(a) A routine case is one determined by the department to involve a de minimus variance or modification that does not substantially affect the code's provisions for the health, safety and security.

(b) If the department determines to treat a case as a routine case under this section, it shall make the decision rather than a board of review, and shall consider the evidence offered, make findings of fact and conclusions of law, and render its decision in writing. Unless objected to by the petitioner or respondent in a writing received by the department, the decision shall become final after 15 days of receipt of the decision by the parties. A decision shall be filed, indexed, and distributed in the same manner as a decision of the boards of review. A decision timely objected to shall be without force and effect, and the matter to which it pertains shall be transmitted to a board of review for proceedings de novo in accordance with the preceding section.