AIR AND VENTILATION 



103 



same, rain can be excluded under any but extraordinary conditions. 

 It i> advisable to have a weather fillet nailed to the upper edge 

 of each louvre-board to form a water check. In the case of 



metal plates the upper edge may 

 be turned up for this purpose. 

 The boards or plates are let into 

 grooves formed in the framing 

 posts. This type of outlet should 

 be kept clean and in good condi- 

 tion by regular painting. The 

 perflating action of the wind pass- 

 ing through the louvred ventilator 

 with its consequent aspirating 



effect is indicated in the figure. 



FIG. 44. Showing the method of _. , . ,. 



ventilating a stable with hopper Down-draughts are frequently 

 inlet windows and a louvre-board caused by the proximity of higher 



buildings or roofs. Adjustable 



or movable louvres are to be condemned as they are often neglected 



and readily get out of order. 



MECHANICAL VENTILATION. Mechanical ventilation is adopted 



where for some reason a purely 



natural method is in itself either 



inefficient or impracticable. There 



are two methods: (1) The 



plenum method whereby hot or 



cold air is forced into a building 



through ducts by means either 



of a propeller or cased fan driven 



by motive power ; (2) the vacuum 



or extraction method whereby air 



is sucked out of a building by a 



fan. The extraction method has 



been found to be more efficient 



under varying conditions than has 



the plenum system. 



VENTILATION OF DOUBLE- 

 STORIED STABLES. It is not 



always possible to build stables 



with only one story, and in cities 



it is often necessary to stable 



horses in two or three flats one 



above the other. It is sometimes 



stated that it is not possible to pro- 



FIG. 45. The ventilation of a double- 

 story or lofted stable. The inlet 

 of fresh air is provided for by 

 hopper windows. The foul air 

 escapes through flues either as 

 shown by A to avoid breaking 

 the loft or overhead stable space, 

 or B, which is preferable by a 

 direct flue carried straight up to 

 the roof ridge. The flues are 

 surmounted by suitable extraction 

 cowls. 



