ARCHES- IMPORTANT TECHNICAL TERMS

An arch is a structure constructed to span across an opening. It generally consist of small wedge-shaped units which are jointed together with mortar. 

The important technical terms used in arch work are as follows:

1. Intrados- It is the inner curve of an arch.
2. Soffit- It is the inner surface of an arch. Sometimes intrados and soffit are used synonymously.
3. Extrados- It is the outer curve of an arch.
4. Voussoirs- These are wedge-shaped units of masonry forming an arch.
5. Crown- It is the highest point of the extrados.
6. Skew back- It is the inclined or splayed surface on the abutment on which the arch rests.
7. Abutment- It is the part of the wall on which the arch rest. In other words it is the end support of an arch.
8. Key stone- It is the wedge--shaped unit at the crown of an arch.
   
9. Springer- It is the voussoir next to skew back.
10. Springer line- It is an imaginary line joining the lowest parts of springer.
11. Haunch- It is the bottom portion of an arch between the skew back and crown.
12. Span- It is the clear horizontal distance between the supports.
13. Pier- It is an intermediate support of an arch.
14. Rise- It is the clear vertical distance between the springing line and the highest point on the intrados.
15. Depth or height- It is the perpendicular distance between the intrados and extrados.
16. Thickness or breatdth of sofit- It is the horizontal distance measured perpendicular to the front and back faces of an arch.