Corrugated iron is used for roofs and sides of buildings. It is usually laid directly upon the purlins in roofs constructed as shown in Figs. 230 and 231, the former being constructed to receive sidings of corrugated iron, while in the latter figure the side walls of the building are brick. Special care must be taken that the projecting edges of the corrugated iron at the eaves and gable ends of the roof are well secured, otherwise the wind will loosen the sheets and fold them up. The corrugations are made of various sizes such as 5-inch, 2 1/2-inch, 1 1/4-inch and 3/4-inch, the measurements always being from A to B in Fig. 232, and the depth being shown by C. The smaller corrugations give a more pleasing appearance, but the larger corrugations are stiffer and will span a greater distance, thereby permitting the purlins to be further apart.

Fig. 229.

Fig. 230.

The thickness of the metal generally used for roofing and siding varies from No. 24 to No. 16 gauge. By actual trial made by The Keystone Bridge Company it was found that corrugated iron No. 20, spanning 6 feet, began to give permanent deflection at a load of 30 lb. per square foot, and that it collapsed with a load of 60 lb. per square foot. The distance between centers of purlins should, therefore, not exceed 6 feet, and preferably be less than this.

Fig. 231.

Fig. 232.

Tables

The following tables will prove of value when desiring any information to which they appertain.

The following table shows the distance apart the supports should be for different gauges of corrugated sheets:

Nos. 16 and 18.... 6 to 7 feet apart.

Nos. 20 and 22....4 to 5 feet apart.

No. 24.....2 to 4 feet apart.

No. 28.... 2 feet apart.

The following table is calculated for sheets 30 1/2 inches wide before corrugating.