CertainTeed fiber-cement siding is manufactured using 30 percent post-industrial fly ash (a byproduct of coal power plants).
When Maricé Chael added on to her historic 1920s cottage in Miami, she wanted to stay true to the look and feel of the neighborhood. Because her home’s original 80-year-old stucco had held up so well, it seemed logical to use the same material on the addition. As Maricé discovered, stucco is durable and requires little maintenance, but its primary ingredient, Portland cement, requires huge amounts of energy to produce.
The truth is, no particular type of siding is a clear environmental winner. The old standbys offer few environmental benefits: Vinyl is persistent in the environment and poses hazards to factory workers, and aluminum is nonrenewable, albeit recyclable. "Ultimately it comes down to picking something that’s going to last a long time, that’s low-maintenance, and that’s going to be a part of a well-insulated and well-drained wall system," says Nadav Malin, vice president of BuildingGreen and editor of Environmental Building News.
Proper installation is key to all siding systems. "It’s important not to think of siding as an isolated product, but as part of a whole system of weather protection," Malin adds. He advocates leaving an air gap behind siding, which allows water to drain away from—instead of remaining trapped within—the walls. "You’re going to be ahead in terms of protecting the house from moisture damage and water problems," he says.
Which wood would you choose?
The iconic American house is sided with clapboard—also called bevel siding, lap siding or weather-board—typically made from tough, insect-repellant cedar, pine, spruce, redwood, cypress or Douglas fir. Ask for lumber that’s certified by the Forest Stewardship Council (FSC). "That’s kind of the gold standard," Malin says.
Reclaimed timbers salvaged from old buildings, river bottoms or downed trees can be superior to new because older logs likely came from slower-growing trees with a denser grain. You may pay a premium for them, though.
The drawback of wood siding is maintenance. It must be painted or stained every few years. Otherwise, it can rot or suffer insect damage.
Getting greener all the time
For the look of wood without the headache, fiber-cement composite is a cost-effective alternative made of sand, cement and cellulose fibers pressed into thin, hardened shingles and planks. The material is termite- and fire-resistant, holds paint exceptionally well for up to 15 years and is available factory primed. Though inexpensive and often made with recycled content, its cement content means it has high embodied energy, although more eco-friendly options are becoming available. Eco-Cem by Coverings Etc contains 20 to 40 percent post-industrial and 10 to 20 percent post-consumer recycled content. CertainTeed makes a variety that includes cement made with 30 percent post-industrial fly ash, a byproduct of coal power plants.
Hire a contractor whose crew uses proper protective gear to avoid silica dust exposure, which can lead to a lung disease called silicosis.
Solid as a rock
Stone and brick, once common siding materials, have become less popular because of their high cost. Alternatives are simulated or cultured stone siding or brick veneer, made of precast concrete colored with pigments. While cement manufacturing is energy-intensive, the material weighs about a quarter as much as whole stones or bricks, so it requires less fuel for transport and no additional foundational or structural support.
True brick is still a classic and can last for centuries. Bricks are made of fired clay and come in a variety of colors, although some brick manufacturers are now applying surface coatings instead of casting the color throughout. "We pressure-washed a new house in Atlanta," says green-building consultant Carl Seville, "and some of the bricks lost their coating. These new bricks require gentler care."
Stucco—traditionally made of lime, sand and water—offers some of the same benefits as brick. Both can last hundreds of years. Modern versions add cement for durability, but this increases its embodied energy. Greener cement-stucco options such as StuccoMax-E—which will be made from 80 percent recycled waste materials, including fly ash—are currently under development.
Siding Material Comparison
||■ Lowest embodied energy
■ Can be sustainably grown
|■ Highest maintenance
■ Susceptible to insects and rot
||■ Holds paint well
■ Eco-friendly versions with fly-ash concrete
|■ High embodied energy
■ Installation precautions necessary
||■ Most durable
■ No maintenance required
|■ Labor intensive
■ Expensive and energy-intensive to ship
||■ No additional foundational support needed
||■ Cement content (energy intensive to produce)
■ Careful maintenance required
■ Can be salvaged
|■ Highest embodied energy
■ Low maintenance
|■ Energy intensive to produce
A Quicker Fix
Before you replace your siding, check into an eco-friendly coating. Look for new exterior paints and stains that contain few or no VOCs (volatile organic compounds).
Mineral silicate paints are a more durable, though more expensive, option that can last for 30 years or more. Popular for years in Europe, where they’ve held up for as long as a century, the paints are made from minerals similar to those found in sand or glass, and they chemically bond to stucco, plaster or cement to create a breathable finish that doesn’t outgas. It’s not for use on wood, metal or other more flexible surfaces, where it can crack.
Liquid siding, also called liquid ceramic or liquid stucco, is a ceramic-based coating that comes with warranties for 25 to 50 years. It’s applied in multiple layers, similar to paint, and water vapor can pass through it, allowing moisture to escape. But it’s important to do your research if you’re considering liquid siding: Poor installation or shoddy products may cause the coating to bubble and peel off.
The National Institute of Standards and Technology’s BEES (Building for Environmental and Economic Sustainability) software analyzes more than 230 building products, including popular siding materials. The online tool measures every aspect of a product’s life—from materials to recyclability—against environmental impacts, from global warming to human health concerns.