Chapter 21A.25 DEVELOPMENT STANDARDS – DENSITY AND DIMENSIONS

Chapter 21A.25
DEVELOPMENT STANDARDS – DENSITY AND DIMENSIONS

Sections:

21A.25.010 Purpose.

21A.25.020 Interpretation of tables.

21A.25.030 Densities and dimensions – Residential zones.

21A.25.040 Densities and dimensions – Commercial zones.

21A.25.050 Measurement methods.

21A.25.060 Reserved.

21A.25.070 Calculations – Allowable dwelling units, lots or floor area.

21A.25.080 Calculations – Site area used for density calculations.

21A.25.090 Calculations – Site area used for minimum density calculations.

21A.25.100 Repealed.

21A.25.110 Lot area – Prohibited reduction.

21A.25.120 Measurement of setbacks.

21A.25.130 Setbacks – Specific building or use.

21A.25.140 Setbacks – Livestock buildings and manure storage areas.

21A.25.150 Setbacks – Modifications.

21A.25.155 Setbacks – Required building separation.

21A.25.160 Setbacks – From regional utility corridors.

21A.25.170 Setbacks – From alley.

21A.25.180 Setbacks – Required modifications.

21A.25.190 Setbacks – Projections and structures allowed.

21A.25.200 Height – Exceptions to limits.

21A.25.210 Lot divided by zone boundary.

21A.25.220 Sight distance requirements.

21A.25.230 Repealed.

21A.25.010 Purpose.

The purpose of this chapter is to establish basic dimensional standards for development relative to residential density and as well as specific rules for general application. The standards and rules are established to provide flexibility in project design, and maintain privacy between adjacent uses. (Ord. O2003-132 § 12)

21A.25.020 Interpretation of tables.

(1) SMC 21A.25.030 and 21A.25.040 contain general density and dimension standards for the various zones and limitations specific to a particular zone(s). Additional rules, exceptions, and methodologies are set forth in SMC 21A.25.050 through 21A.25.220.

(2) The density and dimension tables are arranged in a matrix format on two separate tables and are delineated into two general land use categories:

(a) Residential; and

(b) Commercial.

(3) Development standards are listed down the left side of both tables, and the zones are listed at the top. The matrix cells contain the minimum dimensional requirements of the zone. The parenthetical numbers in the matrix identify specific requirements applicable either to a specific use or zone. A blank box indicates that there are no specific requirements. If more than one standard appears in a cell, each standard will be subject to any applicable parenthetical footnote following the standard. (Ord. O2003-132 § 12)

21A.25.030 Densities and dimensions – Residential zones.

A. Residential Zones.


	Z O N E S	RESIDENTIAL
	Z O N E S	URBAN RESIDENTIAL
STANDARDS		R-1(14)	R-4	R-6	R-8	R-12	R-18
Maximum Density DU/Acre (12)		1 du/ac	4 du/ac (5)	6 du/ac	8 du/ac	12 du/ac	18 du/ac
Minimum Density (2)					85% (15)	80% (15)	75% (15)
Minimum Lot Width		35 ft (7)	30 ft	30 ft	30 ft	30 ft	30 ft
Minimum Street Setback		20 ft (6)	10 ft (7)	10 ft (7)	10 ft (7)	10 ft (7)	10 ft (7)
Minimum Interior Setback (2)(13)		5 ft (7)	5 ft	5 ft	5 ft	5 ft	5 ft
Base Height (3)(16)		35 ft	35 ft	35 ft 45 ft (11)	35 ft 45 ft (11)	60 ft	60 ft 80 ft (11)
Maximum Impervious Surface: Percentage (4)		30% (9)	55%	70%	75%	85%	85%

1. Also see SMC 21A.25.060.

2. These standards may be modified under the provisions for zero lot line and townhouse developments.

3. Height limits may be increased when portions of the structure which exceed the base height limit provide one additional foot of street and interior setback for each foot above the base height limit, provided the maximum height may not exceed 75 feet. Netting or fencing and support structures for the netting or fencing used to contain golf balls in the operation of golf courses or golf driving ranges are exempt from the additional interior setback requirements; provided, that the maximum height shall not exceed 75 feet.

4. Applies to each individual lot. Impervious surface area standards for:

a. Regional uses shall be established at the time of permit review;

b. Nonresidential uses in residential zones shall comply with SMC 21A.25.130;

c. Individual lots in the R-4 through R-6 zones which are less than 9,076 square feet in area shall be subject to the applicable provisions of the nearest comparable R-6 or R-8 zone;

d. Lot may be increased beyond the total amount permitted in this chapter subject to approval of a conditional use permit.

