Verulam (readers' letters)

Jon Morris advocates seeing beyond initial embodied CO2 figures and to think in terms of whole-life carbon content when considering the sustainability of a project.

Exposure trials on timber cladding are valuable sources of information for facade designers. Key material, fire, and structural issues affecting timber cladding design are assessed and robust construction details derived alongside a framework for the emerging sub-discipline of timber facade engineering. The timber used was UK grown Sitka spruce (Picea sitchensis). The work was undertaken because timber is an increasingly common cladding material in the UK, being used on low-rise residential buildings and for medium-rise and non-domestic buildings. The associated risks have, therefore, increased but this is not reflected in published guidance. Around 40 construction details were produced and a selection are shown in this paper. They integrate, for the first time, all of the performance requirements applicable to low- and medium-rise timber facades in the UK. The work’s key benefit is that the guidance arising from this study rationalises and improves facade design.

There is potential to reduce both operational and embodied greenhouse gas emission from buildings. To date the focus has been on reducing the operational element, although given the urgency of carbon reductions, it may be more beneficial to consider upfront embodied carbon reductions. This paper describes a case study on the whole life carbon cycle of a warehouse building in Swindon, UK. It examines the relationship between embodied carbon (Ec) and operational carbon (Oc), the proportions of Ec from the structural and non-structural elements, carbon benchmarking of the structure, the value of ‘cradle to site’ or ‘cradle to grave’ assessments and the significance of the timing of emissions during the life of the building. The case study indicates that Ec was dominant for the building and that the structure was responsible for more than half of the Ec. Weighting of future emissions appears to be an important factor to consider. The PAS 2050 reduction factors had only a modest effect but weighting to allow for future decarbonisation of the national grid energy supply had a large effect. This suggests that future operational carbon emissions are being overestimated compared to embodied.