Timber modern methods of construction: a comparative study

Sanna, Fausto

Abstract

The doctoral research revolves around a comparative study of timber modern methods of construction for low-rise, residential buildings in Scotland.
The building techniques studied involve both timber-frame panel construction (open-panel and closed-panel systems and structural insulated panels) and massive-timber construction (cross-laminated and nail-laminated timber panels). A non-timber technique is also included in the study: more traditional, load-bearing masonry (blockwork).
These different building techniques have been analysed from two complementary aspects: environmental impacts and thermal performance.
The environmental study is based on the life-cycle assessment methodology and embraces various aspects: environmental impacts (e.g., climate change, acidification, eutrophication, ozone depletion, etc.), consumption of energy (renewable and non-renewable resources) and production of waste (from non-hazardous to radioactive). The assessment takes a cradle-to-gate approach and, in its structure and method, is informed by the current recommendations of the international standards in the field (i.e., ISO 14040 series).
Various environmental trade-offs between construction methods have been identified. In terms of global-warming potential (excluding biogenic carbon sequestration), results suggest that timber-frame buildings show a better performance than masonry buildings; this is particularly true for the open-panel system, which emits about 10% less carbon than the masonry counterpart. Massive-timber buildings tend to cause more carbon emissions than masonry ones.
In terms of consumption of non-renewable primary energy, timber buildings do not generally show significant advantages with respect to blockwork-based masonry. In particular, structural-insulated panel systems tend to show very high energy requirements.
Timber-based buildings show a tendency to cause increased acidification, eutrophication and creation of low ozone than their masonry counterpart.
The level of offsite fabrication that is employed for the erection of the buildings plays an important role in the magnitude of most environmental impacts, which show an average decrease between 5% and 10% when some of the operations are shifted from the construction site to the factory. v
The thermal study investigates the performance of the building envelope, and, in particular, of external walls, by means of tests whereby the thermal behaviour of a sample of walls (of full-size section) has been observed and measured over time. On the outside, the walls were exposed to real, natural weather variations throughout the summer.
The study especially focuses on the time-dependent response of three different walling systems (which results from their individual cross-sectional arrangements of building components and the associated combination of heat-storage capacity and thermal resistance): a timber-framed wall, a cross-laminated-timber wall and a masonry wall. Thus, the main goal of the study was to characterise the thermal-inertia parameters of these walls.
This type of thermal behaviour is related to the repercussions of global climate change at UK level, especially in terms of increase in solar irradiance and temperature, which requires an adaptation of the building-envelope such that it can perform well both during wintertime and summertime, by providing maximum indoor comfort with minimum economic and environmental costs from the construction and operation of buildings.
The timber-framed wall possesses the greatest capacity to slow down the propagation of temperature waves from the outer surface to the inner surface (time lag), whereas the masonry wall performs best with respect to reducing the amplitude of temperature oscillation on the inner surface (decrement factor). The cross-laminated-timber wall exhibits intermediate values of both time lag and decrement factor, relative to the other two walls.
Both the thermal and life-cycle assessment of the construction alternatives aim at assisting the design and decision-making process in the residential field and at suggesting areas that need to be addressed and improved, towards a coherent evolution of the building techniques included in this study and a step forward in the realisation of sustainable, low-rise dwellings.

Citation

Sanna, F. Timber modern methods of construction: a comparative study. (Thesis). Edinburgh Napier University. Retrieved from http://researchrepository.napier.ac.uk/Output/1256099

• Thesis Type: Thesis
• Deposit Date: Jul 25, 2018
• Publicly Available Date: Jul 26, 2018
• Keywords: Timber, modern methods of construction, material wastage, climate change, overheating, life-cycle assessment, environmental impacts, burden trade-offs, building envelope, thermal inertia, thermal characterisation.
• Public URL: http://researchrepository.napier.ac.uk/Output/1256099
• Additional Information: In 2 Volumes
• Award Date: Jun 27, 2018