I have decided to install a lowered ceiling in my kitchen, partly to avoid
having to repair it considerably, partly to install downlighters, but
mainly to hide the ducting for the cooker hood which is 6" flexible
aluminium tubing.

My question is what size wood to use for the joists which will cover a span
of approx 2.5m.
If necessary I could support the joists along the middle by a batten fixing
to the existing ceiling.
If I were to use 9.5mm plasterboard can I get away with less substantial
joists than using 12mm.

--
Chris Melluish