Construction drawings and communication: interpreting drawings of domestic buildings, the types of drawing, scales, dimensions and standard symbols.

What this dot point is asking

CCEA wants you to be able to interpret drawings of domestic buildings: to know the main types of drawing (plan, elevation and section), to understand and use scales and dimensions, and to recognise the standard symbols used so that everyone on a project reads a drawing the same way.

The answer

Why drawings matter

A construction drawing is the main way a design is communicated from the designer to the people who build it. Because a building is too big and complex to describe in words, drawings show exactly where everything goes, what size it is and how it is built. Standard conventions for scales, dimensions and symbols mean a drawing produced in one office can be read correctly on any site.

Types of drawing

Together these views describe a three-dimensional building on flat paper: the plan gives the layout, the elevations give the appearance, and the section gives the construction and heights.

Scale

Drawings are smaller than the real building, so they are drawn to a scale.

Common scales include 1:1250 or 1:2500 for site and block plans, 1:100 or 1:50 for floor plans and elevations, and 1:20, 1:10 or 1:5 for detailed construction details. A larger scale (such as 1:5) shows more detail of a small area; a smaller scale (such as 1:1250) fits a large area on the page.

Dimensions

Dimensions are the measurements written on a drawing so the exact size is known without measuring the paper. They are usually given in millimetres on construction drawings (for example 2400 means 2400 mm). Dimensions are essential because paper can stretch or be copied at the wrong size, so the written dimension always takes priority over a measured one.

Symbols

Standard symbols represent common features so drawings stay clear and consistent. Examples include symbols for doors (a line with an arc showing the swing), windows, stairs (a series of lines with an arrow showing the direction up), sanitary fittings (WC, basin, bath), and electrical points (sockets and switches). North is shown by a north point arrow.

Worked example: reading a length off a plan

Examples in context

Example 1. Setting out a house

Builders use the dimensioned floor plan to mark out the exact position of the walls on the ground. Without accurate dimensions the rooms would be the wrong size.

Example 2. Choosing the right scale

A planner looks at a 1:1250 site plan to see how the house sits among neighbouring buildings, but a joiner needs a 1:5 detail drawing to see exactly how a window is fixed. The scale is chosen for the level of detail needed.

Example 3. Reading a section

A section through the wall shows the brick outer leaf, the cavity with insulation, the block inner leaf, the floor build-up and the damp-proof course, all of which a plan or elevation cannot show. This is why a full set of drawings includes all three views.

Being able to read and use drawings ties the whole of construction together: the materials, the structure, the dimensions and the finishes are all communicated through them. These same skills are developed further in the computer-aided design unit, where drawings are produced on a computer.

Try this

Q1. Name the drawing that shows the layout of rooms viewed from above. [1 mark]

• Cue. A plan (floor plan).

Q2. What does a scale of 1:100 mean? [1 mark]

• Cue. One unit on the drawing represents 100 units in real life (one hundredth of full size).

Q3. A wall is 30 mm long on a 1:50 drawing. Find its real length in metres. [2 marks]

• Cue. $30 \times 50 = 1500\ \text{mm} = 1.5\ \text{m}$.