A Grading and Drainage Plan
Must be submitted with Building Permit applications for all new single family residences and separate accessory structures associated with single family residences.
This plan shall be a separate sheet included with the Building Permit submittal and must be prepared by a qualified licensed engineer, surveyor or architect and be wet-stamped and signed by the same. The plan must comply with the following guidelines and include the information listed below:
- Show appropriate spot elevations of existing and proposed grades, especially at high & low points. Show grades at the four corners of the lot. Also provide spot elevations at the back of sidewalk (on the sidewalk surface) and the gutter .
- No more that one foot of fill may be added to the site.
- Provide minimum slopes of 2% where possible to facilitate site drainage. Show this by proposed elevations. Provide arrows showing the proposed site drainage pattern as a result of the proposed grading .
- Provide a minimum slope of 2% away from the building foundation, as required by the Uniform Building Code. Show this by proposed elevations adjacent to the foundation.
- Design the drainage for su!face runoff without the use of area drains and pipe collection systems.
- The use of dry wells is not allowed in the City of Palo Alto.
- If fill is to be added adjacent to the property lines, grades on neighboring properties will need to be obtained to document any potential impacts to these properties. Site grading shall not impede existing drainage from adjacent properties.
- In no case shall the final grading increase the normal sheet flow onto adjacent properties. [Palo Alto Municipal Code (PAMC) 16.28.270(c)]
- Show where the roof downspouts are located. These downspouts should directed to approved splash blocks (minimum 2 feet long) that deflect the water away from the building. Show (with arrows) how the water is proposed to move away from the splash blocks. [PAMC 16.28.270(b) & Uniform Building Code]
- Direct roof and site drainage to pervious areas of the site. Design the site drainage to take full advantage of these pervious areas.
- Provide proposed grades showing drainage paths on and from impervious areas (driveways, patios, etc.). This surface water must be sheet-flow drained into a pervious area. No catching of this water into area drains may occur.
- If a basement is proposed for the project, a drainage plan for the sub grade drainage system must be included in this plan. This should also include the method of outlet. The acceptable method of the outletting of the subgrade system is at the curb face. Only water from the sub grade system may be outletted at the curb face. No connection of roof water leaders may occur with this outlet.