Counties that are required or choose to plan under RCW 36.70A.040 may authorize and designate national historic towns that may constitute urban growth outside of urban growth areas as limited by this section. A national historic town means a town or district that has been designated a national historic landmark by the United States secretary of the interior pursuant to 16 U.S.C. 461 et seq., as amended, based on its significant historic urban features, and which historically contained a mix of residential and commercial or industrial uses.

A national historic town may be designated under this chapter by a county only if:

(1) The comprehensive plan specifically identifies policies to guide the preservation, redevelopment, infill, and development of the town;

(2) The comprehensive plan and development regulations specify a mix of residential, commercial, industrial, tourism-recreation, waterfront, or other historical uses, along with other uses, infrastructure, and services which promote the economic sustainability of the town and its historic character. To promote historic preservation, redevelopment, and an economically sustainable community, the town also may include the types of uses that existed at times during its history and is not limited to those present at the time of the historic designation. Portions of the town may include urban densities if they reflect density patterns that existed at times during its history;

(3) The boundaries of the town include all of the area contained in the national historic landmark designation, along with any additional limited areas determined by the county as appropriate for transitional uses and buffering. Provisions for transitional uses and buffering must be compatible with the town's historic character and must protect the existing natural and built environment under the requirements of this chapter within and beyond the additional limited areas, including visual compatibility. The comprehensive plan and development regulations must include restrictions that preclude new urban or suburban land uses in the vicinity of the town, including the additional limited areas, except in areas otherwise designated for urban growth under this chapter;

(4) The development regulations provide for architectural controls and review procedures applicable to the rehabilitation, redevelopment, infill, or new development to promote the historic character of the town;

(5) The county finds that the national historic town is consistent with the development regulations established for critical areas; and

(6) On-site and off-site infrastructure impacts are fully considered and mitigated concurrent with development.

A county may allocate a portion of its twenty-year population projection, prepared by the office of financial management, to the national historic town corresponding to the projected number of permanent residents within the national historic town.