This arch is so named because the top, or extrados of the arch, is flat. The bottom (intrados or soffit) may be flat or cambered. The camber is traditionally 1/8" per foot span. This is approximately one percent (1%) of the span. However the camber may vary dramatically. The camber is not a structural feature. It acts to disguise the optical illusion of the arch sagging.
The skewback is the face of the arch that meets the face work of the wall. The skewback sits at an angle to the horizontal level. This angle is called the skewback angle. It can be specified as either an angle or a distance past the span.
To specify a flat arch you will need the following information:
Brick type & colour, span, face height (measured vertically at the jamb), skew angle, joint width, number of voussoirs, bond pattern, camber rise (measured at the centre), soffit depth, brick finish (rubbed or sand faced). Will the arch have any special features – a keystone or carved soffit?
Webpage Pics
