In their interpretation and application, the provisions of this chapter shall be held to be the minimum requirements adopted for the promotion of the public health, safety, morals, comfort, convenience or general welfare. It is not intended by this chapter to repeal, abrogate, annul or in any way impair or interfere with any permits heretofore issued or any existing provisions of any law, ordinance, rule or regulation previously adopted relating to the use of buildings or land, except as herein modified; provided, however, that where any provision of this chapter is of a greater restriction than imposed or required by such existing provisions of law, ordinance, rule or regulation, the provisions of this chapter shall control.