44 BULLETi:^" 801^ U. S. DEPARTMEISTT OF AGEICTJLTUEE. 



Walls longer than 100 feet and not tied by cross walls should be 

 braced at intervals of 100 feet by buttresses similar to those in Plate 

 XXIII, figure 2. The top of the wall should extend above the roof 

 to form a parapet 3 feet high if there is an exposure ; this arrange- 

 ment is shown in the photograph just referred to. If there is no se- 

 rious exposure, the wall may terminate as a parapet only 18 inches 

 above the roof, or the wall may be finished with a corbel support- 

 ing a metal gutter as shown in Plate XXIII, figure 2. In the latter 

 case it is important that the division fire wall provide the corbeled 

 wing projection shown. It is preferable that there be no overhang- 

 ing cornice as this is a source of fire hazard. 



Walls not terminating with a parapet should have suitable 

 wrought iron timber anchors built in and secured to the framing, 

 in order to resist the lifting action of wind. The size and design of 

 the anchor depends on the arrangement of framing. 



Openings in the wall should conform to the same size and arrange- 

 ment as stated for fire-resistive construction. Doors may be of thick 

 and substantiaJ wooden construction if there is no serious exposure. 

 (Windows should be metal glazed with wire-glass."^ 



FRAMING. 



The usual arrangement of roof and floor timbers is such that the 

 end of the timber is supported by the division wall. The end of any 

 timber supported by a wall should rest freely upon a ledge, such as 

 an offset or corbel, and not be built solidly into the wall. The free 

 support permits the timber to fall without damage to the wall as 

 previously illustrated. This is one of the most important details 

 of slow-burning construction, and failure to observe this requirement 

 leads to serious damage to the building and also rapid spread of fire. 

 The drawing, Plate XXVI, shows such construction in figure 3 where 

 the floor timbers are supported by corbels and offsets or by pilasters 

 and the roof timbers are supported by corbels. These timber-ends 

 often may rest directly upon the brickwork provided sufficient bear- 

 ing area is supplied for the comparatively light load generally sus- 

 tained. Timbers parallel to and supported continuously by the wall, 



* A condition which requires that doors be constructed as a fire door is occa- 

 sioned by the use of wood platforms. This protection should also be used in 

 the case of doors in one story placed under those above and not separated by 

 a reinforced concrete platform. Wooden doors are used only where no severe 

 exterior exposure is anticipated. A wooden door is satisfactory if all of the 

 provisions here stated are fulfilled, but the fire-resistive door is much better. 

 In any event, doors should fit close to the wall and threshold. If the exterior 

 exposure is very severe, the wall and all openings should be constructed as in 

 a fire wall. 



