There are three commonly accepted ways of preparing rough estimates, each practical in its appropriate connection and each requiring its own suitable set of data. Perhaps the most habitually used method is that of calculating the cubic contents of the structure and pricing it at a certain amount per foot cube, depending on the kind of construction.



Experience will enable moderately precise estimates to be quickly achieved by this method. The data required is the charge per foot cube of various classes of buildings of recent production; but to be of genuine value these prices should be gathered by the estimator from structures which he himself has carried out.

It is a good practice to determine at the completion of each job what the cost per foot cube has actually been and to keep detailed lists. In the case of building differing materially from one that has been built previously, it will be readily clear how difficult it is to evaluate with precision the amount by which such disparity will affect the price per foot cube. When estimating cubic contents for a large building, it is better to subdivide the building into two or more classes and to price each at its own specific rate.

For instance, the primary block of a structure may be of a much more expensive quality than the remaining portion; in this kind of scenario it will be more accurate to price them as separate structures than to attempt any kind of averaging which can only be a slight improvement over a rough guess. In some cases it may be easiest to keep the basement and the superstructure divided.

Where this technique of estimating is implemented, it is customary to let the price include only the building by itself and to put in separate approximations for drainage, heating, etc., which clearly cannot be accurately allotted at per foot cube of building. Fence-walls, yard-paving, and the like should, for an analogous reason, figure separate estimates.

The standard way of determining the cubic contents of a building for estimating reasons is to multiply the area on plan by the height from the top of the concrete foundations to halfway up the roof or three-quarters up if there are attics. Dormers, corner blocks (http://www.ferche.com/), and other projecting elements must also be accounted for.

Another technique assumed in the case of churches and schools is to allow a certain amount per head of seating room. Similarly, the unit of cost in the event of hospitals or stables is for each bed or stall.

This is often a helpful guide where one has exactly like buildings already carried out for contrast; but it is essential that the ratio among the seating accommodation, or bed, and the cubic contents be similar in both cases. Any extra height given to the structure, or an added vestry, plinth blocks, or anything out of the ordinary, will involve additional expense which has to be dispersed over the total.

The most dependable method of arriving at an approximate estimate is by means of rough measurements; but it is not used as often as it should be because of the time involved. It should be the only permitted technique for any large building and for contests, the price per foot cube being determined simply as a check. In rough numbers the chief items only are measured, and in them all finishings and efforts are included.