## 224. Galvanized And Black Iron

The table opposite gives the weight in pounds per square foot of galvanized sheet iron, both flat and corrugated. The numbers and thicknesses are those of the iron before it is galvanized. When a flat sheet (the ordinary size of which is from 2 to 2 1/2 feet in width by 6 to 8 feet in length) is converted into a corrugated one, with corrugations 5 inches wide from centre to centre, and about an inch deep (the common sizes), its width is thereby reduced about 1/10 part, or from 30 to 27 inches; and consequently the weight per square foot of area covered is increased about 1/9 part. When the corrugated sheets are laid upon a roof, the overlapping of about 2 1/2 inches along their sides, and of 4 inches along their ends, diminishes the covered area about 1/7 part more; making their weight per square foot of roof about 1/6 part greater than before. Or the weight of corrugated iron per square foot, in place on a roof, is about 1/3 greater than that of the flat sheets of above sizes of which it is made.

 Number byBirminghamWireGauge. Black. Galvanized. Thickness in inches. Flat.lbs. Flat. lbs. Corrugated. lbs. Cor. on Roof. lbs. 30 .0I2 .485 .806 .896 1.08 29 .013 .526 .857 .952 1.14 28 .014 .565 .897 •997 I.20 27 .016 .646 .978 I.09 1.30 26 .018 .722 I.06 1.18 1.41 25 .020 .808 1.14 I.27 1.52 24 .022 .889 1.22 1.36 1.62 23 .025 1.01 1.34 I.49 1.79 22 .028 1.13 I.46 I.62 1.95 21 .032 I.29 I.63 1.81 2.17 20 •035 1.41 1.75 1.94 2.33 19 .042 I.69 2.03 2.26 2.71 18 .049 I.98 2.32 2.58 3 09 17 .058 2.34 2.68 2.98 3.57 16 .065 2.63 2.96 3.29 3.95 15 .072 2.91 3.25 3.61 4.33 14 .083 3.36 3.69 4.10 4.92 13 •095 3.84 4.18 4.64 5.57

Note. - The galvanizing of sheet iron adds about one third of a pound to its weight per square foot.

## 225. Finial And Cresting

Of the various means of finishing towers, spires, ridges, etc., the finial and cresting are valuable as ornaments, and give a light appearance to the top of heavy and plain roofs.

In the following illustration both are shown. The design can be accommodated either to wrought iron, cast iron, or copper.

## 226. Vault Lights

One of the important improvements in vault lights, and one now generally adopted, is filling concrete around the glass, which, while giving an even, non-slippery and durable surface, is also strong and perfectly water-tight.

The metal being covered by a non-conducting material, the rooms over which the light is laid are warmer in winter and cooler in summer than those over which the old-style lights are placed. The round and elongated knob-protected bullseye lights are known as iron vault lights. There is very little cement used, only enough to bed the lens. The diameter of the lens in both concrete and iron lights is from 1 1/2 to 2 inches.

Wrought-iron illuminating doors are frequently used, in combination with the above lights, for entrances to sidewalk elevators, area steps and hatchways. The doors are made of galvanized sheet iron, with bronze or wrought-iron hinges similar to those for sheet-iron sidewalk doors. Illuminating vault covers with and without frames, from 12 to 36 inches in diameter, are frequently used. The glass is round or square, and set either in plain iron lights or concrete illuminating lights. The concrete light is an inch and the iron light 7/8 inch thick. All the above lights are employed principally for areas, vaults, roofs, floors, skylights, vault covers, etc.

## 227. Wrought-Iron Guard

The following illustration is a simple and neat design of guard. The rings are made of 3/16 X 3/4-inch flat iron, the frame on outside 1/2 X 1 1/2 inches, the wavy bars 3/4 X 3/8 inch, and the cross-bars 3/8 X 1 1/2 inches. To secure the frame to jamb, expansion bolts or lag screws may be used as shown in the plan.

## 228. Dwarf Doors

Dwarf Doors are generally placed below the rolling shutters of store or warehouse entrances. They are from 2 feet 6 inches to 3 feet high, in two, three and four folds, and made of a 3 X 3/8-inch flat iron welded frame, covered with No. 16 gauge black sheet iron. Flat cast-iron mouldings are set against the sheet iron to form panels, showing from outside as a finished door. Dwarf doors are sometimes made of wood two inches thick, and covered with sheet iron similar to that used in the iron door.

## 229. Cast-Iron Wheel Guards

Cast-Iron Wheel Guards are used to protect the jambs of vehicle-entrances, and made of 1/2-inch-thick metal, by the height of wheel hub. Wrought-iron guards are simply three 7/8-inch-diameter bars bent outward, and leaded into flagging and jamb base-stone.

## 230. Fire Pipes

Fire Pipes are generally required in all warehouses, stores and factories, and are made of 4-inch-diameter wrought-iron pipe, built in with the wall, with a hose connection at each floor level, and extending through outer wall a foot or two above the sidewalk.

## 231. Mansard Roof

The best-constructed mansard roofs have a continuous bed plate and top plate of channel iron or angle iron, with uprights of angles 25 inches apart between centres, all bolted together, thus forming a rigid framework of iron, which is then filled in with porous terra-cotta blocks and covered with slate or metal. The uprights may also be made of 6-inch beams 4 feet apart between centres, and purlins of small tees or angles 1 1/2" X 1 1/2" X 3/16" placed on outside; the slate on the iron purlins to be hung with suitable copper wire carefully twisted, two wires to each slate, and the slate made to lie flat.

The sides and roofs of dormers are similarly constructed, the covering being galvanized iron or copper.