What are symbols in construction drawings?
Symbols in construction drawings are agreed signs, line types and hatches that show materials, components and services without writing everything out. Because builder, structural engineer, installer and building control all read the same drawing, many symbols are standardised: hatching conventions in national drawing standards, and electrical symbols in IEC 60617. Still, every practice draws a little differently, so the legend on the drawing always takes precedence.
The main groups:
- Hatching. A section through a wall gets a pattern per material: brickwork, concrete, timber, insulation and blockwork each have their own. Insulation is often drawn as a zigzag or wavy line.
- Levels. A fixed datum, usually finished ground-floor level, is set at 0. Levels are shown as +2.800 or -0.600 relative to that datum, marked with a small triangle.
- Dimensions. Dimension lines with figures, usually in millimetres; grid lines labelled with letters and numbers in circles.
- Windows and doors. A door gets an arc showing its swing. In elevations a triangle on a window shows how it opens; on European drawings the point usually indicates the hinge side.
- References. North arrow, section lines with arrows (A-A, B-B) and detail references in circles.
- Services. Sockets, switches, light points, smoke alarms, drainage and ventilation points each have their own symbol.
In practice
- Start with the legend. Read the key before interpreting anything.
- Check the scale. Never measure off paper without knowing the scale; written dimensions rule.
- Combine drawings. Plan, section and elevation together give the full picture.
- Ask when in doubt. Clear up unclear symbols with the designer before work starts.
Common mistake: ignoring a dashed line. It often shows something above the cutting plane or hidden, such as a beam, a void or an element to be demolished.
Related terms
- Symbol
- Datum level
- Section
- Structural grid
- Pictogram
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