factories in Paris toward the east. In Haussmann's Paris, the streets became much wider, growing from an average of twelve meters (39 ft) wide to twenty-four meters (79 ft), and in the new arrondissements, often to eighteen meters (59 ft) wide. The interiors of the buildings were left to the owners of the buildings, but the façades were strictly regulated, to ensure that they were the same height, color, material, and general design, and were harmonious when all seen together. The reconstruction of the rue de Rivoli was the model for the rest of the Paris boulevards. The new apartment buildings followed the same general plan: ground floor and basement with thick, load-bearing walls, fronts usually parallel to the street. This was often occupied by shops or offices. mezzanine or entresol intermediate level, with low ceilings; often also used by shops or offices. second, piano nobile floor with a balcony. This floor, in the days before elevators were common, was the most desirable floor, and had the largest and best apartments. third and fourth floors in the same style but with less elaborate stonework around the windows, sometimes lacking balconies. fifth floor with a single, continuous, undecorated balcony. mansard roof, angled at 45°, with garret rooms and dormer windows. Originally this floor was to be occupied by lower-income tenants, but with time and with higher rents it came to be occupied almost exclusively by the concierges and servants of the people in the apartments below. The Haussmann façade was organized around horizontal lines that often continued from one building to the next: balconies and cornices were perfectly aligned without any noticeable alcoves or projections, at the risk of the uniformity of certain quarters. The rue de Rivoli served as a model for the entire network of new Parisian boulevards. For the building façades, the technological progress of stone sawing and (steam) transportation allowed the use of massive stone blocks instead of simple stone facing. The street-side result was a "monumental" effect that exempted buildings from a dependence on decoration; sculpture and other elaborate stonework would not become widespread until the end of the century. Before Haussmann, most buildings in Paris were made of brick or wood and covered with plaster. Haussmann required that the buildings along the new boulevards be either built or faced with cut stone, usually the local cream-colored Lutetian limestone, which gave more harmony to the appearance