When It Rains, It’s Porous: Permeable Paving

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This custom driveway incorporates Grasspave2 sections to absorb rainwater runoff.
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Made of recyclable plastic, the Modì Garden Grid creates water-permeable paths.
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Green Innovations’ porous paving grid creates a grassy surface safe for parking.
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Grasspave2 is an inch-thick, recycled-plastic grid that’s installed on top of a gravel and sand bed, then planted with fertilizer and sod.
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Uni-Group’s Eco-Stone pavers are concrete blocks that fit together in various patterns, leaving open space between.

The next time it rains, look at your driveway. Much of the water washes off and into storm drains, carrying oil, grease and chemical residue from cars. This runoff can cause erosion, flooding and contamination of public waterways.

Fortunately, permeable paving materials allow stormwater to soak into the earth, where naturally occurring bacteria help digest contaminants before they reach the water table. Called pervious or porous pavement, these systems keep groundwater clean, help tree roots breathe, reduce the severity of flash-flooding and reduce the urban heat-island effect because they absorb water into the ecosystem and don’t reflect heat back into the environment.

Two-thirds of the rain in urban areas falls on a paved surface, and some local governments encourage pervious paving to improve groundwater. In Chicago, new construction projects are now required to capture the first half-inch of rainfall on site.

Other locales are limiting the amount of a building lot’s land that can be covered by buildings or pavement. Build a house near Maryland’s environmentally sensitive Chesapeake Bay, for example, and no more than 10 percent of your land can be covered by anything that prevents rainwater from reaching the ground directly–a regulation that restricts house size.

If you already have a driveway, does it make sense to rip it up and replace it with something porous? Probably not, if it’s in good shape. However, if your driveway is due to be repaved, or if you’re building a new house, it might be time to look into a pervious system.

Surfaces that allow seepage

The simplest and cheapest way to let water run through your driveway is to build it with gravel, also known as aggregate. Single-size, angular particles–thoroughly washed to remove potentially clogging dust and dirt–create a driveway with as much as 40 percent open space between the stones, allowing practically any amount of rainfall to soak through.

More attractive, but also more costly, are concrete or ceramic permeable paving stones, or permeable interlocking concrete pavement (PICP). These blocks fit together in herringbone, basketweave or other patterns, leaving open space between. The openings, also called voids, are filled with gravel, which allows water to drain through and soaks up fairly heavy rainfall.

Interlocking permeable pavers cost about 25 percent more than conventional ones, and they require that you blow leaves and debris off them periodically to keep the voids from filling. Look for pavers containing a percentage of fly ash, a recycled byproduct from coal burning.

Water-permeable paving

It’s possible to build a driveway that looks essentially identical to everyday driveways but allows water through. Porous asphalt (blacktop) and pervious concrete are versions of traditional paving materials, but they’re made without fine sand. These mixes allow as much as 3 to 5 gallons of rainwater a minute to soak through each square foot. They’re slightly rougher looking than their conventional counterparts, but from a distance, it’s hard to tell the difference.

Porous asphalt is the less costly option, and it can be highly durable if installed correctly over a gravel bed. It also can be the trickiest material to work with. When heated, asphalt can become malleable–think of sticky blacktop on a hot summer day–and early versions of porous asphalt tended to clog as binders in the asphalt filled the open spaces. Today, porous asphalt includes polymer fibers that prevent binders from clogging. Those additives have to be applied at the right temperature; an experienced contractor is a must.

Pervious concrete is less complicated to pour–the National Ready Mixed Concrete Association certifies installers–but it’s more expensive than porous asphalt. Pervious concrete is faster to install than conventional because it doesn’t need to be smoothed with a trowel (finishing would seal the pavement surface, decreasing water penetration). Another benefit is that pervious concrete is lighter in color than asphalt, so it doesn’t absorb heat and radiate it back into the environment like blacktop does.

A solid foundation

For permeable pavers–asphalt or concrete–to work correctly, they need the right foundation. They can’t be laid on compacted soil; lay down fabric if they’re on clay or silt. That lets water through but prevents the soil from moving upward and clogging the paving.

The key is a bed of gravel, usually at least 6 inches thick, beneath the pavement to store the water temporarily while it percolates into the soil. The gravel should be evenly sized, to create voids, and deep enough so the water never rises into the asphalt. It should also be rinsed to remove potentially clogging dust.

Going green

You could also create a driveway that’s literally green–by planting grass. A structural lattice lets healthy grass or other plants grow while providing support to keep cars out of muddy ruts.

Inch-thick plastic grids are installed with a mix of sand and fertilizer on top of a gravel and sand bed. (Look for grids made of recycled plastic.) These systems allow even heavy rain to percolate through the grass roots and into the stone bed below, where suspended pollutants and moderate amounts of engine oils are consumed by active soil bacteria.

DON’T forget about your driveway or patio when looking for ways to reduce your environmental impact.

DO consider what happens to rainfall on your land.

Maintain the Drain

To keep the water flowing through a permeable driveway, vacuum up debris periodically. (Broom sweeping actually drives dirt deeper into the pavement.)

• Permeable pavers require occasional blowing of dust and leaves.

• Pervious concrete and porous asphalt require periodic vacuuming.

• In southern climates, you may need to vacuum every few years. In northern climates–where roads are sanded in winter–you may need to do it twice a year.

• To increase vacuuming effectiveness, pressure-wash the surface to loosen buildup of debris.

• Plant or grade slopes away from the driveway to keep soil from eroding or draining on it.

