In consideration of all appeals and all proposed variations to this chapter, the Board shall, before making any variations from this chapter in a specific case, first determine that the proposed variation will not impair an adequate supply of light and air to adjacent property, or unreasonably increase the congestion in public streets, or increase the danger of fire or endanger the public safety, or unreasonably diminish or impair established property values within the surrounding area, or in any other respect impair the public health, safety, comfort, morals or welfare of the inhabitants of the City of Roseville. The concurring vote of five members of the Board shall be necessary to reverse any order, requirements, decision or determination of a Building Director, or to decide in favor of the applicant any matter upon which it is authorized by this chapter to render a decision. Nothing herein contained shall be construed to give or grant to the Board the power or authority to alter or change this chapter or the Zoning Map, such power and authority being reserved for the City Council of the City of Roseville in the manner provided by law.