5. Mobile home parks shall be allowed a base density of six dwelling units per acre.

6. The standards of the R-4 zone shall apply if a lot is less than 15,000 square feet in area.

7. At least 20 linear feet of driveway shall be provided between any garage, carport or other fenced parking area and the street property line. The linear distance shall be measured along the center line of the driveway from the access point to such garage, carport or fenced area to the street property line.

8. a. For developments consisting of three or more single-detached dwellings located on a single parcel, the setback shall be 10 feet along any property line abutting R-1 through R-8, except for structures in on-site play areas required in SMC 21A.30.160, which shall have a setback of five feet.

b. For townhouse and apartment development, the setback shall be 20 feet along any property line abutting R-1 through R-8, except for structures in on-site play areas required in SMC 21A.30.160, which shall have a setback of five feet, unless the townhouse or apartment development is adjacent to property upon which an existing townhouse or apartment development is located.

9. Lots smaller than one-half acre in area shall comply with standards of the nearest comparable R-4 through R-8 zone. For lots that are one-half acre in area or larger, the impervious surface area allowed shall be 10,000 square feet or 30 percent of the property, whichever is greater. On any lot over one acre in area, an additional five percent of the lot area may be used for buildings related to agricultural or forestry practices. For lots smaller than two acres but larger than one-half acre, an additional 10 percent of the lot area may be used for structures which are determined to be medically necessary, provided the applicant submits with the permit application a notarized affidavit, conforming with the requirements of SMC 21A.70.170 (1)(b).

10. The base height to be used only for projects as follows:

a. In R-6 and R-8 zones, a building with a footprint built on slopes exceeding a 15 percent finished grade; and

b. In the R-18 zone using residential density incentives and transfer of density credits pursuant to this title.

11. Density applies only to dwelling units and not to sleeping units.

12. Vehicle access points from garages, carports or fenced parking areas shall be set back from the property line on which a joint use driveway is located to provide a straight line length of at least 26 feet as measured from the center line of the garage, carport or fenced parking area, from the access point to the opposite side of the joint use driveway.

13. All subdivisions and short subdivisions in the R-1 zone shall be required to be clustered away from critical areas or the axis of designated corridors such as urban separators or the wildlife habitat network to the extent possible and a permanent open space tract that includes at least 50 percent of the site shall be created. Open space tracts shall meet the provisions of SMC 21A.30.030.

14. See SMC 21A.25.090.

15. Subject to the increase in maximum height permitted pursuant to SMC 21A.85.070, preferred low impact development incentives, and SMC 21A.30.020. (Ord. O2009-249 § 1; Ord. O2008-236 § 1; Ord. O2004-143 § 1; Ord. O2003-132 § 12)

21A.25.040 Densities and dimensions – Commercial zones.

A. Commercial Zones.


	Z O N E S	COMMERCIAL
	Z O N E S	NEIGHBORHOOD BUSINESS	COMMUNITY BUSINESS	OFFICE
STANDARDS		NB	CB	O
Maximum Density DU/Acre		8 du/ac (1)	18 du/ac (1)	18 du/ac (1)
Minimum Lot Area
Maximum Lot Depth/Width Ratio			10 ft	10 ft
Minimum Street Setback		10 ft (2)	10 ft (2)	10 ft
Minimum Interior Setback (4)		20 ft (5)	20 ft (5)	20 ft (5)
Base Height (7)		35 ft 45 ft (3)	35 ft 60 ft (3)	45 ft 60 ft (3)
Maximum Floor/Lot Ratio: Square Feet		1/1 (6)	1.5/1 (6)	2.5/1 (6)
Maximum Impervious Surface: Percentage (8)(9)		85%	85%	75%

B. Development Conditions.

1. These densities are allowed only through the application of mixed use development standards and for stand-alone townhouse development in the NB zone on property designated commercial outside of center in the urban area.

2. Gas station pump islands shall be placed no closer than 25 feet to street front lines.

3. This base height allowed only for mixed use developments and for stand-alone townhouse development in the NB zone on property designated commercial outside of center in the urban area.

4. Required on property lines adjoining residential zones.

5. Required on property lines adjoining residential zones for industrial uses established by conditional use permits.

6. The floor/lot ratio for mixed use developments shall conform to Chapter 21A.30 SMC.

7. Height limits may be increased when portions of the structure or building which exceed the base height limit provide one additional foot of street and interior setback for each foot above the base height limit, provided the maximum height may exceed 75 feet only in mixed use developments. Netting or fencing and support structures for the netting or fencing used to contain golf balls in the operation of golf courses or golf driving ranges are exempt from the additional interior setback requirement; provided, that the maximum height shall not exceed 75 feet.

