SAMPLE IMPERVIOUS SURFACE CALCULATION

San Mateo County

Planning and Building Department

SAMPLE IMPERVIOUS SURFACE CALCULATION

SAMPLE 10,000 SF LOT PROJECT

1 2

2,100 ft?

2

900 ft?

5 2

3 4

EXISTING PLAN (E)

PROPOSED PLAN

1 7,000 ft? (E) Pervious Area [e.g., landscaping, pervious pavers, green roofs] 2 3,000 ft? (E) Impervious Area [e.g., roofs, sidewalks, patios, paths, driveways, decks] 3 500 ft? (E) Impervious replaced by new Impervious 4 2,000 ft? (E) Pervious replaced by new Impervious 5 900 ft? (E) Impervious replaced by new Pervious

Existing Conditions (Pre-Project) A. Total Area of Parcel B. Existing Pervious Area C. Existing Impervious Area D. Existing % Impervious

IMPERVIOUS AREA SUMMARY

Proposed Changes E. Existing Impervious Area to be Retained F. Existing Impervious Area to be Replaced w/New Impervious Area G. Existing Pervious Area to be Replaced w/New Impervious Area H. New Impervious Area (Created and/or Replaced) I. Existing Impervious Area to Be Replaced w/New Pervious Area J. Net Change in Impervious Area

*Drainage from this area is required to be detained/retained on-site

Proposed Conditions (Post-Project) K. Proposed Pervious Area L. Proposed Impervious Area*

*Verify that K + L = A

M. Proposed % Impervious

? 100

+ - - + ? 100

A. 10,000 ft? B. 7,000 ft? C. 3,000 ft? D. 30 %

E. 1,600 ft2 F. 500 ft? G. 2,000 ft? H. 2,500 ft? I. 900 ft? J. 1,100 ft?

K. 5,900 ft? L. 4,100 ft?

M. 41 %

2-20-2019/v.1

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