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
Slopes. The slopes of planted areas should permit easy
removed from roads and parking areas.
maintenance. Turf areas shall have a slope of no more
than 3:1 and no less than 1 percent. A 2 percent mini-
Drains should be provided at the entrance to ramps into
mum slope is desirable. Areas with slopes steeper than
parking structures to minimize the amount of rainwater
3:1 must be planted with ground cover or constructed
run-off into the structure.
with materials specifically designed to control erosion.
Paved areas adjacent to buildings will have a minimum
Slopes steeper than 2:1 are not acceptable. Terracing may
2 percent slope away from the structure to a curb line,
be an appropriate solution for sites with large grade
inlet or drainage way to provide positive drainage of
differentials, as long as access for lawn mowers and other
maintenance equipment is provided.
For planted areas adjacent to buildings, the first 3000 mm
Grading. Existing trees or other plant materials to be
(10 feet) should be sloped away from the structure to
preserved shall be reflected in the grading plan. Where
assure no standing water adjacent to basement walls and
trees are to be preserved, the existing grade within the
foundations (which could be detrimental).
circle of the tree drip line must not be disturbed by
No grading will be performed within the boundaries
regrading or paving. Snow fencing shall be erected at
of any wetlands. For additional information see the GSA
the drip line of the tree to protect existing trees from
PBS Wetlands Impact Management Deskguide available
construction materials or equipment.
The minimum slope for grassy swales and drainage
ways is 1 percent to prevent standing water and muddy
Cut and Fill. From a cost standpoint, it is desirable to
minimize grading overall and to balance cut and fill,
particularly in campus settings.
Slopes for walkways will not exceed 5 percent, unless
unavoidable. Slopes greater than 5 percent may make the
Storm Water Detention. Local code requirements for
construction of special ramps for the disabled necessary.
storm water detention must be followed. Detention of
The maximum cross-slope is 2 percent. Preferably,
storm water on GSA building rooftops is not permitted.
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.
34 F A C I L I T I E S S T A N D A R D S
Revised March 2005 PBS-P100