CIBSE Technical Symposium, DeMontfort University, Leicester UK
6th and 7th September 2011
In response to predicted climate change due to increased carbon dioxide concentrations, the UK government has committed to reducing carbon emissions by 80% from 1990 levels by the year 2050 and by 34% by the year 2020. Energy consumption in domestic buildings contributes ~30% of these emissions so is an important area on which to focus effort. The recent “credit crunch” in Europe has focussed minds on the third key issue, the capital investment required to reduce these carbon emissions.
Two blocks, within the Clapham Park Regeneration project (a 20 year programme in south London to either refurbish or rebuild tens of large residential blocks) are used as case studies to investigate these issues. Block A (21 flats) was refurbished, and a new build Block B replaced a demolished block (85 flats). Cost, energy and carbon data was gathered from a number of sources, to build a spreadsheet model which combined embodied energy and operational energy in a lifecycle analysis. The operational energy for both blocks was modelled using a combination of TAS (EDSL 2010 – for calculation of heating energy use) and SAP 2009 (for internal gains & remaining energy use) models of the original Block A, the refurbished Block A and new build Block B were developed. The initial 30 year analysis showed that the cost per tonne of carbon saved for rebuilding was 4 times the cost for refurbishment.
The models were tested for sensitivity to timescale, air tightness and fuel price rises. It was found that refurbishment is more carbon effective and more energy effective than rebuilding over the entire lifespan assessed (120 years).The cost effectiveness of refurbishment compared with rebuilding was sensitive to fuel price increases, with annual increases of ~9% (equal to the average price volatility over the past 4 decades) we found rebuilding is the more cost effective option beyond ~50 years.
In the future, replacement buildings will need to have low embodied carbon and make greater operational carbon savings before they can compete with refurbishments. If this can be achieved and fuel prices continue to rise over the next number of years, then a strong case for rebuilding would emerge.