Permeable Pavers Pervious Concrete Plantable Paver Grids Porous Asphalt
COST $10 to $12 per squre foot (based on 2,500-square foot area) $8 to $10 per square foot* (based on 2,500- square-foot area) $4.50 to $6.50 per square foot (installed, with sand and sod) $4 to $5 per square
foot* (based on a
2,500-square-foot area)
PROS ? Most conventional appearance
? Can be laid in winter
? Snow melts more quickly because water can drain
? National standards for installers set by National Ready Mix Concrete Association
? Faster to install than conventional concrete 
? Looks like lawn
? Can absorb large amounts of water
? Grass and soil absorb pollutants
? Absorbs heat and CO2  CONS
? Looks like conventional asphalt
? Can last 20 years
or more
CONS ? Fine gravel between pavers can pose a tripping hazard ? Requires seven days of above-freezing weather to cure
? Vacuuming and power-washing needed (especially where sand is applied to streets)
? Grass must be watered and mowed like a lawn
? Could pose a tripping hazard
? National standards not well established
? Vacuuming and power-washing needed (especially where sand is applied to streets)
? Additives to prevent clogging can be tricky to install

* Prices vary by region and soil conditions.

Fab Floors: Eco-Friendly Flooring Options for Green Design

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Antique, distressed oak floors from Aged Woods have a rustic character.
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The natural variations of color and texture in these cork tiles from Expanko create a striking floor pattern.
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Bamboo flooring from Plyboo is sustainable and stylish, with exquisite grain.

Your choice of flooring can reflect both your style and your convictions, defining the personality of your entire house. Today’s beautiful, environmentally friendly alternatives–including bamboo, reclaimed or sustainably harvested wood, cork and natural linoleum–make it easy to find a floor that suits your needs.

You can use nontoxic installation methods for these floors, too. Nail down bamboo and wood, or install any of these options as “floating” floors–meaning they’re not glued or nailed down but “float” atop subfloors so they can accommodate the room’s humidity changes.

If you elect to use an adhesive, look for a less toxic, water-based version with low- or no-VOC (volatile organic compound) emissions. And make sure to read the directions to ensure that the adhesive works on your product and in your climate.

Bamboo: Grows like a weed

Bamboo looks so graceful and willowy it’s hard to believe that some varieties are tougher than hardwoods. Bamboo looks a lot like hardwood; but while trees take decades to replenish, bamboo is a quick-growing grass–some species shoot up three feet a day. The downside? Most is imported from Asia, although U.S. sources are emerging as bamboo’s popularity grows.

To make bamboo into flooring, producers cut the plant into strips, boil it to eliminate sugars and insects, and often dry it in a kiln. Then they glue the strips together to make a solid surface. Some manufacturers degrade the sustainability of their bamboo by using adhesives with toxic urea-formaldehyde. The less expensive the bamboo, the more likely it is to have a high formaldehyde content. Always ask the manufacturer or distributor whether formaldehyde is used–or check the Material Safety Data Sheet (MSDS), which manufacturers are required by law to provide, and which is often available online. Some distributors offer floors made completely without formaldehyde; other companies comply with Europe’s E1 standard, which limits formaldehyde concentrations to 0.1 parts per million (ppm).

Saving forests: Reclaimed and sustainable wood

If you want hardwood, look for salvaged wood flooring or flooring certified by the Forest Stewardship Council (FSC).

In recent years, people have sought reclaimed old wood–often from salvaged buildings or standing dead trees–for flooring with history and character. Old wood tends to be irregularly sized in wide planks with nail holes and knots.

You can find recycled-wood floors at salvage stores, including Habitat for Humanity ReStores, where people donate old demolition materials. Locate wood from barn teardowns in newspaper classified sections or from companies such as Aged Woods, which specializes in recycled, remilled woods from barns and warehouses. Locally sourced salvaged wood eliminates transportation costs and energy.

Removing nails from and refinishing salvaged wood yourself is cheaper, but requires more time. If you’d rather pay a professional to do the work, try buying prefinished flooring from a company that specializes in refurbishing old wood.

If you’re going for new wood flooring, make sure it’s certified by the FSC, a third-party agency that ensures eco-friendly standards are met. FSC flooring often costs a bit more per square foot, but you can find it for prices comparable to conventional.

Put a cork on it

Cork flooring is warm, soft and resilient underfoot, and it holds heat and dampens sound better than wood, bamboo or linoleum. Cork resists mold and mildew growth and is fire retardant.

It takes the Mediterranean cork oak tree about 25 years to mature enough for its first cork bark harvest; a mature cork oak regenerates its bark in about 10 years. Because cork oak takes time to grow and cork trees are becoming scarce, demand recently has begun to outstrip supply. Some cork flooring is made from wine cork remnants.

Chemical treatments are necessary to create a hard surface, but green options are available. Avoid formaldehyde binders, PVC laminates and cork blended with synthetic rubber, and opt for low-VOC polyurethane or beeswax-base finishes.

Love linoleum

Most resilient flooring, mistakenly called “linoleum,” is actually toxic, environmentally disastrous vinyl flooring. True natural linoleum–made with linseed oil, tree resin and a combination of ingredients such as cork, sawdust and limestone with a jute or hemp backing–is a durable, biodegradable, antimicrobial, low-cost flooring alternative.

Linoleum’s linoleic acid (from the linseed oil) outgases some VOCs, which may exacerbate health problems if you’re chemically sensitive.

To install, choose an adhesive that’s low in VOCs, water based and formaldehyde free. Heating linoleum tiles so the seams adhere to one another is also an option; however, outgasing from this procedure could create skin and eye irritants.

Easy Refinishing for Hardwood Floors

Sealants and other toxic chemicals emit volatile organic compounds (VOCs) that poison indoor air.

Sanding old, oil-based varnishes releases toxins into the air. If you’re sanding the floor yourself, rent a dust-free sander such as the BonaKemi atomic dust containment system. Or hire a professional who uses dust-free equipment that vents to an outdoor collection unit.

