Walls Foundations

An arch

is the arrangement of bricks, stone or other materials to span an opening. They are named from the outline of their soffits, as seg mental (Fig. 13), semicircular (Fig. 14), or flat (Fig. 17). The terms of the various parts of the arch are shown in Fig. 21. The soffit or under side of the arch is also called the intrados. The back or upper side is also called the extrados. The pieces marked "B" of which the arch is composed are called voussoirs. The skewback is also known as the springing line.

Semicircular and segmental arches are the best as far as strength is concerned and are the simplest to construct. Other forms such as flat, Dutch, elliptical, and three-centered arches are used only where the architectural style of the building makes them preferable.

Fig. 13 shows the two-row-lock arch used in common work. The bricks are laid on edge in two concentric rings extending through the wall.

Fig. 14 shows a segmental arch. Ordinary bricks rubbed or cut to the required shape are used and form a perfect bond.

Fig. 15 shows the flat arch which also requires the use of rubbed or cut bricks. Arches of this form should have a rise or camber equal to about one-eighth of an inch for every foot of span, in order to prevent it from sagging when the arch settles. The skewback is usually made to an angle of 60°. Arches of this kind only appear on the exterior face of the openings ; the inner part of the wall being carried on a wooden lintel as shown in Figs. 16 and 17. On top of the lintel is formed a rough brick relieving or discharging arch ; the object of which to is prevent collapse in case of the destruction of the wooden lintel by fire or rot. The brickwork on top of the lintel and under the relieving arch is called the core (Fig. 16). The construction when this core is omitted is shown in Fig. 17.

Figs. 18 and 19 illustrate the temporary wooden structure required to support the bricks of an arch while the arch is being built. The upper surface of a center corresponds in outline to the soffit of the arch. They consist of two parallel boards cut to the required curvature and covered with narrow wooden strips called "lags" for sup porting the bricks. The centers are supported on wooden uprights with wedges as shown. These wedges can be eased when necessary. The centers should never be removed before mortar has properly set.

Fig. 20 illustrates the Dutch arch, which, as it is of weak construction, is suitable only for open ings of narrow span.

Foundation Construction Stones used for building purposes differ from bricks in being of unequal shape and size; in con sequence of which considerable care must be taken in order to obtain a good bond. Bonding, as in brickwork, is the arrangement of the stones to over lap each other so that no continuous vertical joints occur. The unevenness of the stones, except in the case of cut stonework, also necessitates thicker mor tar joints than are required in laying up brickwork.

To guard against fracture being caused by settlement, the length of the blocks should not., in the harder class of stones, exceed four or five times, nor the breadth be more than two or three times, the thickness. In the softer kinds of stone the length should not exceed three times, nor the breadth be more than one and one-half times, the thickness.

All stones should be laid on their natural that is, laid on that plane of division along which the stones are spilt when obtained from the quarry. A neglect of this precaution very often causes the stones to split.

Fig. 22 shows a wall with the stones laid up random rubble. Stones of all shapes and sizes are used and for that reason require considerable skill in laying, as their irregular surfaces make them difficult to bed and bond. Proper bonding re quires the insertion of through stones (marked T. S.) at intervals of four or five feet in the length of the wall, and about every eighteen inches in the height of the wall. An equally good substitute for a through stone, is a stone extending from the inside of the wall, three-quarters of the thick ness of the wall, and overlapping another stone extending from the outside of the wall three quarters the thickness of the wall. Through stones and three-quarter stones should be of sufficient thickness to prevent fracture through settlement of the wall. Fig. 23 shows a section through the wall.

Fig. 24, at A, shows uncoursed square rubble, and, at B, shows squared rubble built up to courses. Both of these arrangements are superior to random rubble. In both cases the wall is built of rec tangular stones with squared ends. In the latter case, the wall is brought to a level every fifteen to eighteen inches.

Fig. 25 shows a wall built up of field stones. This kind of a wall is used principally in the picturesque cottages and country homes.

Fig. 26 shows an elevation and section of coursed ashlar. Ashlar is a facing of stones, never less than four inches thick, used to cover walls of brick or rough stone, to which it should be securely anchored. Foundation walls, where ashlar is used, should be made of sufficient thickness to carry superstructure, independent of the ashlar unless the ashlar be at least eight inches thick and bonded into the backing, in which case it may be counted as part of the thickness of the wall.

Cellar Windows Plate VI takes up the construction of an ordi nary cellar window in a stone wall. The sash is hinged at the top with heavy wrought iron butts and arranged to swing in. It is secured in place, when closed, by a catch on bottom rail, and, when open is secured with a hook on cellar ceiling or beams.

Fig. 27 shows the elevation; Fig. 28, the section, and Fig. 29, the plan.

Fig. 30 is a section through the head of the frame. The staff bead is sometimes omitted, but, as it makes a better finish at the junction between wood and masonry, hiding the roughness of the stonework where it takes up with the wood, it is desirable to use it.

Fig. 31 is a section through the jamb. The "lug" is a piece left on the ends of head and sill and built into the wall to secure the frame in place.

Fig. 32 is a section through the sill. Stone sills near grade do not require a drip. The inside of the wall is finished in cement.

Figs. 33 and 34 show the head and sill of a window with an iron guard and a window screen outside of the sash. The iron bars are let into the head and sill about an inch.