29. Introduction. The type of building known as the slow-burning, or mitt construction, recommended by the Associated Factory Mutual Fire Insurance Companies of Boston, Massachusetts, is used extensively for the construction of buildings for manufacturing purposes. Wherever reasonable safety from fire is desired at minimum cost, this form of construction is considered the best.

(A.) It is a well-established fact, that cast-iron or steel construction, unless thoroughly protected by a fireproof casing, will collapse in time of fire sooner than heavy timbers, as the heat so softens the metal that it will not sustain its own weight, while a heavy timber, perhaps, would not weaken enough to fail before the fire is under control.

It is not claimed that this form of construction is fireproof; but it is claimed that it does not burn readily, that on account of its peculiarities every opportunity for fire-fighting is given and that a fire, which in an ordinary building might be disastrous, would in one of this type do comparatively little damage.

(B.) Prior to the origin of this form of construction, insurance companies refused to insure, except at prohibitive rates, factories making certain lines of goods; but upon the introduction of this building type by Mr. Edward Atkinson of Boston, to whose courtesy is due the material for this chapter, it became possible for these buildings to be insured if properly constructed. This type of building is rapidly replacing all others; especially is this true of cotton factories, of which a great many have been built in the Northern States, and through the cotton belt of the South.

(C.) Slow-burning construction is used in building moderate-priced factories, warehouses, business blocks, and dwelling houses because of its simplicity, strength, and the rapidity with which it may be erected, and also because of its adaptability to very fine architecture if the designer uses judgment and skill.

Fig. 41. - Floor Plant of a Section of a Mill, showing Two Bays.