In all Residence Districts, a non-conforming use that is listed in Use Groups IV, VI, VII, VIII, IX or X and not permitted as-of-right within C7 Districts, and which is not subject to the provisions of Sections 52-32 (Land with Minor Improvements) or 52-331 (Buildings designed for residential use), may be changed either to a conforming use or:

(a)        to any commercial use permitted as-of-right within C7 Districts, other than those listed in Use Group V, in which case any subsequent change of use shall conform to the provisions of Section 52-34 (Commercial Uses in Residence Districts); or

(b)        in accordance with the provisions of the following table:

provided that such changed use shall conform to all regulations on performance standards applicable in M1 Districts, and that any such changed use, or the storage of materials or products accessory to any changed use, which is not located within a completely enclosed building, shall be screened by a solid wall or fence (including solid entrance or exit gates) at least eight feet in height. Whenever a use located within a completely enclosed building is changed to another use, no activity related to such changed use, including the storage of materials or products, shall be located outside of such building.

In no event shall any change of use permitted in paragraph (b) of this Section extend the statutory period of useful life applicable under the provisions of Section 52-74 (Uses Objectionable in Residence Districts).