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As a demolition contractor, our work is not usually considered a major contributor to the sustainability of the construction process.
However, our experience suggests much can be done at the pre-construction phase to contribute to the overall environmental impact of projects and the influence a demolition contractor can have on the overall sustainability of projects can be considerable.
By taking a holistic approach to environmental management and analysing every environmental aspect of the enabling phases of projects we have been able to find ways of contributing significantly to the overall sustainability.
Waste and pollution are obvious targets. The introduction of the Site Waste Management Plans Regulations in 2008 has raised the bar across the industry and our work has often been subject to limits for noise, dust and vibration emissions.
However, the increasing use of building rating standards such as the Building Research Industry’s Environmental Assessment BREEAM and its counterpart for infrastructure projects, CEEQUAL, have encouraged us to forage further into a project’s environmental aspects such as the consumption of natural resources, protecting the site’s architecture, archaeology and biodiversity to find sources of additional credits to achieve the target for compliance.
Consumption
Enabling works use considerable amounts of natural resources, for example, fuel for plant and transport (muck away) as well as water for dust suppression. The discipline of calculating our greenhouse gas emissions has provided an environmental perspective on the consumption of these resources and the data we needed to identify ways in which to minimise use.
We first encountered the requirement to calculate our carbon footprint in 2007 when working on a BREEAM project in Central London. In the absence of guidelines at the time we developed our own process which included collating fuel and energy bills, mileage for transport and using conversion rates to calculate equivalent CO2 emissions.
Normalising the figure, by expressing it per tonne of demolition arising, enabled us to prepare baseline data and compare emissions across different projects to identify areas for improvement.
CO2 from waste transportation
A significant proportion of our total CO2 emissions (typically a third) are generated by transporting waste from site and in the last year we have developed a comprehensive database of recycling partners. We have extensively researched their capabilities –- materials accepted, recycling rates – to enable our procurement teams to select the nearest suitable destinations for pre-segregated waste which has reduced average muck-away journeys by 10% in last 12 months.
Through the analysis of carbon footprint data we have discovered that water consumption can contribute as much as 7% to our overall emissions. We use water to suppress the emission of dust to the local environment during demolition and the processing of waste – a key environmental measure especially in urban locations. This has traditionally been done by manually damping down the operational area using fire hoses.
Our calculation of water flow involved taking average water pressures (10psi) and hose diameters (2 ¾ in) to calculate typical consumption rates which were 180 litres per minute. By extrapolating these rates across the estimated durations of active operations on-site throughout the project we calculate our total water consumption and equivalent CO2 emissions.
This has enabled us to prepare much more accurate projections and calculations for CO2 and seek ways to minimise the water we use. We have started trialling the use of dust-boss machines which emit atomised water particles in a fine mist across a wide area. Calculations at a recent demolition project in Hendon suggest the dust-boss machines consumed just 5% of the water used by a fire hose and reduced the carbon footprint by 2.2 tonnes.
Predicting a high carbon footprint
We can now predict if a project is likely to produce a high carbon footprint. Characteristics of high carbon projects are a small enclosed site and long distances to recycling facilities.
The demolition of Tower House, an 8-storey office block located directly above Tower Hill tube station is a good example. Due to lack of space we were unable to locate a crusher on-site so all the hardcore was transported off-site to local sites in Dunmow, Essex and Crayford, Kent. The normalised carbon footprint for this project was 13.5kg/tonne.
Unsurprisingly the features of low carbon projects are basically the opposite - large open sites (i.e. able to segregate waste and locate a crusher) and close proximity to recycling facilities.
The demolition of a block of flats located adjacent to the main overground line outside Queens Park Station in West London demonstrates this point.
The site provided us with an ample building envelope to locate skips and a crusher which was able to process almost all of the six thousand tonnes of concrete hardcore into 6F2 for use as a piling mat. This reduced the number of lorry journeys to the nearest MRF in West Drayton by nearly 650 which helped us to reduce the carbon footprint of this project to just 6kg/tonne.
Many contractors view the imposition of environmental targets as simply an irksome a duty that has to be performed to satisfy their clients. However, by looking beyond the credit-system and analysing the data that the measures provide we can identify areas where improvements can be made which help to reduce costs as well as our impact on climate change.
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