The provisions of this chapter shall be construed
to be the minimum requirements adopted for the promotion of public
health, safety, morals, comfort, convenience and general welfare.
It is not intended by this chapter to repeal, abrogate, annul or in
any way impair or interfere with any existing provisions of law or
ordinances, or any rules, regulations or permits previously adopted
or issued or which shall be adopted or issued pursuant to law, relating
to the use of buildings or premises; provided, however, that where
this chapter imposes a greater restriction upon the use of buildings
or premises or upon the heights of buildings, or requires larger yards
or other open spaces, than are imposed or required by such existing
provisions of law or of ordinances, or by such rules, regulations
or permits or by such easements, covenants or agreements, the provisions
of this chapter shall control, and provided further than nothing herein
contained shall prohibit or restrict the revocation of any permit
heretofore or hereafter issued where no vested rights have arisen
in favor of the holder thereof.