3.25 Demolition drawing covering formation of new opening in an existing wall
Note that it would be wrong for the drawing showing new works to make reference to the opening having been formed under the same contract. To do so would be to invite the possibility of the estimator unintentionally including the item twice. Neither is the routine note 'make good to plaster and finishes' included on either drawing. Such a general instruction, which will presumably apply to a number of such door openings throughout the project, is more appropriate to the specification.
Generally speaking, a single demolition plan for each floor will suffice, but if there are complexities of a special nature to be covered then the mode of conveying the information may need to be more elaborate. Figure 3.27, for example, shows the demolition drawing of a reflected ceiling plan, where the fact that certain suspended ceiling tiles and light fittings were to be removed is carefully separated from the new work which is to replace them, (3.28), as well as from the alterations to internal partitions, etc which are covered on another sequence of drawings.
Simple items of making good, such as the replacement of areas of plaster, or the overhauling and repair of windows, are often most simply covered by scheduling on a room to room basis. If only 2m2 of plaster are to be replaced in a given room, it is presumably obvious enough to all concerned which 2m2 are referred to, without the necessity of precisely locating them on an internal elevation. Written description, in fact, is often better than graphical instruction in much rehabilitation work.
If CI/SfB coding is being adopted for the set then demolition drawings will normally be given a (—) 'project in general' code, leaving the more detailed code references for application to the new works.
One extremely important point is often overlooked in drawings of alteration work, with unfortunate consequent effects. It is absolutely vital that everyone should be clear from the drawings as to what is new work and what is existing. Basic structure is not too difficult to distinguish (shading in existing walls and showing the details of construction on new walls will avoid confusion in this respect), but it is the little things—manholes, rainwater pipes, sanitary fittings—often appearing as left-overs from the survey drawing, which need specific annotation.
It is, of course, helpful to issue the survey drawing as part of the set.
The provision of a new door in the existing brick wall given as an example in the section on conversions and alterations was an instance of an activity-oriented approach to the provision of building information. Activity 1, involving the cutting of the opening and insertion of the lintol, was rightly regarded as being distinct and of a different nature from activity 2, which embraced the fixing of a new door and frame. The two activities were separate and complete in themselves; they were potentially capable of being carried out by different people, or groups of people; and they might well have been (and indeed probably were) separated from each other by a significant period of time, during which no work of any kind was being done to either the opening or the door. It was possible, therefore, and on the face of it reasonable, to convey the necessary information to the builder in the form of two separate instructions.
Whilst this approach to building communications is clearly sensible in the very limited context of alteration work, it is also possible to apply it to the whole spectrum of building operations. Hitherto in this book a building has been looked upon as consisting of an assembly of individual elements. It may equally well be regarded as the result of a sequence of different and separately identifiable activities. Such a concept lay behind the development in the 1960s of activity and operations bills of quantities. The theory behind them is simple. The contractor's main problem lies in the organisation of his resources, both material and human.
His bricks have to arrive on site at the right time, his bricklaying labour force has to be sufficient to optimise the length of time his scaffolding is on hire, it must be re-deployed smoothly and economically when the work is finished, either to some other part of the project, or to another project. Success lies in careful and accurate programming.
Conventional bills of quantities do little to assist in this task. To tell the contractor that he is to erect a total of x m2 of brick wall will enable him to put an overall price on the total brickwork/bricklayer section. It will not point out to him that the last brick will be laid some eighteen months after the first; nor that it will be laid on an entirely different part of the site; nor that the nature of the construction involves the total bricklaying operation being split into three separate stints, with substantial gaps of time between them.
Such information may well be deducible from an intelligent examination of the drawings, but the bill of quantities is after all the document he has to price, and were it to be presented in a form which showed the true nature of his work there would be inestimable benefits all round. The contractor would have at his disposal not only a more accurate basis for his estimating, but a flexible management tool which could be used for, among other things, the programming of material deliveries, the deployment of site labour, and the forecasting of cash flow for the project. The quantity surveyor would have the advantage that re-measurement, when necessary, would be restricted to small and readily identifiable sections of the work rather than entire trade sections, and that valuations for interim certificates and final account would be greatly simplified. (It would not be a question of agreeing how many metres of brickwork had, in fact, been erected. It would be a matter of common observation how many activities had been completed.)
The method has not become so widely established as had at one time seemed likely, but it is there, readily available, and consideration should be given as to
3.27 Demolition drawing of reflected ceiling plan (scale 1:50) 70
whether any adjustment of working drawing technique is desirable to accompany it.
The method starts with the establishment of a notional list of building activities which, while not binding on the contractor, is nevertheless intended as a realistic attempt to put the work into a correct order. A typical sequence for a piece of brick walling, for example, might run thus:
1. Strip top soil.
2. Excavate for strip footings.
3. Lay concrete.
4. Lay engineering bricks to DPC level.
6. Build 275 mm cavity wall to wall plate level, etc.
It is not possible for drawings to show activities, only the completed event. There is no reason, however, why an elementalised set of location drawings such as has been discussed in the previous pages should not form a perfectly satisfactory adjunct to an operational bill. In the example given, activities 1 to 4 would all be covered on the foundation plan, and the remaining three on the primary elements plan. To each drawing would be added a note saying which numbered activities were shown on it (or were shown on other drawings to which that drawing referred). Against each activity in the list would be set the number of the location drawing which would initiate the search pattern.
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