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Site Design

Site design and site planning have a large impact on how energy-efficient a home will be. The sun is the main source of heat in all homes. By looking at how houses receive sunlight, site planning can help optimize how much solar energy is available to heat a house and how much heat must be removed with air conditioning.

Lot Orientation

As planners map out lots and roads, they should carefully consider the relationship between buildings and the sun. They plan roads to allow houses to take advantage of great views, or to work around hillsides and other landscape features. Site planning must also consider how road design, lot lines, and orientation will influence the way that houses face the sun.

Lot lines and roads should be situated to minimize home exposure to east and west. These orientations provide the greatest solar heat gains. Subdivisions should be planned so that the longer sides of the houses face north or south. Single-family homes tend to have longer fronts and backs and narrower sides, so lots facing north or south are preferred. Streets should be positioned in an east-west direction. The Florida Solar Energy Center estimates that proper orientation can result in substantial savings of heating and cooling costs, depending on specific site conditions and house designs. Highly efficient houses, especially those with good windows, are less dependent on orientation and shading to manage solar gain.

Shading is not nearly as important when windows with a low solar heat gain coefficient (i.e., SHGC of 0.35 or less) are used. Using a low-solar-gain low-emissivity coating results in great energy cost reductions for all conditions, even with no shading. This is because the glazing itself provides the necessary control of solar radiation, so these additional measures become less important in terms of energy use. The Efficient Windows Collaborative Web site provides a description of the interactions between window performance and shading.

Lot orientation is especially important if a home includes solar heating or electric generation systems. Inexpensive tools can help assess how much solar energy will be blocked by obstacles on a particular site.

In addition to helping manage the sun and providing a marketing advantage, proper street design can reduce the environmental impacts of runoff, encourage walking and bicycling, and discourage speeding by through-traffic.

Subdivision planning can also help homes to gain cooling benefits from the wind. Houses and other buildings that are tightly packed may create a wake in the wind that is four to five times the buildings' eave height.

Curved streets and staggered lots can assist in preventing wind disturbance. Trees can help to keep breezes cool. Taking advantage of breezes will reduce cooling costs. Wind conditions at any individual site may differ considerably from regional averages. Local geography such as ocean beaches, lakes, fields, golf courses, parks, and malls can influence local breezes.

Shade Trees

Truly cool neighborhoods have trees. A study in Florida showed that a subdivision with mature trees had cooler outside air with less wind velocity than a nearby development without trees (Viera et al. 2000). The development with a tree canopy had peak afternoon temperatures during July that were 1.1 to 3.1°F ( ± 0.7°F) cooler than the site without trees. The total effect of shading, lower summer air temperature, and reduced wind speed can reduce cooling costs by 5 to 10 percent (McPherson et al. 1994).

Trees also bring value by providing shade. It is far better to prevent solar energy from reaching a house in summer than to attempt to manage it once it enters. Shade trees block summer sunlight before it strikes windows, walls, and roofs, dissipating absorbed heat to the air where it can be carried away by the breeze. If photovoltaic or water heating systems will be added, trees must be placed not to shade these systems. Deciduous trees work best for letting the sun shine through in winter but providing shade in summer.

Tree preservation brings many benefits, one of which is increased salability. Native trees are most beneficial to the environment. The National Association of Home Builders (NAHB) reports in its survey of buyers, What 21st Century Homes Buyers Want, that more than 80 percent of respondents in the South rated trees as essential or desirable (2002b, page 61). In 1992, the Florida Solar Energy Center (FSEC) estimated that a treed lot may increase the value of a home by as much as 20 percent. American Forests and the NAHB (1995) found that mature trees may add from $3,000 to $15,000 to the value of a residential lot.

Trees are most effective when located next to windows, walls, and air conditioners, and when located on the side of the home receiving the most solar exposure. Shade to the southwest and west is especially important for blocking peak solar gain in the summer in late afternoon. Trees more than 35 feet from the structure are probably too far away for shade.

Site Grading

Proper site grading directs surface water away from building foundations and walls. Moving moisture away from a building is critical to maintaining structural integrity. Grading and landscaping should be planned for movement of building runoff away from the home and its foundation, with roof drainage directed at least 3 feet beyond the building, and a surface grade of at least 5 percent maintained for at least 10 feet around and away from the entire structure. The steeper the slope away from the building, the better the water will drain. Floor levels should always be above the surrounding grade. Basement floors should be higher than the surrounding drainage system. Driveways, garage slabs, patios, stoops, and walkways should drain away from the structure.

Landscaping

Landscaping is a critical element to the marketability of a house. Plants must be placed so they do not interfere with visual inspections of termite access. Plantings also can be used to shade foundations and reduce cooling loads.

Plantings should be held back as much as 3 feet and no less than 18 inches from the finished structure, with any supporting irrigation directed away from the finished structure. Plantings may be selected to shade the foundation edge, especially on the southwest corner of the structure. Choosing drought-tolerant plantings results in less irrigation and less chance for irrigation water to create a moisture problem in the house. Decorative ground cover—mulch or pea stone, for example—should be thinned to no more than 2 inches for the first 18 inches from the finished structure.

Sustainable Site Development

Features that help to conserve the natural environment of a home or development site include:

• Orienting lots to best manage energy and light from the sun.
• Planning land use that preserves the natural environment and minimizes disturbance.
• Designing the site to minimize erosion, paved surfaces, and runoff.
• Preserving and protecting trees and natural vegetation.
• Conserving water indoors and out.
• Designing energy efficiency into houses.
• Selecting materials that are durable and recyclable, or created from recycled products, and considering the energy that goes into making products.
• Recycling construction materials and reducing on-site waste.