ENTRENAMIENTO DEL PERSONAL

It is important to appreciate that the techniques adopted in the preparation of a BQ will vary from one individual to another and between one office and the next. For the most part it is assumed that the operation of transferring drawn and other design information into the descriptions and quantities that are collectively termed ‘a Bill of Quantities’ will be carried out without the use of a computer. Clearly there are significant advantages in using a computer package that can generate digitised quantities and automatically sort measured items into the appropriate Work Section. Nevertheless, in order to fully understand the detail of this process, it will be necessary to examine each step in turn and this cannot be fully appreciated by simply pressing a button. What follows is based on a procedure that has evolved over a number of years and is best described by the term ‘traditional bill preparation’ (Figure 2.1).

dimension paper (Figure 2.2)

2.02.01 Dimension column

Dimensions are read directly from the drawings and recorded to two decimal places of a metre in the middle of the three narrower vertical columns labelled dimension column. Alternatively, these dimensions might be scaled directly from the drawing and entered in the same way. Once these have been recorded or ‘booked’, it will be necessary to provide some form of description. The largest of the four columns, labelled the description column, is used for this purpose.

Figure 2.1 Stages in traditional BQ preparation.

Before describing the purpose of the remaining two columns, it would be prudent to spend some time looking at the various ways in which dimensions are recorded. The technical term for entering dimensions in this way is ‘booking dimensions’, and these should always be recorded to two decimal places of one metre (NRM2 3.3.2.d). Accordingly, 3067mm would be recorded in the dimension column as 3.07. There is no need to write the word metre or use

the letter m, since all dimensions are recorded in the same way. Even when the dimension is a whole unit (5 metres), two zeros should be used after the decimal place (it should be recorded in the dimension column as 5.00).

Figure 2.2 Dimension paper. An A4 page is divided vertically into two identical halves, each comprising a set of four columns. These are labelled above for the purpose of identification (Figure 2.2). The extra column on the extreme left is termed the

Figure 2.3 binding margin and would not normally be used for recording dimensions. The following shows examples of dimensions as they might appear on an architect’s drawing, together with the corresponding dimensions as they should appear once they have been booked on the sheet of dimension paper (Figure 2.3). So far we have only considered recording measurable items in the dimension column: as an example, items represented by the unit of length include rainwater guttering, drainage pipe runs, rafters and skirtings. It would be inappropriate to use this same unit for items such as excavation, which not only have a length but in addition, a width and a depth. It may have been noted in the previous examples that a line was drawn across the dimension column under each set of recorded dimensions. This identified each single entry as an individual length. The technical term for this unit of measurement is linear metres. The principal unit of measurement associated with excavation or in situ concrete is cubic metres, and this is shown in the dimension column with all three dimensions set down one above the other and presented as a dimension set by the inclusion of a horizontal line across the dimension column under the last of these three dimensions. In similar fashion, dimensions grouped together in pairs are automatically associated with items that have been measured in square metres, such as brickwork and plasterwork. In some cases it is difficult to identify an appropriate unit of measurement and in such instances counting or enumeration is used. Door furniture, manhole covers and sanitary appliances are all recorded in the dimension column using enumeration. These appear as whole numbers in the dimension column, with a line drawn horizontally beneath each single entry (there is no decimal point required with enumerated items).

Recording dimensions. To summarise:

• • • • • – – – Figure 2.4 Dimensions are recorded to two decimal places of a metre.

There is no need to identify the unit of measurement since this is clear from the presentation.

Where dimensions appear in sets of two or three, these will be multiplied together (squared) to show an area or volume. Clear, legible presentation, in ink, with items well spaced. The order of recording dimensions is length (followed by) width or breadth (followed by) vertical height or depth.

This last point is of no significance in regard to items of length or enumeration, but is of great value when the need arises to trace the build-up of dimensions for areas and volumes (see Figure 2.8).

The following are examples of each of these.

Figure 2.5

Figure 2.6

Volume (m3).

Figure 2.7

Figure 2.8

Enumerated items (nr).

Figure 2.9 Timesing.

2.02.02 The timesing column

So far we have only considered using the dimension column and the description column.

