Tennessee Valley Authority Economic Development
Sustainable Development Guide
Section 5: Building Design and Placement
Design principles
Configure buildings to reduce impervious roof area, energy use, and operational expenses
Place buildings to maximize the benefits from solar energy
Configure buildings to reduce impervious roof area, energy use, and operational expenses
When the footprint of a building is reduced, the amount of imperviousness of the site is reduced also. This directly reduces its impact on the watershed. When the building’s volume is reduced, the amount of energy needed to heat and cool it is lowered, and operations and maintenance costs also go down.
Connect roof drains to vegetative conveyances to reduce storm-water velocity and improve water quality. Promote “green roofs” for detention and storm-water treatment.
Rooftop greening has become an increasingly common practice in Europe and other parts of the world. This practice involves growing vegetation on the roofs of businesses and homes to intercept rainfall and promote evaporation rather than runoff.
Roofs cover a significant portion of the urban landscape and generate large volumes of storm-water runoff. Green roofs are vegetated roofs. They are specially designed with extra support and special membranes to be covered with soil and plants. They absorb and slowly release excess rainwater and provide greatly increased insulation value. While initially more expensive to construct, this is offset by a much greater life expectancy for the roof and reduced energy needs for heating and cooling the building.
The benefits extend beyond water quality. Green roofs conserve energy by keeping roofs cool in the summer and insulated in the winter. They save money by reducing the land area needed for storm-water management, which is especially important in densely populated areas with high real estate values, and by extending the life of a roof. Vegetated cover reduces wear caused by temperature-related expansion and contraction and protects the roof from ultraviolet radiation and cold winds that break down traditional roofing materials.
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| Fencing Academy of Philadelphia vegetated roof cover. |
Roof gardens typically have a 50-year life expectancy. They cost between $5 and $12 per square foot to install, plus an additional $10 to $20 for roofs that need waterproofing. Green roofs also have substantial aesthetic benefits. They make a building or cityscape more pleasant to look at, and some vegetated roofs, known as "intensive" green roofs, are designed to be accessible and used as park and building amenities. (1) [53]
Place buildings to maximize the benefits from solar energy
Solar accessibility should be a part of site analysis. Careful site selection and building placement provide opportunities for optimal daylight and solar utilization.
Some things to consider when determining if solar energy is a potential for your site
- Does the building receive unobstructed solar radiation and sunshine between the hours of 9 a.m. and 3 p.m.?
- Are there major sky obstructions such as geologic features, trees, or adjacent buildings?
- Does the site allow an elongated east-west configuration as discussed below. (2) [30]
Sunlight can provide ample heat and light and induce summertime ventilation on the well-designed home. Passive solar design can reduce heating and cooling energy bills, increase spatial vitality, and improve comfort. The inherently flexible passive solar design typically provides energy benefits with low maintenance risks over the life of the building.
The south side of the building must be oriented to within 30 degrees of due south. Passive solar design strategies vary by building location and regional climate, but the basic techniques remain the same: maximize solar heat gain in the winter and minimize it in summer.
Specific techniques include the following
- Start by using energy-efficient design strategies.
- Orient the building with the long axis running east-west to increase the potential use of daylight. An elongated building that has its major axis running east-west will capture winter solar gain and reduce unwanted summer sun that strikes the east- and west-facing surfaces.
- Select, orient, and size windows to optimize winter heat gain and minimize summer heat gain for the specific climate. Consider selecting different glazing for different sides of the building. Exposed east- and west- facing glass should be avoided because it will cause excessive summer cooling loads.
- South-facing glass should incorporate properly sized overhangs that limit radiation in warmer months and allow solar gain in winter.
- Add thermal mass in walls or floors for heat storage.
- Use natural ventilation to reduce or eliminate cooling needs.
- Use daylight to provide natural lighting. (3) (27)
- Give the building a compact shape to minimize losses and gains through the skin of the building. (4) [30]
Promote clustering of industrial parks, ride-sharing, and public transportation to reduce vehicle use
As stated before, cluster development, also known as open space design, concentrates density on one portion of a site in exchange for less density in other places.
Urban sprawl, or low-density development, is increasingly recognized as a primary factor in reducing the quality of streams, lakes, and wetlands. Often communities accept cookie-cutter plans that disregard the unique qualities of the site and the social and environmental impacts of the development. A growing body of research clearly documents that the creation of impervious cover accompanying new growth (roads, driveways, parking lots, building footprints) causes a predicable and profound decline in critical elements of aquatic ecosystems. Many studies have shown the quality of streams, lakes and wetlands deteriorates substantially when the percent imperviousness of the watershed reaches 10 to 20 percent. Concentrating development in urban areas also helps to preserve the functions in smaller watersheds at a region’s edge. (5) [68]
In areas undergoing new development or redevelopment, the most effective method of controlling impacts from storm-water discharges is to limit the amount of rainfall that is converted to runoff. By utilizing site design techniques that incorporate onsite storage and infiltration and reduce the amount of directly connected impervious surfaces, the runoff generated from a site can be significantly reduced. This can reduce the necessity for traditional structural approaches to managing runoff. There are a number of practices that can be used. However, onsite infiltration can be limited in certain areas due to factors such as slope, depth to the water table, and geologic conditions. (6) [1]
Why is it so hard to actually implement better site design in so many communities? The major reason is the outdated development rules that collectively shape how development happens—the bewildering mix of subdivision codes, zoning regulations, parking and street standards, and other regulations. Few developers are willing to experiment with better site design as they are not inclined to invest in something that may not be approved.
Changing local development rules is not easy. Progress towards better site development will require local governments to examine current practices in their communities and satisfy a broad range of concerns, such as how the changes will impact the cost of development, local liability, property values, public safety, and a host of other factors. Advocates of better site design are going to have to answer some hard questions from fire chiefs, lawyers, traffic engineers, developers, and many others in the community, such as:
- Will the proposed changes make it more difficult to park?
- Will they lengthen response times for emergency vehicles?
- Will they heighten risks to the community’s children?
- Will they increase the cost of development?
Real change can happen only when these questions are thoroughly addressed and community concerns are fully satisfied. A new movement may make it easier. Developers, water quality managers, and planners are reforming land development rules to permit better site development. Recently, transportation, public works, safety, planning, and engineering organizations that strongly influenced past development rules participated in a national site planning roundtable and developed a nationally accepted set of model principles that foster better site development.
Based on the principles resulting from the national roundtable, the Center for Watershed Protection has produced an approach for communities that want to change the way they are developing land. Known as a local site planning roundtable, the process can be long, arduous, and even contentious, but it can be a very wise investment, given the many economic, environmental, and quality of life benefits that it can produce. (7)