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The final pricing of a project by the constructor or contractor usually takes a different form. The costs are broken down into (1) cost of materials brought to the site, (2)cost of labor involved in every phase of the construction process, (3)cost of equipment purchased or rented for the project, (4)cost of management and overhead, and(5) profit. The architect or engineer seldom follows such an accurate path but should perhaps keep in mind how the actual cost of a structure is finally priced and made up.
Thus, the percent averages stated above are obviously crude, but they can suffice to introduce the nature of the cost picture. The following sections will discuss the range of these averages and then proceed to a discussion of square footage costs and volume-based estimates for use in rough approximation of the cost of building a structural system.
2. Percentage Estimates
The type of building project may indicate the range of percentages that can be allocated to structural and other costs. As might be expected, highly decorative or symbolic buildings would normally demand the lowest percentage of structural costs as compared to total construction cost. In this case the structural costs might drop to 10～15percent of the total building cost because more money is allocated to the so-called architectural costs. Once again this implies that the symbolic components are conceived independent of basic structural requirements. However, where structure and symbolism are more-or-less synthesized, as with a church or Cathedral, the structural system cost can be expected to be somewhat higher, say, 15and20 percent (or more).
At the other end of the cost scale are the very simple and nonsymbolic industrial buildings, such as warehouses and garages. In these cases, the nonstructural systems, such as interior partition walls and ceilings, as will as mechanical systems, are normally minimal, as is decoration, and therefore the structural costs can account for60 to 70 percent, even 80 percent of the total cost of construction.
Buildings such as medium-rise office and apartment buildings(5～10 stories)occupy the median position on a cost scale at about 25 percent for structure. Low and short-span buildings for commerce and housing, say, of three or four stories and with spans of some 20 or 30 ft and simple erection requirements, will yield structural costs of 15～20 percent of total building cost.
Special-performance buildings, such as laboratories and hospitals, represent another category. They can require long spans and a more than average portion of the total costs will be allocated to services (i.e., 30～50 percent), with about 20 percent going for the purely structural costs. Tall office building (15 stories or more) and/or long-span buildings (say, 50 to 60 ft) can require a higher percentage for structural costs (about 30to 35percent of the total construction costs),with about 30 to 40 percent allocated to services.
In my case, these percentages are typical and can be considered as a measure of average efficiency in design of buildings. For example, if a low, short-span and nonmonumental building were to be bid at 30 percent for the structure alone, one could assume that the structural design may be comparatively uneconomical. On the other hand, the architect should be aware of the confusing fact that economical bids depend on the practical ability of both the designer and the contractor to interpret the design and construction requirements so that a low bid will ensue. Progress in structural design is often limited more by the designer’s or contractor’ slack of experience, imagination, and absence of communication than by the idea of the design. If a contractor is uncertain, he will add costs to hedge the risk he will be taking. It is for this reason that both the architect and the engineer should be well-versed in the area of construction potentials if innovative designs ate to be competitively bid. At the least the architect must be capable of working closely with imaginative structural engineers, contractors and even fabricators wherever possible even if the architecture is very ordinary. Efficiency always requires knowledge and above all imagination, and these are essential when designs are unfamiliar.