The centre line of a structure is the imaginary mid-line or geometric centre of a building element, such as a wall, beam, column or foundation. On construction drawings, the centre line is often indicated with a dashed line and the notation ‘c/c’ (centre-to-centre) to denote the spacing between structural members.
Centre-to-centre (c/c)
| Term | Meaning |
|---|---|
| Centre line | The exact middle of a structural element |
| C/c | Centre-to-centre: distance measured from middle to middle |
| Centre line | The imaginary line through the middle |
| Centre offset | The displacement of the centre line relative to another element |
Applications of centre-line dimensions
- Studwork: c/c spacing between studs (often 600 mm for insulation boards)
- Strip foundations: centre lines determine the position of foundation strips
- Piles: c/c spacing determines the bearing capacity of the foundation
- Window frames: position is given as a centre-line dimension from a reference point
- Steel structures: centre lines of columns and beams for calculations
Why work with centre-line dimensions?
- Centre-line dimensions are independent of the material thickness
- Construction drawings become clearer and unambiguous
- Dimensioning remains correct if wall thickness changes
- Standard practice in construction for setting out structures
Tips for the DIYer
- Always measure c/c when indicated on the construction drawing, not from edge to edge
- For studwork at 600 mm c/c with 45 mm studs, the clear gap is 555 mm
- Use a chalk line to snap centre lines on the floor or wall
- Check centre-line dimensions with a cross-line laser for accurate work
Related terms
- C/c: centre-to-centre spacing
- Dimensioning: the system of measurements on a construction drawing
- Grid: the network of centre lines in a building
- Setting out: transferring measurements from drawing to building site