Mass Timber Buildings: The associated risks of rainwater exposure during construction in the Portuguese climate

The increase in the number and complexity of wooden buildings creates a series of challenges, like moisture control and management during the construction phase. The risks associated with the direct exposure of timber elements to rain during construction depend on the severity of the climate and the specific details of each project and therefore must be analysed locally. In this context, the results of 16 weeks of moisture content monitorization of Cross Laminated Timber (CLT) floor-wall connection specimens exposed to the outdoors are presented and evaluated. The monitorization demonstrated that end-grain surfaces are the most sensitive to the action and movement of water in CLT and within a few days of exposure to rain reached alarming moisture content (MC>30 %), with water entrapment at the interface between elements, preventing drying in a reasonable time for construction workflow (MC>30 % after 39 days of drying). On the other hand, zones with faster drying exhibited severe physical damage such as delamination and cracks. Additionally, the study evaluates the feasibility of using satellite-obtained meteorological data to develop a degradation risk map (Scheffer Climate Index) for mainland Portugal. The high coefficient of determination (R 2 ≥ 0.81) and model efficiency (EF ~ 0.80–0.90) demonstrate the reliability of the data. Finally, two degradation risk maps for mainland Portugal are presented. • Alarming moisture content was recorded within a few days of Cross Laminated Timber exposure to rain. • Exposed end-grain surfaces of Cross Laminated Timber are the primary zones of rainwater infiltration during construction. • Zones with faster drying exhibited severe physical damage such as delamination, cracks, and warping. • Interfaces between elements are critical in terms of water entrapment. • Satellite-obtained meteorological data are feasible to develop a degradation risk map for mainland Portugal.