Occasionally the roll at the edge of the flat is formed with its base upon the top of the boarding in the same way as the other rolls on the flat. This is considered by some to have a better appearance than the nosing, as it forms a sort of ridge which ranges with the ridges of the hips of the roof.
1 Chiefly in Scotland and the north of England.
2 Sc. Latchet.
Holloio Nosings may be formed on the same principle as hollow rolls (see N, Fig. 460). This figure shows a flat nosing, but they are often made round or "bottled" for the sake of appearance, being then in section like the roll P, but with the base vertical.
"Welts (see Fig. 461) are formed by bending up the adjacent edges of two sheets - turning one over the other, and then dressing them down close to the flat. When very exposed they are further secured by tingles.
They take up less room than rolls, and are common on curb roofs, but do not form so good a joint.
Lapped Joints are those in which one sheet is dressed down fiat and the edge of the adjacent sheet over it, so as to lap from 4 to 6 inches.
This joint is used chiefly between the different portions of long and narrow pieces of lead, such as flashings, coverings for hips, ridges, valleys, etc., and generally lies across the current.
Drips are joints made across the current of a sheet of lead, thus: -
The surface to be covered is interrupted by steps from 1 1/2 to 3 inches in depth (the deeper the better), running across it at intervals of about 8 or 10 feet. The lower sheet is first laid, dressed close up to and over this step, and its upper edge is generally fitted as in Fig. 462 into a rebate cut for it in the boarding of the higher level of the drip so as to avoid a ridge.
The upper sheet overlaps the lower, and is turned down over it as shown. This upper sheet should stop 3/4" short of the horizontal sheet below, otherwise the wet will be drawn up, by capillary attraction, between the sheets into the boarding above.
The upper lead is often carried down so as to form an overcloak resting an inch upon the flat. This is objectionable, as moisture is drawn up by-capillary attraction. The rebate in the upper boarding is sometimes omitted and the upturned lead stopped 1/4" short of the upper surface of the drip.
Fig. 463 shows a form of drip used in flats and long lengths which have a tendency to blow up.
When long lengths of lead are used, tacks or clips (c), as shown in black in Fig. 463, may be fixed at about 18 or 20 inches apart. The upper end of the lower lead is frequently nailed to the boarding as shown. The tack is usually nailed through the lead below, but it is better to make it extend beyond and nail it separately as shown.
Fig. 464 shows another form of drip used where there is much exposure to wind. It explains itself, and so does Fig. 465, which is used in similar situations and called a clinch.1
In some parts of the country a drip, such as that in Pig. 462, is formed thus: - The boarding on the upper level is allowed to project an inch or so over the bearer; the lower sheet of lead is turned up until it reaches the lower side of this projection, or "bottlenose"; the upper sheet is dressed round the projection, and hangs down over the turned-up lead, to form the apron.
A Eaglet is a groove about an inch deep, and as narrow as possible, cut into masonry or brickwork to receive the edge of sheet lead to be fixed to the walls. Wedges, Wall-hooks. - The lead-flashing, If, Fig. 466, may be secured in several ways - by wooden or lead wedges2 (he) driven in tight between it and the edge of the raglet, or by wall-hooks3 (wh), which are short, flat-shanked spikes of bar iron with one end hammered thin and bent over at right angles to form a head. The lead wedges are more adapted for use in stonework, and the wall hooks in brickwork.
The joint is generally pointed and made good with cement or mastic.
When the raglet is formed along me top of a course, as shown in Fig. 476, and a very secure joint is required, to withstand exposure, the lead may be "burnt in," which consists in inserting the edge of the sheet in the raglet groove, and filling the latter with molten lead, which is then well punched or "caulked" in.
1 Buchan. 2 Sc. lead bats. 3 Sc. Thumbats.
In some cases - for example, in covering a small dome with sheet lead - it is necessary to screw the lead to the woodwork. The screws are generally used in pairs (see Fig. 467), inclining inwards toward one another, and the boarding is countersunk, so that the heads of the screws are well below the surface of the wood. Into the hollow thus formed, the sheet lead is dressed and screwed down, and then a patch of molten solder (a lead dot) is "wiped " in, so as to protect the screws, and bring the whole to an even surface. The screws must be left standing up from the lead so that the solder may get a good hold of them. If screwed right home they would pull through the lead if the wind tended to lift it. If the boarding is not hollowed out where the lead dots occur, they of course project above the surface. The heads of nails may be similarly protected.
Flashings are pieces of sheet lead placed so as to cover joints which would otherwise admit wet to the roof timbers, or other parts of the building.
The term is frequently applied to a piece of sheet lead fixed to a wall, and hanging over, so as to cover the edge of a gutter or other sheet lead turned up against the wall, and to protect the joint between the lead and the masonry. (See aa, Fig. 469.)
In some parts of the country, however, this particular flashing is known as a "cover-flashing" or "apron."
The term "flashing" will be taken in these Notes to include the whole of the lead used for the protection of a joint, and "cover-flashing" or "apron" to refer only to the overhanging piece.
The flashing may be fixed in various ways; it may lie over the slates as in Fig. 471, or under them, as in Fig. 472.1
The portion turned up against the wall should be 5 or 6 inches high, and may itself be secured in a raglet, or the turned-up end may be left free, so as to allow contraction and expansion, and be covered by an apron.
1 This kind of flashing may be considered a form of gutter.
An Apron or Cover-Flashing is a covering piece of sheet lead, of which the upper edge is turned into a raglet, and there secured as above described. The remainder is turned down, and hangs freely over the upright part of a flashing or gutter.
"When the side or end of a gutter or flat is turned up against a wall, the joint between the wall and the upturned lead is thus securely covered and protected from wet, while the lead is free to expand and contract under changes of temperature.
In the best work, sheets of lead which are wide, or of which the outer edge is fixed, should never themselves be secured to the wall, but should be connected with it by means of an apron.
Some authorities recommend that the apron should be of the same width as the upturned lead, as shown at x in Fig. 469, so that it may not be liable to be blown up and expose the joint; this, however, is generally considered a waste of material, and it is objectionable, for it leads to the sucking up of moisture past the joint by capillary attraction. The apron is therefore usually turned down only 3 or 4 inches over the edge of the upstanding lead, so that the lower edge may be clear of any wet which lies upon the horizontal sheet of lead below.
The flashing between a wall or the side of a chimney and the roof that slopes down from it is also frequently called in England an "apron," and in Scotland a "berge."
It is a simple flashing, formed out of lead some 15 or 16 inches wide, of which 6 or 8 inches may be dressed over the slates down the slope, 6 inches upturned against the chimney, and the remainder fixed in the raglet.