Building ecologically means living in harmony with a particular place and the systems that exist there. The key is to explore the architecture, materials and methods that will work in your climate. Consider those that support natural heating and cooling, are locally available and will work within your budget, taste and lifestyle. The first step is exploring who and where you are.
What’s your comfort zone?
“Thermal comfort” is about feeling warm in winter and cool in summer. Study the chart on page 63 for appropriate responses to your climate, then look at how your site may influence the available choices. For example, if your property is on a north-facing slope in dense forest, passive solar heating may not be the best strategy no matter what the regional climate is.
All building materials have inherent properties that can support or thwart your thermal comfort strategy. Two important and often misunderstood characteristics are thermal mass and insulation.
Thermal Mass, a material’s capacity to absorb and release heat, is valuable for both heating and cooling. Earthen materials such as stone, adobe, rammed earth and concrete are high in thermal mass. Thermal mass can help moderate your home’s temperature by absorbing heat when it’s hot and releasing it when it’s cool.
Insulation is a material’s ability to slow heat passage—the more insulation, the more slowly heat travels through it. Whereas thermal mass tends to be dense, insulation is light and fluffy; the trapped air pockets do the insulating. Too little insulation means your home will lose heat in winter and gain it in summer.
Earthen homes
Earth, one of the oldest and most widely used building materials, can be highly durable, and it’s available almost everywhere. Earthen walls are usually thick, dense, high in thermal mass and low in insulation value. Because of its clay content, earth absorbs and releases moisture, helping to balance humidity in the home. The cost of building with earth can be dirt cheap if you do it yourself but very expensive if you pay others.
Adobe is made of sand, clay and fibrous material (straw, etc.) that is dried or baked to form bricks, then stacked and mortared to make walls. “You can make an adobe block almost anywhere. It’s so cheap, anybody can do it,” says engineer Bruce King, who is writing an earthen construction building code through his Ecological Building Network.
Rammed Earth is made by compressing a damp mixture of earth, sand, gravel, clay and sometimes a stabilizer (cement, for example) into structural forms that are stripped away after the walls have solidified. It creates a durable, stonelike, monolithic wall. “Rammed earth is a beautiful finished product when installed by experts,” says architect David Easton, who has been championing the material for decades (Rammed Earth Works).
Cob is a mixture of clay, sand, water and straw hand-sculpted into walls without formwork or machinery. It allows for highly organic forms and lends itself to construction parties. There is no building code for cob in the United States, but many cob homes have been built in areas with owner-builder codes. Cob can be relatively inexpensive for DIYers.
Straw building methods
Straw is the stalk that’s left after the seed heads are removed from hay. As an agricultural waste product that also makes good insulation, it’s a natural for an eco-home. But, as with any fibrous material, moisture can be problematic in straw building.
Straw Bale construction has captured hearts worldwide. Relative amateurs can stack the highly insulating walls in one community work day, and the addition of thick earthen plaster adds thermal mass. The system can be inexpensive if you provide your own labor, but poorly shaped bales may require subcontractor work-arounds, increasing costs.
“I love straw,” says architect Kelly Lerner (One World Design), “but if you’re in a very wet climate, you will need to design carefully. Provide a deep roof overhang and keep the walls well above the ground. If you have an exposed site with wind-driven rain, straw bale walls may not be the best option.” Bale walls might not be best for hot, humid environments, where insulation is less valuable than open structures that admit breezes.
Clay-Straw involves packing loose, clay-coated straw into structural forms that are later stripped. As with bale walls, clay-straw needs protection and isn’t appropriate in tropical or driving-rain environments. Long used in Europe, clay-straw techniques have been developed extensively in this country by Robert Laporte and Paula Baker-Laporte (EcoNest).
“Clay-straw balances insulation and thermal mass,” Baker-Laporte notes. “We often put more clay for thermal mass in the south walls of a house and more straw for insulation in the north walls.”
Building with composite materials
These materials require little or no wood; can be assembled by most construction professionals; encounter little resistance from building code officials; create airtight, energy-efficient buildings; and provide flat, planar surfaces. The materials are high in embodied energy (the total energy that goes into creating and delivering a product), but the energy savings over the lifetime of a composite building is even greater. One thing to keep in mind: Concrete composites inhibit moisture passage, so they require careful ventilation strategies to inhibit mold growth.
Structural Insulated Panels (SIPs) consist of a core of rigid foam insulation surrounded by a composite board (usually oriented-strand board, or OSB). Precut in the factory, they’re delivered to the jobsite by truck and lifted into place by a crane. SIPs provide insulation but no thermal mass.
“With SIPs, you’re putting your money into the materials, more than into the labor,” Lerner says. “If you’re trying to support your local economy, using it probably doesn’t make the most sense. But it can be to your benefit if you’re working with a mainstream contractor because it is more systemized.” Rapid assembly makes SIPs cost-competitive with stick-frame construction if the structure isn’t too complex.
Insulating Concrete Forms (ICFs) are interlocking, hollow, modular units—blocks or panels—that are stacked without mortar. Cavities within the rigid foam structures are reinforced with steel, then filled with concrete.
While foam, concrete and steel are all high in embodied energy and are made from nonrenewable resources, King says ICFs provide an efficient thermal system and a good structural system. The addition of recycled fly ash, a byproduct of coal-fired power plants, improves concrete’s environmental attributes by reducing the amount of energy-intensive Portland cement needed. Some types of ICFs, such as Durisol and Faswall, avoid the use of petrochemical-based rigid foam insulation, instead using reclaimed wood fiber in a cement matrix. Rastra incorporates recycled, post-consumer polystyrene, or Styrofoam.
