SILOS IN STONE AND BRICK 211 



The Roof. — The roof is shown in detail in Figs. 164 and 164a. In 

 it the filling door is constructed, and part of it projects so as to form 

 a roof for a chute down which the ensilage from the emptying doors 

 passes. 



The wallplates, W, 4^ n by 3", are half-checked to each other at 

 the corners, and are further bound together at the corners by 3" by 

 3" angle pieces, S. 



The main principal, D, is especially strong and is put together on 

 the ground. 



The common rafters are 6" by 1£", while the hip rafters, H, are 

 9" by 1£". The hip rafters project above the ordinary rafters and 

 carry the iron ridging for the corrugated iron roof covering. 



The purlins are 3" by 2". The 4£" by 3" filling door frame is 

 fixed at the bottom to an outer wallplate, T, and at the top to the 

 3" by 3" rafters, L, which in turn are nailed to the board, R, between 

 the hip rafters. 



In order to prevent rotting and corrosion of the roof by the gases 

 given off by the silage while fermenting, it must be well ventilated. 

 This is effected by leaving an opening round the eaves between the 

 iron of the roof and the masonry of the walls, and by making the filling 

 door of louvre form. 



The space between the top of the filling door frame and the iron of the 

 roof above it is also left open. 



Another method of ventilating is to have a ventilator on the apex 

 of the roof, leaving the aforementioned opening round the eaves. 



Emptying Doors. — It is important that these should be strong, durable, 

 and air-tight. They should preferably be made of hard wood. Fig. 165 

 is a detail drawing of a good type of emptying door, 2' 6" high by 2' 

 wide. 



The opening in the masonry is spanned by a concrete lintel 9 inches 

 deep, reinforced by four £-inch round iron rods. 



This lintel is moulded in place, the reinforcing rods being meanwhile 

 held in position by their ends, which pass through holes in the ends of 

 the wooden mould. 



The door frame is 4£" by 3" in section, and to secure air-tight- 

 ness is bedded in cement mortar, a strip of hoop-iron being imbedded 

 partly in the wood of the door frame and partly in the mortar all the 

 way round the frame. 



