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Single-Family Ratings Reveal Green Building Trends The Austin Energy Green Building Program (GBP) rates the performance of single-family homes according to a set of Basic Requirements and to the extent that they follow our recommended Green Building Measures. Basic Requirements include:
After the Basic Requirements are met, building
professionals can choose to incorporate Green Building Measures from
five categories:
Each category includes several design, specification, construction, and operation measures worth 1-5 points. A 1-Star rating, considered entry level, must earn a minimum of 40 points; a 3-Star rating earns between 85-114 points; and a 5-Star rating, our highest available rating, earns 150 or more points. Over the past twelve months, the Green Building Program has rated 1,049 single-family homes in the Austin Energy service area. A review of these ratings reveals which green practices are gaining the widest acceptance in the local building industry. And the Most Popular Green Choices Are...
75% of homes have manufactured trusses, use engineered products, or have an alternate roof structure (such as SIPs) in lieu of rafters; 64% use lumber no larger than 2x10; and 42% are framed with finger-jointed studs. Due to the dwindling supply of large timber and the pressure being placed on old growth forests, engineered wood products or non-wood substitutes should be used as often as possible in place of large-dimension lumber. Engineered products are more consistent in quality than solid lumber. They may be made up of smaller pieces of solid lumber, or from small, fast-growing tree species, chips or wood strands, thus saving our old-growth forests. Engineered wood products such as Glulam, Laminated Veneer Lumber, and Parallel Strand Lumber offer many advantages, including:
44% have lawns that are a low-water variety of turf grass. Outdoor water use is the single largest factor contributing to summer water demands. In fact, it accounts for about 60% of total summer water use in Austin. Most people are using that water to keep their turf grass green because many grasses need a great deal of supplemental water to survive our blazing summer sun. However, a number of low-water varieties are available that also thrive better in sunny areas. Once established, Buffalo grass, Bermuda grass, and Zoysia grass (Japonica species) grass typically have these advantages:
More about water conservation>> 63% of homes have three or more fluorescent lights; 53% have no recessed lighting fixtures; and 33% have ceiling fans in all main rooms. Energy use may be the single most important environmental and economic issue to address in home building. The excessive amount of fossil-fuel energy used to heat, cool, light, and power homes results in significant environmental impacts at a local as well as global level, and unnecessarily increases operating and maintenance costs. Using efficient lighting, protecting the integrity of the thermal envelope, and finding low-cost ways to lowering energy use are all good ways to start improving a home’s energy efficiency. New fluorescent lights are readily available and come in just about any color tone. Electronic ballasts insure that they are quiet, start instantly, and have no flicker. The ballast is the part of the light fixture that regulates the amount of power flowing from the electrical circuit to the lamp. Fluorescent bulbs have many advantages over incandescent bulbs:
Not only is installing fluorescent lights the simplest energy efficiency measure available to homeowners, it is also the most cost effective. According to a Lawrence Berkeley National Laboratory study titled The Profitability of Energy Efficiency Upgrades, upgrading to fluorescent lights and fixtures has an incredible 41% rate of return on investment. See our Sustainable Building Sourcebook for more information about lighting>> The Green Building Program previously gave points for not using recessed lighting because early research indicated that installing recessed can lights in insulated ceilings usually punctures the home's thermal envelope, compromising energy efficiency. Newer ICAT (insulated ceiling rated airtight)-type recessed-can fixtures now safely allow direct contact between the can and insulation. This results in less compromise than earlier models, which could not be properly sealed and insulated without risk of fire caused by heat build-up. In our climate, staying cool is a priority, and often a costly one. Ceiling fans are an easy, inexpensive way to be comfortable and save energy. Air moving over the skin increases the evaporation rate of moisture on the skin, which has a cooling effect. A person exposed to moving air will be comfortable at a temperature four to five degrees higher than in still air. In Austin it costs about $800 per cooling season to operate a 4-ton, 12.0-SEER air-conditioner with the thermostat set at 78 degrees. In the breeze of a ceiling fan, a person can be just as comfortable with the thermostat set about 4 or 5 degrees higher. Combining the higher thermostat setting with the use of ceiling fans saves about $150 per cooling season. 