128 



Roofs for Farm-Bidldinrjs. 



ol' which arc adapted to slate coverinG:, and one to tiles. The 

 cheapest of these is Fig. 14. It is the common king-rod truss, in 

 which a wrought-ivon rod takes the place of a wooden post. Its 

 cost will be found to be M. bs. bd. per square of roofing or 5/. 

 per square of ground (10 x 10) covered. This example of com- 

 bined materials, when compared with the cheapest roof of the 

 same span framed wholly of Avood, shows a difference of Id. per 

 square foot of ground covered in favour of timber. 



The next example (Fig. 15) is a form of truss much adopted, 

 for roofs of from 20 to 30 feet span, in France ; but, as far as the 

 writer's experience extends, it is not much used in this country. 

 The tie-rods are double ; and this arrangement reduces the iron 

 employed to a minimum in size. 



The examples of 20 feet span (outside measurement), which 

 include two roofs Nos. 15 and 16, in which the slates are laid 

 upon boards, are as follow : — 



The examples of timber and iron roofs used for 24 feet spans, 

 inside measurement^ are also four in number, but any one of the 

 preceding examples for 20 feet spans might safely be extended 

 to wider spans, with a proportional increase of dimensions and 

 cost. The prices of the four examples are as follow : — 



Three examples of economical arrangement of wrought iron 

 in the roofing of agricultural buildings are shown in Sheet 5. 

 In these iustances wrought-iron rods take the place of tie-beams 