8. The impervious surface area for any lot may be increased beyond the total amount permitted in this chapter subject to approval of a conditional use permit.

9. Subject to the increase in maximum height permitted pursuant to SMC 21A.30.020 and 21A.85.070, preferred low impact development incentives. (Ord. O2009-249 § 1; Ord. O2008-236 § 1; Ord. O2003-132 § 12)

21A.25.050 Measurement methods.

The following provisions shall be used to determine compliance with this title:

(1) Street setbacks shall be measured from the existing edge of a street right-of-way or temporary turnaround, except as provided by SMC 21A.25.170;

(2) Lot widths shall be measured by scaling a circle of the applicable diameter within the boundaries of the lot; provided, that an access easement shall not be included within the circle;

(3) Building height shall be measured from the average finished grade to the highest point of the roof. The average finished grade shall be determined by first delineating the smallest square or rectangle that can enclose the building and then averaging the elevations taken at the midpoint of each side of the square or rectangle; provided, that the measured elevations do not include berms;

(4) Lot area shall be the total horizontal land area contained within the boundaries of a lot; and

(5) Impervious surface calculations shall not include areas of turf, landscaping, natural vegetation, surface water flow control, or water quality treatment facilities. (Ord. O2003-132 § 12)

21A.25.060 Minimum urban residential density.

Minimum density for residential development in the urban areas designated by the comprehensive plan shall be based on the tables in this chapter and adjusted as provided for in SMC 21A.25.090. (Ord. O2004-143 § 1; Ord. O2003-132 § 12)

21A.25.070 Calculations – Allowable dwelling units, lots or floor area.

Permitted number of units, or lots or floor area shall be determined as follows:

(1) The allowed number of dwelling units or lots (base density) shall be computed by multiplying the site area specified in SMC 21A.25.080 by the applicable residential base density number;

(2) The maximum density (unit or lot) limits shall be computed by adding the bonus or transfer units authorized by Chapter 21A.75 or 21A.80 SMC to the base units computed under subsection (1) of this section;

(3) The allowed floor area, which excludes structured or underground parking areas and areas housing mechanical equipment, shall be computed by applying the floor-to-lot area ratio to the project site area specified in SMC 21A.25.080; and

(4) When calculations result in a fraction, the fraction shall be rounded to the nearest whole number as follows:

(a) Fractions of 0.50 or above shall be rounded up; and

(b) Fractions below 0.50 shall be rounded down. (Ord. O2003-132 § 12)

21A.25.080 Calculations – Site area used for density calculations.

(1) All site areas may be used in the calculation of maximum allowed residential density or project floor area except as outlined under the provisions of subsection (2) of this section.

(2) Existing submerged lands, steep slopes and buffers, Categories 1 – 4 wetlands and buffers, Types S, F, Np, and Ns streams and buffers, and property to be used as a street(s) shall not be credited toward base and maximum density or floor area calculations; provided, that subdivisions or short plats that meet the tree retention standards of SMC 21A.35.210(2), Tree retention requirements, shall be credited 10 percent of the environmentally sensitive areas and associated buffers identified above. (Ord. O2009-249 § 1; Ord. O2008-236 § 1; Ord. O2005-174 § 1; Ord. O2003-132 § 12)

21A.25.090 Calculations – Site area used for minimum density calculations.

Minimum density shall be determined by:

(1) Multiplying the density (dwelling units/acre) as set forth in SMC 21A.20.030(A) by the net buildable area of the project site; and then

(2) Multiplying the resulting product by minimum density percentage set forth in SMC 21A.25.030(A). (Ord. O2009-249 § 1; Ord. O2003-132 § 12)

21A.25.100 Minimum density adjustments for moderate slopes.

Repealed by Ord. O2009-249. (Ord. O2003-132 § 12)

21A.25.110 Lot area – Prohibited reduction.

Any portion of a lot that was used to calculate compliance with the standards and regulations of this title shall not be subsequently subdivided or segregated from such lot. (Ord. O2003-132 § 12)

21A.25.120 Measurement of setbacks.

(1) Interior Setback. The interior setback is measured from the interior lot line to a line parallel to and measured perpendicularly from the interior lot lines at the depth prescribed for each zone.

(2) Street Setback. The street setback is measured from the street right-of-way or the edge of a surface improvement which extends beyond a right-of-way, whichever is closer to the proposed structure, to a line parallel to and measured perpendicularly from the street right-of-way or the edge of the surface improvement at the depth prescribed for each zone. (Ord. O2003-132 § 12)

21A.25.130 Setbacks – Specific building or use.

