BedZED: Construction Materials Report. Contents:

Materials in construction

Introduction

This chapter sets the context for the use of materials in construction. It relates the environmental impacts of construction materials to the total impacts of human activity in the UK. 420 million tonnes of materials are used in construction in the UK each year. This equates to 7 tonnes per person. The total consumption of all materials in the UK amounts to some 678 million tonnes or 11.3 tonnes per person. So construction accounts for over half of our resource use by weight! By selecting construction materials wisely, we can really reduce our environmental impact.

Aggregates

Aggregates make up over 50% of construction materials by weight, some 240 million tonnes/year. Virgin aggregates are a finite resource. Extraction of aggregates results in loss of land, disturbance to neighbours, ecological damage both on land and in water courses and effects the landscape. The new aggregates tax (April 2002) has incentivised the use of recycled aggregate products by adding £1.60/tonne to virgin aggregate.

Timber

In the last 30 years, natural forest cover has reduced by 11%. Logging for timber is one of the two main activities responsible for this deforestation, the other being clearance for agriculture. There are two critical implications of deforestation. One is the loss of biodiversity in the world, the loss of habitats and species forever. The other is a reduction in the earth's capacity to absorb CO₂ . This drop of absorption capacity is proving critical at a time of increased CO₂ emissions, leading to global warming and worldwide climatic instability. Although timber is theoretically a renew-able resource, it can only be considered as such if it comes from sustainably managed woodland. The use of certified sustainable timber is a very positive mechanism for moving towards sustainability creating an economy that fosters the conservation of forest resources. The highest accreditation for timber is the internationally certified scheme by the Forest Stewardship Council (FSC).

Reclaimed materials

70 million tonnes of waste is produced from construction and demolition every year in the UK. A large proportion (75%) of this is recycled with only 25% going to landfill. But the recycling is generally as very low grade products. The potential for high grade re-use of waste materials is enormous. Where a waste material is re-used in its existing state without significant processing or alteration, it is generally refered to as a reclaimed material as opposed to a recycled material.

There is a flourishing reclaimed material economy in the small scale reclamation and salvage yards around the country but these cater for the individual DIY enthusiasts or deal in high value architectural salvage. The thousands of tonnes of bricks, timber and steel sections, doors and paving slabs could be re-used directly and provide a local sustainable material resource to the construction industry. The supply chain for such low value, bulk materials is very dependent on efficient handling and transport systems. BedZED has pioneered a number of reclaimed material supply chains and proved that in some cases it can be done economically. (see chapters 6,7 and 10)

Recycled materials

Recycling of construction and demolition waste, as opposed to reclaiming, involves altering the material in some way to produce another material. It introduces extra processing stages and extra journeys compared with reclaimed and therefore can be more environmentally damaging. It does, however, supplant the use of virgin materials. It also diverts those waste materials from landfill. The introduction of the landfill tax and the new aggregates tax has made recycled sand and aggregate replacements significantly cheaper than new.

Housing construction in context

The materials used to build homes require energy consumption during their extraction, production and transportation. This energy consumption has associated CO₂ emissions known as the embodied CO₂ of the materials (see chapter 4). The table below shows the embodied CO₂ of a typical home and relates that to the total CO₂ emissions in the UK. It shows that the construction of our homes accounts for some 3% of our annual CO₂ burden.

The embodied CO₂ of homes is less significant than the energy consumption and CO₂ emissions during their life times. Domestic dwellings account for 29% of UK energy consumption (see Fig.1). BedZED was therefore designed primarily for exceptional energy efficiency during use. Construction materials and products were selected to meet the thermal design criteria. Choices in low impact, low embodied energy materials were considered after thermal requirements had been met. Chapter 9 reports on the embodied CO₂ of BedZED.

Further information

• The full report can be obtained from Bioregional: www.bioregional.com