Developing systemized offsite manufactured timber typologies from Welsh supply chain: A repeating thermal bridge analysis of closed timber framed panels

This thesis investigates the thermal performance of offsite manufactured closed timber-frame panels used for external walls in buildings constructed to satisfy future building regulations for high thermal performance.

The initial industry ethnography study offered a multitude of insights into the Welsh offsite manufacturing (OSM) sector and a deep understanding of tacit knowledge, such as operations, machinery and materials used in OSM production. The observation of day-to-day practices has led to the identification of non-recognized weaknesses of timber frame panels unintentionally introduced, the sources of additional heat losses from wood frames and metal fixings.

The study of linear repeating thermal bridges represented by the wooden studs in timber frame closed panels repeatedly interrupting the core insulation layer involved different methods. Firstly, a theoretical approach to a typical timber frame panel manufactured in Wales has highlighted the vulnerability of the typology as well as presenting the mitigating solutions viable to mitigate the heat losses. Secondly, five timber frame-frame closed panel dwelling typologies from a OSM in Wales revealed the timber quantity in the offsite realization and its increment onsite. Finally, statistical techniques were employed to explore the data collected on timber frame content and draw robust conclusions about panels with and without openings. These approaches highlighted a relevant correlation between timber frame closed panel dimensions and frame density.

Metal fixings represent a case of point repeating thermal bridges within the panels, which are scarcely considered notwithstanding their copious adoption. The investigation has required the calculation of the impact on the thermal performance of typical metal fasteners with Finite Element Analysis methods, coupled with sensitivity analysis to rank eight main design parameters chosen respecting the manufacturers’ capabilities. The outcome has offered insights into the decision-making process of the next-generation of timber frame closed panels.

The study witnesses the importance of producing refined calculations for modern methods of construction as a result of the increasing impact of repeating thermal bridges on high-performance construction typologies, that could be deterimental to the thermal performance of well-insulated dwellings.