Modelos de Negocio en Chile

Few, if any, variations have no effect on the Contract Sum. In order, therefore, to adjust the Contract Sum adequately and satisfactorily within the Conditions of the contract, the quantity surveyor (and the contractor’s surveyor, too, if he wishes) must ascertain the net extra cost or net saving involved. To do that, the affected work will have to be measured, except in those instances where the method of valuation makes it unnecessary, as discussed below. This means that the work originally designed, which will not be required as a consequence of the variation, must be identified, isolated and val- ued, and that which will be required to replace the omitted work must be measured and valued. Such measurement may be done from drawings or, if drawings are not available, by physically meas- uring the substituted work on the site after it has been carried out. This same procedure will be necessary whether the contract is based upon bills of firm quantities or on specification and draw- ings only. In the case of contracts based upon bills of approximate quantities and those based on a schedule of rates, the whole of the Works will have to be measured as described above. In all cases

the valuing will be done in the manner discussed in the section below headed ‘Valuing variations’.

It should be appreciated that in the case of ‘without quantities’ contracts, the work omitted will have to be measured in detail, as well as the substituted work, there being no simple procedure of identifying bill items affected, as in the case of ‘with quantities’ contracts. Where there are bills, it will often be necessary to refer back to the original dimension sheets in order to identify exactly what was included in the bills for the work which has been var- ied. If the items affected constitute complete bill items, they can be identified by their item references either as a single item or a group of items, e.g., ‘item 132B’ or ‘items 132B–G’. If a variety of items is involved, many of which are not complete bill items, the omissions can be identified by reference to the dimension column numbers, e.g., ‘original dimensions, X–X cols. 95–103’, the letter ‘X’ being written on the dimension sheets to indicate the commence- ment and end of the omitted work. The measurement of AIs Nos. 8 and 48 in the examples at the end of the chapter illustrates the alternative procedures.

The quantity surveyor has the duty laid upon him by clause 5.4 of the JCT Form, to provide the opportunity for the contractor to be present when measurements of variations are taken. Although the clauses do not specifically refer solely to measurements on site, in practice the provision is not normally applied to measure- ment from drawings done in the office. It does mean, however, that the surveyor must give the contractor’s surveyor sufficient notice for him to be able to make arrangements to attend on site when measuring is to be done there.

When variations are being measured this must be carried out using the same rules as used for the preparation of the contract bills (see clause 5.6.3.1), which in most cases will be the current Standard Method of Measurement of Building Works produced by the Royal Institution of Chartered Surveyors and the Construction Confederation. When measuring on site, it should be remembered that it is intended by the Committee that prepared the Standard Method of Measurement that the rules of measurement in that document should apply equally to measurement on site and to measurement from drawings.1_{This is important, for example, when}

measuring excavation involving working space and earthwork sup- port. The SMM requires these items to be measured, even though the surveyor doing site measuring may know that they have not

actually been done. The dimensions of the excavation should be those which are the minimum for the required construction, meas- ured in accordance with the rules of the SMM, notwithstanding that the contractor may have excavated wider to avoid the use of earth- work supports or because the excavator bucket available was wider than needed. So, too, the lengths of timbers whose ends are not cut square (e.g., rafters) should be measured by their extreme lengths and inflexible floor tiles (e.g., quarry tiles) should be measured between skirtings, particularly where the latter are coved, and not between wall faces.

Measurements taken on site are normally entered in bound dimension books, which consist of pages with dimension column rulings similar to ‘cut and shuffle’ slips, or to traditional dimension paper but with only one set of columns instead of two. Alternatively, one may use normal dimension paper on a clipboard which, although not so convenient to handle as a dimension book, does give the advantage of having all the measurements, whether taken on site or in the office, on the same size sheets.

Another way of dealing with both the measurements and the working-up involved, is to use A4 size paper ruled with dimension columns on the left and quantity and money columns on the right – i.e., similar to estimating paper. Thus, all the information – measurements, billing and pricing – is presented on the same sheets (see AIs Nos. 15, 23, 28 and 41 in the examples on p. 145).