HEAVY TIMBER 



"It does not consist in leaving windows exposed to adjacent buildings 

 unguarded by fire-shutters or wired glass. 



"It is dangerous to paint, varnish, fill or encase heavy timbers and 

 thick plank as they are customarily delivered, lest what is called dry-rot 

 should be caused for lack of ventilation or opportunity to season. 



"It does not consist in leaving even the best-constructed building in 

 which dangerous occupations are followed without automatic sprinklers, 

 and without a complete and adequate equipment of pumps, pipes, and 

 hydrants." 



"It follows that if plastering is to be put upon a ceiling following the 

 line of the underside of the floor and the timber, it should be plain lime- 

 mortar plastering, which is sufficiently porous to permit seasoning. The 

 addition of the skim-coat of lime-putty is hazardous, especially if the top- 

 floor is laid upon resin-sized or asphalt paper. This rule applies to almost 

 all timber as now delivered. 



"All the faults above recited have been committed in buildings pur- 

 porting to be of mill construction, and all form a part of the common prac- 

 tice in 'combustible architecture.' " 



Mill Construction The terms "mill construction" and "slow- 

 and Slow-Burning burning construction" are used in most 

 Construction instances without a true clearness of 



meaning. It is true that mill construc- 

 tion is one of the best types of slow-burning construction, but 

 there are other types of structures which are referred to under 

 this same classification. The popular distinction is best shown 

 in the building ordinances of various cities. In mill construc- 

 tion, only timbers of large size are used, but in slow-burning 

 construction small timbers protected by metal lath and plaster 

 or other fire resisting materials are frequently installed. In- 

 stead of the thick floors required in mill construction, lighter 

 material is used with a fire retardant layer between the under 

 floor and the wearing surface. Plaster covered steel or iron 

 members may also form the main part of the framing in this 

 latter type of building. The following abstracts from the 

 1915 Revised Building Ordinance of the City of Chicago will 

 illustrate this distinction. 



"Slow-Burning Construction Defined. The term "Slow-Burning Con- 

 struction" shall apply to all buildings in which the structural members, other 

 than walls elsewhere required to be of masonry which carry the loads and 

 strains which come upon the floor and roofs thereof are made wholly or in 

 part of combustible material, but throughout which the structural metallic 

 members, if used, shall be protected against injury from fire by coverings of 

 fireproof material. Underside of joists shall be protected by a covering of 

 three coats of plaster laid on metal lath; and a layer of mortar or other 



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