The commission may authorize the variances from the terms of these regulations as will not be contrary to the interact of public health, safety or general welfare, and where, owing to special conditions, a literal enforcement of the provisions of these regula tions will result in serious practical difficulty; provided, however, that the purpose and intent of these regulations shall be observed and substantial justice done. Where the subdivider desires the variance of any provisions of the foregoing regulations, he shall include a request therefor, with a statement of reasons for such request, with the application for the approval of the preliminary or final plan.
('66 Code, § 63-8)