(1) Any county that is required or chooses to plan under RCW 36.70A.040 may provide by ordinance and incorporate into its development regulations, zoning regulations, and other official controls, authorization for the following:

(1)(a)(i) Middle housing types on each parcel that permits single-family residences in limited areas of more intensive rural development designated according to the requirements in RCW 36.70A.070(5)(d)(i);

(b) (ii) If a county takes action authorized by this subsection (1)(a), it may not authorize more than 4 [four] four residential units per lot in limited areas of more intensive rural development designated according to RCW 36.70A.070(5)(d)(i), and its development regulations must:

(i) (A) Not require any standards for middle housing that are more restrictive than those required for detached single-family residences, but may apply any objective development regulations that are required for detached single-family residences, including, but not limited to, setback, lot coverage, stormwater, clearing, and tree canopy and retention requirements;

(ii) (B) Apply to middle housing the same development permit and environmental review processes that apply to detached single-family residences, unless otherwise required by state law, including, but not limited to, shoreline regulations under chapter 90.58 RCW, building codes under chapter 19.27 RCW, energy codes under chapter 19.27A RCW, or electrical codes under chapter 19.28 RCW; and

(iii) (C) Require that middle housing in limited areas of more intensive rural development in a rural county be served by a publicly owned sanitary sewer system or a large on-site sewage system; and

(D) Require that middle housing in limited areas of more intensive rural development in a nonrural county be served by existing sewer service a publicly owned sanitary sewer system.

(2)(a) (b)(i) Middle housing types on each parcel that permits single-family residences in designated urban growth areas.

(b) (ii) If a county takes action authorized by this subsection (1)(b), it may not authorize more than four residential units per lot within the designated urban growth area and its development regulations must:

(i) (A) Not require any standards for middle housing that are more restrictive than those required for detached single-family residences, but may apply any objective development regulations that are required for detached single-family residences, including, but not limited to, setback, lot coverage, stormwater, clearing, and tree canopy and retention requirements;

(ii) (B) Apply to middle housing the same development permit and environmental review processes that apply to detached single-family residences, unless otherwise required by state law, including, but not limited to, shoreline regulations under chapter 90.58 RCW, building codes under chapter 19.27 RCW, energy codes under chapter 19.27A RCW, or electrical codes under chapter 19.28 RCW; and

(iii) (C) Require that middle housing in designated urban growth areas be served by water and sewer services.

(2) For purposes of this section:

(a) "Rural county" has the same meaning as in RCW 43.160.020; and

(b) "Large on-site sewage system" has the same meaning as in RCW 70A.115.010.