The Board of Appeals, after the proper public hearing and notice, shall hear and decide appeals from and review any order, requirement, decision or determination made by the Code Enforcement Officer or other officer charged with the enforcement of this chapter. Where there are practical difficulties or unnecessary hardships in the way of carrying out the strict letter of this chapter, such Board shall have the power, in passing upon appeals, to vary or modify the application of any of the regulations or provisions of this chapter relating to the use, construction or alteration of buildings or structures or the use of land so that the spirit of this chapter shall be observed, public safety and welfare secured and substantial justice done.