When a building or use is required to maintain a specific setback from a property line or other building, such setback shall apply only to the specified building or use. (Ord. O2003-132 § 12)

21A.25.140 Setbacks – Livestock buildings and manure storage areas.

(1) The minimum interior setback for any building used to house, confine or feed swine shall be 90 feet.

(2) The minimum interior setback for any building used to house, confine or feed any other livestock shall be 25 feet.

(3) The minimum interior setback for any manure storage area shall be 35 feet. (Ord. O2003-132 § 12)

21A.25.150 Setbacks – Modifications.

The following setback modifications are permitted:

(1) When the common property line of two lots is covered by a building(s), the setbacks required by this chapter shall not apply along the common property line; and

(2) When a lot is located between lots having nonconforming street setbacks, the required street setback for such lot may be the average of the two nonconforming setbacks or 60 percent of the required street setback, whichever results in the greater street setback. (Ord. O2003-132 § 12)

21A.25.155 Setbacks – Required building separation.

The provisions of this section do not apply to zero lot line development proposed pursuant to Chapter 21A.30 SMC. The minimum interior setbacks of seven feet required pursuant to SMC 21A.25.030(A) may be reduced to five feet provided that the proposed building(s) and associated projections (which include but are not limited to eaves, bay windows, fireplace structures and uncovered porches) are at least 10 feet from any other existing building(s) and associated projections. (Ord. O2003-132 § 12)

21A.25.160 Setbacks – From regional utility corridors.

(1) In subdivisions and short subdivisions, areas used as regional utility corridors shall be contained in separate tracts.

(2) In other types of land development permits, easements shall be used to delineate such corridors.

(3) All buildings and structures shall maintain a minimum distance of five feet from property or easement lines delineating the boundary of regional utility corridors, except for utility structures necessary to the operation of the utility corridor or when structures are allowed by mutual agreement in the utility corridor. (Ord. O2003-132 § 12)

21A.25.170 Setbacks – From alley.

(1) Structures may be built to a property line abutting an alley, except as provided in subsection (2) of this section.

(2) Vehicle access points from garages, carports or fenced parking areas shall be set back from the alley property line to provide a straight line length of at least 26 feet, as measured from the centerline of the garage, carport or fenced parking area, from the access point to the opposite edge of the alley. No portion of the garage or the door in motion may cross the property line. (Ord. O2003-132 § 12)

21A.25.180 Setbacks – Required modifications.

The following setback modifications are required:

(1) In addition to providing the standard street setback, a lot adjoining a half-street or designated arterial shall provide an additional width of street setback sufficient to accommodate construction of the planned half-street or arterial; and

(2) Where the standard setback for a property is modified within an adopted neighborhood plan area zoning, the applicable setback shall be that specified therein. (Ord. O2003-132 § 12)

21A.25.190 Setbacks – Projections and structures allowed.

Provided that the required setbacks from regional utility corridors of SMC 21A.25.160, as allowed in the environmentally critical areas of SMC 21A.50.210, the adjoining half-street or designated arterial setbacks of SMC 21A.25.180 and the sight distance requirements of SMC 21A.25.220 are maintained, structures may extend into or be located in required setbacks, as follows:

(1) Fireplace structures, bay or garden windows, enclosed stair landings, closets, or similar structures may project 30 inches into a setback and 18 inches into aninterior setback, provided such projections are:

(a) Limited to two per facade; and

(b) Not wider than 10 feet;

(2) Uncovered porches and decks that exceed 18 inches above the finished grade may project five feet into the street setback;

(3) Uncovered porches and decks not exceeding 18 inches above the finished grade may project to the street property line;

(4) Eaves may not project more than:

(a) Twenty-four inches into a street setback; or

(b) Eighteen inches across a lot line in a zero lot line development, provided there are appropriate easements and that any neighboring building and its associated eaves are 10 feet from the lot line; or

(5) Fences with a height of six feet or less may project into or be located in any setback;

(6) Rockeries, retaining walls and curbs may project into or be located in any setback provided these structures:

(a) Do not exceed a height of six feet in the R-1 through R-18 zones; and

(b) Do not exceed the building height for the zone in commercial zones, measured in accordance with the standards established in the International Building Code, SMC Title 16;

(7) Fences located on top of rockeries, retaining walls or berms are subject to the requirements of SMC 21A.30.190;

(8) Telephone poles and lines; power poles and lines; cable TV and Internet lines; light and flagpoles; trellises not exceeding eight feet in height, not wider than 10 feet; culverts; underground water facilities; underground sewer facilities; and accessory facilities for the provision of utilities, such as drains, but excluding electrical and cellular equipment cabinets, and similar utility boxes and vaults;

