The springing of an arch is the point where the arch begins to curve, that is, the transition from the vertical support (pier or wall) to the curved portion of the arch. This point is also known as the spring point or the impost. The springing line is the imaginary horizontal line connecting both springing points.
Components of an arch
| Component | Description |
|---|---|
| Springing (spring point) | The point where the arch begins |
| Springing line | Horizontal line between the two springing points |
| Rise | The height of the arch above the springing line |
| Keystone | The uppermost stone at the centre of the arch |
| Span | The horizontal distance between the two springing points |
| Soffit | The curved undersurface of the arch |
Position of the springing
The springing can be located at various heights:
- On the impost: a projecting block or profile on top of the pier
- Directly on the pier: without an intermediate element
- Within the wall: in blind arches or niche arches
Importance for the DIYer
- The springing determines the clear headroom beneath the arch
- When building an arch in brickwork, the centering (temporary support) is positioned at springing height
- The angle at the springing determines how the first voussoirs are placed
- A higher springing gives more clearance beneath the arch
Types of arches by springing
- Semicircular arch: springing at the point where the semicircle begins
- Segmental arch: springing above the centre point of the circle
- Pointed arch: two curved sections meeting at a point
- Tudor arch: springing with a shallower angle, wider opening
Related terms
- Impost: the support point on which the arch rests
- Rise: the height of the arch
- Keystone: the central, uppermost stone
- Voussoirs: the wedge-shaped stones of the arch