The commission shall require building envelopes, outlining on each lot in each subdivision the area on which a structure may be built, and providing adequate setbacks from proposed property lines. Building envelopes shall be regular in shape to the greatest extent possible, and shall include height restrictions, if said restrictions are more stringent than those required under the provisions of the City’s zoning ordinance, and if the City believes that such additional restrictions are needed to protect views and maintain the City’s environmental quality. (Ord. 89-2 § 2, 1989.)