This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
136. Glass as a roof covering may be used to great advantage for inside halls and passageways, picture galleries, and extensions where ordinary windows cannot be inserted, for dome lights, greenhouses, railroad stations, etc. Wherever used, the construction should be what is known as "puttyless," that is, no putty should be used in bedding the glass whether the bars are of metal or of wood.
137. The frame for all house work except greenhouses, and even the better class of these, should be, preferably, of copper, galvanized iron, or zinc.
The construction of these frames or bars consists of a gutter composed of three pieces, the flange, the gutter, and the cap. In Fig. 115 is shown the general construction of the complete bar. The center member a has a straight web about 1 1/4 inches high, with a circular tube 5/8 inch diameter formed at its lower edge. The gutter or outer member b consists of one piece, bent at the center, capped over the web or centerpiece, and having the edges formed into 3/4-inch tubes which rest on the tube of the web member. The upper flanges of these tubes support the glass. The cleats or holdfasts c, which bind the cap, are secured by the rivets which join the web and gutter members, and the cap d is made of one piece, in the shape of an inverted V, with a simple lock on the two lower edges to receive the flashings. The flashings e are strips of lead, locked at the upper edge into the cap, and bent down close to the glass, in order to make a water-tight connection. The cap is secured to the bar bypassing the clips through a slit cut in its apex, the ends being turned down and soldered and wiped to the cap. In some cases, the ends are simply turned down over the cap.
This system of construction may be applied to the whole or a part of a roof, and also to skylights. It may also be used in conjunction with iron or wood framing for the roof proper.
For small skylights, where an under support may be dispensed with, the light bar, as shown in Fig. 115, may be used. For larger openings, a heavy iron bar incased with sheet metal, as shown in Fig. 116, will give the requisite strength.
Fig. 117 shows an iron rafter for a roof; it is composed of a web plate a, 3 1/2 in. x 1/4 in., and two angles b, b, 2 in.x2 in. x1/4 in. bolted together. The portion a projects beyond the flanges of the angles and a gutter is formed over it with caps, etc., as in the previous example.
The tubular construction imparts strength and rigidity and provides for the expansion of the metal and glass. Provision is also made for condensation, as all the bars, vertical and horizontal, act as branch gutters, which are connected to a main gutter.
138. The glass may be made 3/16 to 3/8 inch thick and of any pattern. For plain work, ribbed or hammered glass maybe used, the rough surface being placed on the outside. The use of a minimum thickness of glass should, for two reasons, receive consideration : first, the cost of repairs, and, second, the dead load to be supported. The size and strength of the rafters and purlins supporting the ribs must be regulated by the weight of the glass, wind pressure, and snow load.
139. The horizontal lap joint of the glass, as shown in Fig. 118, is of the same construction as the gutter proper, but has a lead fillet a, which acts as a cushion and takes up any unevenness of the glass. The lower glass rests on the tube, and the upper on the lead cushion on the top of the rib. The glass should overlap from 1 inch to 2 1/2 inches, according to the pitch. At the end of each light of glass is a stop, or holdfast, made and placed as shown at a, Fig. 119. These stops are placed on each side of the vertical ribs, and are secured to the flanges by small screw bolts about \ or 1/8 or 3/32 inch diameter. The slot b in the flange is cut vertically and is about three times as long as the diameter of the bolt. The slot in the stop or holdfast is cut horizontally and is a trifle longer than the other. These slots provide for adjustment and for any movement that may take place by settlement, and expansion and contraction.
The ribs that come against parapet, fire, or other walls are similar to those shown in Fig. 119. The cap piece c is extended and formed into a flashing; it is let into a raglet, and may be covered with a counterflashing. When the construction to which the glass is applied is of wood, the flange piece is omitted, and the gutter piece rests in and is secured to the woodwork, as shown in Fig. 120.
140. There are other methods of construction, based upon the same principles, but varying in detail to meet different conditions. For the roofs of greenhouses, etc., where wood construction is used, the durability of the wood should be considered. It has been found that cypress has given better results than any other material. The sash bars may be made, as shown in Fig. 121. The rabbets are 5/8 inch deep, allowing for the two thicknesses of double-thick glass at the lap, and also for the nailing. The rabbet is formed with a slight bevel, thus forming a channel which carries away any moisture that may enter. The end or gable bars must also be rabbeted, for the roof glass; and where there is a glass gable, these bars must also be rabbeted, to receive the vertical glass.
In Fig. 122 is shown a rafter bar with grooves run in the sides, to take off condensation; and in Fig. 123 a similar bar fitted with a cap.
141. There are several methods of constructing the plates into which the bars are framed. At (a), Fig.
124, is shown a plate made of 1 7/8" X 5 1/2" material, beveled and throated to form a drip.
At (b), Fig. 124, is shown a different construction, in which the plate piece is 1 7/8 in. x 4 in., and the sill 1 3/4 in. X 6 in. The plate is beveled on the top to receive the bar. and rabbeted on the outside to receive the sill. The sill is beveled to allow the water to flow off, and throated to form a drip. At (a), Fig. 125, is shown a plate and gutter, the inside or plate having the same construction as (6), Fig. 124. If there are two pitches coming together between two ranges of roof, the construction may be as at (b), Fig. 125. Gutters, however, should be avoided as much as possible.
142. At the ridge there may be either a single or double row of ventilators. At (a), Fig. 126, is shown a 3-piece ridge, made up of a ridge piece, a shoulder cleat, and a cap. The ridge piece is 1 3/4 in. x 4 1/2 in.; the shoulder cleat, 7/8 in. X 2 1/4 in., and the cap,1 3/8 in. x 2 3/4 in., rabbeted to receive the ventilator sash. This ridge is made for a double row of ventilators; if used for a single row, it would be rabbeted on one side for the glass, as indicated by the dotted lines at c.
The ventilators should be hinged to the ridge, close against the bars, and a header should be inserted as shown at (b), Fig. 126. The header may be rabbeted or grooved to receive the glass. Where the bars are more than 8 feet in length, they should be supported by purlins.
In glazing the sash, the glass is laid from the bottom up, the sheets lapping each other from 3/4 inch to 1 1/2 inches. The lap is regulated by the pitch, which, in any case, should not be less than 20°.