What about wood?
Can stick-frame construction—with walls of two-by-four or two-by-six studs—be green? “We love to work with wood,” engineer Bruce King says. “It’s more adaptable over time than many other materials. But technically, it’s a terrible building material. It splits, it shrinks, bugs eat it, it burns, and it grows mold and fungus.”
Conventional stick-frame construction can be made more eco-friendly by using responsibly harvested wood and reducing waste.
“I’d start with sustainably forested wood,” architect Kelly Lerner says. “Then I’d use advanced framing, a set of details that avoids redundant wood use. Finally, I’d improve on standard insulation by using spray foam to minimize air leakage, by adding rigid insulation on the outside, or by using a staggered-stud wall to minimize heat loss, then filling the cavities with blown-in cellulose or fiberglass insulation.”
Who Are You?
You and your family are central to your domestic ecosystem. Ask yourselves:
1. What do you love to see and feel around you? What materials, forms, colors and textures make you feel really good?
2. What is your budget?
3. What skills do you bring to the project, and how much do you want to be involved in construction?
4. How much maintenance are you willing to do?
5. Do you have any health challenges that might influence your choices?
6. Where do you work? Increasing your commute may offset the benefits of building a new eco-home.
7. How much house do you need? Good design can make a space-efficient house live much larger than its physical footprint.
Where Are You?
Context is everything. Get familiar with the area where you want to build.
1. What kind of climate are you in?
2. What materials are available in your region? Instead of transporting materials to your site from long distances, use local materials that reflect the culture.
3. Does the local building code enforcement allow the materials and methods you prefer?
4. Does anyone in your area know how to build with your favorite materials? If not, it’s possible for you or your builder to attend workshops, but the learning curve may be steep.
5. What is your site like? Consider slope; sun and shade; vegetation; wind; rainfall and drainage; noise; views; privacy; and the local culture.
Should You Remodel or Build New?
For many years, when people thought “eco-home,” they automatically thought “new custom home.” However, staying right where you are and bringing the home you’ve got into greater harmony with nature may be even more earth-friendly. Consider:
• You aren’t destroying unbuilt land. The country eco-homestead comes with a hidden price tag: topsoil torn up and compacted; drainage patterns disturbed; plant and animal communities uprooted; materials and energy consumed in construction; new roads, wells and septic systems—and greenhouse gas emissions from the driving required to get to jobs and stores.
• You’re working with an existing building. It usually takes fewer resources to make your existing home more eco-friendly than it takes to start from scratch. A lot of energy and materials have already been invested in the house you’re in; capitalize on that.
• You can save money. Chances are, you’ll spend less on a remodeling job than you would on a new custom home. And you can modify your home to save money you currently spend on utilities. Furthermore, you can phase your project and pay cash as you go, avoiding the interest on a home-improvement loan.
• You’re probably in an established neighborhood. You are already part of a community, perhaps even with schools, recreation, stores and services nearby.
• You might start a neighborhood revitalization. Investing energy and money into your home improves your neighborhood and may inspire your neighbors to do the same.
• The infrastructure is already in place. The roads, driveway, water and power are already there. The civic investment in generating and distributing power and treating water and waste has already been made; you don’t need to tear up the landscape or your budget to create them.
THERMAL COMFORT STRATEGIES FOR YOUR CLIMATE
from Natural Remodeling for the Not-So-Green House, by Carol Venolia and Kelly Lerner (Lark Books, 2006)
Climate Zone: Cold (Cold winter)
Possible building forms and materials:
• Compact form most efficient
to insulate and heat; narrow forms good for ventilation
• Thermal mass and south glass required for passive solar heating
Vernacular examples:
• Saltbox
• Scandinavian farm courtyards
• Swiss chalets with shallow roofs to retain snow
• Asian and European roofs insulated and weatherproofed with thatch
Climate Zone: Hot Humid (Mild winter and very hot, humid summer)
Possible building forms and materials:
• Narrow form with openings on opposite sides for ventilation
• Light colors reflect strong sunlight
Vernacular examples:
• Elevated pole houses
• Shaded open porches
• Summer kitchens (porch-like kitchen separated from main house)
• Asian and European roofs insulated and weatherproofed with thatch
Climate Zone: Marine Mediterranean (Mild, wet winter and mild to hot, dry summer)
Possible building forms and materials:
• Narrow forms with openings on opposite sides for ventilation
• Light colors reflect strong sunlight
Vernacular examples:
• Greek fishing villages
• Summer kitchens
• Outdoor living
Climate Zone: Mixed Dry (Cold, dry winter and hot, dry summer)
Possible building forms and materials:
• Narrow wings with openings on opposite sides for ventilation
• Courtyards and loggias (Italian open-air corridors) to provide shade
Vernacular examples:
• Courtyard houses
• Earth-sheltered houses
• High-thermal-mass adobe houses
• Summer kitchens
Can’t Decide? Hybridize
Combining some of these materials, using each to its greatest effect, may be the best way to respond to a variety of needs and conditions. It could be just the ticket to have an ICF foundation, a straw bale wall on the north side for insulation, a rammed-earth wall in the middle to soak up the sun’s heat and a SIP or wood-frame wall on the south side to allow for large windows.
