By WM. PAUL GERHARD, C. E.
In selecting a site, a loose, porous soil is, for obvious reasons, preferable to ground liable to be damp or wet. Pure, dry sand, and gravel, make excellent sites for building purposes. Next to these, rocky soils may be chosen, and are usually quite healthy. Clay soils, which are more or less impervious to water, and therefore always damp and chilly, and alluvial lands, must not be chosen as a site for dwellings. But, above all, avoid made land. Although this refers more particularly to city lots, it is not uncommon, even in the suburbs of large cities, to find low ground filled with garbage, rubbish, and decaying vegetable and animal debris, which are prime causes of impure air in dwellings. Ground which has not before been built upon is, undoubtedly, preferable to sites of old, torn-down buildings. If the latter must be taken, a detailed and thorough examination should be made with respect to the purity of the soil. Some lots are literally honey-combed with cesspools, privy-holes, or have a net-work of broken drains full of accumulated filth, and the soil is at times found to be contaminated from liquid house refuse, or by soakage from barn-yards, stables, etc. A well should never be sunk through such formerly occupied ground. It is quite important to ascertain by preliminary borings, the level of the ground water, for a high water level means continuous dampness, and must be abated by thorough under-drainage.
By underdrainage of a site, we effect a permanent lowering of the ground water, and thus secure to the proposed dwelling, dry foundation walls, and absence of dampness from the house interior. To remove such subsoil water, small porous, round tile-drains, 1¼ inches in diameter, should be laid with open joints at least two feet below the level of the cellar floor. The general arrangement of the lines may vary somewhat in each case, but ordinarily the branch drains can be laid in parallel lines, their distance varying from ten to twenty-five feet, according to the amount of water to be removed. Wherever springs are found, special lines may be required. The trenches should be refilled with broken stones or coarse gravel. All branch pipes should be collected in one main pipe, for which a 2 inch tile pipe will answer in most cases. This main drain should be continued with proper fall to a ditch, ravine or water course. There must never be any connection between such subsoil drains and any foul-water drain, sewer, or with a cesspool or sewage tank.
If the dwelling stands on a hill-side, exposed to subsoil water flowing over an impervious stratum, the foundation walls of the house nearest to the hill are very apt to be wet, often even so much as to have the subsoil water percolate through the cellar walls. In this case, the subterranean water vein should be cut off by a blind drain, i.e. a trench dug above the house sufficiently deep and carried with proper fall diagonally across the lot. The trench to be filled with broken stones and to be carried down the hill to some outlet, either an open ditch or a brook.
Some attention should be paid to the proper removal of surface water. In the case of suburban cottages the rain falling upon the roof is almost always collected and stored for use in underground cisterns. Occasionally a public water supply is available, the cistern is omitted, and the roof water is allowed to run away on the surface, and partly soak into the ground, thereby tending to keep the foundation walls damp and unhealthy. To avoid this evil, the grounds surrounding the house must be properly graded, in order to shed the water off from the walls. At a good distance from the house the surface water may sometimes be permitted to soak away into the ground, the vegetation helping to absorb a part of it. In other cases, however, surface channels or gutters must be arranged, especially with clay soils.
Besides water, the upper layers of the soil always contain ground air, which has a tendency to rise into the dwelling, especially in winter when our heated dwellings act as huge chimneys, drawing up large quantities of air from the ground beneath them. Such exhalations, which consist in the case of a pure soil of carbonic acid and watery vapor, and which in the case of a contaminated soil are largely mixed with gases of decomposing organic matter, should be rigidly excluded from the interior of houses. For this reason, dwellings without a cellar should never be placed immediately on the ground, but must be raised on piers, arches or posts sufficiently to allow of a large air space and perfect circulation between the surface and the floor beams. This will, at the same time, prevent the quick rotting of the joists and floor-boards. To prevent the rapid cooling of the basement floor this should be laid double with an intermediate space, filled with a non-conducting material, such as mineral wool.
It is more expensive, but always preferable, to excavate for a cellar and to build the house on strong, well made foundation walls. The floor of the cellar must be made perfectly tight against ground water and ground air. There are different ways of doing this. One of the best methods is the following: cover the surface of the cellar, which has previously been levelled, with a layer of concrete, at least four inches, better six inches deep. Next put on a thin layer (about ¼ inch) of hot, pure asphaltum, and on top of this a finish of Portland cement.
The cellar walls must always be made impervious to dampness. As usually built, they are extremely porous, and moisture rises in them by contact with the adjoining ground and by capillary attraction. The best plan to prevent dampness of walls is to have a complete cut-off between the foundation walls and the ground, by an open area, carried completely round the building, and well drained and ventilated. This, however, is expensive, and a similar isolation may be accomplished by building double or hollow walls, the space between inner and outer walls being well aired. The foundation walls should be placed upon a bed of concrete, and must be covered on their outside with a layer of asphaltum to a point somewhat above the level of the ground. It is very important to provide, at this height in the wall, a horizontal isolating or damp proof course, which may consist of a thick layer of asphaltum, or of slate, bedded in cement, or of layers of tarred roofing paper, or else of hollow tiles. The sill and the floor joists must, of course, be kept above the damp proof course. The surface water may be kept away from the outer walls by filling the space next to the wall, to a depth well below the foundation walls, with broken stones or gravel. Sometimes a tile drain is placed below the foot course to carry off any accumulation of percolating storm water. This trench may be covered at the top with a stone slab to shed off surface water.