The following additional state requirements are established in accordance with RCW 86.16.041.

(1) Special flood hazard areas with designated floodways. In addition to those NFIP requirements for designated floodways, communities with designated floodways shall restrict land uses within such areas to include the prohibition of construction or reconstruction of residential structures except for: (a) Repairs, reconstruction, or improvements to a structure which do not increase the ground floor area; and (b) repairs, reconstruction, or improvements to a structure the cost of which does not exceed fifty percent of the market value of the structure either (i) before the repair, reconstruction, or improvement is started, or (ii) if the structure has been damaged, and is being restored, before the damage occurred. Work done on structures to comply with existing health, sanitary, or safety codes which have been identified by the local code enforcement or building official and are the minimum necessary to assure safe living conditions shall not be included in the fifty percent determination in (b) of this subsection. A residential dwelling located partially within a designated floodway will be considered as totally within a designated floodway and must comply with this chapter. However, the floodway prohibition in this subsection does not apply to existing farmhouses in designated floodways that meet the provisions of WAC 173-158-075, or to residential dwellings other than farmhouses that meet the depth and velocity and erosion analysis provisions of WAC 173-158-076, or to structures identified as historical places.

(2) Special flood hazard areas without designated floodways. When a regulatory floodway for a stream has not been designated, the community may require that applicants for new construction and substantial improvements reasonably utilize the best available information from a federal, state, or other source to consider the cumulative effect of existing, proposed, and anticipated future development and determine that the increase in the water surface elevation of the base flood will not be more than one foot at any point in the community. Building and development near streams without a designated floodway shall comply with the requirements of 44 C.F.R. 60.3 (b)(3) and (4), and (c)(10) of the NFIP regulations.