Am I right in thinking that the "sill height" of a window as measured from the floor is not actually the height of the top surface of the sill but of the bottom of the visible glass?
I'm trying to calculate whether or not I'll need toughened (or safety) glass for a new window, and those couple of inches could make all the difference - though is there any significant difference in price and practicability between ordinary glass and the strengthened variety?
Incidentally, one window supplier told me that the threshold for toughed glass was 900mm - but it's 800, isn't it?
Many thanks.