If you can’t find a dust-free system or floor refinisher, cover openings with plastic to contain dust. Use a HEPA (high-efficiency particulate air) vacuum to clean up.

Choose low-VOC stains, finishes, sealants and caulks. (For contents and health effects of finishes, obtain the MSDS from the manufacturer; most are posted on manufacturers’ websites.) Avoid fungicides, biocides and high levels of VOCs. Look for Pure Tung OilOS Hardwax Oil, and products by BioShieldTried And True and AFM Safecoat.

Down to Earth Talk about Floors


Pros: durable; easily replenished resource; not made from the species that endangered giant pandas eat; relatively low cost (around $3.50 to $6 per square foot)

Cons: may contain formaldehyde; may be treated with fungicides or pesticides; most is imported from Asia; can warp or weaken in high-moisture areas; best not used in bathrooms, laundry areas or mudrooms; some varieties prone to scratching

FSC-Certified Wood

Pros: supports good forestry practices; encourages local economies that use sustainable forestry; beautiful and sturdy

Cons: tropical woods shipped long distances; more expensive than non-certified woods

Reclaimed Wood

Pros: reuse is most environmentally friendly option; can be acquired locally; inexpensive if purchased from an individual, through www.OldBarnWoodSite.com or from Habitat for Humanity; historic look adds character and beauty

Cons: requires a lot of work if unfinished; irregular sizes more difficult to install; can be expensive, depending on source  ($6 to $12 per square foot depending on width and type of wood)


Pros: a naturally sourced, renewable resource; excellent thermal and acoustic properties; bounces back from dents and gouges; can be installed by homeowners (tiles)

Cons: imported from the Mediterranean; requires adhesives; choose less toxic varieties; can be expensive ($5 to $8.50 per square foot for tiles or floating floors)

Natural Linoleum

Pros: easy to maintain; hides wear and tear; uses natural, renewable resources; comes in many colors and styles for interesting designs; relatively low cost ($3.50 to $5.25 per square foot); biodegradable

Cons: linseed oil outgases VOCs.; requires adhesives to install; conventional ones are toxic; most brands imported from Europe



Smith & Fong
(866) 835-9859

(703) 352-8300

(800) 929-6333


Aged Woods
(800) 233-9307
salvaged wood

(877) 372-9663
FSC and reclaimed wood

(570) 465-3832
salvaged wood

Endura Wood Products
(503) 233-7090
FSC and reclaimed wood

Pelican Teak Products
(904) 838-7359
FSC-certified teak


Forbo Marmoleum
(866) 627-6653

Cork Expanko
(800) 345-6202

Natural Cork
(800) 404-2675

(800) 828-2675

Cooking with Sunlight: Learn How to Cook Food With Solar Cookers

Author Photo
By Jennifer and es

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A parabolic cooker, such as the one above, cooks nearly as quickly as a conventional oven.
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This box cooker, made of wood, is used in Sri Lanka.

When Louise Meyer and Dar Curtis invite guests over for dinner on a late summer afternoon, all the cooking is done outdoors. There are no charcoal grills or other fossil fuel-burning stoves to heat up and clog the air. Instead, appetizers, entrée, and dessert are all prepared with abundant, free, clean energy from the sun.

Find out how to build and use your own solar oven.

Meyer and Curtis use special ovens called solar cookers to prepare their food. With eight people expected for dinner, they have four solar cookers at work on Curtis’s patio. The food is ready one or two hours before dinner but stays warm in the cookers until the chefs transfer it to a buffet table where guests help themselves. The evening’s offerings: chicken baked in its own juices, ratatouille, Italian peppers–“slightly overdone,” Curtis allows–and to top everything off, banana cake. “Perfect!” Meyer proclaims, noting the dessert is moist on top yet browned around the edges.

Meyer and Curtis, both of the Washington, D.C., area, are partners along with Minneapolis sociologist Barbara Knudson in Solar Household Energy (SHE), a nonprofit organization that offers an alternative to wood-burning fuel in developing countries where trees are overharvested. Solar cookers, or ovens, also are useful in the United States as easy, practical, and economical ways to bake, braise, or stew food. Not only are they an earth-conscious cook’s best friend, but their outdoor location conserves energy. “In summer, you don’t have the air conditioner fighting with the oven to keep the house cool,” Meyer says.

Solar Cookers International (SCI), a nonprofit organization assisting communities to use the power of the sun to cook food and pasteurize water for the benefit of people and environments, traces solar cooking to the late 1700s, when European naturalist Horace de Saussure set out to show that a place is hotter when the sun’s rays pass through glass. He built a miniature greenhouse out of five glass boxes stacked inside each other on a black table. The outermost box stayed cooler, and the smallest box recorded the hottest temperature, 189.5 degrees Fahrenheit. “Fruits… exposed to this heat were cooked and became juicy,” he wrote. De Saussure experimented with other “hot boxes” and was able to achieve cooking temperatures that reached 230 degrees Fahrenheit regardless of the outside climate. He couldn’t explain how the hot boxes cooked the food, but physicists today say the phenomenon will work in any glass container exposed to the sun.

A solar cooker is a device that directs sunlight onto a dark-colored cooking pot, maximizing the amount of light energy that reaches the pot and minimizing the amount of heat loss. The essential elements of a solar cooker are sunlight, a black pot, reflectors, and a glass-covered box or a clear plastic bag. The black pot attracts the sun’s rays while the panel reflectors amplify them. Meanwhile, the glass or plastic prevents the heat from escaping, thus creating a “greenhouse” inside the solar cooker. As inventors and ecologists have experimented with hot boxes over the years, a variety of solar cookers have become available.

