The most common fault with stairs, particularly in dwellings, is the lack of sufficient head room. One should never calculate on less than 6½ feet from the under side of the floor opening to the top of the tread below, and 7 or 8 feet of head room is much better.
With the ordinary thickness of floors in dwellings the well room should extend over at least 12 risers when the rise is over 7½ inches, and 13 or 14 risers when it is less.
Where one flight is built directly above another the vertical distance between the two should not be less than 7 feet 6 inches in the clear, measured over the face of the riser.
The architect or draughtsman cannot be too careful in this particular, as expensive and otherwise well-arranged stairways are often greatly marred by too close head room.
When planning the stairs for buildings of a public nature the first consideration should be the comfort and safety of the people using them.
Landings should be provided every ten or twelve steps, which should be as long as the width of the stair, and winders should be entirely avoided, unless placed on a circle, as previously described. The rise of the stairs in public buildings should not exceed 7 inches. All sudden alterations in the length of flights should be avoided and no flight of less than three risers should be permitted. The use of single or isolated steps in public buildings is dangerous and is prohibited in most of our large cities.
Width of Public Stairs. - The width of the stairs should be proportioned to the greatest number of people that may possibly have occasion to use them at one time. The law regulating the construction of buildings in the city of New York provides that "Stairways serving for the exit of fifty people must, if straight, be at least 4 feet wide between railings, or between walls, and if curved or winding, 5 feet wide, and for every additional fifty people to be accommodated 6 inches must be added to their width." "In no case shall the risers of any stairs exceed 7½ inches in height, nor shall the treads, exclusive of nosings, be less than 10 ½ inches wide in straight stairs. In circular or winding stairs the width of the tread at the narrowest end shall not be less than. 7 inches."
In general the stair shown in Fig. 291 is the best for public buildings, and next to this is the straight stair with a platform near the centre, as in Fig. 296.
Stairs should be well lighted, particularly at their approaches, and in hotels, factories and other buildings of a public nature a skylight should be placed above the stair-well, both for lighting and for ventilation.