On the Foundation and Basement — Walls of Buildings, Damp Prevention, and Fire Proof Construction
The foundations of buildings require careful consideration. When a house approaches completion and shows cracks in the upper walls, they arise either from insufficient attention having been given to the solid character of the earth forming the site, or from bad construction at the basement. The building in fact settles down unequally. As a settlement of every building is certain to take place upon its completion, the greatest precaution should be taken to make it as equable as possible. No portion should settle deeper than another, and this can only be secured by care at the foundations.
It often happens that portions of a selected site are of unequal quality. In such cases it is necessary to excavate the worst portions deeper to reach a good stratum, and to take the brickwork lower, no filling up beyond the usual thickness of concrete being allowed.
There is another very serious evil, in building, to be guarded against. Owing to the moisture of the earth rising through the foundations and saturating the walls above, the health of the occupants of such houses may be seriously affected by its presence in the walls. About twenty years ago it was the universal practice in good buildings to place wide stone landings—three times the thickness of the wall above—under the foundations, for the purpose of preventing the damp from rising as well as to spread the width of the wall.
A bed of concrete is now used as a substitute for this plan; the engraving below shows the best method of constructing foundation walls. A trench, three times the width of the wall is dug, at least 2 feet 6 inches in depth. Into this is thrown a quantity of concrete, which soon dries and becomes solid. In the superior class of buildings a layer of concrete, six inches in thickness, is placed entirely over the ground, inside the foundation. Upon this concrete the walls are built, the lowest footing being twice the width of the wall above. On a few courses above the top footing a course called a “damp course” is put; this is shown at a, page 152.
Two courses of slate are laid in cement; but other materials are often used, as a thin sheet of lead, for the whole width of the wall. Zinc might answer, but it has not yet been tried. A thin coat of asphalte, or asphalted cloth, tar, pitch, or a plain coat of cement are also often employed, but the two courses of slate in cement are considered sufficient. The first course of bricks above the ground is often formed entirely of air bricks, originated by Mr. Aldin, the builder, of Kensington. Each brick has eight or ten perforations, ½ inch in diameter, through its whole length; a small piece of perforated zinc is placed upright between the bricks to prevent insects from entering. This is shown at b. The timbers and stone flooring of the basement do not enter the walls, but rest upon dwarf walls, the joists having oak sleepers to rest on. The brick fenders of the foundations are entirely filled with dry rubbish or ironfounder’s ashes, and the stone hearths bedded solid either in mortar or concrete. This is the construction shown in all the designs of this volume. To illustrate still further the attention given in constructing foundations, the engraving below is given, showing a section of a foundation executed several years ago at Westminster, where the ground was uncertain. Its scale is only half that of the previous figure, the upper wall being 3 feet in thickness instead of 1 foot 6 inches. Above the bed of concrete, which is 9 feet in breadth, by 3 feet in thickness, are York landings, a, 4 inches thick and exceeding 6 feet in width. Upon these are laid two lines of wood sleepers, b, bedded in brick and cement, the size of each sleeper being 12 by 6 inches, and in long lengths. Above this is a course of planking, c, placed diagonally across the wall; each plank being 12 inches by 6 inches, and about 9 feet in length. Above this are the footings, each two courses in height: in the return walls the landings, sleepers, and planking are placed a course higher, so that they might be tied together. The brickwork goes down twelve feet, and invert arches are turned at every opening.
In order to keep the walls as solid as possible in the lower part of a building, the ground floor joisting should rest on projecting corbel bricks as here shown,—the joists going between the cross walls rest upon projecting bricks, the upper one being of peculiar strength; tall piles are put between each joist against the wall, for the skirting in cement to be formed upon it. Air bricks in open iron-work, two to each front, are placed so as to admit air within the joisting.
This mode of construction is carried throughout the ground floor.
The stone landing of the passage by the side of the servants’ stairs, is supported on the part next the wall by corbel bricks, and on the other side by an iron bar let into the wall at each end; as shown above. In the upper floor, the joisting should be reversed and go front to back, notched on wall plates let into the wall, thus tying both walls together.
The introduction of rolled iron girders into buildings renders fireproof construction very easy. They are made of all sizes, and can be placed over any opening, so as to carry the weight above them. Kitchens in many London houses are constructed in the back yards, with an area between them and the house. This confines all the smell of the cooking to the precincts of the kitchen. As it is very important that no roofing should interrupt the light from the back ground-windows of the house, the roof of the kitchen is so constructed that the yard is only moved upwards; it belongs to the ground floor and not to the basement. For this purpose, cast iron girders, standing on brick piers, bear up rolled iron six-inch girders, between which half-brick arches are turned. Above all these is concrete, cement, or asphalte. The courses of tiles and cement are laid at such a slope as will be sufficient to take the water off quickly. It is easy to put skylights, or any kind of opening, in this construction, and to make the whole water-tight.
