Forms of Roofing.

The principal form in which iron and steel sheets are used for roofing are known as roll roofing, pressed standing-seam roofing, and corrugated roofing.

Roll roofing is made of iron or steel plates or sheets, 26 to 28 inches wide, and about 5 feet in length. The thickness or gauge of the sheets is usually from No. 26 to No. 30. The iron is either black or galvanized (which is preferred). These sheets are joined together at the ends to make strips about 50 feet long. One such strip is sufficient to cover 1 square (100 square feet) of the roof surface. These strips are rolled up as shown in Fig. 18. From this fact this form of roofing is known as roll roofing. In joining the sheets to form the strips, cross-seams, shown known at a in Fig. 18 are used. Note: In current times these joints in a roll is rare. We mainly use long continuous sheets unless a roofer is trying to match a historically accurate existing roof.

These seams are made with a single lock, as shown at a in Fig. 19, or with a double lock as at a in Fig. 20. The double-lock seam offers more resistance to the passage of water through the joints than the single seam. Moreover, as these seams are not soldered, the double-lock seam is less likely to come apart than the single-lock seam. The single-lock and the double-lock seams are also used for other forms of roofing, and are sometimes referred to as flat-lock seams.

This form of roofing is used these days mainly for historical renovations. There is a revival however for copper roofing over bay windows and architectural additions to larger, more expensive homes. In the past these roofs were used for industrial buildings, farm buildings, and for buildings where the appearance of the roof is of less importance than the protection that the roof affords. This form of roofing is adapted to roofs having a pitch of 2 inches or more to the foot. The work becomes more difficult as the pitch of the roof increases beyond the angle at which a workman can comfortably stand.