CHAP. I. 



ROOFS FOR COVERED YARDS. 



667 



air between every slate. This space, 2 inches wide by the thickness 

 of the slate, is, in the aggregate, something very considerable. These 

 spaces being distributed evenly over the whole roof there are no 



9"x2J 



Fig. 198. Section showing a Roof Covered with Open Slating. 



A. Section of open slating. B. Elevation of open slating. 



draughts, so that this is another cheap way of getting roof ventilation. 

 The weight being much less than in ordinary slating, the roof-trusses 

 may be placed farther apart, thus resulting in a less costly form of 



Fig. 199. Section Showing a Roof Covered with Boards. 



structure. Those who have yards covered in this way speak very 

 favourably of them, and, as the cost is moderate, it is probable that, as 

 the plan becomes better known, it will be more widely adopted. 



In fig. 199 is illustrated a form of board roof that has obtained con- 



