What is Green Construction or Sustainable Design?
In a sustainable building design, sustainable materials and construction methods are used for building, and the natural energy sources available from your local climate are used to help meet the need for heating, cooling, and lighting. You may be familiar with the terms “Passive Solar” or “Design With Climate.” Sustainable design involves these same principles, as well as the materials used in construction, the gas and fuel infrastructure that supports the building, and more. For this reason, the term “Sustainable Design or Green Construction” is the preferred term used here.
The Benefits Of Green Building
Benefits to building owners:
- More Affordable: A Sustainable Design or green construction can cost slightly less to slightly more than an average building, but from one-third to one-half as much to heat and cool!
- Better Indoor Environment: Stay warm and cozy in winter, and cool and comfortable in summer, largely through natural means. Sustainable Designs are also more spacious, and better-lit than an average building. And for people with sensitivity to indoor air pollutants, they include more environmentally good materials in their construction.
- Help Save The Planet For Future Generations: Reduce air pollution and preserve limited resources for future generations.
- Higher Home Quality and Resale Value: A Sustainable Design is simply a higher quality building because it has been more thoughtfully designed and built to work in harmony with the natural environment. Owners of these buildings enjoy heating and cooling bills a fraction of the size of the counterparts in their community. Resale values tend to be higher than those of comparable buildings, according to several studies conducted by the US Department of Energy. Here is a building design that won’t be obsolete in the next century. Which isn’t very far away if you think about it!
Benefits to Builders and Developers:
- Builders and developers are finding the benefits of Sustainable Design increase a building’s appeal and marketability. New home buyers are increasingly concerned about the quality of a home, and a SunSmart home offers excellent attention to quality. And because of a builder or developer deals with a limited number of models, typically repeated sometimes within a subdivision, the cost to “Design With Climate” is extra low because the costs of a given model can be spread over all of the homes (of that model) built.
- A Sustainable Design gives the seller “the green advantage” by standing out from the competition in a highly competitive market.
Frequently Asked Questions
How Much Can I Save?
For simplicity, let’s use the example of a home. How much you save depends on where you live, the final design of the home, and how well it is built. In general, cost-effective savings for heating and cooling can range from 52% to 87% (see below table for more information).
The Potential For Cost Effective Savings In Residential Buildings
The untapped potential for homes to save energy, cost effectively, is summarized in the table below:
Cost-Effective Savings For Various Home Types
| Electricity | Fuel | Site | Levelized Cost (1990$) | Average Site Cost-Effective Savings ($/MBtu) | |
|---|---|---|---|---|---|
| Multifamily retrofit | |||||
| Fuel heat | 58.7% | 51.1% | 51.7% | 44.4 | 1.48 |
| Electric heat | 62.3% | 69.2% | 68.2% | 128.9 | 6.14 |
| Multifamily new | |||||
| Fuel heat | 51.8% | 54.4% | 54.2% | 73.8 | 2.84 |
| Electric heat | 52.3% | 71.8% | 69.1% | 134.2 | 7.51 |
| Single-family retrofit | |||||
| Gas heat | 56.2% | 65.0% | 64.0% | 209.2 | 3.68 |
| Electric heat | 78.7% | 89.0% | 87.4% | 518.1 | 9.11 |
| Heat pump | 80.9% | 67.8% | 71.2% | 256.9 | 8.93 |
| Single-family new | |||||
| Gas heat | 55.7% | 62.9% | 62.0% | 160.7 | 4.95 |
| Electric heat | 54.9% | 78.4% | 74.6% | 146.2 | 5.27 |
| Heat pump | 67.9% | 69.1% | 68.8% | 204.7 | 11.98 |
| Home Appliances | |||||
| Refrigerator/freezer | 76.1% | — | 76.1% | 25.7 | 10.35 |
| Freezers | 72.6% | — | 72.6% | 21.0 | 10.65 |
| Electric hot water | 64.9% | — | 74.9% | 82.1 | 7.94 |
| Gas hot water | — | 38.7% | 38.7% | 21.0 | 2.41 |
| Lighting | 76.0% | — | 76.0% | 17.7 | 6.83 |
| Clothes washer | 45.8% | — | 45.8% | — | — |
| Electric clothes dryer | 85.7% | — | 85.7% | 29.8 | 9.62 |
| Gas clothes dryer | — | 59.4% | 59.4% | 10.5 | 4.9 |
| Electric oven/cooktop | 38.9% | — | 38.9% | 6.9 | 6.98 |
| Gas oven/cooktop | — | 44.9% | 44.9% | 4.0 | 4.37 |
For example, assuming a typical home in Sacramento, California, you could cut home heating and cooling energy in half simply by facing most of the glass area south, shading windows from the summer sun, and using a better quality window.
