This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
217. When a wooden building is constructed of good, sound, well seasoned material, and the workmanship on that material is first class in every respect, there is no reason why the house should not last 80 or 100 years, or even more, providing it does not burn down. In both braced-frame and balloon-frame buildings, the construction consists of a number of small pieces, such as studs, braces, floorbeams, etc., which burn rapidly and fiercely when a fire once gets started, and the spaces between the beams and studs form flues which give draft to the fire and spread it throughout the structure. If the building is not entirely destroyed the contents is usually ruined by smoke and water, and the beams and studs are burned and charred so that they are too weak to carry their loads, and have to be reinforced, or replaced. The immense quantity of water thrown into a building to extinguish the flames saturates all the material of which the building is composed, passes through the floors and partitions, runs down the staircases into the cellar, and soaks into the ground and foundation wall, often causing the house to settle in places and render a good job of repairing almost impossible.
In mills and factories where the floors carry heavy machinery, the fire eats the beams underneath, until the floor finally gives away and the machinery crashes through into the basement, causing the complete destruction of everything in its path.
In order to obviate many of these difficulties, Blow-bunting construction was introduced, and though at first used only in factories and mills, it is now frequently applied in every form of wooden building, including even residences and barns.
218. The fundamental principle of this form of construction lies in the omission or alteration of every detail of balloon or braced frame construction which would tend to make combustion rapid or easy. The individual members, such as beams, columns, etc., are so proportioned that they retain strength enough to do the work required of them even after one-third of their bulk has been charred or burned. Instead of a large number of small pieces, as in balloon and braced frame construction, there is a small number of very large pieces in the slow-burning construction. Instead of 2"x9" or 3" x l0" floor joists spaced from 12 to 24 inches on centers, we have 6"X 10" to 12"x14" floor-beams spaced from 3 to 10 feet on centers. On top of these beams the rough floor is placed, but consists of from 3"x6" to 3"x9" planks grooved on both edges to receive 3/4"x1 1/2" hardwood tongues, or splines, as they are called. The boards may be blind-nailed to each beam through the under lip of the groove. Before the spline is inserted the joints should be driven close and tight. Over this flooring is spread a layer of heavy felt, then cross-furring with 7/8 inch strips at 12-inch centers, the spaces between the strips being flushed with ordinary lime mortar. The finished floor is then laid with 1 1/4-inch matched material. The furring strips may with advantage be run diagonally, thus reducing the effect of vibration caused by the machinery. The lime preserves the wood from decay; being a non-conductor, it retards the passage of heat between the floors, and at the same time it tends to make the floor waterproof, as it absorbs the oil which drops from the machinery.
The roof is covered with 2-inch plank and is rendered waterproof with tin, copper, tar and gravel, or painted canvas, though when the pitch is steep, slate and shingles are both used. When slate is the covering material, care must be given to see that the roof-boarding is extra thick and close-laid, as in case of fire, when the roof becomes heated and water is thrown upon it, the slates will crack and fall off. The inside walls of mills and factories are not plastered or finished in any way more than to make the construction clean and neat where it is fully exposed to view.
219. The ultimate objects of this form of construction may be summed up as follows: To make a building strong enough to stand any ordinary stress, even after its timbers are partly burned; to make the floor so tight and strong that when a fire starts in one story, the water poured in to quench it will not run through and ruin goods on the floor below; to avoid any corners, pockets, or flues where fire could get started without being immediately discovered; and, above all, to provide a building where every part is easily accessible and the fire can be attacked and extinguished at close quarters without flooding the entire structure.
220. The details of this construction can be best understood by referring to Fig. 90, which is a perspective view of the flooring and supports of a portion of a mill erected according to the rules of "slow-burning construction."
In this example wood alone is used, though iron, brick, stone, and other refractory material often enter into the construction of buildings of this class. The posts a in the first story are 10" X 10" Georgia, or long-leaf, pine, and those in the second story a' are 9" X 9" of the same material. The girders b are of 12"xl4" Georgia pine, with a span of 15 feet from center to center of posts. Between the top of the posts and the bottom of the girders is placed a bolster c, which is 6 in. x12 in. in section and 2 feet 3 inches in length. On top of this bolster the next column is placed, and on its projection, on each side of the column, rest the ends of the girders b, which may be secured in place by means of lag-screws.
