(Contributed by T. H. Bishop, A.R.I.B.A.)

External plumbing consists mainly in covering roofs with lead to make them weather-tight. If laid successfully, lead surpasses every other material, as it combines lasting and waterproof properties. In towns, lead coverings are more economical than zinc, the former being practically indestructible, while the latter requires frequent renewal.

The lead used for external work is of two kinds, cast and milled. Cast lead is lead molten and cast in moulds, and may be obtained in sizes up to 20 feet in length and 7 feet wide; it is hard and durable and suitable in positions subjected to great traffic, but has the disadvantage of being subject to flaws and sand-holes. Milled lead is first cast and then passed through rollers, which toughens it, and may be obtained in sheets 7 feet wide by 33 feet long, and from some manufacturers even longer, and 8 feet in width when specially ordered. When subjected to variations of temperature it changes its dimensions, and it is therefore not advisable to lay it in large sheets. It should never be rigidly fixed, as this interferes with its expansion and contraction, and the use of solder should be avoided where possible; care should be taken that the lead is laid so that the edges do not blow up. Lead does not rapidly decompose, and is usually protected by a coat of oxide; it decays rapidly when in contact with damp wood, and by galvanic action through being brought into contact with zinc or copper. It is also rapidly destroyed by some acids, and by decaying vegetable matter.

Lead is specified by weight. The following table gives its weight and corresponding thickness:-

Weight in Lbs. per Foot super.

Thickness in Inches.

Weight in Lbs. per Foot super.

Thickness in Inches.

I

0.017

7

O.118

2

0.034

8

0.135

3

0.051

9

0.152

4

O.068

10

0.169

5

0.085

11

0.186

6

0.101

12

0.203

Lead usually expands .00285 of its length between 32° and 212° Fahr.

The following weights of lead can be recommended for their varying positions:-

Roofs, flats, and main gutters

. . . .

7-lb. lead.

Hip ridges and small gutters

. . . .

6 „

Flashings ..

. . . .

5 ,,

Soil pipes ..

. . . .

8 to 10 ,,

No length of lead should be used exceeding 7 feet, and there should be no nailing unless absolutely necessary.

Bossing is working lead to the required angles with boxwood dressers, and is prferable to soldering where the lead does not exceed 12 inches in depth, as soldered joints are liable to crack.

Lead tacks, sometimes called tingles, are narrow strips of lead from 1 to 2 inches in width, used to secure one of the free edges of the lead.

Passings, which are usually 4 inches, are laps of one piece of lead over the adjoining piece, when the lead cannot be used in one length.

Raglets are grooves or chases cut into brick or stonework about 1 3/4 inch deep, to receive the turned-in edge of the lead flashings.

Cover flashings, usually 6 inches wide, are used to cover the edges of flashings turned up against walls to prevent rain from driving in, and to allow the lead underflashing to expand.

Apron pieces are the lower horizontal flashings of a chimney shaft or wall, and are 6 inches deep.

Tilting fillets are usually of wood, triangular in section, used where inclined surfaces abut against walls, to tilt the slates or tiles so that they carry the water away from the weakest points.

The joints usually used in external leadwork are:-

Joints Across The Flow Or Current

Lap and drip joints.

Joints Parallel With The Flow

Rolls, hollow rolls, seams or welts.

Lap joints are used when inclined surfaces of pitched roofs are covered with lead. The length of the boards should be placed parallel to the inclination. The lead is then fixed between rolls, the upper sides being turned over the boarding, and copper nailed so that the sheet is secured from sliding. The lower edge of the upper sheet should lap on the top edge of the lower. If the roof has an inclination of not less than 45 degrees, 6-inch lap is sufficient; but if the angle of roof is less than 45 degrees, the lap should be increased or a drip formed.

Ridges

These should be in 6-lb. lead, in lengths not exceeding 7 feet. There is a choice of two ways in fixing ridges -

1. The lead tacks, or copper clips, are first nailed to the ridge board, and the wood roll (never less than 1 1/2 inches in height) is then fixed. The lead ridge is then dressed over the roll and secured by the lead tacks or copper clips (see Fig. 174).

Ridges 262

Fig. 174.

2. The lead can be nailed direct on to the roll, and the tacks nailed to the tilting fillet abutting on the ridge board (see Fig. 174).

Fig. 175

Fig. 175.

In all cases the lead should be well dressed into the bottom edges of the roll, and should lie 6 inches on the slates or tiles on each side of the ridge. The joints are formed by lapping the lead.

Valleys And Hips

If the inclinations of two roofs form a hollow, that hollow is called a valley; and if they form a ridge, it is called a hip.

Hips may be made watertight in three ways -

1. By dressing lead of similar size as described for ridges. The lower end is bossed over the end of the hip and securely supported by a lead tack placed in the centre of each length of lead, as shown for ridges (Fig. 175).

2. The hips may be formed by soakers. These are small pieces of lead, one to each slate, made to lap over one another. They are fixed over the roll, where they are visible, or the roll may be omitted in order to save lead.

3. In some cases a secret gutter is formed, as shown in Fig. 176, and the slates are then cut close. This forms a very neat finish.

Valleys And Hips 264

Fig. 176.

Valleys may be arranged to form a small gutter, the lead being dressed over fillets, as shown in Fig. 177

Valleys And Hips 265

Fig. 177.