A home with the predominant glass facing south is referred to as “Sun-Tempered” design, because the major window area faces south, using the Sun to help Temper the need for heating. The smaller window areas are faced to the north, east and west and south windows are shaded by overhangs to minimize the need for cooling in summer. Figure 1 below shows the difference in performance for the Sacramento CA example.
FIGURE – 1
Typical Home versus “Sun-Tempered” Design
Assumptions behind Figure 1:
- Source: Passive Solar Design Strategies: Guidelines for Home Builders
- 1,500 s.f. Single story house located in Sacramento, CA, USA. Sacramento example was used as Sacramento is a fairly “average” U.S. city regarding climate.
- Miscellaneous assumptions used are noted in the table below. Note that the biggest difference between the “Typical” and “Sun – Tempered” home is in window placement and R-value.
| Roof | Wall | Floor | Glass | AC/hr | West Glass | North Glass | East Glass | South Glass | Heating (Btu/yr-sf) | Cooling (Btu/yr-sf) | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Typical | R-27 | R-15 | R-18 | R-0.9 | 0.75 | 45 sf | 45 sf | 45 sf | 45 sf | 23,390 | 13,717 |
| South | R-30 | R-15 | R-19 | R-1.8 | 0.72 | 30 sf | 40 sf | 40 sf | 100 sf | 14,399 | 5,409 |
Figure 1 helps illustrate the savings possible from simple, cost-effective efficiency measures combined with (predominately) south-facing glass. But this is just the first step in Sustainable Design. Further savings are possible by adding additional south-facing glass and some heat-storing “thermal mass.” Figure 2 below shows the difference in performance.
FIGURE – 2
Typical Home versus “Direct Gain” Design
Assumptions behind Figure 2:
- Source: Passive Solar Design Strategies: Guidelines for Home Builders
- 1,500 s.f. Single story house located in Sacramento, CA, USA. Sacramento example was used as Sacramento is a fairly “average” U.S. city regarding climate.
- Miscellaneous assumptions used are noted in the table below. The south facing windows, insulation, and air-tightness are increased, and thermal mass is added. There are a variety of ways to add “Thermal Mass” to a home, including plaster walls, tiled surfaces, double sheetrock, and interior concrete walls (low height walls are typically used to avoid the high cost of tall walls due to structural requirements in earthquake zones).
| Roof | Wall | Floor | Glass | AC/hr | West Glass | North Glass | East Glass | South Glass | Heating (Btu/yr-sf) | Cooling (Btu/yr-sf) | Thermal Mass | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Typical | R-27 | R-15 | R-18 | R-0.9 | 0.75 | 45 sf | 45 sf | 45 sf | 45 sf | 23,390 | 13,717 | 0 sf |
| South | R-35 | R-19 | R-23 | R-1.8 | 0.72 | 30 sf | 40 sf | 40 sf | 180 sf | 9,671 | 2,678 | 450 sf |
How Much Does It Cost?
Assigning an “added value” price tag to Sustainable Design is not easy. They can cost much less or much more than a “comparable home” in the same area. It all depends on the (original or base) home design, the climate, and the available materials, expertise, and cost of same.
The available data show that most design elements are low-cost and require only small changes in a builder’s design. The modest increase can be attributed to higher quality windows, shading, new tiled floor or some other heat storage material such as plaster, and a ventilation system.
Energy design services for a $300,000 home can range from $160 for a few hours of professional consulting time to $2,000 (less than 1% of contracted construction cost), or more, for complete energy services. “Complete services” might include, for example, consultation with your designer, an energy and economic analysis of your energy alternatives and the design and specification of the heating, cooling, and water heating systems. The total cost of the recommended options, including the professional services that lead you to those alternatives will, with rare exception, provide a return on investment of 10%-20% or higher (the stock market performance over the past 30 years is approximately 10%).
