Valley Gutters are formed in somewhat the same manner as those of lead.

For roofs laid with wood rolls the wooden trough is lined with sheet zinc, - the sides of which are turned up, and the upper edges bent inwards under the bead formed by the lower edge of the sheet at the eaves.

Where Italian corrugated zinc is used the sides of the zinc lining to the gutters are turned up, and the edges bent over the thickness of the wood sides of the trough.

The minimum fall for such gutters should be 1/40

Zinc Tiles, generally of diamond or shield shape, are sometimes used for roof coverings, each Heine hung from a hook fixed upon battens or boarding, and passing through a hole near the top of the tile.

Zinc Eaves Gutters2 are made of various forms, very similar to those of cast-iron, and are fixed in the same positions.

They soon perish, and are hardly strong enough to bear the weight of snow or even the pressure of a ladder.

Zinc gutters, not being so strong as those of iron, require stays about 1 foot 6 inches apart. These are simply hollow cylinders of zinc - placed across the gutter - through which is passed the screw fixing the gutter to the wood-work. The stay keeps the upper part of the gutter from bending inwards as the screw is driven home.

1 For the thickness of the various gauges see p. 346, Part III. 2 Sc. Rhones.

The various gauges for zinc and other metals are given in Part III., whence the following remarks are taken.

Zinc should not be allowed to be in contact with iron, copper, or lead. In either case voltaic action is set up, which soon destroys the zinc. This occurs especially and more rapidly when moisture is present.

Zinc should also be kept clear of lime or calcareous water, and of any wood, such as oak, which contains acid. Zinc laid on flats or roofs where cats can gain access is very soon corroded.

An objection to zinc for roofs is that it catches fire at a red heat, and blazes furiously.1

Glass is very frequently used as a covering for the whole or parts of roofs, such as those of railway stations, manufactories, etc. etc.

In some cases where a maximum of light is required, clear glass must be used ; but, as a rule, patent rolled rough plate will admit sufficient light, and it is always much stronger.

The glass is laid upon sash bars of iron or wood. The former may be of cast-iron, similar in section to wooden sash bars, or of wrought-iron of section. The unequal contraction of iron and glass renders it difficult to keep a tight joint between them.2

Asphalted Felt

This material is, as has already been noticed, often used under slates on account of its being waterproof and a non-conductor of heat.

It is, however, also adapted as a roof covering alone, for temporary buildings, being fixed to boarding by copper, zinc, or iron clout nails (the last being dipped in oil). The felt should be stretched tight, the joints between the pieces overlapped, and the whole paid over with hot tar and lime boiled together, and then sanded.

Willesden paper and wire wove roofing are also used for temporary roof coverings, and are described at pages 456, 457, Part III.

1 Bloxam.

2 For patent systems of glazing see p. 204.