It is possible to continue ad infinitum with these illustrations but horizontal space divisions are nearly always present in some form, due to structural necessity or aesthetic requirements. It is an easy matter to say that these lines must divide the primary mass into "interesting" spaces, well related to each other, or "pleasingly located," but the designer must have some definite yet flexible rule to govern his work. From the analysis of many famous historic buildings and well designed industrial projects it has been found that all horizontal masses may be analyzed as dividing the primary mass into either two or three divisions or spaces, regardless of the complexity of the project.
Analysis of Horizontal Space Divisions
Two Horizontal Space Divisions
Rule 2a. If the primary mass is divided into two horizontal divisions, the dominance should be either in the upper or the lower section. [Plate 7] shows this division of the primary mass—the simplest division of the space. A space divided just half way from top to bottom would be monotonous and expressive of the ratio of one to one. This arrangement as we have already discovered in the [second chapter] is not conducive to good design.
By the stated rule, 2a, the varied adjustment of this double horizontal division affords all possible latitude for constructive purposes. It is better to place the division in such a manner that the upper division (or lower) will not appear pinched or dwarfed by comparison with the remaining area. Thus a ratio of one to three, or three to five, or five to eight is better than a ratio of one to one or one to eighteen, but there is no exact or arbitrary ruling on this point.
Two Horizontal Divisions in Wood
[Figure 8] illustrates two horizontal divisions in wood construction and also the freedom of choice as to exact proportions. The eye will be found a good judge of the proper spacings subject to the limitations already mentioned.
Plate 9