Risk of Moisture in Diffusionally Open Roofs with Cross-Laminated Timber for Northern Coastal Climates

Abstract

The paper is an attempt to answer the question whether the material-optimized roof construction using cross-laminated timber (CLT) is safe in terms of moisture content in the demanding northern costal climates. The proposed roof structure meets the strength requirements. The partition is diffusionally open, which facilitates moisture transport. However, there is a concern whether the applied layer system allows maintaining a safe level of moisture content below critical moisture content (CMC), which has been set at 20%. The article presents the annual hygrothermal calculation of the proposed roof slope for four locations of northern Europe and Greenland characterized by costal or subpolar climate. Four scenarios of indoor air relative humidity were considered: free floating, RHmin = 40%RH, RHmin = 50%, RHmin = 60%. In all cases, the minimum indoor temperature was 20 °C. The analysis was carried out using WUFI®Plus software. The calculation results showed that the moisture content did not exceed 20% in the CLT layer at any of the described locations. However, for the two coldest climates the assumed level of safety has been exceeded in the roof oriented strand board (OSB) sheathing.

Moisture Risk Analysis for Three Construction Variants of a Wooden Inverted Flat Roof

“…The acceptable moisture content in wood depends on the final choice of the wood, the type and thickness of wood, and the average RH in the environment where the wood is to be used (e.g., for the coastal climates, the EMC of wood is greater than for inland ones). Based on common guidelines or recommendations, the acceptable moisture content for wood objects used indoors is 9% to 14% for construction [29].…”

“…Several studies on timber products (including CLT and OSB-Oriented Strand Board) using hygrothermal simulations were carried out [29][30][31][32][33][34][35][36][37]. In the majority of these, calculations were performed with the support of WUFI-a commercial hygrothermal simulation software (developed by Fraunhofer Institute for Building Physics).…”

“…Omission of this aspect may lead to the degradation of the partition in a short time and, consequently, to its destruction. It is, therefore, necessary to design a layering system that will allow proper CLT performance by maintaining a safe level of moisture content in the partition and will not allow for its condensation inside the structure [29].…”

Modeling the Drying of Capillary-Porous Materials in a Thin Layer: Application to the Estimation of Moisture Content in Thin-Walled Building Blocks

“…Then at the moments of time t and ̃= + ∆ , the mass of moisture is Mwater and (Mwater -ΔMwater), respectively; the mass of a sample at the same times is equal to M and (M -ΔMwater). At the same moments of time, relative moisture content (2) is determined by relations (9) and (10), respectively: Relations (5) and (6), as well as Figure 1 suggest that it is easier to use C water from Equation (2) as an indicator of moisture in a theoretical study.…”

“…Note that in addition to forced drying in artificial conditions, drying in natural conditions is also used [4]. The elements of wooden roofs function in conditions of cyclical effects of natural drying and humidification [5][6][7], for the diagnosis of which the considered models can be used. The same models can be adapted as a tool for studying the life cycle of building materials [8,9], thermal insulation materials and wall structures [10], as a contribution to achieving the main goal of sustainable development.…”