Sustainable alternatives or the new mainstream?

Green roofs

‘Diggers’ self-build Brighton during construction

‘Diggers’ self-build Brighton
during construction

I maintain an interest in conservation as my first business was as main contractor for London Conservation Services, the contracting wing of the London Wildlife Trust. My landscape business in London encompassed a wide variety of projects from woodland and estate management, to large-scale planting, wetland creation and restoration and planted roofs. I installed the first grass roofs on a self-build housing development in Brighton, known as the ‘Diggers’ self-build, designed by Architype Architects. My colleague, Gary Grant, of Ecoschemes Ltd, did the specification and went on to design the roof for the now famous Horniman Museum extension (CUE), also by the same architects, and my business was short listed for this contract. For more information about green roofs go to www.livingroofs.org, a website initiated by conservationist Dusty Gedge, who has a wealth of information, a discussion forum and links to suppliers. You may also wish to have a look at Gary Grants book, ‘Green roofs and Facades’ (BRE Publications 2006), which gives a good overview on developments Europe wide.

The sheer scale of wasted roof space is staggering and whilst the UK is catching up slowly and very patchily, Germany, Switzerland and Scandinavia are years ahead in making planted roofs not only obligatory on new-builds but part and parcel of their planning system. Whenever ground is lost to development, it should be a planning requirement to at least consider having a planted roof. It brings life to what would be a sterile, hostile surface when tiled or slated, replaces lost ground as habitat, increases the insulation value of the house and as importantly, slows down the rainwater draining into storm drains causing local flooding and damage to property.

If you wish me to have a look at a flat or pitched roof you want to retrofit or a new-build project you’d like to see ‘greened up’ then please contact me for more information. I can draw up a specification and install a green roof for you together with any structural work you may need to strengthen an existing roof.

Rammed Earth

Another area I am exploring is using stabilised earth for walls. This is an ancient technique where earth, clays and sand are mixed and dampened and then compressed into formwork, much as reconstituted stone ornaments are cast today.

rammed earth formwork

constructing the formwork

part complete rammed earth wall

part complete wall

formwork removed

formwork removed

completed end wall detail

finished end wall - detail

Now known as Rammed earth or Stabilised Rammed Earth, see links

it has been used widely in Australia since the 50’s and more recently has become popular here in the UK with research departments at Universities and sustainable Architects and builders. (As always, there are two schools of thought-one doesn’t use any stabiliser and the other does, in some form of cement). It provides a way of re-using suitable soils from excavations and reducing the amount of Portland cement (OPC) used in building. The cement industry is very energy intensive and produces large quantities of CO2 as a by-product so any way of reducing our dependence on it would be a good thing. There is a cement alternative using the waste from blast furnaces known as slag cement or Ground Granulated Blast Furnace Slag (GGBS) (www.civilandmarine.co.uk) that effectively does the same job as OPC but sets lighter in colour and a lot slower. A mixture of slag cement and a small proportion of OPC, already used widely in Ready mix concrete, sets quite rapidly and when used in the compacted earth/sand mix enables the formwork to be released on the same day, so quite high structures can be achieved relatively quickly. Not all soils are suitable for this treatment but where possible, it provides a safe, strong, visually interesting and low embodied energy structure that can be used inside and out. All sorts of materials can be added into the overall mix and its possible to create a kind of geological strata by layering different coloured aggregates together.

Related to the use of cement is the use of Hydraulic Lime as an alternative. Lime built structures breathe, are flexible, reclaimable and also reabsorb some of the CO2 emitted in their production. Restoration companies have long used lime mortars on historic buildings but their use has now expanded into all sustainable building practises. I will be experimenting with using Lime alternatives in future projects and seeing if the extra costs involved add significantly to the overall budget.

Fortunately, there are a quite a number of new companies making specialised ‘green’ products for this burgeoning market and they deserve our support and encouragement where feasible. For a comprehensive list of companies and products see: www.greenspec.co.uk

Gabion walls

rammed earth formwork

Small steel gabions
can be stacked to
create retaining walls

part complete rammed earth wall

Gabions come in a large
range of sizes and can be
filled with almost anything -
shown here, excavated
stone and old statuary

I include these here because its one of those materials that has filtered down from civil engineering projects into domestic use. Wire cages or gabions have been used for years for slope stabilisation or retaining walls on waterways and motorway embankments and in their current incarnation offer the landscaper a solution to wall building without the need for traditional concrete footings, blocks or mortar. The assembled cages are simply filled or faced with a chosen material, stone, wood, bottles in fact almost anything reasonably tightly fitting and heavy, and then backfilled with excavated earth or rubble to make a stable structure. When detailed correctly, it’s possible to build substantial walls and reuse waste material at the same time. The look isn’t always appropriate but in the right setting and where access is good, gabions are a very good sustainable choice.

Recycled and reclaimed Materials

Bricks and stone for building and paving have been available for years and easily sourced from reclamation yards. There are a few I use regularly that supply reclaimed building materials and all types of stone ornament. Reusing materials that are far from worn out is a preferred sustainable choice as it cuts out the environmental impact of new quarrying and results in an aged aesthetic that blends well with older properties.

Because of the cost of landfill, a number of companies now separate waste and sell it on for processing into useful materials for garden and landscape projects. Glass, broken ceramics, concrete, brick, rubber and even seashells are all being marketed as recycled products.

I can source these materials and get them delivered ready for use. As with all specialist materials, they are only processed by a few companies nationwide so whilst the cost of the actual material is competitive, the transport costs add significantly to the bill, especially for small quantities.

I’ve used or specified crushed concrete for years as a cheap sub-base for paths and drives and have always thought it looked too good to cover up but now its possible to get a more refined version as a visible surface in its own right. There’s a company recycling old ceramic tiles and waste from ceramics factories into an aggregate as a substitute for limestone chippings and a more colourful version as a mulch or path surface. Rubber has been used for years as a safe fall surface and is generally made from reclaimed tyres, ground down carefully avoiding the metal braiding. A coarser grade is now available for paths.

Seashells of cockles, oysters and scallops reclaimed from fisheries are available crushed and cleaned ready for use as a mulch or path surface. Because the shells are made of calcium, care should be exercised when used as mulch as they could lime the soil over time, however the effect is slight and the appearance, in the right context, more than offsets any problems you might have.

© spacemagic garden design 2012