Preserve Existing Vegetation

However it is performed, grading disturbs the soil by alter­ing its natural profile and compacting it. It is undertaken by heavy equipment such as a bulldozer, Bobcat, or backhoe, although fine grading is frequently done by hand. Structures that must be located under a tree should be elevated above the ground on posts to minimize the necessity of excavating into the ground for linear footers. This can create severe slopes that are suscepti­ble to erosion and ruin the natural contours of the ground. Removing existing vegetation diminishes these potential benefits and exposes the site to increased runoff and erosion, higher summer air temperatures, wind, and other related problems. This may require the house being placed so that it is not in the middle of the site or aligned with the property lines. During construction, the sensitive ground below all tree canopies should be fenced off to prevent grading, movement of construction equipment, and the storage of con­struction materials. Additionally, existing vegetation is almost al­ways removed if not disturbed, and drainage patterns are modified. If some of it must be removed, then vegetation that is in poor health, invasive, or a nonnative species or that is simply in the way should be removed first. Existing vegetation fulfills a number of vital environ­mental functions, such as stabilizing soil, retaining soil moisture, cooling summer air temperatures, reducing the impact of wind, removing carbon dioxide and dust parti­cles from the air, and producing oxygen. The topsoil can later be spread back over the graded area to pro­vide a beneficial growing medium. Finally, all topsoil within the graded area should be carefully removed and stockpiled before additional grading takes place. To safeguard trees that are to remain on a site, the ground below the canopy within a tree’s drip line should not be altered or compacted in any manner. Figure 3-1
The ground directly below tree canopies should not be compacted or altered in any way. Minimize Grading
As already mentioned, some site grading or earth moving is a common and necessary activity during construction in order to fit the house and other structures into the landscape, to direct site drainage, or simply for aesthetic objectives. On steep sites, grading can be reduced by using retaining walls up­hill and/or downhill from the house, building the house into the slope with a lower walkout level, or elevating the house above the slope with post-and-beam construc­tion (Figure 3—3; also see “The Sloped Site,” Chapter 13, page 460). Likewise, paved surfaces under trees should be porous or in the form of a deck (also see “The Wooded Site,” Chapter 13, page 456). To minimize grading, the house and site structures should be located on rela­tively level ground or parallel to the contours, as portrayed in Figure 3—2. Vegetation is also a habitat for many birds, animals, and insects. The proposed design should locate all structures, paved areas, and heavily used lawns outside the tree drip line as well.