test setup is described. The measurement results agree with those from literature where some of the materials presented here were also tested. Modelling results using previously available material properties are compared to measurement results: none of the AAC and longitudinal spruce material properties can reproduce the moisture content levels achieved in the study, while CCR-optimized CaSi material data is close to the measured results. The best agreement between measurements and modelling of spruce perpendicular to grain are achieved with material properties which discard liquid conductivity and presume increased vapour permeability due to increase of moisture content instead.