The three basic types are:

1. Panel: The most affordable solar cookers rely on foil-covered panels or reflectors that concentrate sunlight onto a pot surrounded by a plastic bag. SCI, which has been selling panel cookers for $20 each since about 1994, markets its products internationally, with about 100 buyers per month. The “CooKit” includes plastic oven bags, a single sheet of foil-covered cardboard that folds to form the base and four reflective panels, and an instruction pamphlet that includes recipes. The panel cooker folds to the size of a three-ring binder and weighs less than two pounds. Cooking pots are not included; SCI sells them for ten dollars each, or they can be found at many stores. Lightweight, dark Granite Ware generally works best. Metal pots painted black on the outside or blackened in a fire also work well.

2. Box: More elaborate, box-shaped cookers are made from a variety of materials including cardboard, wood, bamboo, metal, stone, fiberglass, clay, tree bark, and cloth stiffened with glue. Insulation, which is essential for the cooker to reach hot temperatures, can be made from foil-lined cardboard, down feathers, spun fiberglass, crumpled newspapers, or any number of other materials. A glass panel covers the box, and reflectors on one to four sides direct the sun’s rays to the inside of the cooker. Illinois-based Sun Ovens International has manufactured a common box cooker, the Global Sun Oven, for the past fifteen years. About thirty dealers around the world, including SCI, sell the Global Sun Oven for about $229 each. Sales have remained steady, says Paul Munsen, president of Sun Ovens International, but tend to peak during energy brownouts or blackouts. The Sun Oven box cooker is sturdier than the cardboard panel cooker and gets hotter, so food cooks faster, which means it can be used during more months of the year.

3. Parabolic: Consisting of a concave disk that focuses light onto the bottom of a pot, parabolic cookers cook about as quickly as a conventional stove. In fact, Curtis says the temperature inside the pot on a good parabolic cooker can actually fry food, which is not possible with the other cookers. The reflectors, he explains, direct the sun’s energy onto a small focal area within the cooker with such intensity that a rolled-up newspaper would burst into flames. Parabolic cookers can cause burns if used incorrectly, and, because the concentrated sunlight heats the pot quickly, food must be stirred and watched carefully. Parabolic cookers cost $100 or more and can be ordered through E.G. Solar, a German company.

Solar cooking made easy

Catch some rays. On a clear day with strong sun, food can be put in the cooker in the morning and left all day until it’s time for the evening meal. Just place the cooker so that it faces the sun’s position in the early afternoon sky, and the food will cook slowly and at an average temperature of about 225 to 275 degrees Fahrenheit, depending on the quality and type of cooker. “Some higher-quality cookers can even cook on partly cloudy days or during the winter months, but temperatures will generally be somewhat lower, and it is best to rotate the cookers more frequently to track the sun,” says Kevin Porter of Solar Cookers International.

Cloudy days. The cookers’ efficiency depends more on the intensity of the sun than on the outside air temperature. Food will not cook on days when clouds completely block out direct sunlight, yet Dar Curtis, director of Solar Household Energy (SHE), cooked a chicken at his Washington, D.C.-area home one Christmas. “It was one of those cold, bright days with no passing clouds,” he says.

Timing is everything. It’s not always easy to tell when food is ready, and people new to solar cooking will have to test food and rely on trial and error. As a guideline, Curtis and his one of his partners in SHE, Louise Meyer, say it takes about 50 percent longer to cook food in a solar cooker than in a conventional oven. And like a gas or electric oven, a solar cooker cooks some foods faster than others. A three-pound chicken, for example, may be ready in two hours, whereas stews may need five or six hours. Bacteria growth in the food is not a concern as long as the cooker stays hot. Food is pasteurized at 160 degrees Fahrenheit, Curtis explains, and begins cooking at 180 degrees.

Here’s the dish. Panel cookers usually hold only one pot, which can cook food for up to five or six people. Many box cookers, though, will hold several pots, allowing you to cook more than one dish at a time. The pots should preferably be thin metal to allow for the most efficient transfer of heat; they should also have a dark-colored, tight-fitting lid.

Keeping it warm. Even after you finish cooking in your solar cooker, you can still keep it warm. In a box cooker, the heat is trapped inside and retained even after cooking is finished. A CooKit, in which the black pot is contained by a plastic bag, will not retain its heat for very long. You can, however, transfer the cooked dish into a Hay Box or Heat Retention Box that will keep the food warm. A Hay Box is a box insulated with hay, straw, wool, or feathers and will insulate for two to four hours, depending on how hot the dish was originally and how well the box is insulated. Kevin Porter at SCI also suggests adding rocks or a brick alongside the pots in a box cooker. This will keep the food warm even longer but will cause the cooker to heat more slowly.

On the menu. Curtis and Meyer advise newcomers to solar cooking to start with a panel or box cooker and prepare something simple such as rice, cereals, egg dishes, fish, poultry, fruits, and vegetables. Other easy-to-cook foods include cornbread, gingerbread, medium-size roasts, quick breads, yeast rolls, and buns. More advanced solar chefs may want to try cooking whole turkeys or large roasts. Dried beans are difficult to cook in a solar cooker unless they have been presoaked for at least eight hours.

Hot, hot, hot. Always use potholders when removing lids or pots from a solar cooker.

Even Exchange: Heat Recovery Ventilators

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Unlike windows, heat recovery ventilators (HRVs) can filter out dust and pollens, such as these, before they enter your home.

Only a few years back, a “tight” house still lost 40 percent of every heating dollar to air infiltration. Plenty of fresh air found its way in through small cracks in the foundation and walls and around doors and windows, replacing the warm air that escaped through cracks and gaps in the ceiling and roof. Because of this constant exchange, older homes are notoriously drafty and expensive to heat. But from a clean air standpoint, they’re a healthier place to live.

