Best Soil for Building a House On
A Healthy Site
Healthy conditions and surroundings are the first essentials for any site, for no amount of care in the construction of a house will altogether avail if its situation is unhealthy. In many cases selection is not possible and some particular spot may have to be utilized. Then it is especially necessary to turn the peculiar circumstances to the best advantage, and it may save many heartburnings later on if an architect be consulted early in the matter.
The healthiness of the site depends largely on its surroundings, the nature of the subsoil, vegetation and sources of contamination in the immediate vicinity. In addition, the temperature, rainfall, moisture of soil and the nature of the prevailing winds materially affect it. The general climatic conditions of a district cannot be altered, but they may be modified by drainage and by the judicious plantation or removal of trees. Many diseases such as phthisis and affections of the respiratory system, including bronchitis, pneumonia and whooping-cough, appear to be derived from or fostered by dampness, which is also conducive to rheumatism, neuralgia and catarrhs.
All authorities agree that the condition which principally governs the healthiness of a soil is the relation which the ground air (i.e. air in the soil) bears to the ground water (i.e. moisture in the soil), and this depends mainly upon the rainfall, which varies greatly in different parts of the country. The principal evil is damp, caused by the evaporation of the moisture in the soil, which lowers the temperature of the air and is therefore injurious. This moisture is bound to rise, unless the level of the ground water is kept sufficiently below its surface ; for the lower the water is in the soil the less the evaporation and the warmer the adjacent air.
Subsoil drainage facilitates the passage of the surface water into the ground beneath, and thus reduces the amount of the evaporation. This is usually effected by means of unglazed, unjointed agricultural drain-pipes, butted against each other, and generally placed about three feet six inches below the surface of the ground with a good fall to a ditch, stream or river. The lines of pipes are placed at distances which vary from three feet to six feet apart, according to the nature of the soil, for it is obvious that in a sandy soil a single drain will lower the level of the ground water over a larger area than in a stiff clay soil, where drains must be placed closer together. Some authorities hold that ground water should not be allowed nearer than five feet from the surface, but this appears to involve unnecessary expenditure. The drains, it need hardly be said, should be entirely independent of any drain used as a vehicle for sewage.
Drained and undrained sites have been tested by various authorities, and many years ago Sir Douglas Galton found that a well-drained field had a temperature of as much as six or seven degrees Fahrenheit higher than an adjacent undrained field.
Kinds of Soil
Rock is an impermeable formation which makes in many respects an admirable site for houses, but care must also be given to the surface soil, as it may consist of decaying organic matter. This was found to be the case at the Peninsular Sanatorium near Hong-Kong, where, although the site is of granite formation, a severe epidemic broke out amongst the troops quartered there, owing to the nature of the soil on the rock.
Clay soil is generally impervious and holds the surface water, and is consequently bad unless carefully drained. The suitability of this soil depends largely upon the subsoil, and if the latter be of gravel and the clay not very deep, it may form an excellent site to build upon.
Houses near some towns have to be built on such soils, and provided they are properly drained they can be made at least unobjectionable, although clay, being a good conductor, is generally rather cold.
Gravel, free from loam and with a pervious subsoil, is generally considered good for building sites, as it allows the surface water to rapidly drain away. Porous soils may, however, be objectionable if there is an impervious stratum beneath, which holds the water as in a basin.
Marshy soils, including muddy sea-beaches or river banks, are unhealthy and even dangerous, and are shown by statistics to be responsible for malarial and other affections.
Made ground, i.e. ground which has been used as a dust and refuse shoot is frequently found on the outskirts of towns and in the suburbs, and is, of course, unhealthy to build upon.
Chalk, if permeable and free from clay, is generally considered to be healthy, but many chalks are impermeable, and therefore damp and cold.
Next: Selecting a Site.