Andrew,
As you're message appears to come from the UK, you may like to
know about British Standard 1808 from the British Standards
Institution. BS 1808 specifies the design of business
letterheads and forms. It details where the address panel and
fold lines should appear for A4 paper folded into a DL envelope.
It also specifies how much white space should appear around the
address panel so that nothing but the address shows through the
envelope's window. The same specifications also work correctly
with larger window envelopes of the right type.
However, this information will only be useful to you if your
window envelopes also comply with BS 1808 in the position of the
window (see more below). Unfortunately some envelope
manufacturers still flog imperial, instead of metric, envelopes.
The BSI recommends that the paper should *not* be folded exactly
into three equal parts. The first fold should be at 103 mm from
the top edge of the paper. (A4 paper is 297 mm tall.) The
first fold line at this position will prevent electric letter
openers (at the letter's destination) from cutting the paper in
two (because the second fold can then never touch the top edge
of the envelope).
I designed the corporate letterhead templates used by all staff
at one of the London Boroughs. It'd be difficult to explain the
details here. However, if any of your envelopes comply with the
following specifications and you would like a copy of one of my
blank templates, let me know.
DL Window Envelope:
Size - 220 mm wide by 110 mm tall.
Window size - 93 mm wide by 39 mm tall.
Window position:
20 mm from left edge of envelope to left edge of window.
18 mm from bottom edge of envelope to bottom edge of window.
Good luck with your project!
Geoff