The term ‘timesing’ (Figure 2.9 and Figure 2.10) is used by measurers where there are a number of identical sets or repeats of the same item being measured. For example, when measuring a number of identical internal doors it is convenient to simply record the dimension and description once, and then ‘times’ this by however many times the item being measured occurs. In order to do this the measurer uses the furthest left of the three narrow columns and inserts the number of times the item in question is repeated. This is followed by inserting a short diagonal ‘slash’ line between the booked dimension and the number by which this will be ‘timesed’. It may also go some way towards providing an indication of the layout from the presentation of the dimensions (see Figure 2.27, adjustments).

2.02.03 The squaring column

Attention can now turn to the function of the squaring column. As previously noted, dimension figures are recorded in the dimension column to indicate the unit of measurement. In the case of area and volume, dimensions will be multiplied and the result of this computation entered in

Figure 2.10

the squaring column. There is never any need to include a multiplication sign, since this is assumed (Figure 2.11).

Figure 2.11 Squaring dimensions. Past experience has shown that students find it difficult to resist the temptation to square the quantities as they are recorded. In practice this should be avoided since all the dimensions and descriptions must be completed before the squaring process can commence. 2.02.04 The description column As the title suggests, this is where the worded part of the measurement is recorded. The order and form of wording is important, as this should convey concisely all the information necessary to allow a price to be established. The tabulated arrangement of NRM2 provides an appropriate framework around which to build descriptions. Despite this, there still remains a degree of flexibility in the interpretation and presentation of written descriptions. As far as possible, the structure and terminology of NRM2 has been adopted when writing descriptions in the preparation of this text.

This is one of the more difficult parts of booking dimensions, and those new to drafting descriptions are advised to spend some time looking through a BQ before attempting to write descriptions for measured work (Figure 2.12).

2.03 Dotting-on

Where identical dimensions are repeated it may be necessary to add rather than to multiply. For example, six pits of identical size are to be excavated and the following dimensions are recorded (Figure 2.13a).

Figure 2.12

Figure 2.13a

Interpreting NRM2: relationship between drawings, NRM2 clauses and booked dimensions.

Timesing.

Subsequently, an additional two pits are spotted. Rather than enter another set of dimensions together with an identical description, the original recorded dimensions can be adapted by ‘dotting-on’ another two as follows (Figure 2.13b).

This technique may also be carried out in the timesing column and (technically) any number of additions can be made, although this will be somewhat restricted by the limitations of space and the need for legible presentation. The dot will usually be placed below the original figure to allow more space, and the timesing slash will be placed above it. In practice, these two techniques are often combined (see Figures 2.14 and 2.15).

Figure 2.13b

Figure 2.14

Dotting-on.

Figure 2.15 Dotting-on and timesing.

2.04 Geometric forms

Frequently it is necessary to book dimensions for triangles, circles and other irregular figures. The important point to remember when booking dimensions using geometric formulae is the unit of measurement. Most geometric formulae are quite easily transposed to booked dimensions. For example, the formula for the area of a triangle is half the base multiplied by the height. This can be recorded on dimension paper as follows (Figure 2.16).

The area of a circle with radius 8.64 m (formula πr2_{) can be recorded as seen in Figure}

2.17, and of a sector of a circle as in Figure 2.18.

If, on the other hand, we needed to record the circumference (perimeter length) of this circle, only a single dimension would need to appear in the dimension column (Figure 2.19; formula 2πr).

The inclusion of a fraction in combination with the above can give the circumference length of any portion of the circle, e.g. a semi-circle (see Figure 2.19).

The formula for regular geometric forms and how these should appear as booked dimensions is included in Appendix II.

Figure 2.17

Figure 2.18

Geometric forms area of a circle.

Figure 2.19 Geometric forms perimeter length of circle and semi-circle.

2.05 Waste calculations

Ideally, dimensions can be read directly from the drawings and entered to two decimal places of a metre on dimension paper. Frequently this direct transfer is not possible since some adjustment is required to the dimensions before they can be booked. These preliminary calculations are known as ‘waste calculations’ or ‘side-casts’ and are presented to the nearest millimetre (three decimal places of a metre) on the right-hand side of the description column, immediately above the item to which they relate (Figure 2.20). Once the required dimension is identified by waste calculation, it is reduced to two decimal places after transfer to the dimension column. There may be a temptation to scribble these in note form or even carry out simple arithmetic in the head. Both should be avoided since it is important to identify and demonstrate to others the process by which the dimension was established. Double-underlining in a waste calculation usually indicates that the result has been transferred to the dimension column.