The Director of Public Works may vary or modify the application of any provision of this Chapter or of any regulation adopted pursuant thereto, consonant with the spirit and intent of the law, upon application of the owner or his representative, if any of the following conditions:

(a) When there are practical difficulties involved in carrying out structural or mechanical provisions of this Chapter or of a regulation adopted pursuant thereto, or

(b) Where the proposed variation or modification will not substantially affect the structural integrity designed to be achieved by the provisions of this Chapter or of any regulation adopted pursuant thereto.

SOURCE: GC § 31016.