The centre line of a structure is the imaginary middle 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 abbreviation “c/c” (centre-to-centre) is used to indicate 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 offset | The shift of the centre line relative to another element |
Applications of centre-line dimensions
- Stud walls: c/c spacing between studs (often 600 mm for insulation batts)
- Strip foundations: centre lines determine the position of foundation strips
- Piles: c/c spacing determines the load 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 structural calculations
Why work with centre-line dimensions?
- Centre-line dimensions are independent of the thickness of the material
- Construction drawings become clearer and unambiguous
- Dimensioning remains correct even if the wall thickness changes
- It is the standard in construction for setting out structures
Tips for the DIY enthusiast
- Always measure c/c when that is what the drawing specifies, not edge to edge
- For a stud wall at 600 mm c/c with 45 mm studs, the clear space is 555 mm
- Use a chalk line to snap centre lines onto the floor or wall
- Check centre-line dimensions with a cross-line laser for accurate work
Related terms
- Centre-to-centre spacing
- Dimensioning
- Grid (structural grid)
- Setting out
- Construction drawing