4.4 Key to sub-divided plan forms part of the title block

4.4 Key to sub-divided plan forms part of the title block

With computer aided draughting, of course, it is possible to alter the scale of the drawing at will, and print out at a scale convenient to the size of sheet available. If the line thickness used for the original plot is compatible with legible reduction then this option saves a lot of time and trouble.

Apart from this upper limitation it is clearly sensible to restrict as far as possible the number of different sized drawings issued on any one project. An early appraisal of the size of the job and of the appropriate scale for the location plans will probably establish the format for the complete set of location drawings, and normally it is not difficult to contrive that the assemblies and the ranges of component drawings should also be drawn on sheets of that size.

The majority of the drawings in the average set therefore will appear in either A1 or A2 format, depending upon the size of the project.

The nature of sub-component drawings and schedules, however, tends to make a smaller format more suitable for them, and there will always be in addition a number of isolated small details on any project which it would be pointless to draw in one corner of an A1 sheet, and which it would be confusing to attempt to collect together on a single sheet (the 'miscellaneous details' approach which has been condemned earlier).

Where the format for the other drawings is A2 it is probably worth wasting a little paper for the sake of obtaining a manageable set of consistent size. Where the general size is Al, however, a smaller sheet becomes necessary, and whether this should be A4 or A3 is a matter for some debate.

A3 or A4? It may be helpful to set out the pros and cons. The advantages of the A4 format are:

• A substantial amount of the project information is already in A4 format—specification, bills of quantities, architect's instructions, correspondence, etc

• Trade literature is normally A4, and if you wish to include manufacturers' catalogues as part of your set (and why not?), then they are more readily absorbed into the structure of the set if you already have an A4 category

• Most users—both producer and recipient—will possess or have access to an A4 photo-copier with the facility that this offers to, for example, the contractor who wishes to get alternative quotes for a particular item and can rapidly produce his own copies of the particular drawing. The A3 copier is still something of an expensive rarity

• The restricted size of sheet makes it more suitable for producing standard drawings, where it is necessary to limit the amount and extent of the information shown in order to preserve its 'neutrality'

• Architect's instructions are frequently accompanied by a sketch detail and the A4 format simplifies filing and retrieval

• A bound set of A4 drawings is suitable for shelf storage. A3s are an inconvenient size to store, whether on a shelf, in a plan chest drawer, or in a vertifile

• A4s can be carried around easily.

The disadvantage of the A4 format is:

• The drawing area is altogether too small. One is constantly being forced into the position of limiting what is shown because there just is not room on the paper, or of selecting an inappropriately small scale. The choice is not easy, but on the whole the author is inclined to favour A3 as the smallest sheet of a set, if only for the pragmatic reasons that you can, at a pinch, hang them landscape in a vertifile; that you can, at a pinch, bind them into a specification or a bill of quantities and fold them double; that you can, at a pinch, copy them in two halves on an electro-static copier and sellotape the two halves together; and that wasting paper is, in the last resort, cheaper than re-drawing a detail which in the end just would not quite go on the sheet.

Drawing conventions

Building elements

In the same way that line thickness is influenced by considerations of scale and the relative importance of the objects delineated, so too is the degree of detail by which various elements are represented. The manner in which a door or a window is shown on a 1:20 assembly drawing is not necessarily appropriate to their representation on a 1:200 location plan.

kept simple in convention. Often a simple diagonal hatching, with the diagonals running in different directions, will suffice to illustrate the function of two components of the same material, without requiring that the user look up some vast code book to see what the material is. He is told that in the accompanying notes.

Gridded hatching, where the grid is parallel to the axes of the element being hatched, is not only time-consuming to draw but downright confusing to interpret.

In all the foregoing, however, it should be borne in mind how simple and rapid it is to apply hatching within defined areas by the use of CAD.

As always, common sense and absolute clarity of expression are the criteria. If a door frame is detailed elsewhere in the set at a scale large enough for the intricacies of its mouldings to be described accurately, then it is a waste of time and a possible source of confusion if an attempt is made to reproduce the mouldings on a 1:20 assembly drawing whose real function is to indicate the frame's position in relation to the wall in which it sits.

