§ 101. Requirements for fireproof construction. 1. Every such dwelling exceeding six stories or seventy-five feet in height shall be fireproof. No multiple dwelling shall be altered so as to exceed either of such heights without being made fireproof.

2. In a fireproof multiple dwelling the walls, floors, roof, stairs and public halls shall all be fireproof except as provided in subdivision three. No beams, lintels or other structural members shall be of wood. No wood or other inflammable material shall be used in any of the partitions, furrings or ceilings. For the portion of a multiple dwelling more than one hundred fifty feet above the curb level, no wood shall be used except as provided in subdivision three and except for interior trim of windows.

3. The foregoing requirements shall not be construed as prohibiting:

a. Elsewhere than within, or in the openings to, the public halls, stairs and shafts, the use of wood for sleepers, grounds, nailing blocks, underflooring, finish flooring, interior doors with their assemblies and saddles, floor base not more than one foot in height, picture and wall moulding, shelving, closet and kitchen fixtures, cupboards, cabinets and wardrobes.

b. The use of wood for windows and for interior trim and finish backed solidly against, or filled with, incombustible material when located not more than one hundred fifty feet above the curb level and elsewhere than within, or in the openings to, the public halls, stairs and shafts.

c. The use within apartments of wood for decorative wall panelling, wainscoting, mantels or other interior finish, and the use in an entrance hall of wall panelling or wainscoting made of fireproof wood or other material capable of successfully withstanding standard fire tests prescribed in the local building code and in a manner approved by the department.

d. Where fireproof doors are required, the use for such doors, with their assemblies and saddles, of material and construction capable of successfully withstanding a one-hour standard fire test prescribed in the local building code and in a manner approved by the department. Should any door required to be fireproof be found to have deteriorated so that it shall after installation fail to conform to the standard fire tests prescribed, such door shall be removed by the owner and replaced by him with a door capable of successfully withstanding such tests.

4. All materials combustible in their natural state which are constructed, processed or protected so that they will not support combustion shall, before being installed in a multiple dwelling for any of the uses herein specified, be permanently identified by label or marking with the name of the manufacturer and the year of manufacture in a manner approved by the department.

5. When required to be fireproof, any outer wall or any wall or partition which carries any load in addition to its own weight shall, unless otherwise in this chapter expressly required, be constructed of materials capable of successfully withstanding a four-hour standard fire test prescribed in the local building code and in a manner approved by the department. When required to be fireproof, any wall or partition which carries only its own weight, other than an outer wall, shall be constructed of materials capable of successfully withstanding a one-hour standard fire test prescribed in the local building code and in a manner approved by the department.