(9) The following may project into or be located within a setback, but may only project into or be located within an interior setback area if an agreement documenting consent between the owners of record of the abutting properties is recorded with the King County department of records and elections prior to the installment or construction of the structure:

(a) Sprinkler systems, heat pumps, air conditioning units, electrical and cellular equipment cabinets and other similar utility boxes and vaults;

(b) Security system access controls;

(c) Structures, except for buildings, associated with trails and on-site recreation spaces and play areas required in SMC 21A.30.140 and 21A.30.160 such as benches, picnic tables and drinking fountains; and

(d) Surface water management facilities as required by Chapter 9.04 KCC as adopted by Chapter 15.05 SMC;

(10) Mailboxes and newspaper boxes may project into or be located within street setbacks;

(11) Fire hydrants and associated appendages;

(12) Metro bus shelters may be located within street setbacks;

(13) Unless otherwise allowed in SMC 21A.45.080, freestanding and monument signs four feet or less in height, with a maximum sign area of 20 square feet may project into or be located within street setbacks; and

(14) Storm water conveyance and control facilities, both above and below ground, provided such projections are:

(a) Consistent with setback, easement and access requirements specified in the surface water design manual; or

(b) In the absence of said specifications, not within five feet of the property line.

(Ord. O2009-249 § 1; Ord. O2005-171 §§ 3, 4; Ord. O2004-143 § 1; Ord. O2003-132 § 12)

21A.25.200 Height – Exceptions to limits.

The following structures may be erected above the height limits of SMC 21A.25.030 through 21A.25.050:

(1) Roof structures housing or screening elevators, stairways, tanks, ventilating fans or similar equipment required for building operation and maintenance; and

(2) Fire or parapet walls, skylights, flagpoles, chimneys, smokestacks, church steeples, crosses, spires, communication transmission and receiving structures, utility line towers and poles, and similar structures. (Ord. O2003-132 § 12)

21A.25.210 Lot divided by zone boundary.

When a lot is divided by a zone boundary, the following rules shall apply:

(1) When a lot contains both residential and nonresidential zoning, the zone boundary between the zones shall be considered a lot line for determining permitted building height and required setbacks on the site;

(2) When a lot contains residential zones of varying density:

(a) Any residential density transfer within the lot shall be allowed from the portion with the lesser residential density to that of the greater residential density;

(b) Residential density transfer from the higher density zone to the lower density zone may be allowed only when:

(i) The units transferred from any R-12 or R-18 zoned portion of the lot are maintained in an attached dwelling unit configuration on the lower density portion receiving such units;

(ii) The transfer does not reduce the minimum density achievable on the lot;

(iii) The transfer enhances the efficient use of needed infrastructure;

(iv) The transfer does not result in significant adverse impacts to the low density portion of the lot;

(v) The transfer contributes to preservation of environmentally sensitive areas, wildlife corridors, or other natural features; and

(vi) The transfer does not result in significant adverse impacts to adjoining lower density properties;

(c) Compliance with these criteria shall be evaluated during review of any development proposals in which such a transfer is proposed; and

(3) Uses on each portion of the lot shall only be those permitted in each zone pursuant to Chapter 21A.20 SMC. (Ord. O2003-132 § 12)

21A.25.220 Sight distance requirements.

Except for utility poles and traffic control signs, the following sight distance provisions shall apply to all intersections and site access points:

(1) A sight distance triangle area as determined by subsection (2) of this section shall contain no fence, berm, vegetation, on-site vehicle parking area, signs or other physical obstruction between 42 inches and eight feet above the existing street grade;

(2) The sight distance triangle at:

(a) A street intersection shall be determined by measuring 15 feet along both street property lines beginning at their point of intersection. The third side of the triangle shall be a line connecting the endpoints of the first two sides of the triangle; or

(b) A site access point shall be determined by measuring 15 feet along the street lines and 15 feet along the edges of the driveway beginning at the respective points of intersection. The third side of each triangle shall be a line connecting the endpoints of the first two sides of each triangle; and

(3) The director may require modification or removal of structures or landscaping located in required street setbacks, if:

(a) Such improvements prevent adequate sight distance to drivers entering or leaving a driveway; and

(b) No reasonable driveway relocation alternative for an adjoining lot is feasible.

Note: The area of a sight distance triangle between 42 inches and eight feet above the existing street grade shall remain open.

(Ord. O2003-132 § 12)

21A.25.230 Personal services and retail uses in R-4 through R-18 zones.

Repealed by Ord. O2009-249. (Ord. O2003-132 § 12)