Drawing the set
as coordinating planes—representing the theoretical
boundary between adjoining building elements. A
diagrammatic indication of the window in the wall will
clarify this definition (4.10).
The coordinating dimension is the one which will be
shown on the general arrangement and assembly
drawings, and is the nominal dimension to which both
the bricklayer and joiner will work. If that dimension is
1500 mm, then we may speak quite properly of a
‘1500 opening’ and of a ‘1500 window’. The nominal size
of the frames will be reduced by the manufacturer to a
size which is smaller all round by 10 mm, this being the
dimension laid down by the British Woodworking
Manufacturers’ Association as an appropriate reduction for
timber products in order to produce a final or ‘work size’.
We now have a situation which may be shown
diagrammatically as in 4.11.
It must be borne in mind, however, that neither the
bricklayer nor the joiner is likely to achieve 100 per cent
dimensional accuracy and the best that can be done is
to specify the degree of inaccuracy that will be regarded
as acceptable.
In the present example two trades are involved, and the
degree of precision to be demanded must be realistically
related to the nature of the materials in which each is
working. It may be assumed that the bricklayer will set up
a temporary timber framework as a simple template to
which this brickwork may be built to form the opening. For
the bricklayer therefore, an opening which varies in size
between x5 mm and x0 mm with xbeing the
coordinating dimension may be considered reasonable.
In the timber component however, it will be reasonable to
accept variation in size between y5 mm and y5 mm
where yis the laid down work size of the component.The final assembly of window and brickwork may
therefore have two extreme dimensional situations, with
a range of intermediate possibilities (4.12).The selected method of sealing the gap between
component and opening must take account of these
variables if it is to work in all situations. The sizing of4.10 The coordinating dimension
4.11 The work size