In this system of framing, timbers of small section are used to construct a light, skeleton frame, whose rigidity depends entirely on its thin, canvas-like covering. This is the distinguishing feature of balloon framing compared with braced framing, in which the rigidity depends upon a well-arranged system of mortise-and-tenon joints and diagonal bracing, irrespective of covering. A practical application of balloon framing is shown in Fig. 6, which is a perspective sketch of part of a building during erection. In this connection, a few points on good construction will be noted.

After the wall a is completed, the 4" X 8" sill b should be laid in a bed of lime mortar, tamped, and carefully leveled, as from it all heights are measured. The edge should be kept back from the face of the wall, so that the outside boarding will be flush with the latter. The sill should also be accurately squared, to obtain satisfactory results. A very simple and practical method of squaring depends on the geometrical principle governing right-angled triangles; namely, the hypotenuse is equal to the square root of the sum of the squares of the other two sides. This principle is illustrated at the near corner of the sill in the figure. Lines are drawn on the top of the sill equidistant from the outer edges, and a nail is driven at their intersection. From this point 3 ft. is measured on one line and 4 ft. on the other, and nails are driven at the points marked. Where the pieces are square to each other, the hypotenuse will measure just 5 ft. Triangles with sides which are multiples of 3, 4, and 5, such as 6, 8, and 10, 9,12, and 15, etc., may be used also.

Balloon Framing 325

Fig. 6.

The sill having been bedded, leveled, and squared, the cellar posts c are set up on base stones, and the beam d placed in position; the beam may be attached to the tops of the posts by toe-nailing, but a more workmanlike method is to secure it by means of iron drift-pins, driven through the beam from above; or by inserting dowel-pins of wood or iron in the tops of the posts, and boring the beam to suit.

In order to reduce the depth of the wood liable to shrinkage, the top of the beam is kept up 4 in. higher than the lower edge of floor joists e, gains, or notches f, being cut out of its upper edge, into which seats the joists are fitted; unless this is done, the joists will be liable to split when loaded, as indicated at 1 and 2. At the wall bearings g the joists are simply checked over the sill, but the heels or bearing of the joists on the wall should be supported by wedging up each one with a piece of slate, after the joist has been spiked to the sill and stud. The space between the joists should be filled in with stone or brick (usually the latter) up to the top of the joists, and 7 in. higher between the studs, as at h; this prevents the passage of air-currents and lodgment for rats and mice. To equalize the shrinkage at the bearing beam and wall sill, the joists should rest on top of the sill instead of being checked over it, as shown; but in common work this is seldom done, as 4 in. of effective height of the stud would thus be sacrificed. In order to provide for the inevitable shrinkage, the joists should be kept about 1/4 in. higher at the center of the building. "When 4" studs are used, a firm, solid corner post can be made by nailing a 2" X 4" stud to the face of a 4" X 6" scantling.

The second tier of joists should be butt-jointed at the center partition i, toe-nailed into the plate j and further secured from spreading by a fish-plate well nailed to each joist. Sometimes the joists are lapped over one another and spiked, which gives each joist a 4" bearing on the partition; but this affects the equal spacing, and allows vibration, which may crack the plaster. Also, if hot-air pipes are to pass between the studs, the space thus contracted necessitates a narrower pipe, with less heating capacity. The wall ribbon is shown at k; over this ribbon are notched the joists I.

Where there are continuous partitions, the studs should be toe-nailed to the plate beneath and spiked to the second-floor joists. The plates being lapped and spiked to the plate surmounting the wall studs, tie the building lengthwise, and stiffen the partition.

Before the building is sheathed, the corner posts m should be again carefully replumbed and adjusted by means of a plumb-bob suspended from the wall plate and run down to the sill, when the most accurate adjustment can be made. The sheathing n should be placed diagonally at an angle of 45°, and be well nailed to each stud with two or three nails, according to the width of the board. The butt joints should be cut on the center line of the studs. With boarding thus placed, well fitted and nailed, the structure is completely braced in a very simple and effective manner. The outer surface should be covered with a layer of heavy building paper o, lapped at the edges and tacked in place. Paper, being of close texture and a non-conductor of heat, makes an excellent covering material, rendering the building warmer in winter and cooler in summer. The base p should be capped to throw off the rain water, and should project about 1 1/8 in. outside the wall. The corner boards, as at q, 1 1/8 in. thick, should be firmly nailed in place, the inner edges being slightly beveled, so that the siding, when sprung in, will fit tightly. The siding r should be clear, white-pine boards, beveled on section, as shown, from 5/8 in. thick at the lower edge to 5/16 in. at the upper edge, and generally from 4 in. to 5 in. wide, according to the weathering, or exposed surface. The siding should have a lap of 1 in. or more, and should be nailed at each stud, the nails being of sufficient length to pass through the boarding and enter the stud; this gives better results than if they are simply driven into the sheathing. The gauge, or exposed width, of the siding varies where it comes in contact with door and window frames, in order that the horizontal lines of the siding will aline with those of the sill and head of the frame. Great care should be exercised in fitting the siding in place; when cut to the required length it should be somewhat longer than the distance between the vertical casings, in order that, when sprung into position, the end fibers will enter the edge wood of the casings, and thus insure a close joint, even after the casings have slightly shrunk.