Abstract
Large timber buildings are becoming more common in cold climates due to their low greenhouse gas emissions and the abundant availability of timber. However, there is uncertainty about the long-term airtightness of these buildings, especially when using cross-laminated timber (CLT) in external walls, due to potential timber shrinkage and swelling and the following cracking of the CLT. To prevent moisture transport from inside to outside through gaps in the joints of CLT external walls, two measures are often recommended: applying a vapour barrier on the outside of the CLT elements and/or locally sealing the joints. The long-term effectiveness of local sealings alone is uncertain. This paper examines the airtightness and thermographic performance of a new zero-emission office building constructed in Trondheim, Norway in 2020. The building features a timber load-bearing system, including external timber frame walls and CLT-based walls. The timber frame walls have a vapour barrier on the warm side of the construction, while the CLT-based walls only have local sealing measures. Three thermal imaging and airtightness tests were conducted: one at the completion of construction, another after one year of operation, and the last one five years after construction to assess changes in the building envelope’s airtightness over time. The air leakage results from the three tests, conducted over a five-year period, showed similar air change rate values of 0.46-0.47 h −1 at a pressure difference of 50 Pa. However, a slight increase of the air leakage (0.52 h −1 ) was observed after five years. The increased air leakage rates in recent years are primarily due to insufficient sealing pressure between the window glazing and frame. Furthermore, thermographic inspection from inside the building revealed that local sealings had cracked in several places due to the movement of the wooden elements.