Purple . North Wales (Bangor, Penrhyn, Dinorwic), Newfoundland,
Germany.
Green . South Wales (Precelly), Cumberland, Westmorland, Lancashire, Ireland, Newfoundland, Norway, United States and Germany.
Slates are cut to many different sizes varying in length from I0 in. to 36 in. and in width from 5 in. to 24 in. There are perhaps thirty or more recognized sizes, each distinguished by a different name. In common practice those generally used are “large ladies, " 16 in. by 8 in.; "courltesses, " 20 in. by IO in.; and “ duchesses, " 24 in. by 12 in. Generally speaking, the rule governing the use of the different sorts is that the steeper the pitch the smaller the slate, and vice versa. Buildings in very exposed positions naturally require steeply pitched roofs. Some of the technical terms used by the slater are as follows:- Bed, the under surface of a slab when laid. Buck, the upper surface of the slate. Gauge, the distance between the lines of nailing. This depends on the length of the slate and equals half the length of the slate after the lap plus an inch for the nail-hole has been deducted. This is for slates nailed near the top edge; for those fixed near the middle the gauge would be half an inch more, as no allowance for nail-holes is required.
Margin, the width of the exposed portion of each course which equals the width apart of the nailing. Head and tail, the top and bottom edges of the slate. Lap, the lap of the tail of one course of slates over the head of the second course below it. The lap is made from 2% in. to 4 in. (usually 3 in.), and for this distance there are three thicknesses of slate, namely, the tail of the top course, the middle of the next and the head of the third course.
Slates may be fixed by nailing at the head (see fig. 22) or at about the middle. The latter method is the stronger, as the levering effect of the wind cannot attain so great a strength. There is a small economy effected by centre nailing, as the margin is slightly larger and fewer slates are required to cover a given space; longer nails, however, are required, for as slates are laid at an angle with the pitch of the roof their centres cannot be made to approach so near ””* sh
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F xc. 22.-Detail of a Slated Roof.
to the slating battens or boarding as the head, which lies close on the surface to which it is fixed. Another point worth noticing is that the nail-holes in the centre nailed slating are only covered by 3 in. of the tail (the amount of the “lap ”) of the course of slates above, and rain is very liable to be forced under by the wind and cause the wood battens or other woodwork to rot. Head-nailed slates, on the other hand, have their holes covered by two layers of slate, and are removed from exposure by the length of the gauge plus the lap, which in the case of “ Countess ” slating equals II in. “ Openslating " is an economical method of laying slates that is often adopted for the roofs of sheds and temporary buildings. The slates in the same course are not laid edge to edge as in closing slating, but at a distance of two or more inches apart. This forms a roof covering light in weight and inexpensive, which, although not strictly geather-proof, is sufficiently so for the buildings upon which it is use .
Slates are laid upon open battens fixed upon the rafters or upon close boarding or upon battens fixed upon boarding. The battens are % in. or I in. thick and 1% in. to 3 in. wide, and are spaced to suit the gauge of the slates. When close boarding is used it is often covered with in odorous asphalted felt. Nhile taking these precautions to make the roof sound and tight it should be borne in mind that slate is liable to decay if not ventilated, and to effect this the battens are sometimes fixed vertically, ridge ventilators introduced and air inlets arranged at the eaves. The bed of slates laid without provision for the admission of air will be found on removal after some time to have rotted so as to scale off and easily crumble into powder.
The nails used in slating are a very importantvitem, and the durability of the Work depends to a large extent upon them. They should have large fiat heads. The most satisfactory are those made of a composition of copper and zinc, but others of copper, zinc, galvanized iron and plain iron are used. Those of copper are most durable, but are soft and expensive. Zinc nails are soft and not very durable; they will last about twenty years. Iron nails even if galvanized are objectionable in permanent work, though they may be used for temporary roofs. When the plain-iron nails are employed they should be heated and plunged in boiled linseed oil. The pitch of a roof intended for slating should not incline less than 25° with the horizontal, while 30° is a safer angle to adopt. Tiles for roofing purposes are made from clay and burned in a manner similar to bricks. The clay from which they are made is, however, of a specially tenacious nature and prepared T” with great care so as to obtain a result as strong and as es nearly non-porous as possible. Tiles are obtainable in many different colours, and some of these have a very beautiful effect when fixed and improve with age. They comprise a large number of tints from yellowish red, red and brown to dark blue. As with bricks the quality depends to a large extent upon the burning; under burnt tiles are weak and porous, liable to early decay, while over burning, though improving the tiles as regards durability, will cause them to warp and will spoil colour. The usual shape is the “plain tile, ” but they are made in various other shapes with a view both to easier fixing and lighter weight, and to ornamental effect. There are also several patented forms on the market for which the makers claim special advantages. The ordinary tiles are slightly curved in shape to enable them to lie close one upon the other. Some of them have small “ nibs ” moulded on at the head by which they may be hung upon the battens and nailing avoided (see fig. 23). Nail-holes are provided, and upon
steep slopes it is advisable
to make useof
them. Others are
made without the
nibs, and are fixed ' »
either by nailing to
the battens or boarding or
hung by means
of oaken pegs wedged
in the holes to the battens,
the pegs in the
latter case acting in
the same way as the
above-mentioned nibs.
Plain tiles are of rectangular
form, the
standard dimensions
are 10% in. long by
6% in. wide. They are
usually % in. thick and
weigh about 2% lb each.
There are many forms of ornamental tiles, which are plain tiles having their tails cut to various shapes instead of moulded square. A number of patented forms of tiles also are on the market, some of which possess considerable merit. Pantiles are suitable for temporary and inferior buildings such as sheds and outhouses. They are laid on a different principle from plain tiles, merely overlapping each other at the edges, and this necessitates bedding in mortar and pointing inside and sometimes outside with mortar or cement. This pointin plays an important part in keeping the interior of the building free from the penetration of wind and water. Pantiles are generally made to measure 13% in. long by 9% in. wide, and weigh from 5 lb to 5% lb each. Moulded on at the head of each tile is a small projecting nib which serves for the purpose of hanging the tile to the lath or batten. They are laid with a lap of 3% in., 2% in. or 1% in., giving a gauge (and margin) of 10 in., II in. and 12 in.. respectively. The side lap is generally 1% in., leaving a width of 8 in. ex osed face. There are many other forms based upon the shape ofp the pantile, some of which are patented and claim to have advantages which the original form does not possess. Among such are “corrugated tiles, " of the ordinary shape or with angular flutes, and also the Italian pattern “ double roll tiles, " “ Foster's lock-wing tiles.” Poole's bonding roll tiles are a development of the Italian pattern tile.
Glass as a roof covering and the different methods of fixing it are dealt with in the article GLAZING.
There are many other materials used for roof covering besides those already described, many of them of considerable value. Some have in the past enjoyed considerable vogue, but have Ml practically died out of use owing to the development and 5 cheapening of other forms of roofing. Among these may 2 '::;:J';s be included thatch and wood shingles, the use of which in " these .days is practically reduced to special cases. Other, little used roofing materials are those of recent invention. some of 'shit h perhaps milf ty
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F IG. 23.-Detail of a Tiled Roof.
