Westminster City Council King Street Low Carbon Trial - Client Report

EXECUTIVE SUMMARY

This report provides an analysis into the King Street Low Carbon Trial by evaluating the carbon reduction measures introduced on the scheme. This was the first time that carbon was measured for a scheme in Westminster and now sets the baseline for monitoring carbon usage and measuring the savings that can be made by changing methods and/or materials. The report has split the carbon savings into:

• Operational Carbon – based on FM Conway’s carbon outputs for installing the scheme

• Embodied Carbon – which considers the greenhouse gases emitted throughout the production of the materials, from extraction of raw material, through manufacturing process and transportation to site. It also takes into account the expected lifecycle of the product The report primarily concentrates on the elements of work within FM Conway control, such as travel, deliveries, and operations, but also reviews the embodied carbon within materials. The working operations, including travel and deliveries were recorded daily with the carbon then calculated using the UK Government Conversion Factors for Greenhouse Gas (GHG) Reporting 2020, published by the Department for Business, Energy and Industrial Strategy and the Department for the Environment, Food and Rural Affairs. The results of the trial have been compared to a standard Planned Preventative Maintenance (PPM) scheme of a similar size and scope, Marlborough Hill, running during the same timeframe to establish the carbon savings made against traditional construction techniques. The embodied carbon contained within the site materials was measured by a tool designed by Metis Consultants Limited on behalf of Westminster City Council. For the trial only, a minor change to the specification was installed to maintain the same look and feel to the street, meaning that there was a limit to the carbon that could be saved. • 79% carbon saving in operational delivery against a standard scheme - 1.74t of carbon was emitted during the operational phase of the scheme, saving over 4t when compared to the comparison site at Marlborough Hill, which equates to just 0.04t per day • 46% carbon saving per m2 in the materials used. The paving slabs were reduced to 50mm from 63mm, with the foundation 58mm shallower and using concrete sub-base grade C10 instead of C20, which reduced the embodied carbon to 17.93t, making a saving of nearly 23t against Marlborough Hill and 53% more carbon efficient overall with a total carbon saving of 27t It was accepted at the outset that there would likely be a trade-off between cost and carbon to make significant carbon savings. The final cost of £94,000 was £53,000 higher than the estimate to carry out the works with traditional techniques. However, it is noted that there were several extraordinary costs against the scheme that would not normally be incurred. The key results of the trial are:

In addition, it is expected that these costs would reduce as electric plant becomes more readily available and is able to service several concurrent schemes on the programme.

It has been calculated that £45,000 of these costs were classed as extraordinary costs, thereby making the like for like comparison £49,000 for a carbon efficient scheme, against £41,000 for a diesel-powered scheme. Therefore, a cost uplift of 20% has saved over 50% of carbon on this scheme. This was the first trial of its kind in the UK and there are challenges for a wider rollout, including the lack of electric charging points for vehicles and plant, limited plant options available from suppliers and the cost of making the change.

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