Made-up Timbers 147 



In the construction of large bridges the timbers, 

 where exposed to the weather, are made up of 

 smaller timbers, since they are then not only 

 stronger but more durable and less subject to 

 dry rot than if they are solid (Fig. 58) . 



Plates are made uj) of material 2 inches 

 thick and as broad as the studding is wide, 



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Fig. 58. Constnietiou of a large bridge 



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doubled, with joints mismatched. This most 

 valuable principle of building up timbers of sev- 

 eral thin pieces is a somewhat recent practice. 

 Where very large timbers are required, as in 

 trussed or self-supporting roofs, the timbers of 

 which are not exposed to view, they are fre- 

 quently made up of boards 1 inch thick and as 

 broad as the vertical dimensions desired. This 

 method is sometimes used in constructing 

 timbers for both houses and barns (Fig. 59). 



Roofs of houses are, of necessity, extremely 

 variable, as the house is not planned to suit the 

 roof, but the roof to suit the house. Flat metal 

 roofs of all kinds should be avoided, as far as 