Maintenance and operation costs for a Sustainable Design are negligible. On the cost savings side, they will have smaller heating and cooling systems, which helps pay for other improvements. In some cases, the cooling system can be eliminated with the cost savings going to pay for the necessary efficiency improvements (to “make it so”). It all depends on the particular home design you begin with, the location, and how much the homeowner must “interact” with the home (such as opening and closing windows instead of purchasing a fan).
Do “Sustainable Designs” Have To Look “Unusual”?
The sustainable design lends itself to virtually all types of building styles and has been practiced for centuries in many cultures around the globe. The ancient Anasazi Indians, Mesopotamians, ancient Anatolians and ancient Greeks built their homes facing south much like the historic American buildings called New England “Salt Boxes” to benefit from the sunbeams all day long, to help families stay warm in cold winter days. By the arrival of fossil fuel heating and refrigeration cooling, people lost interest in “design with climate” approach.
Some solar homes may appear unusual because of the shape and design, the arrangement of windows used, but it does not necessarily need to be that way. All types of design can benefit from sustainable design practices without sacrificing appearance. It’s the designer that determines how the building will look.
For example, the “sun-tempered” design, whose energy performance is shown in figure 1, has its window area distributed similarly to many average tract homes. With a tract home, a 60/20/10/10 percent breakdown of the window is used on exterior wall “facets” (back/front/left side/right side respectively) whereas the “sun-tempered” home example is 40/24/12/24. In either case, the appearance of the windows on these homes can accommodate just about any architectural style.
“When I am working on a problem, I never think about beauty. I think how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong.” R. Buckminster Fuller
How the “Thermal Mass” is designed into the home can also create an appearance issue, but it doesn’t need to be that way. There are a wide variety of thermal storage mass wall and floor materials commonly available, such as “hard-wall” plaster. In the case of plaster, it can be used on walls or ceilings with no visible impact and can even save on wall finishing time compared to conventional sheetrock in some locations.
Why Don’t More Home Builders Use Sustainable Design?
Builders identify two barriers to orienting buildings to the south: cost and adaptability of certain building lots. However, both of these barriers are easily overcome.
Orientation is a matter of planning. Many builders and developers have found that the cost to reposition the building is quite small. Even when home plans are changed to add more windows to the south side of a home, they are windows that the builder planned to include in the home anyway, so just shifting them adds little or nothing to the overall cost.
Physical barriers to orienting a home toward the sun, such as steep slopes, conflicts with the direction of a view or existing street patterns, can frequently be overcome with proper design. Most building lots are adaptable to solar site design. A little extra effort brings valuable benefits to both the home buyer and the builder by adding another dimension to a home’s comfort, efficiency, value, and marketability. With resources available to help in planning solar subdivisions, there’s no reason not to design with climate!
How Does One Obtain a “Sustainable Design?”
Generally speaking, the best way is to use a professional. They use advanced technology to find the most cost-effective mix of features. In a home designed with the climate, the home’s energy and economic consequences can be evaluated, before a single nail is driven, with a “Building Simulation” computer software package. Most of the modern computer design tools have been validated against real buildings and other such tests to assure the relative accuracy of results and include features like heating/cooling equipment sizing and economic analysis.
But most advanced “Building Simulation” design tools are not likely to be very useful to non-professionals. And one of the most important things these tools can’t provide – an evolving knowledge of what materials and services are available locally and at what cost – may also escape most non-professionals. For these reasons and more, consider professional assistance.
What Are The Basics Of “Design With Climate?”
First, place the home’s front face on the building site in a way that the home takes full advantage of the sun’s beams and the natural heat. By facing the long side of a home to the south (north in the southern hemisphere) and the short sides to the east and west, the building can capture more solar heat in winter and more efficiently block solar heat in the summer. Although it is best to face most of the windows due south, they can face up to 15 degrees away to the east or west without much loss in energy savings.
Placing most of the windows on the home’s south side will expose them to the low winter sun. Carefully designed overhangs and other features can be used to shade them from the high summer sun. Window areas on the east and west should be much lower, because the wall is smaller, and they will cause fewer problems during the summer. Carefully balanced window locations can enhance architectural appeal, balancing natural light, view, and comfort.
There are some physical constraints, such as existing street patterns, shading from buildings and trees, and steep lots, when orienting a home on a lot. However, with fifteen degrees of flexibility, it is much easier for builders to place the home on the lot in a “south-facing direction.”
