Component, sub-component and assembly drawings
Whilst this approach to building communications is clearly
sensible in the very limited context of alteration work, it is
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 1970s and 1980s of activity and operational 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 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
xm^2 of brick wall will enable him to put an overall price
on the total brickwork/bricklayer section. It will not
necessarily 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 remeasurement, 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 matter 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
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
5 Lay DPC
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 general arrangement 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 3would 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 general arrangement
drawing which would initiate the search pattern.