Comparaci´ on con otros m´etodos de la familia AESA . 115

The philosophy of cost planning can be divided into two main ideological groups – those that pertain to ‘costing a design’ and those that pertain to ‘designing to a cost’. The difference is significant. Costing a design refers to methods of estimation that can arrive at a cost for a given (predetermined) design. Naturally some formalized drawings need to be in existence for this process to function. Designing to a cost on the other hand means guiding the development of a scheme so that it not only sets a budget amount and ensures that the project does not exceed same but provides the client with the greatest value for money possible.

5.4.1 Costing a design

Costing a design covers the majority of cost planning techniques whose main purpose (in theory) is to develop the most economic form of a given design. The emphasis is intended to be placed on the phrase ‘of a given design’ since this cost planning philosophy does not investigate alternative design solutions. It does, however, identify cost-significant items contained in the scheme that may be deleted or substituted during the project’s design stage.

The principles of costing a design are well known, as this philosophy is easily the most common process now in use in most countries. But its advantages, limited as they may be, are not being fully capitalized upon at the present time.

The initial decisions that significantly involve the developing design are commonly made by the architect. They may be based on aesthetic considerations, previous projects, experience, or even an assumed economic configuration. But no objective analysis is undertaken and no facts are compiled to verify the choices made. The sketch plans are prepared as a result of the initial decisions. This is the point at which the quantity surveyor usually becomes involved. His/her task is largely pre-defined as estimating the cost of a project using one of the many methods available and thence preparing the initial cost plan.

The quantity surveyor monitors the costs as the drawings progress and makes suggestions (although these are not necessarily implemented) about possible savings. Very little constructive criticism pertaining to design decisions takes place for reasons that perhaps are more concerned with maintenance of professional relations than anything else. The level of interaction between cost consultant and designer is largely governed by whether or not the developing cost is remaining within the original budget allowance.

During the pre-tender period the cost plan is continually revised, and as the number of unknowns is reduced, since there are obviously less unknowns, the design contingency (an allowance for future detailing – also called design risk) is progressively reduced. The final cost plan should provide an estimate of the total cost equivalent to that produced by the successful tenderer who has priced a bill of quantities based on the same set of drawings, although the cost plan is presented in a completely different format. If the cost plan is founded on the pricing of measured quantities, and there has been due consideration of market conditions, then this will usually be the result.

It was suggested that in theory costing a design refers to the majority of cost planning techniques whose main function is to develop the most economic form of a given design.

In practice, however, this is not always the case. Costing a design in the most part is the control of a project’s developing construction cost with reference to a pre-determined budget amount. If the derived cost is below the budget then often no further investigation at that particular stage is carried out. If the derived cost is above the budget then activity does occur and items of cost significance are identified and either deleted or substituted with less expensive alternatives.

Government projects frequently have the budget set by a government-employed quantity surveyor who is independent of the consultant quantity surveyor involved in the cost planning process. The budget amount is derived from a standard procedure that, in simplified terms, utilizes information from past projects. Any new design, ignoring special factors and site works which are both separately allowed for, should be capable of being built for the same price as an average of previous projects escalated and adjusted to the new tender date.

Costing a design is widespread. Very little optimization takes place on an objective and formalized level as intuition seems to play an important role in the decision-making process. Generally alternatives are analysed only on specific instruction, not as a matter of course. In crude terms, the philosophy of costing a design when used in practice is merely a process of cost estimation. This situation is considered an unsatisfactory one and fails to achieve the overall cost planning objective of providing value for money.

5.4.2 Designing to a cost

Designing to a cost covers the majority of cost planning techniques whose main purpose, unlike the costing a design approach, is to develop the most economic design solution possible. It is implied that alternative methods of achieving the intended result are examined objectively as an essential aid in the decision-making process. Since neither the architect nor the quantity surveyor nor any other member of the design team can reasonably fulfil this objective in isolation, a co-operative effort is required.

In order that this philosophy can function properly it must be implemented before any formalized attempt at documentation has begun. A feasibility study optimally examining all possible design solutions in respect to cost is ideal, but in practical terms the scope of the investigation should be confined to a much smaller selection.

The architect, in association with the quantity surveyor and other consultants, formulates a number of proposals that all have the potential to achieve the stated design objectives. The quantity surveyor then investigates each such proposal from a cost point of view and ranks them in order of merit. After further discussions with the architect, and perhaps further investigation, an optimum configuration in respect to the original selection, based on cost and performance, is nominated as the concept design.

Using this information the sketch plans are prepared.

During the design process, the architect, the quantity surveyor or others may suggest more specific ways in which the project may be further optimized. Such suggestions should take the form of a collection of proposals and each proposal should be objectively investigated using quantitative techniques. As each cost plan is prepared an opportunity is provided to review the status of the project. It is important to note that the level of interaction is largely governed by the co-operation achieved between architectural and economic constraints.

Designing to a cost is generally not common in practice. The philosophy relies fundamentally on co-operation between the architect and the quantity surveyor at the concept stage as well as during the development of a selected design. It is therefore necessary that the quantity surveyor takes a more prominent role in the design of a project, especially before sketch plan stage has been reached. It is only during this period that significant cost savings are possible, for after commencement of doc-umentation the basic concept is fixed and design alterations are thus non-productive and impractical to implement. Until initial decision making is changed from the role of the architect to that of all members of the project team this efficient cost planning process will remain merely of academic interest. It is the client, not the architect, who can change the current situation.

5.4.3 Comparing cost planning philosophies

Design variables is a term applied to the fundamental characteristics of a given project, e.g., plan shape, height, floor area. The advantage of the ‘designing to a cost’ philosophy is related to the mechanisms that allow the design team to search for and identify the optimum design variables that are capable of guaranteeing value for money. Hence options can be individually appraised prior to commencement of drawings in order to select a building configuration within available funding limits. Attempts at optimization after drawings have been started are of little practical benefit.