27% of rated homes interiors are finished with very low or no VOC paints and 24% of homes have a ventilated or detached garage (or none at all). Health concerns have increased in prominence as homes have become tighter and more energy-efficient. By now, we've all heard that indoor air can be more than 10 times as polluted as outdoor air. The best way to improve indoor conditions is to eliminate or reduce the source of indoor pollutants and contaminants. Products such as paints and lacquers, paint strippers, cleaning supplies, building materials and furnishings, glues and adhesives all contain volatile organic chemicals (VOCs) that easily evaporate when exposed to air. This evaporation continues for a long time in a process known as out-gassing and may cause a variety of health problems, including irritation of the eyes, nose, throat and upper respiratory system, and a weakened immune system. Many of these chemicals also contribute to regional low-level smog and to the global greenhouse effect. The good news is that low-VOC paints are now readily available from all manufacturers at minimal, if any, additional cost. Low-VOC interior paints are a Basic Requirement for a rating. Our standard for paint VOC’s is no greater than 150 grams per liter for latex paint and no greater than 380 grams per liter for oil-based paint. Note that oil-based paints have greater out-gassing than latex at the time of painting, but typically cure more quickly than latex paints, which may out-gas for many months, particularly in warm, humid weather. Be aware that paint labels do not always give you the information you need. Some may say "low-VOC", but have higher levels than this standard. Some labels state only a maximum. In that case, the actual amount is typically much lower. You may have to ask the manufacturer for accurate information. See our Sustainable Building Sourcebook for more information about low-VOC paints>>
Another way to keep a large pollutant source from entering a home is to build the garage away from the home, use an open carport, or have no garage at all. Car exhaust fumes are dangerous and easily trapped in a garage. Even after the car is turned off, fumes are emitted until the engine has cooled. If the garage is attached to the house, fumes can migrate into living space and ductwork, endangering the health and safety of occupants. At a minimum, use passive vent openings in the garage walls or door or, better yet, install an exhaust fan on an automatic timer to exhaust fumes to the outdoors. 49% of homes are within ¼ mile of a transit stop and 37% are within ½ mile of a public park or hike/bike trails. There's not much to love about sprawling, low density, car-dependent construction. Suburban living produces more traffic, more strip malls, more impervious cover, more fertilizer and water use, and costly infrastructure expansion. On the other hand, investing in existing neighborhoods and building more walkable, transit-accessible neighborhoods lowers pollution, improves the local economy, and creates community. Building homes close to public transit stops, retail establishments such as a corner grocery store, and green belts or parks creates easy opportunities to travel short distances without needing to drive. Using public transit eliminates pollution caused by automobiles and eliminates the stress of driving. In some cases, it may eliminate the need for a second automobile. After a day of working or commuting in rush-hour traffic, many people consider it a great convenience to be able to walk to the market instead of getting back into their automobiles and driving miles to a shopping area. In addition, proximity to neighborhood amenities, such as a trail, green belt, or park can raise the quality of life and increase the value of a home significantly. A recreational area provides a place for people to get out in the fresh air, exercise, walk the dog, and meet neighbors. 32% of homes are on smaller than traditional lots. By small, we mean lot size is less than 5,750 sq. ft; however, we are now seeing many subdivisions with smaller lots. Depending on zoning ordinances, there are several neighborhoods in the City of Austin that allow lot sizes between 3,600 and 5,750 sq. ft. It is true that a small lot can pose design challenges and constraints but it can also encourage us to design and construct a space efficient, or not-so-big, home. Building on a small lot also increases density, thereby decreasing the need for sprawling new development and supporting infrastructure. Increased density typically reduces automobile use and resulting pollution, since jobs, mass-transit, "life-support" businesses, and recreational facilities are more likely to be located close by. Moreover, the cost of development infrastructure increases as lot size increases. Easy, Yet Often Unused, Green Choices The ratings review also found that there is room for improvement in a few areas that have a big impact on energy use. Only 2.7% of the houses rated had roof overhangs of 24 inches or more.
