No part of said sidewalk shall be taken for private use, by lowering or cutting down the same next to the building, or railing off the same by any wooden or iron railing, or by shutting off the public from passing along and over the same, and said sidewalks shall not be raised up next to the building, by constructing a platform or platforms on the same, of either wood, iron or stone, but said sidewalks shall be built flush up to the building on a uniform grade as herein provided. Entrances to areas and basements and flights of stairs or steps may be made which shall extend into or upon the sidewalk more than two feet next to the building, and the width of the steps, stairs or entrances to areas and basements inside walks shall not be more than four feet. Said steps, stairs or entrances shall be securely protected, and no open space next to the building other than entrance ways to areas and basements forming a portion of the sidewalks shall be allowed.