Sustainable Concrete Masonry: Building Green
Concrete masonry homes operate in perfect harmony with their environment.
Homeowners are becoming increasingly aware of these environmental issues. Of the consumers surveyed by the National Association of Home Builders (NAHB), over 50 percent want to buy an environmentally friendly home and over 33 percent are very willing to pay more for that feature. This is partly because energy-efficient, durable structures save homeowners big money over time by decreasing the ongoing operation costs (heating/cooling and maintenance) of the home.
Energy Efficient Building Envelope
According to Morrisville, North Carolina builder Mangum Design-Build, concrete masonry structures are not only authentic, affordable, and sustainable; they are often 20 percent to 50 percent more energy efficient than the same home built with wood walls. This is partly because the thermal mass of CMU stores and emits energy as the temperature rises and falls. In summer evenings, after the temperature drops, the concrete masonry wall will continue to give off heat for three to four hours until it returns to the ambient temperature of the outdoor environment. When it’s cool in the early morning, the wall stores thermal energy with a very slow increase in temperature to provide a buffer against the heat and provide a coolness effect well into the hot part of the day. These walls remain warm or cool long after the heat or air-conditioning has shut off, reducing heating and cooling loads. This shifts the peak heating and cooling loads to off-peak hours, providing welcome relief to power companies. It also enables heating and air-conditioning equipment to operate more efficiently. Buildings in southern regions of the U.S. subject to significantly warm and humid climatic conditions often use CMU walls for this reason, but the energy savings can be realized in almost any climate.
Because of its thermal mass, concrete masonry walls do not need nearly as much insulation for the same energy efficiency light wall systems. If higher R-Values are needed, insulation can be injected into the hollow cores of the CMU. Other insulation strategies can also be exercised to increase R-Values that augment the energy efficiencies provided by thermal mass. In addition, this type of structural CMU design may contribute to LEED Credit EA 1: Optimize Energy Performance. When designing with CMU walls, architects can often downsize the HVAC system, which operates at higher efficiency with lower peak demand, thus saving more in ongoing heating and cooling costs.
In general, concrete masonry products are made from water, aggregate, and cement which are made from the most abundant materials on the earth. These products also can be made from local recycled materials and are often manufactured close to construction sites, minimizing fuel required for handling and transportation. Concrete masonry products themselves have a very long life, but if demolished, can be recycled and used as crushed aggregate for new concrete, instead of disposed of in a landfill. Using recycled crushed aggregate eases the pressure on already overburdened landfill sites (where demolition waste would otherwise be dumped). This means that less sand and quarried stone is required to create products. Recycled content can contribute to LEED Credits MR 4.1 and 4.2 —Recycled Content.
The Road Less Traveled
Concrete masonry constituent materials are most commonly extracted and the units themselves are manufactured close to the jobsite, thus reducing the environmental impacts of lengthy transportation. LEED credits can be earned for using materials extracted, harvested or recovered within 500 miles (800 km) of the site. In addition, unused CMU can be redirected to other projects or donated to charitable organizations such as Habitat for Humanity. LEED credits can also be earned for reducing construction waste. This can be accomplished by designing on 8-inch (203 mm) modules to minimize cutting and construction waste.
Site-Friendly Building Practices
Another way to build green is to minimize damage to the surrounding site as much as possible. Minimizing the impact of excavation is a must for preserving a site. The Downing residence sits on a steep north-facing slope in the foothills of the Tucson Mountains. Relying on standard gray CMU as the primary building material helped the builders preserve the delicate environment around the home site. Luis Ibarra, of Ibarra Rosano Design Architects, points out that “we built the house from the inside. The construction zone was limited to the footprint of the house.” The concrete block walls were reinforced by anchoring them directly into the bedrock, just below the surface. “That hillside is largely solid rock,” Ibarra says. “We did that rather than pull the rock out and replace it with concrete.”
The energy savings of concrete masonry homes reduce the household budget, but concrete masonry homes offer relief to their owners in other ways too. CMU is naturally sound insulating and provides a low-stress living environment by blocking sound transmission from room to room or from the outdoors. Concrete hardscaping can help to block out neighborhood noise from outdoor living spaces just like sound walls used along the sides of highways contain road noise. The upkeep of concrete masonry homes is also low-stress because the walls are maintenance free. Owners do not need to cover or paint concrete walls, thus reducing their exposure to harmful chemicals. Concrete masonry helps resist dust, mold and insect infestations. These are some of the major sources of indoor allergies. The bottom line is that concrete masonry offers many “green” benefits including thermal mass, durability, energy-efficiency, and low maintenance costs. Altogether this makes it an environmentally sound material and a financially sound investment.
Resource: National Concrete Masonry Association: www.ncma.org – Concrete Masonry Designs – May 2008