Slopes. The slopes of planted areas should permit easy maintenance. Turf areas shall have a slope of no more than 3:1 and no less than 1 percent. A 2 percent minimum slope is desirable. Areas with slopes steeper than 3:1 must be planted with ground cover or constructed with materials specifically designed to control erosion. Slopes steeper than 2:1 are not acceptable. Terracing may be an appropriate solution for sites with large grade differentials, as long as access for lawn mowers and other maintenance equipment is provided.
Grading. Existing trees or other plant materials to be preserved shall be reflected in the grading plan. Where trees are to be preserved, the existing grade within the circle of the tree drip line must not be disturbed by regrading or paving. Snow fencing shall be erected at the drip line of the tree to protect existing trees from construction materials or equipment.
The minimum slope for grassy swales and drainage ways is 1 percent to prevent standing water and muddy conditions.
Slopes for walkways will not exceed 5 percent, unless unavoidable. Slopes greater than 5 percent may make the construction of special ramps for the disabled necessary. The maximum cross-slope is 2 percent. Preferably, walkways should not have steps. Where steps are necessary, cheek walls enclosing the risers and treads should be used to make a smooth transition to planted areas on the sides of the steps if grass is planted.
Parking areas or large entrance plazas should have slopes of 1 percent minimum and 5 percent maximum. Drives within parking lots should not be crowned. In areas with snowfall, provisions should be made for piling snow removed from roads and parking areas.
Drains should be provided at the entrance to ramps into parking structures to minimize the amount of rainwater run-off into the structure.
Paved areas adjacent to buildings will have a minimum 2 percent slope away from the structure to a curb line, inlet or drainage way to provide positive drainage of surface water.
For planted areas adjacent to buildings, the first 3000 mm (10 feet) should be sloped away from the structure to assure no standing water adjacent to basement walls and foundations (which could be detrimental).
Cut and Fill. From a cost standpoint, it is desirable to minimize grading overall and to balance cut and fill, particularly in campus settings.
Grading and Flood Plains. No buildings shall be built within the 100 year flood plain. Exceptions will be approved by the PBS Assistant Commissioner for Portfolio Management and by the Chief Architect. If the building location is approved, mechanical and electrical equipment rooms must be located 1500 mm (5 feet) above the level of the 100 year flood plain.
No grading will be performed within the boundaries of any wetland.
Storm Water Detention. Local code requirements for storm water detention must be followed. Detention of storm water on GSA building rooftops is not permitted.