More and more, people want a green, environmentally efficient home. In short, a house that’s both healthy for the environment and for its occupants, with the main criteria being energy efficiency, sustainability, durability, and human health.
Consider Your Home’s Energy Efficiency
Energy efficient homes began catching people’s attention in the 1970s, when building science was in its infancy. Many of those original energy efficient houses failed, and the green home of today is light-years ahead of those early models. Building science is far better understood, even if applying it hasn’t quite become mainstream. For example, it’s become understood that controlling air movement through a house (air sealing) is at least as important as insulation. New building codes include airtightness standards and require testing to certify that those standards are met. And insulation standards now require that in many climates simply filling stud bays with fiberglass isn’t enough to meet code. A layer of rigid insulation on the outside is often called for as well.
Still, that’s only the code minimum. “Net-zero” homes, where the house imports zero energy overall, are being built throughout the country. Net-zero requires not only virtually air-tight construction and high levels of insulation, but also mechanical ventilation to ensure indoor air quality and photovoltaic (PV) solar panels to supply power.
There are several programs, such as Passive House and LEED, that can be used to design and rate high-performance homes. Insulation levels in these houses can’t even be accommodated in a regular wall—it takes both inner and outer stud-walls to provide the insulation required for these high-performance homes.
Appliances, including heating, air conditioning, and water heating, contribute a great deal to a house’s energy load. Choosing ones that save energy and water is a definite step in the right direction.
Energy efficiency is much easier to build into a new home than into a remodel. However, it’s definitely possible to tighten up existing homes, add insulation, and add on-site PV.
Sustainability in the Home
For a house to be sustainably built, it must use resources in a way that can continue without depleting them. For example, wood is a sustainable resource because when properly managed, trees grow back at a rate that’s at least as fast as they’re cut down. Not all forestry practices meet this standard, however. Several rating agencies, such as the Forest Stewardship Council (FSC), exist to help you determine where to buy sustainable lumber.
Another consideration is embodied energy, which relates directly to embodied carbon and its global warming potential. Embodied energy is the amount of energy it takes to make a particular product, and embodied carbon is a way to measure the greenhouse gases emitted during manufacture. It can be hard to get this part of green building right. For example, some types of foam insulation seem very green because they are excellent at keeping heat in, but their manufacture emits more greenhouse gases than they are likely to save over their lifespan.
Location plays a part in sustainability as well. Clear-cutting lots from forestland or building on a former farm clearly have an impact on the environment. Building on a vacant lot in town has a lower impact, in obvious ways and in less obvious ones. For example, the long-term environmental effect of having to drive to a job in the city from a former forest or farm is greater than the environmental effect of walking or taking public transit to work from that former vacant city lot.
Your Home’s Durability Factor
A home that doesn’t require much maintenance will probably be greener than one that does. It’s common sense that if a building material can be installed once and last for, say, a century, the environmental impact will be lower than if it’s replaced every 20 years. Choosing durable materials that aren’t susceptible to decay is usually the green thing to do.
It’s not just the material, but how it’s installed that makes it durable. For example, wood siding can be a great choice in terms of durability—or a poor one. For wood siding to hold up, it has to be installed correctly, with its back and cut ends coated with a quality primer/sealer. It will also hold up better if installed over furring strips in a “rainscreen” assembly that allows it to dry. Windows are another example. You can buy the most energy efficient windows made, but if they aren’t installed and flashed correctly, the house around them will rot.
Insulation itself can directly affect a home’s durability. While its ability to control heat loss or gain is an unmitigated good, if it’s installed with poor air sealing, moisture that’s carried into the wall or ceiling by air currents can condense on cold sheathing in the winter and cause rot over time. The reverse can happen in air-conditioned homes in hot climates, where moisture can condense on the backside of the drywall, also leading to rot or mold growth.
It’s more and more important for you and your contractor to understand how insulation and air movement affect a home.
Consider Human Health
Green homes are tight homes with no more ventilation than is required, so indoor air quality (IAQ) takes on a greater importance. Sources of pollution that might have been at acceptable levels in an older, leaky house must be controlled. These sources include volatile organic compounds (VOCs) that come from carpet, paint, engineered lumber, and synthetic fabrics in furniture. Others are combustion byproducts from a gas stove, fireplace, or improperly vented boilers, furnaces, or water heaters. Naturally occurring radon gas is its own category, as are spores arising from mold blooms.
The first step in good IAQ is to minimize pollution sources. Look for low-VOC interior finishes and furniture. Make sure that anything inside the house that emits a flame is properly vented and installed with its own combustion air. Control humidity to control mold..
New homes in radon-prone areas should include a passive ventilation system. Air testing post-construction will determine whether that system needs the addition of a vent fan. This is more expensive to do in existing houses, but worth the money, particularly if you or anyone living in your home is a smoker. Radon in combination with tobacco smoke increases one’s risk of lung cancer significantly.
A properly designed and built green home will have either a heat-recovery ventilator (HRV) or an energy-recovery ventilator (ERV). Both exchange stale indoor air for fresh outside air, passing them through a heat exchanger that minimizes heat or air conditioning losses. ERVs also regulate moisture, which is particularly helpful in areas with variable humidity.
Educate Yourself on the Impact of Green Living
Building green is complex, yet increasingly important. Take the time to educate yourself—or be sure to hire a contractor who is schooled in building science.