The very root of what makes a home green is how effectively it responds to its surrounding environment. You could say that this has defined the primary material pursuit of mankind for all time – building better shelters to keep us warmer, cooler, and drier. Many of the native building techniques employed centuries ago are still reliable in similar climates today, and used as optimal models for environmentally conscious architects. However, since global acceptance of the air conditioner in the 1950s, the benefits of responding to a unique climate have been left by the side of the road.
Considering that homes now account for over 20% of the nation’s annual energy consumption, LEED-H has established guidelines to help home owners get the most out of their heating and cooling, while using as little energy as possible. We’ve reduced the jargon to four basic plans of attack (and added one ourselves) for making sure your home is best suited for both your indoor comfort and the global climate. Here they are:
Illustration of passive solar heating and cooling.
Take advantage of your site
The USGBC’s residential program doesn’t establish requirements for site orientation because every homeowner has a unique building and site. However, the relationship of your home to the sun and wind is paramount in maximizing thermal efficiency. Situating your home (and your rooms, doors and windows) in a way that makes maximum use of sun-paths and wind patterns is called Passive Design, because it allows your house to function without active mechanical heating and cooling. Passive Design is the best and most-obvious way to start a green building, because it improves ventilation, it’s more comfortable than living with constant heating and air-conditioning, it significantly reduces electricity bills, and it reduces greenhouse gas emissions from heating, cooling, mechanical ventilation and lighting.
There are some basic rules you can abide by, such as capturing the breeze for cross ventilation in warmer climates, or deflecting the wind over and around your house in colder ones. The shade of trees not only makes the outdoors more livable for people, but it keeps the mass of your house from absorbing unwanted heat. No trees? Consider porches, pergolas and deep overhangs. Although they won’t shield your roof from the sun, they will help cool walls and create a cooler microclimate around the home. If you’re in a cold climate, turn the broadest side of your home toward the sun. In a warm climate, turn the broadest face away; this principle also applies to windows and any other openings that let in light and heat.
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Aside from taxes and legal documents, there are few subjects that might cause your eyes to glaze over faster than insulation. It’s just the stuff that goes in the wall, right? Well, there’s a lot to be gained both in comfort and money by a little extra knowledge of the subject. Every material has a specific ability to resist heat traveling through it; this is its R-value. Higher value = better insulation. Insulation can range from plain fiberglass batts (R-2.2) to high-tech aerogel based products (R-50). For the residential market, however, there are essentially three forms of insulation: flexible sheets, rigid boards, and spray or blow-in products. Rather than get too in-depth here, you can visit the DOE website for a better breakdown, or check back this week for a more complete discussion on the pros and cons of typical insulation and some of the more environmentally friendly alternatives.
Photo of expanding foam being installed.
Make Your Building Air Tight
Much like carrying water in a strainer, this can be a tricky problem. Half the challenge is in pinpointing just where and how your home is leaking precious climate controlled air. Suspect areas might be around light fixtures (especially recessed,) electrical outlets, attic access openings, old wood floors, cracks in walls, and most often through gaps around windows. With newer homes, an air/moisture barrier such as Tyvek is wrapped around the frame of the house before the exterior cladding goes up. In respect to air leakage, this helps tremendously, but the pros and cons of sealing off structures is a passionate debate within the architectural and building community (think mold – which is a whole other topic of discussion.) Should you desire, there are testing companies which can determine where you might have air leaks by performing a blower door test.
The ubiquitous building wrap.
More than views pass through windows
Your windows can be engineered to block heat in the summer and cold in the winter. Windows let in not only visible light, but infrared and ultraviolet light as well. These forms of radiation hit interior objects and raise their ambient temperature – such as your napping cat, for example. Nowadays, most windows have a factory-applied coating, but you can also pick up IR and UV blocking tints at your local home improvement store. If you’re purchasing windows, be sure to take note of the U-value, which is a measure of how much heat makes it through an assembly (as opposed to an R-value, which is a measure of resistance.) The lower the U-value of your windows, the more insulation they provide.
Due to U.S. energy codes, insulated glass is becoming more common in new construction and renovations (two panes of glass sandwich an airspace, which serves as an insulator). To improve upon this, commercial manufacturers often use a specially type of glass with a coating on the outside called “Low-e” (low-emissivity) glass, and then fill the gap between the double panes with argon gas, which thermally responds slower than air. This might sound a bit excessive to those of us living in warm climates, but it’s very common for new buildings in Germany and Scandinavia to have triple glazing to really help knock out the cold.
So how do you improve your old fashioned single pane windows? Re-caulk them. Replace the weather stripping. Repaint them, filling in any gaps between the glass and the frame. And if that doesn’t help, try storm windows. When placed directly outside an existing window, these light-weight plexiglass assemblies essentially create another barrier between your conditioned air and the outside. They’re generally not very beautiful, but they succeed at creating an insulating air pocket.
Condensation is a good indicator of poorly insulated windows.
Air Conditioning & Machine Efficiency
If you live in a perfect climate and your house was built to utilize passive solar design elements, you might not need air conditioning or heating. Unfortunately, most of us are not so lucky. We live in houses and apartment buildings that can’t be shifted around on site or significantly renovated. With that in mind, the most obvious place to look for improving your home’s energy efficiency is the mechanical systems that provide heating and cooling. First, run out and buy yourself some duct tape (it’s really wonderful stuff) and check to make sure all your ducts are tightly sealed to the grilles and air handler. Try to seal off all potential leaks – putting more of the air you’re paying for into the space that you occupy. The next step comes with a hefty price tag: If you’re in the market for a new central air system, be sure that it has a Seasonal Energy Efficiency Rating (SEER) of 13 or greater. As of 2006, it is illegal to buy anything less efficient anyway. If your twenty-year old system is running at 9 SEER and you upgrade to 13 SEER, you’ll save 30% annually. The greater the SEER, the greater the savings – but you will pay a premium upfront. If you live in a relatively cool location, weigh the cost of a higher SEER rating against the price. You may not get your money back over the lifespan of the unit, but you’ll have that warm fuzzy feeling that you’re doing something a little better for the environment.
Most importantly, make sure it all works together!
Great insulation with drafty windows gets you nowhere. You will defeat your high efficiency air conditioner if you also have large expanses of sun-collecting windows. To test the efficiency of these components, you can conduct a home energy audit to find problem areas.
Or for an easier approach, invest a little research into the EPA’s Energy Star project. This not only encompasses the super-efficient appliances that you’ve seen for sale at Sears, but extends to nationwide building partners that abide by a strict set of guidelines to build high performance, energy efficient homes. And the EPA is always the first place to go for tips on energy efficiency.
And of course, check back next week, where we will have more tips for greening your home!