Continuing my series on various aspects of landscape sustainability, I’d like to get into the subject of sustainable landscape building materials. Landscape construction uses a wide range of materials, including natural things like plantings and soil. However in this case I am talking about manufactured materials such as stone, concrete, tiles, irrigation piping, lumber, and so on.
Your choice of landscape materials effects the environment in many ways, but generally you are looking for materials that conserve natural resources, reduce energy use, reduce greenhouse gas emissions, don’t contain toxic substances, and/or keep waste out of the landfill. With so many aspects to this subject, it is good to begin evaluating a material in terms of two general concepts: embodied energy and life cycle analysis.
A major part of sustainable materials is reducing energy use, especially non-renewable fossil fuels that contribute substantially to global warming. Embodied energy is the sum of all the energy used to create the material and get it to the building site, including raw materials extraction, manufacture, and transportation. A deck board may not take much energy to get from the lumber yard to the site, but if it came from a rainforest in Brazil it has a much higher embodied energy because of the transportation involved. Although we won’t get into the details here, the calculation of embodied energy for various materials is an evolving science with great promise for making informed choices, and it is a useful concept to keep in mind.
Life Cycle Analysis
It is also important to consider the environmental impacts of a material throughout its “life cycle”. This is often called the “cradle to cradle” view where you consider everything from how the raw materials are extracted to the ability to recycle or re-use a material at the end of its current ‘life’. A clay brick may take a lot of energy to create, but if installed in the landscape without mortar it is completely salvageable for reuse again and again for many years, making it highly sustainable. Again, we can’t get too much into this complex topic, but it does help us to think about how a material is or is not sustainable.
Based on these concepts, there emerge three main categories of sustainable materials that are best at minimizing environmental impacts: locally produced items, salvaged materials, and those with recycled content.
In an ideal situation, the structures and paving of a landscape would consist of materials taken directly from the project site – trees cut down would be milled into lumber, rocks would become stone pavings, and clay soils would be turned into adobe walls. This not only eliminates the considerable environmental cost of transporting heavy building materials, it gives the design a pleasing uniqueness tied to its location. A beautiful example that I have seen is the incorporation of site soils into building walls using a technique called rammed earth. There are also a variety of mixes that combine site soil with concrete and other binders that have promising landscape uses.
More commonly the materials are transported to the site, requiring the use of gas-guzzling, polluting trucks, but you can still seek out relatively local materials to minimize this impact. Often the heavier landscape materials such as stone, gravel, concrete and sand are already mined/manufactured locally to keep transportation expenses low. However in our modern world of cheap global container shipping, many things such as finish stone materials come from other countries. These materials are made cheaper than local stone in part because of a lack of environmental regulations and cheap, exploitative labor – definitely not sustainable.
I often curse at the lack of information on exact sources for many landscape materials, especially things like river rock and decorative gravel. I am hopeful that people will increasingly question the sources of those materials and pressure suppliers to make that information available.
Salvaged materials are things that you save from going to the landfill, but don’t require any manufacturing to make them useable. These materials fall into two rough categories: commonly used materials and unique items. Unique items can be almost anything that you can find; your creativity is the only limit to how they can be used in the landscape. To find unique items takes some time, creativity and even luck. I think that the best way to put it is “let the materials inspire the design.” One beautiful example is incorporating colorful glass bottles into an adobe or concrete-like wall.
Commonly salvaged materials include stone pavers, concrete, brick, lumber, metalwork, tiles, tires and many others. Using reclaimed wood lumber from old buildings has become quite the trend lately, showing up as a finish material in bars and restaurants all over the Bay Area. Its use is ubiquitous enough to make me wonder how much of the reclaimed wood is truly a waste product being re-used. Of course if you are using it for your own project, be sure to get documentation of the source.
One good common material that can be re-used is concrete. When you have a concrete slab or sidewalk that is going to be removed, you can break it up into pieces commonly called “Urbanite” for re-use. It can be stacked into low walls or laid in a gravel area as stepping stone paving. One thing I learned in doing my own small urbanite wall was that not all concrete sidewalk pieces have a uniform thickness, this can make it harder to create nice brick-like rows for a wall.
With urbanite and all salvaged materials it is especially important to carefully design their installation to make them lasting pieces. It is also critical that you use an expert installer for construction, someone with experience working with your specific salvaged materials. Don’t forget that these materials have already had years of wear and tear and if you don’t fit them into your new garden appropriately they won’t last very long.
Recycled Content Materials
Recycled content materials are those that are manufactured using waste products. This isn’t guaranteed to have a net positive overall benefit, but is generally better than putting trash in landfills. One question to ask of recycled materials is the transportation and manufacturing energy that goes into converting a waste product into something useful – it can be energy intensive. But there are many great recycled materials for use in the landscape including asphalt and crushed concrete, yard waste, plastic, rubber, glass, paint and many others.
Here in the Bay Area we have pretty established systems for collecting and recycling yard waste into mulch and compost. Curbside pickup in many cities collects yard and kitchen waste and takes it to centralized facilities where it is composted into soil. In my neighborhood the garbage company actually holds regular events where it gives away bags of this composted waste that is ready to go back into the garden as a soil amendment. City landscape maintenance staff as well as private tree companies often offer chipped tree trimmings for free to use as bark mulch. Just be careful of the source, there is some risk of plant diseases contained in the chips, and some that are heavy in Eucalyptus or Pine chips may alter your soil chemistry negatively.
Tumbled glass and ceramic bits are one of my favorite recycled materials, with great design potential. Crushed glass bottles and tiles are tumbled to remove the sharp edges, they start to resemble the “beach glass” you may have seen while beachcombing. I have experimented with the use of tumbled glass in the landscape and it does have its limits – it is fairly expensive so you don’t want to use it over larger areas, it is better as a filler for gaps between paving or as a mulch in pots. It also does lose its brightness over time, especially when set at ground level where it easily collects dust and other debris, so keep that in mind.
You can start to see how your materials choices matter to the environment. As the Bay Friendly Landscape Guide says: “use materials for the highest use – avoid ‘down-cycling’.” In terms of embodied energy the best materials are locally made, are salvaged from the waste stream, or at least have recycled content. There are, however, other considerations for the overall sustainability of materials, such as potential toxins they release into the environment, or how renewable their raw materials are. We will get into these and other topics in Part Two, to follow soon.
The ongoing challenge with sustainable materials is finding consistently good ones that perform as well as the mainstream materials. Many innovative materials have great promise but still lack the testing and proof of long term durability. Unfortunately this is enough to deter their use by the construction industry because any failure leads to angry clients and expensive replacements. I am hopeful that good research on sustainable materials will continue, and that the total environmental cost of building materials will become clearer so that conscious consumers like you can make better decisions.
Bay Friendly Gardening Guide and Landscaping Guidelines https://www.bayfriendlycoalition.org/publications.shtml
Bay Friendly Landscaping Guide to Recycled-Content and Salvaged Materials https://www.bayfriendlycoalition.org/publications.shtml
Sustainable Landscape Construction, by J. William Thompson and Kim Sorvig
A sampling of Salvaged Materials Suppliers:
Urban Ore (Berkeley) http://urbanore.com/
Building Resource & Red Shovel Glass Co.: (San Francisco) http://www.buildingresources.org/index.html
Artefact Design and Salvage (Sonoma) http://www.artefactdesignsalvage.com/
Green Waste Recycle Yard (Richmond)
Driftwood Whole House Salvage (Peninsula)
California Materials Exchange CalMAX
California State Recycle Store: searchable listing of companies making products from recycled materials