No dwelling shall be erected on any lot having a street frontage of less than 75 feet. The street frontage may be reduced, however, provided that, for each foot or fraction thereof that the width of the lot is decreased below 75 feet at the frontmost line of the house proposed to be built, the area of the lot shall be increased by 100 square feet above the minimum area required for the district, but in no event shall the street line of the lot be less than 40 feet or the width of the lot at said frontmost line of the proposed house be less than 65 feet. Whenever a street frontage of a lot shall be less than 75 feet, the lot survey on the plat submitted to the Planning Board for approval shall contain thereon the frontmost line of the house to be built on said lot or lots.