When interpreting and applying the provisions of this chapter, they shall be held to be the minimum requirements adopted for the promotion of the public health, safety, comfort, convenience and general welfare. Except as specifically herein provided, it is not intended by the adoption of this chapter to repeal, abrogate, annul or in any way to impair or interfere with any existing provisions of law or ordinance or any rules, regulations or permits previously adopted or issued or which shall be adopted or issued pursuant to law relating to the erection, construction, maintenance, establishment, moving, alteration or enlargement of any building or improvement; nor is it intended by this chapter to interfere with or abrogate or annul any easement, covenant or other agreement between parties; provided, however, that in cases in which this chapter imposes a greater restriction upon the erection, construction, maintenance, establishment, moving, alteration or enlargement of buildings, or the use of any such buildings or premises in said several districts or any of them, than is imposed or required by such existing provisions of law or ordinance or by such rules, regulations or permits or by such easements, covenants or agreements, then in such case the provisions of this chapter shall control.