This figure shows a way of supporting walls over openings, instead of the old method of arching in brick; the iron girders or plates have often no timber between them; they rest upon iron shoes or stone slabs, their depth being proportioned to the opening and the weight above. Strong large hollow bricks or tiles are placed over them, and above all is the brickwork.
The upper floors of buildings are made fire-proof in a similar manner, and for this purpose there are several excellent patented methods. The iron girders are closed up by brick arches, or filled between with concrete. The only objection to this mode of construction for upper floors is the great weight, and the walls require to be made of extra strength. Several years ago a hollow brick was used to form such arches and roofing, e.g., the dome of the Rotunda, at the Bank of England, is formed with them. The brick is somewhat similar to a flowerpot, but flat and closed at each end. There were several varieties of these cone bricks, as they were called; a few are preserved in the Soane Museum. One sort was 7½ inches in height, 4⅛ by 2⅜ inches at the top, and 3-2/8 by 2 inches at the bottom. They were curved inwards with a small opening, 1 by 2/8 inch in the centre. The edges of the brick were slightly splayed, and the sides scored; these were as strong as the common bricks, and very much lighter. When the East India House was pulled down a large quantity of these bricks was obtained; they were brought to Kensington, and the builders did not know what they were intended for; their purpose being pointed out, they were used up in the construction of fire-proof flooring.
Fire-proofing.—A method of rendering buildings nearly fire-proof was introduced about 1770 by Mr. David Hartley, M.P. for Hull. It consisted in placing thin metal plates between the flooring boards and the joists, so as to prevent any upward currents of air. For domestic buildings the system was one of great value. After several successful trials it obtained considerable notoriety, and being thought capable of an impossibility, that of rendering a Theatre fireproof, it was applied to the Pantheon Theatre in Oxford Street. On that structure being burnt to the ground the plates lost their character, and went out of use. It was clearly a mistake to apply them to such a building. Thin iron plates hung at a short distance below the ceiling were successfully adopted by Mr. Walter Crum, to prevent the spread of fire from one room to another in his calico printing works, near Glasgow.
Damp.—The damp rising from foundations is more easily guarded against than damp coming against a building laterally. Houses in exposed situations and subject to driving winds, are often very wet inside the walls, the rain being driven through them. Sometimes the best construction will not keep out wet. As a rule, a well-built wall wherein proper material has been used, should not be damp.
A rectory, not far from Salisbury, where the author was engaged a few years ago, was in such an exposed situation that on three of its sides no tree or any other object in a direct line could be seen for three miles. Clothes, if placed against the external wall of the dressing-room, were often quite wet. The Rector had tried several preventives himself; one was a mixture, used to water-proof cloth—a wash of soap and alum.
The ingredients were mixed in the following proportions: ¾ lb. of mottled soap to 1 gallon of water. This mixture, when in a boiling state, was laid over the surface of the brickwork steadily and carefully with a large flat brush, so as not to form a froth or lather on the surface, and was permitted to remain twenty-four hours to become dry and hard. Another mixture was then made in these proportions: ½ lb. of alum to 4 gallons of water, which, after standing twelve hours, in order that the alum should be completely dissolved, was applied in like manner with a flat brush over the coating of soap. The coating had to be very often renewed. The wall most exposed was made free from wet by being covered with a coating of cement.
Walls exposed to damp should be coated with a thin layer of Portland cement, mixed with a little plaster of Paris, and after this is thoroughly dry, it may be hardened and rendered impervious to water by painting it with boiled linseed oil and red lead, mixed together.
In very exposed situations all external walls should be battened, lath and plastered within, or built with a hollow cavity in the middle, with proper bond and a proportionate increase of thickness,—the hollow could be filled with concrete, or the back of the bricks covered with pitch. There are several other methods for keeping walls free from damp. One is to saturate the walls with some kind of mastic, or a wash composed of two or three parts of resin and one part of drying oil, to the extent of as many washes as the wall will absorb. This must be quite dry at the time, or be dried by means of a small portable furnace. The plan is effectual, but it is a difficult operation to perform. A cement composed of lime, boiled linseed oil, white lead, and sand, has been recommended.
Besides these various compositions, there are several excellent well-known paint and metallic cements, which have stood very severe tests, and are largely made use of; but walls properly constructed should not require their application.