This is an exciting time to be involved in construction. There is a widening acceptance of ecologically-minded practices among the American public, and a growing number of builders and architects are promoting and taking pride in their adherence to the philosophy of Green or Sustainable Construction.
But how does stone fit into this equation? There are multiple sets of
official standards that are being 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 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:
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 to 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.
The sustainability of a material is largely graded on its carbon
footprint (the sum amount of CO² emitted through 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, compared to most mining operations which often devastate many dozens of acres.
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.
As an interior surface, stone can create a more hypo-allergenic atmosphere
because, unlike many common building 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.
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 (ie, mortarless) retaining walls have a lower carbon footprint than concrete, and due to their flexible nature, they have a much longer life span 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.
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. Reuters news service reported in August that: “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. By making 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.
Mark Shepherd www.ShepherdStoneworks.com
Bringing the finest in Stone Masonry to the Greater Seattle Area.
Natural stone walls, patios, steps and rockery of all sizes.
Mortared stone veneers, fireplace surrounds, and interiors.
Integrated landscape design and installation.
(Originally published 10/22/09)
(For more up-to-date and technical information about stone, please visit the
Natural Stone Council’s site at http://www.genuinestone.com/home.php)