BUILDING 171 



roofs it is necessary to provide steeper inclines than with gravel 

 roofs so that the water may run off rapidly. The height of the 

 trusses should be about one-third of the span. Monitors are 

 sometimes provided so as to give additional ventilating facilities. 



Roof trusses with a raised chord, as in Fig. 101, are in many 

 instances of great advantage in that they provide an increased 

 headroom without unnecessarily raising the walls of the building. 

 This is of special importance in the high-tension part of the sta- 

 tion, where ample headroom must be provided for the busbars. 



Windows. A good lighting is imperative, and large windows 

 are therefore essential. They should be symmetrically located 

 with regard to the generating units and their design should be 

 such as to harmonize with the building, arched windows being 

 very generally used. Skylights of glass tile placed in the roof 

 will also add considerably to the lighting. The window sashes 

 should preferably be metallic and the glass reinforced with wire 

 netting so as to prevent shattering when broken. Ribbed or non- 

 transparent glass is also desirable, because it keeps out the intense 

 rays of the sun. In order to provide for ventilation provision 

 should be made so that the windows can be readily opened, and 

 in large stations they are operated by electric motors controlled 

 from the main switchboard. Precautions should also be taken 

 so that rain, snow or dust will not blow in on the machinery or 

 apparatus. This is especially important on the switchboard side 

 where the wiring is exposed and it is, therefore, better practice 

 not to provide any means for opening the windows on that side. 

 For tropical climates all windows which are liable to be opened 

 should be equipped with mosquito screens. 



Doors. The location of the doors is naturally governed by 

 local conditions. One of the openings should be of a sufficient 

 size to admit a railroad car and tracks should therefore also be 

 provided. Very often these doors are of the rolling type, this 

 design being most economical as regards space. 



Traveling Crane. Provision should always be made for sup- 

 porting the track for a traveling crane, which should span the 

 generator room and run the full length of the station. The track 

 is generally supported on pilasters in the outside wall and on the 

 steel columns separating the generator and switch rooms. There 

 should be ample headroom allowed so that the various machine 

 parts can be readily removed when repairs are to be made. This. 



