§ 17.28.030. Hillside development standards.

A.

Residential Districts. The development of residentially zoned property shall minimize changes in grade, cleared area, and volume of cut or fill on those hillside portions of the property with twenty percent or greater natural slopes. Approval of a final site plan for a "critical lot" established by the subdivision regulations shall be based upon a demonstration that the proposal takes into consideration factors such as, but not limited to, soil conditions, degree of slope and feasibility of construction. The standards for review of critical lots from the adopted subdivision regulations shall apply.

1.

Single or Two-Family Lots. The following provisions of this section shall not apply to single or two-family lots equal to or greater than one acre in size. For lots of less than one acre, any natural slopes equal to or greater than twenty-five percent shall be platted outside of the building envelope and preserved to the greatest extent possible in a natural state. The planning commission may authorize the creation of a single or two-family lot of less than one acre in size with natural slopes equal to or greater than twenty-five percent subject to the following standards and conditions:

a.

The resulting lot shall be designated as a "critical lot" on the final plat of subdivision approved by the metropolitan planning commission and the department of public works;

b.

For natural slopes that generally rise away from the fronting street, the building envelope width shall be as approved on all preliminary plats approved prior to March 1, 2006. After March 1, 2006, a building envelope on less than twenty percent natural slope and a minimum width of seventy-five feet at the building line shall be provided, or

c.

For natural slopes that are generally parallel with fronting street, the building envelope width shall be as approved on all preliminary plats approved prior to March 1, 2006. After March 1, 2006, a building envelope on less than twenty percent natural slope and a minimum width of seventy-five feet at the building line shall be provided, or

d.

For natural slopes that generally fall away from the fronting street, a building envelope on less than twenty-five percent natural slope shall be provided;

e.

A certified engineer can demonstrate, through the use of special design and construction techniques, that a residential structure will be constructed on the lot in a manner which effectively minimizes disturbance of the hillside and optimizes the preservation of mature trees and will not adversely impact the storm water runoff on down slope or adjacent properties;

f.

All specially noted design, construction and drainage standards shall be incorporated into the preliminary and final subdivision plat approvals, and recorded in the form of a covenant running with the land; and

g.

The clearing of trees exceeding eight inches in diameter from those natural slopes equal to or greater than twenty-five percent shall be minimized by sensitive construction techniques.

2.

Cluster Lots. Single and/or two-family subdivisions in areas characterized by twenty percent or greater slopes are encouraged to employ the cluster lot option provisions of Section 17.12.080. In general, lots so created shall be clustered on those portions of the site that have natural slopes of less than twenty percent. The planning commission may authorize lots on natural slopes ranging up to twenty five percent, subject to the special standards and conditions noted above. Large contiguous areas containing natural slopes in excess of twenty-five percent should be recorded as common open space and permanently maintained in a natural state.

3.

All Other Development in Residential Districts. For any multifamily or nonresidential form of development occurring within a residential district (the RM40, RM40-A, RM60, RM60-A, RM80-A and RM100-A districts excepted), manipulation of the natural slopes by grading shall result in an effective impervious surface ratio (ISR) for those portions disturbed as shown in Table 17.28.030A.

a.

That portion of a multifamily development site containing large contiguous areas of natural slopes of twenty-five percent or greater should be permanently maintained in a natural state. The clearing of trees exceeding eight inches in diameter from those natural slopes shall be minimized by sensitive construction techniques.

b.

The use of retaining walls, rip rap or hydraulically applied concrete to stabilize slopes within multifamily developments shall be screened as follows:

i.

When oriented towards a lot or parcel zoned R/R-A or RS/RS-A, apply the next higher landscape buffer yard standard from Section 17.24.240;

Table 17.28.030A
ISR ADJUSTMENTS (RESIDENTIAL DISTRICTS)

Natural Slope (%) ISR	Standard ISR	×	Adjustment Factor	=	Effective ISR
< 15%	Table 17.12.020B	×	1.0	=	Effective ISR
15 < 20%	Table 17.12.020B	×	0.66	=	Effective ISR
20 < 25%	Table 17.12.020B	×	0.33	=	Effective ISR
25% +	Table 17.12.020B	×	0.0	=	0

 

* For the purposes of calculation, slopes may be averaged for the entire lot area employing slope contour intervals of two feet.

ii.

When oriented towards another lot or parcel with an RM zoning classification, apply landscape buffer yard Standard A from Section 17.24.240; and

iii.

When oriented towards a public street, apply landscape buffer yard Standard B from Section 17.24.240.

B.

Nonresidential Sites.

1.

In all nonresidential zoning districts except CF, MUI and MUI-A, manipulation of the natural slopes by grading shall result in effective impervious surface ratio (ISR) adjustments for those portions disturbed as shown in Table 17.28.030B.

2.

Grading standards for hillside sites in nonresidential zone districts are as follows:

a.

For lots or parcels containing natural slopes of twenty percent or greater, approval of a final site plan shall be based upon a demonstration that the development plan minimizes unnecessary disturbance to those slopes in the placement and orientation of building and parking areas. Architectural and engineering features which reduce unnecessary encroachment on steep slopes may include, but are not limited to, the use of retaining walls and structural foundations to return to natural grade.

b.

The use of retaining walls, rip rap or hydraulically applied concrete to stabilize slopes on nonresidential sites shall be screened as follows:

i.

When oriented towards a lot or parcel zoned R and R-A, RS and RS-A or RM, apply the next higher landscape buffer yard standard from Section 17.24.240; and

ii.

When oriented towards a public street, apply landscape buffer yard standard B from Section 17.24.240.

Table 17.28.030B
ISR ADJUSTMENT (NONRESIDENTIAL DISTRICTS)

Natural Slope (%)	Standard ISR	×	Adjustment Factor	=	Effective ISR
< 15%	Table 17.12.020C	×	1.0	=	Effective ISR
15 < 20%	Table 17.12.020C	×	0.66	=	Effective ISR
20 < 25%	Table 17.12.020C	×	0.33	=	Effective ISR
25% +	Table 17.12.020C	×	0.0	=	0

 

* For the purposes of calculation, slopes may be averaged for the entire lot area employing slope contour intervals of two feet.

(Ord. BL2015-1153 § 16, 2015; Ord. BL2011-898 §§ 11, 13, 2011; Ord. BL2009-586 § 1(Exh. A, § 40), 2010; Amdt. 1 to Ord. BL2006-1045 § 1, 2006; Ord. BL2006-1045 § 1, 2006; Amdt. 1 with Ord. 98-1268 § 1 (part), 1998; § 5(2), (3) of Amdt. 1 with Ord. 96-555 § 7.1(C), 1997)