Basements shall be permitted in areas that are not designated as special flood hazard areas, as defined in Chapter 16.52, subject to the following regulations:
(a) Permitted Basement Area
Basements may not extend beyond the building footprint and basements are not allowed below any portion of a structure that extends into required setbacks, except to the extent that the main residence is permitted to extend into the rear yard setback by other provisions of this code. Basements which serve the primary unit may not extend under an attached ADU or JADU to the extent those secondary units utilize the bonus floor area, lot coverage, and/or maximum house size exemptions identified in Section 18.09.
(b) Inclusion as Gross Floor Area
Basements shall not be included in the calculation of gross floor area, provided that:
(1) basement area is not deemed to be habitable space, such as a crawlspace; or
(2) basement area is deemed to be habitable space but the finished level of the first floor is no more than three feet above the grade around the perimeter of the building foundation. Grade is measured at the lowest point of adjacent ground elevation prior to grading or fill, or finished grade, whichever is lower; or
(3) basement area is associated with a historic property as described in Section 18.04.030(a)(65)(D)(vii).
(c) Lightwells, Stairwells and Other Excavated Features
Excavated features shall not affect the measurement of the grade for the purposes of determining gross floor area, so long as such features meet the following provisions:
(1) Lightwells, stairwells and similar excavated features along the perimeter of the basement shall not affect the measurement of grade, provided that:
(A) such features are not located in the front of the building;
(B) such features shall not exceed 3 feet in width;
(C) the cumulative length of all such features does not exceed 30% of the perimeter of the basement;
(D) such features do not extend more than 3 feet into a required side yard nor more than 4 feet into a required rear yard, but where a side yard is less than 6 feet in width, the features shall not encroach closer than 3 feet from the adjacent side property line;
(E) the cumulative length of any features or portions of features that extend into a required side or rear yard does not exceed 15 feet in length;
(F) the owner provides satisfactory evidence to the planning division prior to issuance of a building permit that any features or portions of features that extend into a required side or rear yard will not be harmful to any mature trees on the subject property or on abutting properties; and
(G) such features have either a drainage system that meets the requirements of the public works department or are substantially sheltered from the rain by a roof overhang or canopy of a permanent nature.
(2) Below-grade patios, sunken gardens or similar excavated areas along the perimeter of the basement that exceed the dimensions set forth in subsection (1), are permitted and shall not affect the measurement of grade, provided that:
(A) such areas are not located in the front of the building;
(B) All such areas combined do not exceed 2% of the area of the lot or 200 square feet, whichever is greater; that each such area does not exceed 200 square feet, and that each such area is separated from another by a distance of at least 10 feet. Area devoted to required stairway access shall not be included in the 200 square foot limitation.
(C) the cumulative length of any excavated area or portion thereof that extends into a required side or rear yard does not exceed 15 feet;
(D) such features do not extend more than 2 feet into a required side yard nor more than 4 feet into a required rear yard;
(E) the owner provides satisfactory evidence to the planning director prior to issuance of a building permit that any features or portions of features that extend into a required side or rear yard will not be harmful to any mature trees on the subject property or on abutting properties;
(F) such features have either a drainage system that meets the requirements of the public works department or are substantially sheltered from the rain by a roof overhang or canopy of a permanent nature;
(G) any roof overhang or canopy installed pursuant to subsection (F) is within and is counted toward the site coverage requirements established in Section 18.10.040;
(H) such areas are architecturally compatible with the residence; and
(I) such areas are screened to off site views by means of landscaping and/or fencing as determined appropriate by the planning director.
(Ord. 5585 § 7, 2023: Ord. 5432 § 5, 2018: Ord. 4964 § 10, 2007: Ord. 4875 § 2 (part), 2005)