The building industry has in many sectors begun to embrace the concept of Green Building. While this is still very much a voluntary standard, an increasing number of builders and architects are touting their adherence to the philosophy of Green or Sustainable Construction.
But how does stone fit into the equation? There are multiple sets of official standards that have been established to rate the “green”-ness of a project or a type of material. The most notable of these standards is called LEED (Leadership in Energy and Environmental Design). The field of masonry is only now beginning to conform to these standards, so it is a little difficult to find an authoritative voice on the matter. I thought I would take a look at the available data and try to provide an overview of a very multi-layered subject, plus provide a few insights of my own. In general, the sustainablility of a any building project is rated according to the following
parameters: Does it use renewable resources? Does it reduce the impact on the environment? Does it minimize waste? Does it create a healthier indoor environment? Does it increase energy efficiency? The following is a breakdown of these five categories as they relate to stone masonry.
Renewable Resource
As you might imagine, there is basically an unlimited supply of stone right under our feet. It is a material which is not manufactured, but merely unearthed, shaped and transported to its destination – no factories or by-products involved (I'll get into the impact of quarrying and shipping later on). Furthermore, it is a very reusable material in every way. Scraps of stone that are discarded can be not only reused in other applications, but ground into aggregates for things like road construction and the production of cement. And reclaimed stones from demolished buildings and structures are often used in new construction. Impact The sustainability of a material is largely graded on its carbon footprint (the sum amount of CO² emitted though its production), and in this regard, stone scores pretty poorly. Most of the cost of stone comes from transporting it, and these days it is often shipped from places as far away as India, Brazil and China. Even when domestic product is used, it often comes from other states. We have a good variety of stone here in the Northwest though, and if you can stick to using material that's brought from less than 500 miles away, you're saving a lot of energy. Quarrying stone can involve clear-cutting and dynamiting into hillsides which definitely impacts the surrounding environment. However, measures can be taken by quarries to greatly minimize the damage, like controlling runoff to avoid the pileup of silt in riverbeds and reducing the use of explosives by drilling & wedging off large chunks. Also, the average stone quarry takes up only a few acres.
Waste Reduction Stone materials are 100% recyclable which takes landfills out of the equation entirely. Stone is more durable than most other products, allowing reclaimed pieces to be used again. And unused scraps can often be used in other applications such as mosaics, aggregates for paving, or as back-fill behind a retaining wall. A common test for sustainability in construction is a Life Cycle Analysis, which takes into account a) the life span of a structure, b) how much resources are required to make it, and c) how much in resources it can save over time. Masonry scores very well in this regard. A well-made wall can last for hundreds or thousands of years and a quality veneer is unlikely to be thrown away in favor of the latest brand of siding. Indoor Environment
As an interior surface, stone can create a more hypo-allergenic atmosphere because, unlike wood or other common materials, it doesn't emit contaminants, is easily cleanable, doesn't require sealants or paint, and discourages the growth of mold and fungus. Plus, due to it's thermal mass (the capacity of a substance to store heat), it can stabilize temperature spikes, allowing for a more evenly-cooled/heated climate. Energy Efficiency Due to stone's high thermal mass, it can be utilized to reduce the amount of energy needed for the heating and cooling of a home. A heat sink, for instance, is a common element in Passive Solar Design which involves having a large stone or cement structure, like a porch or a wall, that absorbs heat during the day and radiates it back during the cool hours of nighttime. There are masonry stoves which ingeniously recirculate heat so that an armload of wood will heat your home for 24hrs, and others that are made of soapstone which has a very high amount of thermal mass. Landscaping with stone can be a green practice as well: 1. Dry-stacked (mortarless) retaining walls have a much lower carbon footprint than concrete, and due to their flexible nature, they have a much longer lifespan if properly built. 2. Dry-laid patios are likewise superior to cement because they cut down on non-permeable surfaces and aren't prone to cracking. 3. Pavement using stones with a high level of reflectivity can help deflect the sun's rays in the heat of the summer, reducing the need for air conditioning. 4. By expanding your living space into the outdoors with a patio, you can decrease the amount of household energy consumed by being outside more of the time. 5. By using locally quarried stone you can green your yard even further. Cement – not so much! Not to diminish the miracle of concrete, but all-in-all its production is one of the most polluting industries in the world. Manufacturing cement (the key ingredient of concrete) requires massive amounts of fossil fuel and it continues to release greenhouse gases into the air as it cures. This essay out of Princeton in 2020 stated: “With an annual production of more than 2.5 billion tons, conventional Portland cement is responsible for an estimated 5% of global CO² emissions, more than the airline industry.” Most of the major cement manufacturers boast that they have reduced emissions by 30%, but as demand has increased 100%, these efforts are largely nullified. Luckily, new formulas for making cement are being developed which actually absorb more CO² than they produce and may be widely available in a few years.
I personally think stone has the potential to play a larger role in our architecture the way it has throughout history. Whereas solid-stone construction was once a highly treasured technology, in today's world it has been largely reduced to mere decoration. I would like to see more structural uses of natural stone in new civic projects and even in residential architecture. If it is well designed, whatever costs involved could be offset by the permanence of a building made to stand for many centuries.
And lastly, I would add another category to the list of the sustainable qualities of stone, and that is its . Cultural Sustainability. As we make our world more beautiful, we influence the lives of those who come after us. Stone betters our surroundings, thus our quality of life. Stone promotes a more long-term outlook on our future, and also reminds us of where we came from.
(For more up-to-date and technical information about stone, please visit the Natural Stone Council's site at https://www.naturalstoneinstitute.org/)