“Design With Climate” concepts are applied most in a new building where they can be incorporated into the original design. However, existing buildings can be modified or retrofitted to collect and store solar heat passively.
How Does “Direct Gain” Design Work?
In a “Direct Gain” design, the living space is warmed – direct – with heat gain from the sun. A sunspace is a typical example of “indirect gain” because heat indirectly enters the living space. There are two:
Sun-Tempering:
The term “sun-tempering” is applied to a house or other building that collects solar radiation through large south-facing windows but does not have additional “thermal storage mass” for long term heat storage.
The south window area must be sized carefully because without storage mass there is the possibility that the living space can overheat during the day. Sun-tempering is used when the goal is to reduce the use of the conventional furnace while the sun shines; the furnace will probably be needed at night. Sun-tempering may be particularly suited to buildings that are used primarily during the day.
Direct Gain Solar Design:
Direct Gain solar design, in full form, uses both solar (directly gained) and additional thermal storage mass for long term heat storage. With the thermal storage mass distributed throughout the home, it works very well for homes in climates with significant heating needs, cooling needs, or both. How it works is relatively straightforward:
Winter: Capture the sun’s energy by day – Hold onto it through the night
On a cold winter day, sunlight enters the house through a large area of south-facing windows and strikes “thermal storage mass” in walls and floor surfaces. Here, the solar energy is absorbed and stored for the evening (see Winter Day, below).
During a cold winter night, the energy stored during the day is naturally released, as the home begins to cool in response to dropping outdoor air temperatures, providing a portion of the energy needed to heat the home. Because the heat collected and stored on the walls and floor surfaces make these surfaces warmer than in a typical home, a passive solar home is more comfortable as well (see Winter Night operation, below).
Summer: Capture the cool night climate – Block the hot daytime climate
To naturally cool the home, cool night air can be vented into the home to absorb and carry away the heat gained from the day. This also helps “pre-cool” the home for the following day. The night air may be introduced either naturally, through open windows, or by a whole house fan system. A roof overhang, awning or other device is used to shade windows from the hot summer sun during the day to make the most of this night cooling. Other measures, such as light colored exterior surfaces, insulation, and radiant barriers may also be used to increase the effectiveness of night cooling further. In some cases, natural night cooling is so efficient that no air conditioning is needed at all!
It is important to install the correct amount of thermal storage material about south facing glass. If there is not a balanced amount of heat storage, large temperature swings will occur in the heated space, and problems with overheating may also occur. The ratio of thermal mass to glazing varies with the type of system, type of storage, climatic conditions, and the fraction of heat to be supplied by solar. Likewise, sufficient summer shading and other “heat source” controls are needed to maintain cool indoor temperatures through a hot summer day using natural cooling alone. Professional assistance is recommended for getting the best results.
How well does a Sunspace work?
Known by many names – solar room, greenhouse, solarium – the sunspace has been a popular approach to solar space heating. A sunspace can be created as part of new construction or as an addition to an older building. Although not provided with backup heating or cooling during extremely hot or cold weather, due to cost, they are used as extended living space when comfortable.
Solar heat is collected through the sunspace glazing. The distribution of heat from a sunspace can be accomplished in a variety of ways. A masonry wall between the sunspace and the living space can collect and store solar energy for nighttime heating. Heat can also be moved from the sunspace into the house with the help of a small fan or blower or circulated into the home by just opening connecting windows and doors between the sunspace and the house. A sunspace also provides a “buffer zone” for the house. It will help cut heat loss, and it adds another space to the home, a space that can be used for a variety of purposes, including plants.
Sunspaces are used primarily as a passive heating device since they do not provide any cooling benefit. Sun spaces with roof glass may add to a home’s cooling needs. The heat storage in a sunspace is more concentrated (smaller area & thicker) than distributed (larger area and thinner as in Direct Gain). Sunspaces are typically considered for climates where cooling is not a problem.
Other Options: The use of one approach to passive solar heating does not preclude the use of another in the same building. It is not unusual for different approaches to overlap. An attached sunspace, for instance, can be combined with direct gain windows in the south-facing wall. The variety of passive options leaves plenty of room for the individual tastes of homeowners and the market considerations of homebuilders.