Hello again from Olson Defendorf Custom Homes. We are a custom home builder in Austin, TX.
This month we are blogging about masonry and green alternatives. This article is from Michael Morris, a former carpenter and builder, who reports on construction topics as an EcoHome contributing editor.
When it comes to building materials, masonry is about as elemental as
it gets. Available in many forms, from adobe to terra-cotta to brick
and concrete, masonry products are typically cost-efficient, extremely
durable, and recyclable. Much of the material that goes into these
products is naturally abundant. In fact, most masonry building products
are entirely natural, consisting of little more than earth itself—namely
clay, silica, and other materials.
Based on this, one might think
that masonry is the most environmentally acceptable type of building
material, but this is not necessarily true. The raw materials must be
excavated or mined, which can be ecologically disruptive. Because
masonry is inherently heavy, the cost of transporting it from
manufacturing plant to building site, and the fuel burned as a result,
can be higher than for competing materials. And despite its basic
earthen makeup, some amount of processing, along with considerable heat
for cement and kiln-fired masonry, is typically required to transform
the raw materials into finished products. These efforts can require
significant energy consumption and produce carbon dioxide and other
environmentally harmful by-products.
Manufacturers and
associations representing masonry products defend their green building
value, saying that the raw materials are generally available in most
locations and easily obtainable with limited environmental impact.
Proponents also cite the sustainability of masonry compared with other
building materials, and they note that, after manufacture, the products
are inert and can be ground up for use as clean fill or recycled into
other masonry products. These claims are supported by the fact that
masonry building products contribute toward green building credits in
LEED, National Green Building Standard, and other programs.
Improvements
to masonry products have been developed to reduce the environmental
impact of manufacturing and transportation, improve the materials’
insulating properties, and increase their overall green building value.
Innovations such as autoclaved aerated concrete, using fly ash and
industrial waste as binders, and even returning to pre-industrial
products and production methods (like adobe) are just a few of the
alternatives available to builders.
Masonry manufacturers are also
striving to meet the challenges of increasingly demanding energy codes,
green building standards, and industry initiatives like the 2030
Challenge for Products, a new program that has set carbon-metric goals
that include a 50% reduction in the “carbon footprint” of building
materials by the year 2030.
Here’s a rundown of considerations to keep in mind when evaluating masonry products:
Adobe
is perhaps the most basic masonry block. This prototypical “mud” brick
has been used in construction throughout the world since the beginning
of recorded time. It is manufactured and used here in limited
applications, primarily in the American Southwest, due mainly to its
indigenous architectural value. Although it can be made locally from
almost any common soil mixed with a small amount of binder, such as
straw or even animal dung, manufacturers today add stabilizers,
including Portland cement and asphalt emulsion, to provide consistency
and strength. Traditionally, adobe is made at the building site,
sun-dried and stacked without mortar, then parged with a thick stucco
coating, all of which adds to its energy-saving, environmental, and
economical credit. However, it is less durable and more difficult to
transport than other masonry products, and suitable mainly for
structures in areas with low humidity and little rainfall.
Brick
is a similarly ancient building block composed primarily of clay and
silica. But because brick is baked or “fired” in a kiln, it is
transformed into an extremely hard, durable ceramic material that
resists erosion from water and wear. Various materials like lime, iron
oxides, and magnesium, along with colorants, can be added during
manufacture to impart a range of desired qualities, such as hardness,
density, appearance, and uniformity. As with adobe, brick has distinct
environmental attributes, including sustainability and recyclability,
and the fact that its basic materials are locally or regionally sourced.
However, the prolonged heat required to fire it and the energy used to
transport its considerable bulk weigh against it as a green building
material (according to one source, transporting brick for just 10 miles
via horse cart in 18th century England could more than double its
price).
Terra-cotta (Latin for baked earth) is
another contemporary “all-natural” building product rooted in history. A
ceramic, clay-based material much like brick, it is typically baked
into tiles for use in flooring, roofing, and exterior cladding. In
modern construction, terra-cotta is often used for rain-screen systems
or ornamental embellishment on commercial buildings. It is commonly used
as a structural building block in Europe and elsewhere, but not in the
United States. Terra-cotta products used here are typically imported, so
transportation weight, bulk, and cost are factors that limit its green
building value, along with the heat energy and carbon dioxide generated
in its production.
Concrete blocks and pavers,
along with clay brick, are the most widely used structural masonry
products in the United States and perhaps the world. Concrete is
relatively inexpensive, can be mixed on-site or locally sourced and
formed into virtually any shape, and, although it is easily recycled, it
is as close to indestructible as any man-made building material ever
produced. On the downside, the key ingredient in concrete is Portland
cement, a manufactured material with high embodied-energy content.
According to the Portland Cement Association, the industry has worked
diligently to improve this process, and since 1972 has reduced energy
consumption and fuel CO2 emissions in manufacturing by more than 37%.
The association claims that cement production today “accounts for less
than 3% of all U.S. industrial CO2 emissions, well below other sources”
such as the petroleum, chemical, and iron and steel industries.
Over
the years, substitute binder materials have been developed to reduce or
eliminate Portland cement in concrete, such as industrial by-products
like fly ash, steel slag, agricultural waste, and recycled post-consumer
waste. New types of products have been created as well, such as
pervious concrete pavers, which allow rain and groundwater to naturally
drain into the soil through patios and parking areas. Autoclaved aerated
concrete (AAC) is another innovation with green building
benefits—precast blocks are resource-efficient, lightweight, and
thermally insulating. However, AAC has only half the compressive
strength of standard concrete, and, because it is porous and relatively
soft, it must be parge-coated or enclosed to prevent deterioration.
The
bottom line in all this is that most structural masonry products will
contribute to green building credits simply because of their inherent
sustainability, but builders can improve the performance, quality, and
desirability of a structure by choosing masonry units that offer
additional benefits such as resource efficiency, reduced weight,
insulating value, recycled content, and other environmental attributes
whenever possible. Masonry has always been an intrinsic part of
residential construction. The innovations available in today’s materials
just make it better.
