When the height of the balustrade does not conform to the orthodox proportions the method of determining the relative proportions is as follows:—The height is divided into seven parts; of these one part gives the height of the capping, four the baluster and two the plinth.
The mouldings in character and detail are the same as those of the pedestal, and should be in harmony with the order used.
When balustrading forms part of a stair, the height on landings should be three feet two inches. On the rake two feet ten inches from the step at a line vertical with the face of the riser. The plinth is invariably used as a string enclosing the ends of the steps and following the rake or angle in a straight line, and carried to the levels by means of curving ramps.
In interior work the bulbous shafts of balusters are often decorated with carved detail, and the mouldings also may be enriched.
Use of Columns
Columns were originally used in the porticos and courts of temples and other buildings, and sometimes to form supports for vaulted roofs. Wherever employed their function was directly structural, but this was not the case at the time of the Renaissance. The requirements demanded by widely different social conditions led to their being used more as decorative than structural features.
The use of engaged columns and pilasters in a façade can be justified to some extent. Although such columns and pilasters may not be absolutely essential for support, yet they act as buttresses and add to the strength of the structure with a certain economy of material. Also they are æsthetically satisfactory in their effect of light and shade.
Disposition and Spacing in Colonnades
The disposition of columns either in a façade or a colonnade is controlled by proportions which have been found to be desirable or are necessitated by special features of the order itself. The latter is the case with the Doric order, the spacing being determined by the trigylphs and metopes. If the triglyphs are placed centrally over the columns or pilasters the spacing of these apart will be two and a half diameters centre to centre, three and three-quarters, or five diameters, with two, three or four metopes respectively between them in the frieze. With the wider spacing of five diameters it is usual to employ coupled columns to add to the appearance of strength. As the triglyphs are one and a quarter diameters apart centre to centre, the coupled columns are brought very close together, entailing a slight modification of the bases. Since the ordinary projection of the plinth of a sixth of a diameter beyond the line of the shaft is not possible between the two columns, the plinth-blocks are united, and the torus moulding made slightly less in projection.