This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
In long gutters on roofs of low pitch the uppermost length of the gutter may be so broad that it will not be wise to lay it in one piece. A longitudinal roll-joint is then necessary, as shown at c in figs. 78 and 79. At the outlet end of the gutter a small box or "cesspool" is often formed, as at G, Fig. 78, and lined with lead, out of which a lead pipe 3 or 4 inches in diameter conveys the water through the wall to the head of the rain-water pipe.
Fig. 70. - Tranaverae Section through Lead Gutter.
A, B. C, D, as Fig. 78; E, roof -boarding covered with felt or waterproof paper; F, gutter-bearer; H. states 20 in long laid to a lap of 3½ inchs.
The lead should extend up the roof-slopes to a vertical height of not less than 6 inches above the flat portion of the gutter. In roofs of low pitch this entails a great quantity of lead, and it may be advisable to construct a box gutter with vertical sides in lieu of the ordinary gutter.
The junctions of lead flats and gutters with walls and chimneys must be carefully made by means of lead aprons and step-flashings, secured into the joints of the brickwork or stonework with lead wedges, and pointed with mastic. The lead used for flats and gutters should weigh 7 or 8 lbs. to the square foot, while that for aprons and steps may be 5 lbs.
Felt is sometimes used under lead flats, as under slates and tiles; but as it is difficult to dress the lead properly on such a yielding material, plumbers prefer it to be laid under the boards and not above them.
Over all gutters in roofs snow-boards should be fixed. These consist either of longitudinal bearers to which transverse laths are nailed, or (better) of transverse bearers arched to allow the passage of water down the gutter, and covered with laths laid in the direction of the gutter, as shown in Fig. 81. The laths should not be more than J inch apart The object of snow-boards is to keep the snow quite clear of the gutter, and so afford a free passage for water. When the snow rests on the gutter itself the passage of water is impeded, the snow forming a dam, which raises the water over the top of the leadwork and so drives it into the rooms below.
Fir &Raquo;.-Lead Drip.
Zinc is sometimes used instead of lead, being cheap, and is laid in much the same way, great care being taken to allow free play for expansion and contraction. The sheets used for roofs weigh from 1 to l½ lbs. per square foot, the heaviest being used for Hat-.
The best zinc is supplied by the Vielle Montagne Company, and this, if properly laid, will last perhaps -0 or 30 years. As a general rule, however, zinc cannot be recommended, as the inferior kinds are soon corroded by the smoky and acid-laden air of towns, and by contact with other metals (iron, copper, lead), and with lime.1 It is combustible, but has the merit of lightness. Copper is a far more durable material than zinc, and being used in thinner sheets, it provides a lighter roof-covering. Copper sheets weighing only 16 or 18 oz. per sq. foot are quite thick enough for flats, and in this respect the material has a great advantage over lead, which ought not to weigh less than 7 lbs, per sq. foot. Some of the characteristics of the three materials are given in the table on p. 139, from which it will be seen that as regards expansion and fusibility, the advantage rests with copper, while in respect of weight it is only slightly heavier than zinc, hulk for bulk. The durability of a sheet of copper weighing 1 lb. per sq. foot is said to be equal to that of lend weighing 6 or 7 lbs., while its hardness renders it suitable for roofs over which there is likely to be traffic. It is laid in a somewhat similar manner to lead and zinc.
Sheets of Iron, usually corrugated, are often employed for the roofs of outbuildings. They may be "galvanized" (i.e. coated with zinc) or painted. They are never used for the roofs of houses except for temporary purposes.
Fig. 81- Tranverse section of Parapet gutter with snow,boards. a. snow boards on arched bearer; B orerflow in case the rain-water pipe it stopped.
1 Cement, however, does not act injuriously upon sine, and the ill effects of iron are, for a time at least, prevented by galvanizing it.
8.85 to 8.94
6.86 to 7.21
Atomic weight, ......
Weight per sq. ft.1/10 in. thick, ..
5. 9 lbs.
Melting-point in degrees Fahr., ..
Conductivity (silver being 100), ..
Linear expansion between 32 and 212° F.
Relative linear expansion,..
Weight per sq. ft. used for roofs,...
1 to 1⅛ lbs.
6 to 8 lbs.
1 to 1½ lbs.
A kind of Hat roof which has been largely adopted in recent years, is really a floor, usually of fire-resisting- materials, covered with asphalt. Roofs of this kind, if properly executed, possess several advantages over those already described: they are fire-resisting, undecaying, jointless, and durable, besides affording a surface pleasant to walk upon, and capable of withstanding a considerable amount of wear and tear. A common example of this kind of roof is given in Fig. 82, where a a are steel joists, b concrete, 0 floated coat of cement and sand (1 to 2), D natural asphalt applied in two ⅜-inch or ½-inch layers, E asphalt fillet, and F asphalt skirting tucked into a joint in the parapet, the joint being first raked out to the depth of an inch, and pointed with cement mortar after the insertion of the asphalt. Such roofs should be laid to an inclination of not less than 1 in 40, and cesspools should be formed in the concrete and covered with asphalt, with lead pipes leading from the cesspools to the heads of the rain-water pipes.
For roofs, artificial asphalts must not be used, as they are too much exposed to the action of the weather, and may become soft in hot weather, and perhaps crack in cold weather or with the slightest inequality in the settlement of the building. I have before me a piece of such "asphalt", which a light kick broke like pot from a roof-skirting, where by command of the building-owner it had been used instead of the natural asphalt which I had specified.
Fig. 82- Flat Roof of Concrete and Asphalt.
Thin solid roofs, like that illustrated in Fig. 82, are not an effectual protection against extremes of temperature, and may with advantage be ceiled beneath with wood or metal ceiling-joists, and wood or metal lathing covered with plaster. The air-sapace thus formed will increase the comfort of the room beneath. Or instead of the solid concrete, one of the numerous kinds of floor may be used in which hollow lintels of brick or fire-clay extend between the joists. These lintels are keyed beneath to receive plaster. See Fig. 89.
Occasionally an ordinary flat of joists and boards is formed and covered with felt and asphalt, but this cannot be recommended, as - especially if the ceiling is plastered - the wood is almost certain to decay. A modification of this, in which the ventilation of the confined space is considered and the wood boards are super-seded by steel webbing, deserves mention. Short fillets of wood are nailed along the top of the joists, but with spaces between the ends to form air-pasr- on these steel webbing or metal lathing is fixed and floated over with hair-mortar. When this is sufficiently hard, it is covered with a layer of concrete and a double layer of asphalt. The system is applicable to floors as well as to roofs, - tiles, mosaic, terrazzo, wood blocks, or parquet taking the place of the asphalt.