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Background, aim, and scope: One third of the total housing stock in the Republic of Ireland has been built in 10 years up to and including 2006 and of this approximately 34% was built in the Greater Dublin Area (GDA). Much of the housing was low-density with poor public transport links leading to doubts over its sustainability—particularly in terms of energy use. Although the country is committed to reducing greenhouse gases to 13% above 1990 levels by the period 2008–2012, by 2005, emissions were already 25.4% higher than the aseline and current projections are that this figure will rise to 37% over the period. The residential sector is estimated to contribute to approximately 24.5% of energy-related CO2 emissions. This paper estimates total emissions from residential developments in the GDA constructed between 1997 and 2006. Materials and methods: Carbon dioxide equivalent (CO2) emissions are estimated using a life cycle assessment approach over a 100-year building lifespan and employing process, input–output and hybrid energy techniques. Life cycle stages include: construction, operation, transport, maintenance and demolition. The main data sources include: national population and industry census data, household travel survey data, residential energy performance surveys and national accounts. The GDA was split into four zones each encompassing development at increasing radii from Dublin’s city centre, namely: city centre, suburbs, exurbs and commuter towns. Results: Per capita CO2 life cycle emissions in the GDA were found to be approximately 50–55% greater in the exurbs and commuter towns than in the city centre. Of the five life cycle stages studied, operational energy requirements (predominantly space heating and hot water, but including power) contributed most significantly to emissions (68%), followed by transport (17%), construction (9%) and maintenance/renovation (6%). Discussion: Operating emissions from dwellings in the commuter town and extra-urban zones were almost twice those in the city centre both due to larger dwelling sizes and the predominance of detached and semi-detached dwellings (with large amounts of exposed walls) in the former and the prevalence of smaller apartments in the latter. Car use was most pronounced in the zones furthest from the city centre where per capita emissions were almost twice those of residents in the city centre. Despite their smaller size, the per capita construction CO2 emissions of apartments were approximately one third greater than for low-rise dwellings due to the greater energy intensity of the structure. However, this difference was more than compensated for by the significantly lower operational emissions referred to above. Conclusions: In 2006, recurrent CO2 emissions (operational, transport and maintenance) from dwellings built in the GDA over the ten preceding years were 2,108 kt while construction-related emissions in that year were 1,325 kt giving a total contribution from the residential sector of 3,434 kt CO2/annum— representing 4.9% of national emissions for that year. Had the development policy prescribed ‘city centre’-type development and transport modes, then emissions for the year 2006 would have been 2,892 kt CO2—a reduction of almost 16% over the actual figure. However, in this scenario recurrent emissions would have been reduced to 1,417 kt CO2—a reduction of 33% over actual levels. Recommendations and perspectives: This study supports Irish and international governments’ policies aimed at curbing CO2 emissions from the domestic sector which focus primarily on reducing operational emissions from new and existing housing through design and construction improvements. However, it demonstrates that significant reductions in operational emissions are associated with high-density residential development with modest floor areas. Furthermore, it highlights the scope for transport emissions’ reductions through better spatial planning leading to reduced car travel.
Duffy, A.: Land use planning in Ireland:a life cycle energy analysis of recent residential development in the Greater Dublin area. International Journal of Life Cycle Assessment, Vol.14, 3, 2009, pp.257-267. doi:10.1007/s11367-009-0059-7