The interest for wooden constructions is on the rise, and there is a political drive to encourage the use of wood in building projects to mitigate carbon emissions. This paper investigates whether exterior wall constructions made of Cross-laminated timber (CLT) in Nordic climates can be constructed moisture safe, without a vapor barrier made of PE foil. The study is carried out using hygrothermal simulations in WUFI® Pro and the theoretical risk of mould growth and wood decay are investigated. Several variations of CLT walls with and without PE foil, a smart vapour retarder, a traditional wind barrier board, and combinations of membranes and boards are examined. The results indicate that non-critical relative humidity levels are achieved in the CLT element if no vapour barrier is used. In case of built-in moisture in the exterior CLT, results indicate to leave out PE-foils, as they limit the drying process and increases the risk of mould growth and wood decay.