Wherever greater strength of wall is desired than can be formed by a single 2 × 5 studding, as at the corners, or by a single 2 × 10 joist, as where partitions are to be placed, it is better to spike two or more pieces together than to have pieces sawed of the dimensions desired. These made-up pieces or timbers are stronger than solid pieces of the same character and dimensions, since the continuity of the cross-grain of the wood is broken in the made-up pieces. 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]).
Fig. 58. Construction of a large bridge.
Plates are made up of material 2 inches thick and as broad as the studding is wide, doubled, with joints mismatched. This most valuable principle of building up timbers of several 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 frequently 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 possible, on the farm house, however well they may be adapted to buildings in the city. Metal roofs are not objectionable in themselves, but only when they are laid flat on farm houses.
Fig. 59. A made-up plate, constructed of boards.
Fig. 60. Showing the principle of construction of [Fig. 59].
The pitch of roofs, like their shape, is also variable. Nothing below one-third pitch should be used except for special conditions. In [Fig. 38], page 127, is an illustration of the common pitch of roofs in fashion fifty years ago. Some roofs were even flatter than the one shown. The fashion now is to construct house roofs with nearly or quite half pitch. While steep roofs are desirable if made of wood, there is some danger that the change from the nearly flat roof to the steep one will be carried too far (see [Fig. 13], page 95). Various pitches of roofs are shown in [Fig. 61]. Steep roofs do not require as strong rafters, thrust less upon the plates, are more durable, and are less likely to leak than flat roofs.