Coal Tar Pitch Roofing Handbook - 1896 - Pages 20 and 21
BY natural instinct, born in the early days of the thatched roof and bred through the succeeding eras of slabs, shingles, slate and other roof coverings, man felt that there must be considerable pitch to the roof to carry the water away swiftly, else it would get through the covering. The inertia of a natural instinct thus firmly rooted is slow to overcome. While it is desirable for architectural effect that many buildings have steep roofs and be covered with Ready-Roofing, Shingles, Slate, Tile or Metal, as best suits particular cases, we contend that for commercial purposes, mills, warehouses, and similar constructions, roofs are frequently made too steep, from no other cause or reason than this old instinct. Of course they must be steep, if Ready-Roofing, Shingles or Slate are to be used, but as it has been clearly demonstrated in the last fifty years that a Barrett Specification Roof for Manufacturing, Railway or Commercial buildings is the most economical weatherproof and fire retardant roof obtainable, why not furnish a foundation for it, on which the roof contractor can do his best for the least cost per square foot?
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WE are advised by eminent authority on the construction of roof trusses that for all ordinary spans and with the usual spacing or length of bays, that trusses with a comparatively flat top chord, say two inches to the foot, can be designed as economically as the conventional Fink truss with the steep top chord. (See pages 22 and 23.)
The best results are obtainable with a Barrett slag or gravel roof, at not over two inches to the foot and this is readily obtainable with a truss as shown on page 22. As compared with steeper pitches, the slight pitch of this truss enables the roof contractor to use the maximum quantity of material at the minimum labor cost for any given area and as compared with a pitch of six inches to the foot, there is about eleven per cent less area of purlins, roof plank and roofing. The work thus planned, therefore, has the advantages of economy and increased durability.
From an insurance stand-point, flat roofs are looked upon with greater favor than steep ones. Moreover, this form of roof truss permits strong longitudinal bracing if desired for the support of shafting, traveling cranes, etc., which it may be found desirable to attach to the roof — an advantage nearly impracticable in a steep truss such as is shown on page 23.
We are, however, aware of the necessity for steep roofs on the backs of the skylights in “Sawtooth'' Mill construction. Of the various materials and methods used in the last fifteen years, on this class of work, the best results have been obtained along the lines of the five-ply Barrett Specification.
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