Comparison of thermal comfort conditions in multi-storey timber frame and cross-laminated residential buildings

In recent years, timber construction systems have been increasingly used in multi-storey residential construction in Europe. In line with this international trend is the choice of the Trentino social housing company ITEA to build two five-storey multi-family apartment buildings in Trento (Italy) using two different timber wall systems. The two buildings are identical except for their structural system: timber frame (TF) and cross laminated timber (CLT). The design and the construction of these two buildings are the result of an international collaboration between ITEA and the Canadian social housing company Quebec Societè D’Habitation in order to evaluate and compare timber construction systems for social housing from the two countries. Since the two buildings have identical floor plans, layouts and finishes and differ only in their structural system, they present a unique opportunity for comparison of the two key forms of timber construction in terms of economic, engineering and indoor comfort issues. This paper investigates the difference in indoor conditions and analyse the achieved thermal comfort by measuring physical parameters and surveying the occupants’ perception. The two structural systems used for the buildings represent two widely used but fundamentally different forms of timber construction. The light timber frame is extremely lightweight, which gives the building low thermal mass and consequently low thermal inertia. This can lead to a lack of thermal comfort, particularly in summer, due to temperature fluctuations. Cross-laminated timber, used to form the timber shear walls in the south building, is a comparatively modern building component. Again, it can be highly prefabricated, and used with computer controlled cutting techniques to pre-cut openings for windows, doors and services to a high degree of accuracy. This system, known as ‘massive timber’, provides a higher thermal mass, if compared to the previous system. By means of indoor comfort monitoring and subjective questionnaires to the users’, it has been investigated to what extent this difference of thermal properties affects the indoor conditions provided and the final users’ satisfaction towards the thermal environment. This experimental campaign falls into a broader policy adopted by ITEA to engage closely with the performance of the buildings they build and manage, in accordance with an increasing interest globally in building performance assessment and post-occupancy evaluation (POE), whose main purpose is to investigate occupants’ reported levels of comfort and satisfaction and the degree to which they perceive their needs are being met by the building’s indoor conditions.