PRINCIPLES Or CONSTRUCTION.
Planning. —The first task to be performed in connection with the erec tion of a building is to form an approximately accurate conception of its characteristics. In works of a complex nature, especially if they have features embodying novel arrangements or artistic effects, an architect is usually' employed, and one of his first duties is to furnish a plan or design which shall represent as closely as possible, in specially convenient and economical modifications, the leading ideas of the projector. In the mass of buildings, however, most of the details of adjacent structures or of printed descriptions are closely imitated, and such aids leave little necessity for planning except in reference to matters about which the advice of com petent contractors or constructors furnishes all necessary information.
In the planning of any building-structure the builder will be guided primarily by the uses it is intended to snbserve, then by the nature and area of the available site on which it is designed to erect it; and it will be obvious that that plan will be best which, with the proper regard for the foregoing considerations, combines the highest degree of fitness and con venience with the lowest cost. In many cases, bov:ever, the mstlietic feat ure enters as an element of greater or less importance. But, while this should receive due consideration, the architectural design should always be subordinated to the prime conditions above noted, and it is universally held to be evidence of the correct use of the principles that should be fol lowed in the application of architectural design when the building exhib its at a glance the purpose for which it is intended.
Substructure: Foundations. —The term " foundation " is properly re stricted to that part of an edifice which is intended to serve exclusively as the basis upon which to erect the superstructure, the word being frequently applied to that portion of ground which supports the building, and also to the various artificial arrangements prepared to support the base, which lat ter would be more properly tertned the " foundation-bed." Solidity of base is the primary consideration, and the main object is to insure the sta bility of the superstructure by preventing any movements of its parts after completion. As, however, nearly all soils are to some extent compressible under weight, and as works of masonry settle slightly, it would be more ex act to say that the builder exerts his art to insure that this settlement may be unimportant and uniform rather than in the hope of preventing it en tirely. The condition and the quality of the soil to be built upon detnand
primary consideration in determining the character of the foundation, and the firmness of the ground should be thoroughly tested.
and Quality of Soils. —Foundations can be considered under two general classes—those constructed in a natural soil capable of bearing the weight of the intended superstructure, and those in situations where the conditions of the soil necessitate the creation of an artificial support. To determine the quality of the soil in ordinary circumstances, when exca vations such as wells and culverts have not already' revealed the conditions, it is only necessary to dig a pit in order to examine the strata. A bed of firm soil from 2 to 4 feet in thickness immediately below the foundation is sufficient to support any ordinary structure, even though it should be under laid, in turn, by a much softer stratum. When a greater stability is deemed essential for important edifices, the nature of the subsoil can be ascertained by the introduction of the auger-pump, or other means of boring.
Founa'ations Contioact Soil.—In compact and stony earths, such as sand and gravel, foundations are dug from 4 to 6 feet in depth, in order to reach below the action of frost, and, when necessary, drains are required to carry off all surface-water. Strong gravel is considered as one of the best soils, being easily levelled, almost incompressible, and unaffected by exposure to the atmosphere. Sand has also the advantage of incompressi bility, but demands special treatment on account of its want of cohesion. In proceeding with the walls it is necessary to give them a bearing greater than their own width, in order to distribute the weight over a greater sur face. This increased width in the foundation-courses is styled the "spread " or " footing." When the soil is as firm as the principal con stituent of the wall itself, it is not necessary to give much width to this spread. In firm earth it is usually made one and a half times the width of the wall, and in sand and ordinary soil twice that width. Clav soil, even when sufficiently firm, is affected by water, and the bed should be prepared by digging- a trench to drain the ground. The foundation must also go below the frost-line, as clay soils are much affected by cold and should be protected from exposure to the weather as much as possible.