Opening a window is the simplest solution, although doing so defeats the purpose of a tight house and provides only temporary relief. Local exhaust fans can be used to remove moisture and other pollutants from high-use rooms, such as kitchens and baths, but the negative pressure created by these systems draws in outside air from every crack and crevice. A negatively pressurized home can potentially draw in carbon monoxide from an attached garage or radon gas from the surrounding soil. The biggest problem with both solutions is that they sacrifice the heat your home was designed to save.

A heat recovery ventilator (HRV) is a better option. HRVs work much like an open window, but they can recover up to 85 percent of the outgoing heat. In addition, HRVs (unlike windows) can filter out pollens and dust before they enter your home.

HRVs aren’t new. They’ve been used throughout Europe–where super-efficient homes first encountered air quality and humidity problems during the winter–for more than a decade. Consumers and builders in the United States have quickly adopted the new technology. Today, many local building codes require mechanical ventilation systems in new construction.

How HRVs work

In one of Aesop’s fables, a satyr befriends a man, lost on a winter’s night. As they reach the satyr’s cave, the man starts blowing on his fingers. When asked why, the man answered, “My breath warms them.” The satyr then placed a dish of stew before his guest. When the man raised the spoon to his mouth, he began blowing on it. The satyr again asked him what the man was doing. He answered, “The stew is too hot, my breath will cool it.” The satyr, wanting nothing to do with a creature who can blow both hot and cold with the same breath, promptly threw the man out of his cave.

What the satyr considered magic is actually the principle of heat transference; heat energy was transferred from the man’s breath to his fingers, and later from the stew to his breath. This is basically how HRVs work. At the heart of an HRV is a heat-exchange core. This core is made up of alternating aluminum or plastic passages that allow incoming and outgoing airstreams to flow next to each other but prevent the streams from mixing. In winter, the heat energy derived from the outgoing stale air blowing out preheats the incoming fresh air blowing in; in summer, the opposite occurs.

An energy recovery ventilator, or ERV, is a close cousin to the HRV, except that it transfers moisture in addition to heat. The added humidity control can be a big advantage in climates where dry winters last for months. (By expelling all the moist air, an HRV can make a home too dry in the winter.)

Although wall- and window-mount models are available, most HRVs and ERVs are designed as centralized whole-home units. HRVs can be easily retrofitted into homes that already have forced air heat, simply by feeding the fresh air intake directly into the furnace. Independent HRV systems are also available for homes with hot water, steam, or electric heat; however, the required five-inch to seven-inch diameter ductwork and extra labor usually limits this option only to new construction or major remodeling projects.

The cost of installing an HRV system varies widely. Depending on your existing heating system, existing ductwork, and the size of your home, adding an HRV can cost anywhere from $1,000 to $4,000 or more. When shopping for a system, look for units that have high-efficiency filters to trap pollutants before they enter your home. Some units also offer pre-heater or pre-cooler coils to make incoming air more comfortable during temperature extremes.

Do I need an HRV?

Not all homes can benefit from an HRV. According to the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), the minimum standard for residential ventilation is .35 air changes per hour (ACH), or about eight changes per day. Many older (drafty) homes exceed that minimum naturally, especially on windy days. However, even for older homes, higher circulation rates may also be desirable when more people are home, or if you suffer from home-related allergens.

To test if your home is tight enough to benefit from an HRV, contact your local utility company or heating contractor and ask them to conduct a blower door test. This test checks your home’s tightness by using a fan to blow air into the house and then gauging how well it holds pressure. Your heating contractor should also be able to help you decide on the size of the HRV and the proper locations of the intake and exhaust vents.

Want to compare HRVs?

The Home Ventilating Institute’s product directory compares dozens of HRVs by their recovery efficiencies, airflow capacities, and other features. For more information, call (847) 394-0150.

Home with Standard Vents
Mechanical vents are good at expelling unwanted moisture and pollutants, but if a home’s tight, they can depressurize the inside space. The replacement air that’s drawn in may bring pollens, molds, and in some cases, radon. Air entering through vents and chimneys can also cause fuel-burning appliances to vent carbon monoxide and other pollutants inside (back drafting).

Home with an HRV
Whether run independently or hooked into the existing hot-air system, HRVs provide a balanced clean-air airflow. Note that HRVs and ERVs can replace bathroom exhausts, but you’ll still need a vent hood over your stove–vaporized grease could clog the exchanger and contaminate the ducts. Install supply and return vents, about ten feet apart, in each bedroom, bathroom, and common area.

Plugging into the Sun: Solar Energy for the Future

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This grid-connected 1.8 kW system features Altair Energy’s Family-Safe system, which provides backup power for pre-selected appliances.
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The PV panels on this California roof are connected to the grid and have a battery backup. Shown here is a Silicon-Film SunUPS System with 4.8 kW-rated peak-array capacity.
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Boston Edison commissioned this demonstration home, known as Impact 2000, to highlight future technology trends. The house features a 4.5 kW utility interactive PV system and solar thermal system, which form a uniform glass plane on the south roof.
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The roof of this Massachusetts house is composed of 480 Sunslates that generate almost 7,700 kilowatt hours annually. Electrical installation: Solar Works, Wilton, New Hampshire; roof and flashing: Copper and Slate, Waltham, Massachusetts.
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PV shingles and slates such as this Sunslate from Atlantis Energy Systems can take the place of conventional roofing materials and generate electricity.

In a way, all of us are already using solar power. Burning coal, oil, and natural gas to run the turbines in our power plants releases the solar energy trapped by plants millions of years ago. Unfortunately, the process also releases tons of carbon dioxide, sulfur dioxide, and nitrous oxide emissions. Mining and drilling operations further damage our environment.

