(This is Part 2 of a two-part series. See Part 1.)
In conversations about home building these days, I often hear the terms “sustainable approach” and “sustainability.” What exactly do they mean?
When I asked a number of architects, builders, engineers, environmentalists and ecologists, I got some interesting answers.
A sustainable approach is another name for green building, my informants said. The aesthetics are as varied as those for conventional construction, but the environmental impact of a house in both the near and far term is equally important and this has produced a criteria for selecting materials that is much more extensive. Energy efficiency is also a central concern.
A material can be selected for many reasons besides price and durability. For example, a locally produced material requires less energy to get to your building site than one manufactured across the country. A natural material, such as quarried stone, requires less energy to process than fired brick. Carpets made from plastic milk jugs and soda pop bottles keep these materials out of a landfill. Beautiful floors made with reclaimed logs that fell to the bottom of a river en route to a sawmill are not affecting old-growth forests. Nor are reused doors that were plucked from a disassembled building. Materials that are chemically stable are better for healthy indoor air than those made with substances that off-gas volatile organic compounds (VOCs). The most objectionable VOC is formaldehyde, which is now classified as a confirmed human carcinogen by the World Health Organization.
In many cases, material choices are not clear-cut. For example, bamboo has become a popular flooring material, in part because it seems to meet the sustainable criteria. Because it is a grass and not a tree, bamboo “self-renews” and regenerates quickly. It grows amazingly fast, maturing in three to five years. But, on the negative side, bamboo flooring is produced in Southeast Asia. It must be shipped across the Pacific, and across the country to get to your house. In addition, each floorboard is actually made up of smaller pieces that are laminated together with glues that can contain formaldehyde that can off-gas in your house.
With energy use, a sustainable approach maximizes efficiency with a mix of high-tech, low-tech and conventional heating equipment. From the very beginning of the project, energy use is an important consideration. When a builder and architect walk the site with the owner to find the best views, they are also checking the feasibility of the least costly energy option — the free warmth of the sun for winter heating. When the living spaces can be oriented towards the south, the sun will warm the rooms in winter. An overhang will shade these same spaces in summer, keeping the sun out.
As the design of the house begins to take shape, the energy focus shifts to the building envelope and the ways that heat gain (the summer sun coming in) and heat loss (warm air going out in winter) can be minimized.
At the same time, another low-tech energy option can also be explored — adding “thermal mass” to the south-facing rooms to “store” the free solar heat. A thermal mass absorbs the sun’s heat and stores it for many hours before it starts to reradiate it back into the room. This means that after the sun has gone down, you’re still getting its heat.
A well-designed, passive solar/thermal mass combination will not, in most cases, entirely supplant a furnace. But in North America, it will, on average, provide about 20 percent of your home heating needs, said Canadian energy expert William H. Kemp. A furnace would also be needed to provide backup on cloudy days, he added.
Thermal mass provides benefits in the summer as well. With properly sized overhangs, the south-facing rooms will not get any direct sun. Solar heat will still pass thorough the walls, but the thermal mass will absorb it, keeping your rooms cooler. At night when the mass releases its stored heat, you can open the windows to catch the evening breezes.
The summer benefits of passive solar/thermal mass are greater than the winter ones. Depending on where you live in North America, a well designed passive solar/thermal mass system can provide on average, as much as 40 percent to 50 percent of your air conditioning needs, Kemp said. You may still need conventional air conditioning and dehumidification, but not as much as you would with conventional construction.
In some climates zones, including half the ones in California, you won’t need an air conditioner at all if your passive solar/thermal mass is properly designed, said Malibu, Calif., architect Murray Milne.
Although thermal mass may sound like a piece of awkward equipment you’ll have to somehow camouflage, in fact it’s simply a finish material that can absorb a sufficient quantity of heat. The more common ones include adobe brick (a favorite in the Southwest), exposed stone, exposed concrete, or an additional half-inch layer of gypsum drywall to make a finish wall 1-inch thick.
The high-tech energy options — wind turbines and photovoltaic solar cells — are the most expensive. They are also the most sustainable because their operation does not consume any carbon fuel or produce any green house gases. Which one might work for you depends on where you want to put it. Kemp uses a 1.5-kilowatt, 100-foot-high wind turbine to provide power his house in rural Ontario, Toronto, but he said a wind turbine is not feasible in an urban or suburban setting. It can be noisy, it can create a “disco effect” — the neighbors next door thinks someone is shining a strobe light in their living room — and it must be at least 30 feet above the highest landmark in your neighborhood, which is impossible to control.
In contrast, photovoltaics, which convert solar energy into electricity, will work on any house, rural or urban, said Kemp, who also has a 1.25-kilowatt system for his house. The main drawback to photovoltaics, commonly called PVs, is their cost — a 2.5-kilowatt array of solar panels on your roof — big enough to supply about half the power needs for a typical household in a 2,400-square-foot house — runs about $25,000. This deters most buyers, but in some states including California, homeowners have been offered subsidies that can be as much as 50 percent of the total cost.
You might suspect that a sustainable house costs more money, but the builders said that sustainable, green building practices save money. A good example is job site disposal.
For decades, most builders have filled and emptied a huge Dumpster several times during the construction of a house, periodically dispatching the contents to a local landfill. This practice is expensive; the value of the materials that are pitched and the cost of disposal can quickly add up. It’s also largely unnecessary; with a little more care, as much as 75 percent of the waste could be eliminated, several builders said. When he started tackling it, Matt Belcher of Wildwood, Mo., founded it has other benefits as well.
Instead of clear-cutting the entire building site and throwing all the debris into the Dumpster, as he did in the past, Belcher now clears the site by hand, cutting only those trees that will interfere with construction. This cut his tree-related expenses in half. Belcher fells the trees towards the middle of the site so that the falling trees do not hit and damage the trees he is saving. He sells the largest felled trees to a local lumberyard and the smaller ones for firewood. What’s left is ground up and stockpiled, to be used as mulch for the new landscaping. The saved trees not only provide aesthetic benefits, they also provide shade in the summer, which lowers the homeowner’s cooling cost for as long as they live in the house.
Though sustainable, green building practices are not as yet widespread, many builders are adopting them as they learn about the benefits and cost savings, Austin, Texas, builder Ray Tonjes said.
“In 10 years, we won’t have green building, we’ll just have building,” he predicted.
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