Appropriately sized overhangs have two major functions: they block hot summer sun from heating a home and they help protect the home from moisture damage caused by precipitation. At Austin’s latitude, a 24” wide overhang will completely shade most south-facing windows (typically all of a one-story or the top story of a multi-story home) during the midday hours of summer. When properly sized, overhangs block direct summer sunlight from entering windows while allowing heat gain during the winter. Over entries, roof overhangs offer convenient protection during inclement weather and protect the door's finish from moisture around jambs, trim, and thresholds, thereby minimizing the need for maintenance. Overhangs can also enhance a home's visual appeal. Although heat gain through roofs increases the need for air conditioning, only 3% had roofs made of tile, metal or another "cool" material, and just 3.7% had roof radiant barriers. Roof radiant barrier may just need to be marketed more effectively - once homeowners understand the benefits of a radiant barrier system, they will likely insist on having one. A roof radiant barrier is a major defense against the sun's heat. It is especially valuable when cooling equipment and/or ductwork is installed in the attic, as it typically is in Austin. Since duct insulation is a mere R-6 or R-8 (less in older homes) and ducts rarely have a perfect air seal, they gain a lot of attic heat, which mixes with the conditioned air in the ducts and gets distributed to the living space. This means the AC system will have to work longer to provide comfort. Properly installed, roof radiant barrier blocks 95% of the heat radiated down through the roof. With a radiant barrier, attic temperatures will not get any more than about 20% hotter than the outside air. For example, if it's 100 degrees outside, the radiant barrier will keep the attic from getting over about 120 degrees, whereas without a radiant barrier, the attic might get up to about 150-160 degrees. According to the Florida Solar Energy Center, an attic radiant barrier can reduce annual air-conditioning costs by 8-12%. See our Sustainable Building Sourcebook for more information about roofing>> and roof radiant barrier>> Less than 10% of the rated homes had HVAC systems that met the program’s goal of at least 600 square feet per 12,000 Btu/Hour of cooling (this is a requirement for 4- and 5-star rated homes) and only 17% of the rated homes had their duct systems tested for leakage. Houses built today are much tighter and more energy efficient than those built 10 or 20 years ago. They also have far more energy-efficient windows. Given these improvements, and the fact that building code requires HVAC systems to be sized using Manual J, it is down right shocking how many homes continue to have air conditioning systems that are oversized. An oversized AC unit is inefficient because it does not run long enough to do two important things: properly dehumidify the home and meet its rated efficiency. For example, a 13 SEER unit may not actually run more efficiently than an 8 SEER if the unit is too large for the square footage. A correctly-sized unit will run long enough to dehumidify and reach it’s rated efficiency. An added benefit of longer cycles is reduced wear and tear on the blower motor and the compressor (like highway versus city driving). Not only will a correctly-sized unit last longer and be quieter, the homeowner’s electricity bill will actually be lower, because a smaller unit costs less to run than a larger one. It also costs less to buy, maintain and replace. Another important factor of cooling (and energy efficiency) is the integrity of the duct system that distributes heated and cooled air throughout a home. Field surveys have shown that the ducts in most homes leak 20 to 30% (or more!) and, according to Lawrence Berkeley National Laboratory, the rate of return for duct sealing is equal to that of installing fluorescent lighting. Testing is the only way to be sure that ducts have been properly installed and will deliver good performance. The GBP considers performance testing to be a critical measure of the success of a home’s design and construction. Performing the tests and meeting the standards set out in our official Home Performance Testing Form is required for all 4 and 5-star ratings. View a list of local home performance testing companies>> The Green Building Program will continue
to encourage adoption of technologies and building practices
that demonstrate the greatest energy savings – and make
Austin homes more comfortable, more durable, healthier and
more affordable. |
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