In stark contrast, photovoltaic (PV) systems produce electricity with no noise, air pollution, or moving parts, and use an inexhaustible resource–the sun. According to some estimates, by 2010, PV systems will reduce carbon dioxide emissions by ten million metric tons per year by replacing fuel-burning power plants.

Bill Lord of Cape Porpoise, Maine, invested $25,000 in a 4,200-watt array for his house. His six-year-old home generates 4,100 kilowatt hours (kWh) annually–330 kWh more than he uses. “I’m happy to donate the surplus to my local utility company,” he says.

Now that recent advances in PV technology have created thin-film PV modules that can be integrated into asphalt shingles and metal roofs, solar systems are no longer as unsightly as they were, and more homeowners are considering sun power. However, think before you leap; according to Lord, solar electricity can be a “free lunch–just as long as you are willing to pay for breakfast [installation].” Here’s how you can decide if a solar system makes sense for you.

PV primer

In 1994, Subhendu Guha, executive vice president of United Solar Systems, was lecturing on the benefits of solar energy and showing a picture of solar cells arrayed on the roof of a house when an architect in the audience said, “But it’s so ugly. Who would want that on their house?” Two years later, Guha developed a solar shingle that could be nailed directly on the roof. The shingle uses a thin-film solar cell made from amorphous silicon, an environmentally safe element found in sand, applied to a sheet of stainless steel. Unlike traditional solar modules, which attach to the roof, these PV shingles are the roof. Most recently, United Solar has developed a solar film that can be easily affixed to standing-seam metal roofs. Although less efficient than earlier crystalline cells, these modules can be integrated into an asphalt roof or used instead of traditional roofing materials, and they have brought solar electricity back into the spotlight.

Is PV for me?

There are many good reasons for investing in PVs, but first you must be prepared to make some changes. According to Steve Strong, an architect who has been designing energy-autonomous homes for twenty years, solar systems can easily be integrated into new designs, but they’re much more difficult as a retrofit. “It’s important to make your home worthy of the investment,” he says. As a first step, Strong advises investing in a home energy audit to improve your home’s overall efficiency.

Next, consider your home’s location and orientation. For maximum solar gain, your solar array should be installed on a south-facing roof. “The problem is that most homes are oriented according to a zoning map, not for solar efficiency,” says Strong. He points out that houses in the Sunbelt will be candidates regardless of orientation, but that orientation becomes more important as you travel north.

Lastly, a well-designed PV system needs clear access to the sun’s rays for all or most of the day–unobstructed by trees, roof gables, chimneys, or other features. “PVs don’t like shadows,” says Strong. For example, the shadow from a flagpole creates a resistance field that will impede the entire module’s flow of power production.

A photovoltaic installer should be able to assess the viability of outfitting your home with solar array. For a rough estimate, you can check out the National Renewable Energy Lab’s PV calculator, PVWATTS (see “Resources” on page 76). The site also contains a “pollution prevention calculator” that will determine the yearly amount of pollutant release your system will prevent.

Paying for PV

Even though improved manufacturing processes have reduced the cost of photovoltaics to less than 1 percent of what they cost in the 1970s, solar electricity still costs two to five times more than electricity from the utility companies.

Determining the price of a system depends on several variables. The most significant factor in determining the total and per-watt cost of your PV system is size (see “Stepping into Solar Power,” below). For example, a seventy-five-watt single-PV-panel system with a built-in inverter can cost as little as $900 installed, or about $12 a watt. In comparison, a five-kilowatt system that can completely satisfy the electrical needs of most homes may cost $30,000 to $40,000 installed, or $6 to $8 dollars a watt. For those who choose to live completely off the grid, or who require backup power, batteries can increase the system’s cost by an additional $1.50 to $3 per watt. Although it may seem like a sizeable investment, “buying a photovoltaic system is like paying for years of electric bills up front,” explains Lord.

There are times when investing in PV can pay off immediately. For example, in remote areas, PV electricity can cost about as much as paying the local utility to bring in a new line. And because being “at the end of the line” can mean lengthy outages, using PV means that no one will be able to cut your power off.

To help defray costs, many states are now offering financial incentives, including income tax credits, property tax exemptions, state sales tax exemptions, loan programs, grant programs, and net-metering programs. A few utility programs are also offering financial incentives, such as leasing programs, rebates, low- and no-interest loans and grant programs.

Some of the best deals can be had in California. Currently, state rebates will pay up to half the cost of the PV system, and other tax incentives are offered. There is also a $750 rebate available from the California Energy Commission. California homeowners are responding enthusiastically to the incentive program. In fact, California Home Depot outlets are now selling PV kits, made by AstroPower, that are designed for do-it-yourselfers.

Investing in PV isn’t simply about saving money. As Strong points out, “Photovoltaics allow people to take control of their energy destiny. For those people who want to be technological pioneers, to fix future operating costs, and simply tread lightly on the earth, it’s their best option.”

Salvaged Wood: New Life for Your Floors

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This curly heart pine and cherry inset decorates a vertical heart pine floor.
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River-recovered flooring and railings add character and warmth to a room.
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River-recovered flooring and railings add character and warmth to a room.

Twenty-six years ago George Goodwin didn’t know much about salvaging old-growth lumber. But he’d seen logs pulled up from the rivers of the South, and he knew they were unlike anything found in lumberyards or hardware stores.

George’s plan–to sell heart pine pulled from the rivers where it was lost more than 100 years ago in transport to mills–hit a nerve. “People would call us,” his wife, Carol, recalls, “and they were just ecstatic that they had found a source for material of this quality that was last available to their grandparents.”

