This section is from the book "Practical Real Estate Methods For Broker, Operator & Owner", by Thirty Experts. Also available from Amazon: Practical Real Estate Methods for Broker, Operator, Owner.
The act distinguishes between outer and inner courts, an outer court being one with one entire side open to the street or yard, and an inner court being one enclosed on all four sides or enclosed on three sides and bounded on the fourth side by the lot line of the building. All courts must be open at every point to the sky unobstructed. Outer courts, where situated on the lot line, must be at least six feet wide in every part for buildings sixty feet in height, and for every twelve feet of increase in the height of the building the width of the court must increase six inches throughout the entire height of the court, and may similarly decrease six inches in width for every twelve feet in height of the building less than sixty feet. Outer courts between wings of the same building, or between different buildings on the same lot, must be twelve feet wide in every part, and must increase one foot in width for every twelve feet of increase in the height of the building over sixty feet, and may similarly decrease one foot in width for every twelve feet of height less than sixty feet. An exception is made to this rule, however, by providing that where an outer court is less in depth than the minimum width prescribed by the act, its width may be equal to its depth; for example, if an outer court between wings is only eight feet deep, it may be only eight feet wide instead of twelve feet wide, etc. Similar exceptions are made for offsets in recesses in such courts. Inner courts when situated on the lot line are required to be twelve feet wide in every part and to increase six inches in width for every twelve feet in height beyond sixty feet, and may decrease similarly in width for every such decrease in height. Inner courts not on the line, but enclosed on all four sides, must not be less than twenty-four feet in each direction and must increase one foot in each direction for every twelve feet of increase in the height of the building beyond sixty feet, and may decrease one foot in each direction for every twelve feet of decrease in the height of the building below sixty feet. Similar exceptions to those provided for outer courts are provided for, but no windows except windows of water closets, bathrooms or halls shall open upon any offset or recess less than six feet in width. Every inner court must be provided with one or more horizontal intakes or ducts at the bottom to provide a circulation of air, and such intakes or ducts may not be less in total area than 4 per centum of the area of the inner court, and a minimum size of five square feet for each intake is prescribed. These intakes must always communicate directly with the street or yard, and may consist either of a metal duct or pipe, or may be an open passageway provided with iron grilles or grates at each end. In new buildings not over three stories high and arranged for not more than two families on a floor or six families in all, outer courts are permitted four feet wide, if not over twenty-four feet long, and inner courts are permitted to be eight feet wide and fourteen feet long.
Rear tenements are prohibited on any lot less than fifty-one feet in width, and whenever any building is hereafter placed on the same lot with a tenement house the space between the buildings is to be regulated in a manner similar to the rules laid down for the size of inner courts.