Take the distance F L in the plan and place it a shown from Fo to Lo, and draw a line from Lo to F1, which is the true length of the valley shown by L F in the plan. Multiply this length by 2, which will give the required number of feet of valley required. This length of valley can also be obtained from the plan by taking the vertical height of the roof of the wing, shown by Fo F1 in the side elevation, and placing it at right angles to F L in the plan,k from L to F2, and draw line from F2 to F which is the desired length similar to F1 Lo in the side elevation.


The first step necessary in preparing the plates for flat seam roofing is to notch or cut off the four corners of the plate as shown in Fig. 199 which shows the plate as it is taken from the box, the shaded corners a a a a representing the corners which are notched on the notching machine or with the shears.

Care must be taken when cutting off these corners not to cut off too little otherwise the sheets will not edge well, and not to cut off too much, otherwise a hole will show at the corners when the sheets are laid. To find the correct amount to be cut off proceed as follows:

Assuming that a 1/2-inch edge is desired, set the dividers at 1/2 inch and scribe the lines b a and a c on the sheet shown in Fig. 199, and, where the lines intersect at a, draw the line d e at an angle of 45 degrees, which represents the true amount and true angle to be cut off on each corner. After all the sheets have been notched, they are edged as shown in Fig. 200, the long sides of the sheet being bent right and left, as shown at a, while the short side is bent as shown at b, making the notched corner appear as at e. In some cases after the sheets are edged the contract requires that the sheets be painted on the underside before laying. This is usually done with a small brush, being careful that the edges of the sheets are not soiled with paint, which would interfere with soldering. Before laying the sheets the roof boards are sometimes covered with an oil or rosin-sized paper to prevent the moisture or fumes from below from rusting the tin on the underside. As before mentioned, the same method used for laying tin roofing would be applicable for laying copper roofing, with the exception that the copper sheets would have to be tinned about 1 1/2 inches around the edges of the sheets after they are notched, and before they are edged.

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Fig. 199.

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Fig. 200.

In Fig. 201 is shown how a tin roof is started and the sheets laid when a gutter is used at the eaves with a fire wall at the side. A represents a galvanized iron gutter with a portion of it lapping on the roof, with a lock at C. In hanging the gutter it is flashed against the fire wall at J; after which the base flashing D D is put in position, flashing out on the roof at E, with a lock at F. Where the base flashing E miters with the flange of the gutter B it is joined as shown at b, allowing the flange E of the base flashing as shown by the dotted line a. As the water discharges at G, the sheets are laid in the direction of the arrow H, placing the nails at least 6 inches apart, always starting to nail at the butt e e, etc. Care should be taken when nailing that the nail heads are well covered by the edges, as shown in W, by a. Over the base flashing D D J the cap flashing L is placed, allowing it to go into the wall as at O.

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Fig. 201.

When putting in base flashings there are two methods employed.

In Fig. 202 is shown a side flashing between the roof and parapet wall.

A shows the flashing turning out on the roof at B, with lock C, attached and flashed into the wall four courses of brick above the roof line, as shown at D, where wall hooks and paintskins or roofer's cement are used to make a tight joint. Flashings of this kind should always be painted on the underside, and paper should be placed between the brick work and metal, because the moisture in the wall is apt to rust the tin. This method of putting in flashing is not advisable in new work, because when the building is new, the walls and beams are liable to settle and when this occurs the flange D tears out of the wall, and the result is disagreeable leaks that stain the walls. When a new roof is to be placed on an old building where the walls and copings are in place and the brick work and beams have settled, there is not so much danger of leakage.

The proper method of putting in flashings and one which allows for the expansion and contraction of the metal and the settlement of the building is shown in Fig. 203, in which A shows the cap flashings, painted with two coats of paint before using. When the mason has built his wall up to four courses of brick above the roof line line the cap flashing A is placed in position and the wall and coping finished; the base flashing B is then slipped under the cap A. In practice. the cap flashing is cut 7 inches, then bent at right angles through the center, making each side a and b 3 1/2 inches. The base flashing B is then slipped under the cap flashing A as shown at C.

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Fig. 202.

Roof Mensuration Part 2 0900223

Fig. 203.

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Fig. 204.

Where the cost is not considered and a good job is desired, it is better to use sheet lead cap flashings in place of tin. They last longer, do not rust, and can be dressed down well to lay tight onto the base flashings. Into the lock C the sheets are attached. After the sheets are laid the seams are flattened down well by means of a heavy mallet, with slightly convex faces, after which the roof is ready for soldering. When a base flashing is required on a roof which abuts against a wall composed of clap boards or shingles as shown in Fig. 204, then, after the last course of tin A has been laid, the flashing B with the lock a is locked into the course A and extends the required distance under the boards D. The flashing should always be painted and allowed to dry before it is placed in position. In the previous figures it was shown how the sheets are edged, both sides being edged right and left. In Fig. 205 is shown what is known as a valley sheet, where the short sides are edged both one way, as shown at a a, and the long sides right and left as shownat b b. Sheets of this kind are used when the water runs together from two directions as shown by A in Fig. 206. By having the locks a and a turned one way the roof is laid in both directions.