ESTIMATING COST OF CONSTRUCTION To predict with accuracy what it will cost in time or money, or both, to accomplish work, is at best an exceedingly difficult task. To begin with, in out-of-door work the conditions are—many of them—speculative. We do not know the per sonalities of most of the men who are to be em ployed; we do not know how much rain or frost we shall have to contend with; and we are re quired to work under a contract many of the terms of which are vague, and some of them pro hibitory. What wonder that estimates for the same work differ—and differ widely? There is a certain cost at which projected work is going to be done; but no two men will guess alike be fore the fact; and, after having guessed, no two men would come out with the same figures of performance on identically similar jobs, if it were possible to get together two identically similar jobs. In this volume we have given a number of conditions which affect costs, without by any means exhausting the possibilities of the field. An ideal estimator should take into con sideration all the conditions which affect costs, and should allow each condition to have just the correct influence upon his figures.
157 Conditions Affecting Cost. The conditions affecting the cost of construction work will nat urally group themselves into three classes: 1. Those whose quantitative effect upon cost can be reasonably predicted.
2. Those of which the qualitative effect can be de termined only in advance.
3. Those conditions the influence of which may be to increase or perhaps to decrease the cost above or below an assumed normal.
By way of example, (1) we can say in ad vance about how much more it will cost to haul bricks two miles along a known highway than to haul the same bricks only one mile along the same road; (2) we know that when we have to blast out a medium-hard shale, the work will cost more if the rock is full of seams and faults, with dikes of hard material, than if ordinarily regu lar in structure; but just how much more, or even nearly how much more, we cannot predict. Again, (3), the coming of a new superintendent upon the work will surely have an effect upon it, good or bad; but until he has been tried out, there is no telling which it will be. This last-men tioned fact accounts in large measure for the re luctance with which contractors let their old men go after they have run out of contracts.
In addition to the above, there are emergency and unforeseen conditions that from time to time unexpectedly arise and make a carefully pre pared estimate seem like a poor affair.
Obviously it is impossible to eliminate the ele ment of uncertainty in estimates. The problem for us is how to make the closest estimate possi ble from the known facts. The most careful rules and the most elaborate system, if followed, would not reduce the art of estimating to an exact science. Much must depend upon the intelli gence, the information, the aptitude, and—above all—the experience of the estimator; lastly, he must have the elusive and intangible but never theless positive and essential quality of judg ment, without which all theory is helpless.
It is possible, however, by the use of cumula tive evidence, to reinforce a man's experience with the facts contributed by other men; and it is possible, by the presentation of correct theory, to show a man how to make his own experience of the most value with the least effort and fa tigue. As a step in this direction, the present article has been prepared.
Men Who Make Estimates. Estimates in general are made by three classes of men: 1. The Engineer or Architect, who makes them as the basis for designs, preliminary to obtaining contracts.
2. The Contractor, who undertakes to carry out the work.
3. The man in the field, who is carrying on the work.
1. The Engineer or Architect. The engineer or architect who makes his estimates as a guide to his client in deciding what work shall be planned, is usually in the position of the man who estimates without having to carry out the work himself; and he is always in great danger of making his estimates too low. The reasons for this are not generally appreciated. Some of them are as follows : (a) His client is seldom willing to pay for a thorough investigation of the conditions that are to be met, it being assumed that since a con tractor is willing to spend his own money in ma king an estimate on the chance of obtaining a profitable contract, the cost of estimating is so low that the engineer or architect can do it him self out of what he receives as his fee, and that it should therefore be a part of his office ex penses. He cannot afford to make an extended investigation at his own expense, and thus fails to take into consideration many conditions which are more likely to increase the cost than to de crease it.