Some conventional methods of representation which are generally speaking appropriate for a range of elements at various scales are given in appendix 1.

Handing and opening

The conventions for describing the side on which a door is hung are many and varied. These are sometimes ambiguous, at worst contradictory, and few areas where precise description is vital suffer so much in practice from imprecision as this one.

Possibly the simplest and most easily remembered convention is this: that the hand of an opening is the side on which the hinges may be seen. (BS 1192's 'clockwise closing' and 'anti-clockwise closing' cut across long-ingrained terminology.)

The use of this convention provides a ready mental reference for checking the handing of any component, and for providing instructions to others. Like any other convention, however, it is of little use to the recipient unless he is in on the secret. So he must be told, preferably by a simple statement at the start of the component schedules.

The conventions determining window openings are in more general use, presumably through the early development of the metal window industry with its requirements for off-site hanging of casements and a consequent clear system for describing the handing.

The normally accepted convention is that the window is drawn as viewed from the outside. Conventional representations for both door and window openings are given in appendix 2.


The use of hatching of various kinds to give a graphical indication of different materials was first developed as a readily reproducible alternative to the laborious colouring of opaque originals which had preceded it. BS 1192 sets out a range of conventions for various materials, now co-ordinated into a definitive recommendation of existing conventions currently in use within various disciplines.

The existing ranges of conventions are all based on building techniques of the last century, and were they to be brought fully up to date an enormous expansion of conventions would be necessary. Such concepts as rigid and loose-fill insulation, for example, fibre-glass mouldings, or glass-reinforced cement would all require consideration.

One should first question the necessity, or indeed the desirability, of hatching in the first place. BS 1192 itself suggests that it only be used when confusion is likely to occur in the interpretation of drawings, and in most cases such potential confusion may usually be avoided by other means. Building elements shown in section, for example, may be distinguished from lines in elevation or grid lines by affording each their proper line thickness, without recourse to hatching. Different materials are less likely to be confused with one another when drawings are elementalised; and in any case the mere differentiation between, say, brickwork and block work which is possible with hatching is not normally sufficiently precise for present day purposes. We want to know if the bricks are commons, or engineering quality, or facings. We want to know if the blockwork is lightweight for insulating purposes or dense and load-bearing. Such subtleties can only be covered by proper annotation, and such annotation will often render other methods redundant.

Where hatching is used (and BS 1192 itself suggests that this be limited to larger-scale drawings), it should be

Some conventions in common use, simplified from their original sources in some instances, are given in appendix 3, but their use should be very much conditioned by the comments above.

Electrical symbols

The architect frequently becomes involved in the production of electrical layout drawings, particularly on smaller projects where no M & E consultant is engaged, and appendix 4 gives some of the more commonly used symbols in general practice.

Two points may usefully be made about the method of showing wiring links between switch and fitting. In the first place, of course, any such representation on the drawing is purely diagrammatic; no attempt need be made to indicate the precise route the wiring should take. (If ducted provision has been made the fact should be noted on the drawing, and the ducting shown on the appropriate builder's work drawing.)

In the second place, the links are far better drawn curved than in straight lines which are liable to conflict with other building elements (see 2.8).

Non-active lines

Lines on a drawing which delineate the actual building fabric are termed 'active lines'. Those lines which are essential to our understanding of the drawing, but which form no part of the building, such as grid lines, dimension lines, direction arrows, etc are termed 'non-active lines'.

Recommended conventions for non-active lines are given in appendix 5.


Numerous plastic cut-out templates are now on the market covering many of the symbols given in the appendixes. Templates are also available for the production of circles and ellipses, and for drawing sanitary fittings.

Such templates are a time-saving aid, even though one of the corollaries of Murphy's Law ensures that the symbol you really need is missing from that particular template. A word of warning should be added about the indiscriminate use of templates for sanitary fittings, where it is dangerously easy to fool yourself about dimensions. Some manufacturers of sanitary fittings

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