When the zinc is required to be laid without boarding - which is, of course, a great saving - it must be strengthened by corrugations, i.e. by curved indentations or flutes formed along the sheet.

The ordinary corrugated zinc consists of flutes about 3 inches wide, lying close together.

It is laid in a similar way to corrugated iron (p. 61), the purlins being placed about 2 feet 6 inches apart.

Italian Corrugated Zinc Roof

In this form of zinc the corrugations are spaced more widely, being 1 foot 3 inches apart.

In Fig. 122 one sheet is shown in section by the thick black line, the ends of the adjacent sheets being scored in section.

Italian Corrugated Zinc Roof 200109

Fig. 122.

The zinc may be laid upon rafters, so spaced and shaped as to fit into the corrugations (Fig. 12 2), but for the sake of durability it is better to lay it upon boarding.

The sheets are secured to them, either by patent holding down clips shaped so as to allow of the expansion and contraction of the sheets, or by patent sliding studs. Both methods are fully described in Messrs. Braby's pamphlet.

Fig. 122 shows in section a portion of a roof covered with Italian corrugated zinc. The zinc rolls or rafters are 1 foot 3 inches apart, and are supported upon purlins, which in large roofs may be 10 feet apart.

The depth of the rolls when they act as rafters, and are laid upon purlins about 7 feet apart, is about 3 inches; but when laid upon boarding they are only 2 inches deep.

Thickness Of Zinc For Roofing

The gauges1 recommended by the Vielle Montagne Company are Nos. 14, 15, and 16 zinc gauge (see Part III.) for the roof covering.

"No. 14 to be used only where it is necessary to exercise the greatest possible saving in the first cost."

No. 15 or 16 for gutters.

Nos. 14 and 15 for flats.

Nos. 13 and 14 are frequently used for roofing, where economy is an object.

It must benotedthat these are the numbers of the Vielle Montagne Company's zinc gauge, not of the ordinary Birmingham wire gauge.

Zinc Flashings are very similar to those of lead described in Part I.

An illustration of one is shown at F in Fig. 117.

The edge of the sheet is generally turned up about 6 inches against the wall, and the apron over it is finished and stiffened by being bent round to form a bead b as shown.

The ridge roll is covered with zinc in nearly the same manner as with lead, except that the zinc is not worked so much into the angles under the roll. It is secured by forks, similar to those described in page 64.