Ideally local stone is used, or in regions where there is predominantly clay such as London, brick. However for practical, cost or design reasons there are many alternatives:
Reclaimed stone is a perfect alternative to quarried stone and can also add an interesting footnote to your garden: We've been able to source original stone saved from iconic buildings such as St Paul's Cathedral and the Bank of England that have become surplus after restoration projects
Imported stone from India and China
Indian sandstone is very popular at the moment due to its relatively low price. It uses up to 70% more CO2 than local stone and reconstituted stone. It is important to note that Indian Sandstone has only a few suppliers that can guarantee that none of the 15-20% of children that are estimated to make up the Indian quarry workforce are used in it's production, in what are on the whole terrible conditions. The conditions of production of stone imported from China at the moment cannot be guaranteed by any British companies.
The previous Indian sandstone terrace in this garden was to be removed. However, instead of sending it to landfill we machine-sawed it into 'bricks' to create a curved wall, framed by a reclaimed brick path. Gaps in the stone wall have now been filled with succulents.
Limestone pavements are rare habitats found in the UK and Ireland. It is often illegally taken for use in rock gardens and water features. Check with your garden centre or builders merchant when buying Limestone that the source is ethical.
Shingle is by far the cheapest material to buy and lay. It is extracted from land and sea; the latter can cause devastating damage to the seabed so it is imperative that the gravel is quarried locally.
More resources and energy go into making man-made paviours than straightforward quarried stone. The results may be of questionable quality and the dyes in them can fade over time. Many companies are starting to add recycled materials to them, which is a welcome concession to sustainability.
Bricks are very durable and often appropriate to a garden design. However high levels of energy are used in firing bricks, clay is not a renewable resource and cement is generally used in assembling brick features. Using reclaimed bricks is therefore preferable and although slightly more expensive they will nearly always look more attractive than new bricks.
Cement is the third ranking producer or CO2 in the world, and its' production is increasing by approximately 5% per annum. There are substitutes that have the dual benefit of replacing the energy intensive Portland cement and avoid other materials going to landfill. These are pulverised Fuel Ash and Ground Granulated Blast-Furnace Slag (GGBS), a by-product of the Iron Industry. GGBS in cement can reduce CO2 emissions by up to 50%.
The cement industry in the UK is self sufficient for materials and is usually made locally so there are less transport miles. You can use 100% recycled steel to reinforce it, which can then be recovered and re-cycled again in the future. Lime render and mortar is a better alternative when possible as it produces 20% less CO2 output and can absorb nearly its own weight in CO2 in the curing process. Also lime mortar can be recycled. It is strong, flexible and permeable so can avoid expansion joints. It can be used with hemp to create very effective rendering.
Landfill obviously absorbs and contaminates land, which could be habitat for important plant and animal species and human habitation. When designing a garden it is worth trying to reduce the amount of waste by redistributing soil rather than removing it as well as re-using any waste concrete or brickwork in the foundations for new hard-landscaped areas. Green waste should always be composted if possible.
Many skip companies attempt to recycle up to 80% of waste, with for example reclaimed concrete going on to be used in road construction.
Carbon neutralising, measuring and trading
The idea that you can offset your carbon waste by 'buying' it back is a contentious issue. Most people think of planting trees when neutralising their carbon emissions but it is still unclear how much CO2 trees absorb. A large portion of your offset cost also goes on administration and marketing costs at such companies. The Government has created a Gold Standard to help the public judge these companies, and of the four to receive one so far none of them use forestry, but by sponsoring renewable energy initiatives or by retiring the certificates traded by bigger polluting businesses. If you do want to audit the amount of carbon used in your garden's construction this can be calculated by specialist firms, such as the Carbon Neutral company.