Source: https://www.newavenuehomes.com/permit-rules-for-a-master-bedroom-master-bath-remodel-and-guest-house-addition-in-san-mateo-ca/
Timestamp: 2019-04-23 13:59:59+00:00

Document:
Permits are always complicated in San Mateo, CA. A large remodel that is approximately halfway through counstruction as of October 2016 started with permit research in 2014.
The detailed planning research that a New Avenue partner architect completed in 2014 is shared here for research purposes. We can guarantee your project will be different.
A; The accessory building must be can not occupy more than 50% of a required rear yard. It must be separated from the main house by at least 4′.
A: yes…through a complicated formula: Sec 27.04.200 (4) San Mateo Zoning Code: (c) Measurement, for single family dwellings in R1 zoning districts, shall include the following: (1) All area enclosed within the walls of the principal structure (measured from the outside perimeter of said walls). (2) The area of all accessory structures, including garages, carports, and storage sheds, and covered patios, porches (excepting covered porches of up to 100 square feet), and other similar structures that are enclosed on three or more sides. (3) Any interior space where the vertical distance between the upper surface of the floor and the floor above is 15 feet or more shall be counted as twice the floor area. If there is no floor above the space, then the distance shall be measured to the underside of the roof structure. (4) Attic space is considered floor area when area “A” is at least 50% of areas “A” and “B” combined in the following plan-view diagram: Area “B” (ceiling height between 5’ and 7’ 6″) Area “A” (ceiling height 7’ 6″ or greater) Area “B” (ceiling height between 5’ and 7’ 6″) (5) A basement is considered floor area and a story when more than one half the area of the outermost basement walls are above finished or pre-existing grade (whichever is lower) and the surface of the finished floor level above is either: (A) More than 4 feet above finished or pre-existing grade (whichever is lower) for more than fifty percent of the total perimeter, or (B) More than 12 feet above finished or pre-existing grade (whichever is lower) at any point. (d) Off-Street Parking and Loading. Floor area for determining off-street parking and loading requirements as contained in Chapter 27.64, shall be based on physical floor space and shall not include the following: (1) Storage areas except for areas located within selling or working space such as counters, racks, and closets; (2) Utility areas including, but not limited to, elevator shafts, telephone switching rooms, stairwells, rest rooms, and heating and cooling rooms; (3) Accessory facilities to be used only by employees of the principal uses; (4) Off-street parking and loading facilities, including aisles, ramps, and maneuvering space; (5) Basement, attic, or mezzanine floor area other than area devoted to retailing activities, to the production of processing of goods, or to business or professional offices. (6) Floor area designated for day care centers accessory to and intended to serve a multi-family, commercial, office or manufacturing use. Such floor area may be located within the primary structure or may be in a freestanding structure accessory to the primary structure. (7) Floor area computed for building volume. Additional parking shall be required in the event of change of excluded floor areas into uses generating parking. (e) Interpretation. All interpretations of floor area shall be subject to the review and approval of the Zoning Administrator. (f) No change in the definition or calculation of floor area, except to the extent that the City Council expressly states that the change allows greater floor area, shall be construed to authorize an expansion of the allowable floor area of a building or structure, whether pursuant to Chapter 27.72 or otherwise. (Ord. 2009-7 § 5, 2009; Ord. 2002-10 § 1; Ord. 2001-36 § 2; Ord. 2000-2 § 1, 2000; Ord. 1995-15 § 2, 1995; Ord. 1994-2 § 3 & 4, 1994; Ord. 1992-15 § 4, 1992; Ord. 1989-18 § 1, 1989; Ord. 1985-17 § 9, 1985; Ord. 1982-22 § 9, 1982; Ord. 1981-27 § 12, 1981; Ord. 1979-26 § 2, 1979; Ord. 1978-18 § 25, 1978: prior code § 142.01(66,67,68)).
Q: Can the Accessory Dwelling have two floors?
Q: Can the Accessory Dwelling have a loft, mezzanine, open storage, closed storage, and/or attic?
What is the rear setback?
15′ for single storey, but see exceptions for 27.18.100 (c): 27.18.090 REAR YARD. A rear yard of not less than fifteen (15) feet shall be provided; a rear yard not less than twenty-five (25) feet shall be provided for new construction above a single story. (Ord. 1992-16 § 10 (part), 1992; Ord. 1985-17 § 28, 1985; Ord. 1978-18 § 84, 1978: prior code § 146.02(G)(6)). image006.jpg image007.jpg 27.18.100 STRUCTURES AND BUILDING PROJECTIONS IN REQUIRED YARDS. (a) The following structures, building projections and features shall be permitted in all yards: (1) Arbors and trellises, having a maximum height of eight (8) feet, except in no case shall any such structure be used to cover driveways located in required setbacks in the front 2/3 of the property; (2) Awnings, canopies and covered patios, having a maximum height of eight (8) feet; (3) Basements completely below grade; (4) Eaves, projecting a maximum of three (3) feet of fifty percent (50%) of the required yard width, whichever is less; (5) Chimneys, solariums, greenhouse windows and oriel bay windows projecting two (2) feet or less into the yard, provided that the outside face of the projections shall be at least three (3) feet from the property line; (6) Balconies and decks projecting two (2) feet or less into the yard, excluding projections into interior side yards above the first floor, and provided that the outside face of the projection shall be at least three (3) feet from the property line; (7) Flag poles, garden ornaments and play equipment; (8) Steps which are necessary to provide access to the first floor of a permitted building, or to a parcel from a street or alley; (9) Uncovered decks which do not exceed eighteen (18) inches in height within five (5) feet of property lines or thirty (30) inches elsewhere in required yards; (10) Open parking spaces within a rear yard. (b) The following structures, building projections and features shall be permitted in front yards: Covered porches projecting two (2) feet or less into required front yards, and only when the required yard meets current yard setback requirements. The projection into the required yard may not be enclosed with walls or other material. The projection shall not exceed 50% of the width of the house as measured at the front property line, (c) Location of detached accessory buildings. A detached accessory building located within the rear one-third of a parcel is exempt from the requirements for interior side and rear yards, provided that such structure: (1) Shall be separated from the principal building by a distance not less than four (4) feet in width that is open to the sky, and (2) Shall not exceed a height of nine (9) feet to the plate line and sixteen (16) feet to the roof peak, and (3) Shall not extend above or beyond a daylight plane having a height of nine (9) feet at each side and rear property line and extending into the parcel at an angle of forty-five (45) degrees, excepting eaves and flues, and (4) Shall be limited to one habitable floor on the ground level. Habitable floor for the purposes of this subsection shall mean that served by permanent access and containing windows and/or plumbing fixtures, but shall exclude basements. image008.jpg (d) Maximum coverage of required rear yards. Accessory buildings shall not occupy more than fifty (50) percent of a required rear yard. (Ord. 2009-7 § 17, 2009; Ord. 2006-9 § 1 (part), 2006; Ord. 1992-16 § 10 (part), 1992).
What are the required setbacks to the Main Home?
Q: What are any other required setbacks? Special setbacks may be needed for creeks, power lines, key or corner lots, etc.
Note that the exact location of the rear yard on this odd shaped lot is not entirely clear although the Planner did say that the existing rear yard shed is definitely in the rear yard.

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