The Goodwin Heart Pine Company started back in 1976. Today, demand for old-growth wood has never been greater.

Other firms such as Mountain Lum­ber in Virginia, Conklins in Pennsylvania, and The Joinery in North Carolina salvage wood from old barns and abandoned warehouses. Their customers use the reclaimed lumber for everything from window casings to front doors. A few have been known to construct entire houses from vintage wood, but most people use it for floors that some say will last another lifetime at least, while lending a measure of beauty nearly impossible to recreate.

Old growth

“It’s the wood that built America,” George likes to say.

“It smells good,” Carol adds. “It feels good, and it’s beautiful to look at. And you’re preserving a bit of what was once the largest contiguous forest on the North American continent.” She’s referring to the forests of longleaf pine that once covered some 85 million acres. Today less than 10,000 acres of old-growth stands remain.

One hundred years ago, heart pine was used for everything from ship masts to bridges, warehouses, and wharves–not to mention houses. The wood was so abundant, Carol says, that “people stained it to look like walnut. They tried to make it look like something else. They just got tired of it.”

Not any more. These days, homeowners love heart pine for its aged red gold patina, intricate grain patterns, and durability. And, perhaps, for the fact that it takes thirty years for a longleaf pine to grow just one inch in diameter.

Salvagers are also making available old-growth ash, elm, hickory, hemlock, red oak, and walnut. And if you can get your hands on the rare American chestnut–decimated in a blight early in the twentieth century–you’ve got quite the prize.

Before they were cut down, says Pattie Boden of Mountain Lumber, “the old trees had been growing 400 years. Because of the age, the old growth is very densely grained with very, very tight growth rings–eight to fifteen per inch. Tightness equals durability and stability. The new wood, they just pop it in the field, and when it’s long enough, they cut it down. It has four growth rings per inch. It doesn’t have the maturity. The old trees have a lot more heartwood than sapwood. Sapwood is what we call the by-product. It’s softer.” (Heartwood is the part of the tree that was already dead when cut. The sapwood is the portion that was still living, and it is not nearly as dense.)


Reclaimed lumber also makes for a healthy living environment. “I have a lot of allergies myself,” Sandy Conklin says. “By using this wood, I don’t have to worry about formaldehyde or any of the chemicals used in processed wood. Old growth has been airing for 100 years, so you don’t have outgassing. With rebuilt wood, the only chemicals you get are what you put on to finish it, and you can finish it with water-based products.”

Because they give, wood floors are also gentler than tile and stone on the joints, and they’re far easier to clean than carpet. Then there’s the environmental aspect.

“If we didn’t use the old wood,” says Boden, “many old timbers would go to the landfill. Our product is totally reclaimed. We don’t ever cut down trees.”

However, not every company’s wood is purely salvaged. Boden cautions, “You need to ask how much new wood is mixed in” before you buy.

Premium pricing

Prime cuts of old-growth wood can go for as much as three times that of new wood, with river-salvaged lumber averaging 15 percent more than that taken from a demolished structure.

“We have grades of heart pine that are as low as $3.50 per square foot,” Carol Goodwin says. “This grade comes with nail holes, stains, and knots, and it’s called our character floor. It’s what I would put in my mountain or beach cabin. But if you want the pristine no-knots, then you’re looking at $10 per square foot and up.”

“There’s really a labor and waste factor that makes the product more expensive,” says Jon Hubert, owner of Singing Saw in Nederland, Colorado. “When you cut down a tree, the lumber industry can guarantee you’re going to get so much use. But with vintage timber, you may have to go through ten barns to find enough good materials. Most things in the recycling world tend to be more expensive for the searching factor. But the unique look, the fact that your wood is old and being reused–those things help people justify the expense.” nNH

How To Use Graywater

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Resembling a tropical jungle, this greenhouse-enclosed system manages all of the graywater for a three-bedroom home as part of a zero-discharge wastewater system.
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The indoor graywater-irrigated planter bed in Wellfleet Audobon Sanctuary, Wellfleet, Massachusetts, manages all of the graywater from the building’s sinks. Treated water also flows to the exterior gardens to irrigate and fertilize the plants.

When you wash your hands and then watch the water slip down the drain, do you ever wonder if there’s a less wasteful way to make use of it? Take heart! Increasing numbers of home­owners are using the water that drains from showers, tubs, and washing machines–known as “graywater”– to irrigate plants, flush toilets, and even wash clothes.

A wide variety of systems and components are available to filter, treat, and use household graywater–from ponds and aerobic planter beds to peat filters, sand filters, aerobic aquatic systems, and reverse osmosis membranes. “It’s all a matter of context,” explains Art Ludwig, author of Branched Drain Graywater Systems (Oasis Design, 2000). Because of climate, environmental conditions, costs, and laws, what works for Southern California might not work for the Northeast, Ludwig says.

Although it’s difficult to generalize, here are the basic components and guidelines for creating your own graywater system.

Choosing a system

When choosing a graywater-use system, consider these questions.

How will you use the water? Using it for growing nonedible plants requires little filtration and no disinfection. To recycle it for flushing toilets and washing clothes requires potentially costly advanced filtration and disinfection. Weigh the costs, the avoided costs, and the benefits.

What’s in the water? Know what you pour down the drain. Can you avoid toxic substances such as chlorine bleach?

What do local wastewater regulations allow? Installing a graywater system may require a special permit. Call your local health agency.

What are you willing to spend? The cleaner you want your graywater, the more it may cost.

