Roofs for Farm- Buildings. 143 



that tlie period lias not yet arrived when iron can economically 

 be substituted for timber in the construction of the roofs of farm- 

 buildings. 



The employment of cast iron in roofing has not been mentioned, 

 as its weight and expense must ever preclude its use in ordinary 

 buildings, although the roofs of the Houses of Parliament are 

 constructed of wrought-iron principals, covered with sheets of 

 cast iron three-eighths or half-an-inch thick. 



Some other forms of roof-covering have also been omitted in 

 the following descriptions, but enough have probably been 

 selected for the present purposes of comparison : — 



Descriptions and Estimates of the Cost of Eleven Span-Eoofs, constructed 

 of various materiqls, hut each covering a Bidlding 50 feet long ly 20 feet 

 wide. 



No. 1.— The cheapest roof that can be constructed is foitned with six pair 

 of principals of the following scantling : — Tie-beams, 8 x 3 in. 

 Principals, 4x3 in. King-post, 4x3 in. Stnitts, 3i x 2 in. 

 Iron straps and wedges. Wall-plates, 44 x 3. Ridge, 7 x I3 in. 

 Covered with Croggon's patent asphalte felt,* tarred and sanded, 

 on purlins about 1 ft. 9 in. apart, 41 x -h in.f 



The cost of which, as i^er detail, is 26?. 10.?. 11(7. 



Or about 21. per square.^ 



A roof of this kind would, of course, be only desirable in outbuildings, 

 where no flues are used. It forms a warm covering, and if properly attended 

 to, and coated from time to time with tar and sand, may last a good while, 

 whilst it admits of easy repair ; but unless it receives more than ordinary 

 care, it soon shows cracks and openings, through which the rain finds its 

 wa}', and speedily decays the timbers. This kind of roofing is extensively- 

 used on railways. The chief objection is, that the felt lies hollow. This is 

 obviated iu 



Xo. 2, — A stronger roof than the foregoing, formed of principals of the same 

 scantling, but with fir rafters, 3 x I5 in., 1 ft. (j in. apart, on two 

 purlins, 4^- x 2^ in., and covered with 1-in. rough battens about 

 6 in. apart, and Croggon's felt tarred and sanded, as before de- 

 scribed. 



The cost of this is 31Z. 17s. 4c7.f 



Or about 2.1. 7s. per square.t 

 This makes a much stronger and more sighth' roof. 



jSTo. 3. — A roof formed of wood principals of the same scantling as before, 

 covered with Morewood's patent continuous iron roofing, nailed on 

 wood purlins, 4^ x 2? in., 1 ft. 9 in. apart, with wall-plates, 

 4^ x 3 in., and ridge, 7 X I2 in. 



The cost of which is 457, 9s. S^/.f 



Or about 37. 7s. C,d. per square. J 



* Croggon's asphalte felt costs 14s. per square. 



t See tor details of cost, pp. 145, 146. 



X The details show 13 square in the 3 first roofs. 



