Talk:Jack arch

Mardin Arch
Addition of the Mardin arch. Likely to be the first Jack arch anywhere, unless others are known.

Not Flat
As stated in the article jack arches are not flat in design. A rise of 10 mm in every 900mm span is incorporated into its setting out. This is due to the fact that if the arch was constructed flat it would give the illusion of a sag in the arch when finished even tho it would be perfectly flat, hence the need for the slight rise in the centre of the arch. Thanks: Kevin H
 * You are correct in principle, and in high-profile projects this would be done. In most cases in domestic architecture the span is too short for this effect to be noticeable, and it is laid flat.  It's worth a paragraph in the article - would you like to have a try at it?   Acroterion  (talk)  17:20, 25 October 2008 (UTC)

All and every jack arch should have this 10mm rise per 900mm span. It is noticible if the arch is constructed flat. Any flat arch i set out and build has this design incorporated into it. Thanks: Kevin H —Preceding unsigned comment added by 86.40.246.2 (talk) 23:25, 9 January 2009 (UTC)