The front building wall of any building shall extend along the full length of its front lot line not occupied by existing buildings to remain and shall rise without setback up to a height of six stories or 65 feet, or the height of the building, whichever is less. Above that height, the front building wall shall set back at least 10 feet. Front wall recesses are permitted provided that the aggregate length of such recesses, excluding window fenestration, at the level of any story does not exceed 25 percent of the length of the front wall where such recesses are permitted. In the event that a development occupies an entire block frontage, additional recesses are permitted provided that there are no front wall recesses within 10 feet of the intersection of two street lines. The exterior building materials of the front wall shall be predominantly of masonry.