Longitudinally through the center of each post a, and also through the bolster c, is bored a 1 1/2-inch hole, and at e are shown 1/2-inch holes bored transversely through the ends of the column to give ventilation to the interior and prevent dry rot. Sometimes the under side of the bolster is countersunk, or rabbeted, about an inch deep in order to fit over the top of the post below, but a simpler method of securing it in place is by means of a piece of iron pipe inserted into the hole d as a dowel. Drift pins, or long spikes, may also be used for this purpose. After the columns and bolsters are set and the girders are in place upon them, the 4" X 6" cleats f are bolted to the lower edge of the girders through the holes g, which have been previously bored to receive them.
These cleats serve the double purpose of tying the girder system together longitudinally, and of forming a seat for the ends of the floorbeams h
221. The floorbeams h are 6"x9" Georgia pine, their lower sides being notched about 1 inch to bring their upper edges in line with the top of the girders b and are spaced 3 feet on centers. About 3 inches from each end of each floorbeam a 3/8-inch hole is bored 2 inches deep, as shown at j, into which iron "dogs," shown at k, are driven; when the beams are in place, a dog made of a 3/8-inch round iron bar, 22 inches long, with 2 inches of each end bent at right angles, is driven tightly into the holes in the top of the floorbeams. This is shown more clearly in Fig. 91, where a, a are the 3/8-inch holes bored in the top of the floorbeams c. The purpose of the iron dog is to secure the ends of the floorbeams h, prevent them from slipping off the cleat f, and thereby form a continuous tie throughout the length of the building.
The floorbeams being in place and anchored, the under floor m is laid. This consists of 3-inch planks not more than 6 inches wide and planed on both sides, giving a finish to the ceiling in the story below. Two of these 3" x6" planks are shown at a, a, Fig. 92, b, b being the grooves cut in both edges of each plank, and c, c the tongues of 1 1/2" X 3/4" Georgia pine inserted in each groove as the board is laid. This renders the floor rigid, and the surfaces of the planks are. kept flush.
The finished floor n is then laid with l"x4"or 11/8"x4" maple, or hard pine, tongued and grooved and surfaced. The furring strips and felt lining above referred to are omitted in the cut to avoid confusion of lines.
Instead of the mortar filling between the rough and finished floors, several layers of waterproof sheathing paper is sometimes substituted, and though it renders the floor quite as water-tight, it is not so impervious to heat as the mortar, and, consequently, will not retard the progress of fire as well.
222. The outside walls of the building are built in the same manner as the interior; that is, posts support the outside ends of girders, and girders support the outside ends of floorbeams. The rectangular space enclosed by two posts and two girders, or floorbeams, is then closed in with 2-inch tongued and grooved plank laid vertically, as shown at o, in Fig. 90. The sill p is laid on the brick foundation wall, and may be rabbeted at g to receive the ends of the two-inch plank o. The entire exterior of the building is then sheathed with ordinary l"x8" sheathing boards s, over which matched and beaded planks may be laid vertically to form the exterior finish, or patent or beveled siding may be laid in the same manner as in a balloon frame. When the latter course is pursued, the sheathing boards s are usually laid diagonally, in order to prevent irregular courses of the clapboards, due to the shrinkage of the sheathing.
The window frames, being thicker than the boarding of the walls, are allowed to project inside, and are finished with a casing, as shown at t. The enclosing walls, therefore, act only as a protecting screen to the building, as the floor system is carried entirely by the posts and girders, and although these walls are but 4 inches in thickness, they are warmer and better in every way than the 7-inch stud and plaster partitions of the balloon frame.
223. Interior partitions are constructed of 2-inch tongued-and-grooved plank laid vertically from floor to ceiling, each plank being toe-nailed to the floor and ceiling cleats and driven well up against its neighbor. Where a neat finish is required on the partitions, as would be the case in enclosing a private office, the 2-inch plank may be lined with 7/8 x 3" matched boards of oak, or hard pine, laid horizontally or diagonally, or it may be plastered as explained further on in the application of this form of construction to residence work.