Copper Flashings - A Manual - 1925 - Page 50
SEAMS IN CAP AND BASE FLASHINGS
Cap flashings against walls are usually made in 8-foot strips. The ends are lapped about 3 inches to form a cross seam, no soldering being necessary.
The seams in base flashings are of the flat type (see Fig. 74). They are about 8 feet apart, and should be so spaced that they do not occur with the seams in the cap flashing. The seams are made as is usual in flat seam construction and should be lapped in the direction of the flow so that no water will enter them. The ends of the sheets are tinned and sweated full of solder.
The double or copper-lock is sometimes used in this construction. (See Fig. 73).
SLOPES OF ROOFS
Roofs with a slope over 15° to the horizontal are called steep roofs. This slope is about 1 on 4. On such slopes, or steeper ones, no solder is necessary in the joints and seams, as the locking and flattening is water-tight.
Where there is a sudden change of slopes, as occurs at the intersection of two planes, large surfaces of copper should be connected by a large, free-moving locked joint, unsoldered.
There are many places where it is necessary to provide for expansion where usual methods do not apply. Particularly is this so at the intersection of different roof planes and at the top of built-in gutters which connect with copper roofing. At these locations the use of a large loose-locked seam is recommended. This consists, practically, of a standing seam bent flat, or a loose double lock. It acts as an expansion joint and prevents creasing and folding at the line of intersection. Of course, care must be taken to place the lock, which is not water-tight, so that it will not leak. It should also be placed as close as possible to the line of intersection.
The principle is the same as is used on decks, such as is shown in Fig. 22. Here the seam is left standing up. Were the slope of the roof greater it would be turned down to form a "free-locked" or "loose-locked" seam.
When used as shown it is held in place with a cleat. In box-gutters where the roofing sheet is secured on the roof no cleat is necessary. As such a seam is not water-tight it must, of course, be located above the outside edge of the gutter.
THE DOUBLE LOCK OR COPPER-LOCK
The double or copper-lock (Fig. 73) is made by folding the joined sheets over twice, instead of once, to form the seam. It has these advantages:
1. No soldering is necessary to make a water-tight joint.
2. It allows ample provision for expansion.
An objection is that it uses more copper than does the single lock, 2½ inches being needed instead of 1½ inches. This amounts to about 7% of a 24 by 30-inch sheet. However, this loss is compensated by the saving in soldering.
A second objection is that water is liable to work its way under the unsoldered edge, freeze, and open the seam. This can be overcome by making seams with the slope and by tipping those on flat surfaces with solder along the outer edge. If properly malleted down this is unnecessary.
A third objection is that the number of folds, 21 in all, at the corner of a sheet staggered with adjoining ones, make a hump in the seam. This can be overcome by special notching, or by using the single lock on one set of seams.
Its merits are such as to recommend it for all work, and especially for large built-in gutters where expansion is difficult to handle.
FASTENINGS FOR FLASHINGS
Fundamental in installing copper flashings are proper fastenings.
A good rule to follow is:
I. All fastenings of copper must be of copper or brass.
This rule applies not only to nails but to gutters, hangers, brackets and braces, and to screws, rivets and washers.
When steel or iron (either plain or galvanized) is used with copper work a galvanic action takes place between the copper and the other metal which quickly destroys the latter.
Two equally important rules are:
II. Never secure copper in any manner which will prevent its free movement.
III. Fasten copper flashings over 12 inches wide by cleats. Do not nail.
The greatest source of trouble from failure to observe these two simple rules is in valley flashings. These, by their very nature, are usually from 16
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