Filter it

Graywater must be filtered to remove particles and dirt that can clog pipes and soils. This is especially important for washing machines, because many modern clothes contain fibers that do not biodegrade. Filters designed to be installed at each source of graywater include thirty-micron filters, which are connected to sink and laundry drains, and grease interceptors (typically made for kitchen sinks), in which grease floats to the top and heavy solids fall to the bottom. Some systems catch and filter graywater flows with peat, sand, and other media. Higher-tech filter options include reverse osmosis systems, which push effluent through porous membranes.

All filters must be emptied out or cleaned with a backflush of water periodically. Never dispose of their contents in the sink drain.

Treat it

If graywater is going to be used for flushing toilets or washing, its nutrients, bacteria, and carbon must be treated so it meets water treatment standards. One option is to run graywater through an aerobic planter bed that contains chunky growing media such as sharp sand, peastone, or gravel (even broken glass). The growing media and the plant roots provide spaces for air-using beneficial bacteria to destroy potential pathogens and convert the nutrients to a form that plants can use. These systems usually contain phreatophytes–thirsty broad-leafed tropical plants–and other fast-growing plants such as bamboo and reeds that use up the water and nutrients. (Because graywater contains few nutrients, the plants may need to be fertilized.) The plants are periodically harvested and composted or discarded.

Disinfect it

If the recycled graywater is to be used for anything that involves direct contact with people, such as flushing toilets, washing clothes, or watering edible plants, it must be disinfected. This is best done with ozone or ultraviolet light devices rather than chlorine, which is potentially carcinogenic.

Graywater use made simple

Keep a container near the sink to catch warm-up water and rinse water for watering plants. Place a bucket in the shower to collect warm-up water and shower water. Use it to flush the toilet by pouring a gallon or two into the bowl. Or use it to water your plants or compost pile.

Is it safe?

Graywater typically contains oil and grease from soaps and skin, as well as dirt, cleaning solvents, and pathogens (disease-causing organisms) from washed bodies and clothes. But separating graywater from blackwater (the effluent discharged from toilets and, under some state laws, kitchen sinks) keeps most of the potentially harmful pathogens out of graywater.

“Graywater usually has some fecal coliform in it, so it does have to be treated,” says David Del Porto of Sustainable Strategies, an engineering firm in Concord, Massachusetts. “Graywater is also high in carbon, can be alkaline, and can have lots of nonbiodegradeable particles from clothing, so it needs to be filtered.”

Using graywater also requires a consciousness of what is put down the drain–toxic chemicals, drain cleaners, and strong disinfectants must be avoided.

Is it legal?

As both regulators and property owners come to accept the merits of graywater recycling, it is going public. Many graywater systems–some legal and some not so legal–have been installed in California, the first state to enact graywater regulations and promote graywater’s use during droughts. Now several others, including Massachusetts, Arizona, and Washington, are following this lead, and more will likely come on board as the laws relax and system costs decrease.

Is it foolproof?

Careful design and planning is key, or your graywater experience may go sour. Inadequate ventilation of indoor systems can lead to unpleasant odors. Using soil in a graywater system is another common mistake, Del Porto explains. Carbon from soaps, detergents, and body oils can clog the soil, making it anaerobic, foul-smelling, and ineffective. “You need air spaces for aerobic transformation and nitrogen to avoid carbon buildup that will clog the soil,” he explains. “That’s why chunky sand and other large and porous growing media are best.”

Graywater at work

Ludwig, whose small Santa Barbara home features an Eden-like variety of fruit trees irrigated with graywater, says that few of the graywater systems he designs get legal approval because of the cost and complication of meeting codes. An exception is a “branched drain system” that he designed for a neighboring home, which distributes graywater under eight inches of soil (in the root zones of plants) in a yard filled with fruit trees. Basins of mulch provide more aerobic treatment and evaporation.

In a central Massachusetts home, graywater irrigates an aerobic planter bed containing thirsty tropicals such as banana trees, birds of paradise, bamboo, and bougainvillea. The entire system is housed in a greenhouse that also helps heat the home. “The owners are thrilled,” says Del Porto, the system’s designer. “They didn’t know that such a system was possible.”

Del Porto’s firm designs systems for clients whose homes in environmentally sensitive areas require nonpol­luting wastewater solutions. Many clients learn about such systems when touring his ecologically retrofitted home near Boston. Outside the home, a bed of evergreen shrubs is irrigated by filtered graywater from Del Porto’s washing machine. Within a two-story attached solar greenhouse, graywater from some of the home’s sinks is filtered, treated in aerobic planter beds, and then drained to a fountain and pond containing koi fish and water hyacinths.

In a small atrium hallway at the Wellfleet Audubon Sanctuary in Wellfleet, Massachusetts, a twenty-foot-long planter bed brims with a dense riot of tropical greenery. This planter manages all graywater from the restroom sinks and the employee kitchen. Any overflow drains to an outdoor sand filter planted as a garden to attract butterflies.

More and more graywater-use options and installations will emerge as economy meets ecology over issues of wastewater pollution and water supply. “In the near future, a building’s landscape will also be part of its wastewater treatment system,” Del Porto predicts. “Water is getting too expensive to throw away, and wastewater is becoming even more of a water pollution problem. Increasingly, it will be strategically used up on site.”


Aquatic Eco-Systems
Apopka, FL
(407) 886-3939

Center for Ecological Pollution Prevention
Concord, MA
(978) 318-7033
Books and workshops about graywater systems

Earthship Biotecture
Taos, NM
(505) 751-0462

Jade Mountain
Boulder, CO
(800) 442-1972

Nutricycle Systems
Jefferson, MD
(301) 371-9172

Oasis Design
Santa Barbara, CA
(805) 967-9956

Sustainable Strategies
Concord, MA
(978) 369-9440

Round River Alternatives
Finland, MN
(877) 391-0888

Published on May 1, 2001

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