ceiling question re. downstairs garage.

G'dall all. Still going through my options as to enclosing downstairs into a bar/rumpus.

My question is, since I will be putting up a ceiling (will be an A/C rumpus), should I just up the ceiling and leave the space between the ceiling and top floor boards open? Or should I seal the outside off? I want to insulate the ceiling to improve A/C performance and reduce noise to upper level.

I have heard though that it's better to leave this area open to ventilation to prevent moisture problems with the upper level floor boards. Is this true?

Attached are 2 pics to give a better idea of my situation.

Cheers.

Ben

http://members.westnet.com.au/bstone82/DSCN06662.jpg

http://members.westnet.com.au/bstone82/DSCN06652.jpg

I'd stick up some Rondo 129 battens and fix the plasterboard to that. the insulation will probably help a bit. Use polypropylene twine zig-zaged between the joists to hold up the insulation. Or just tack up some reflective building paper.

Cheers
Pulse

Seal it up (cavity to the outside), so as to stop anything getting in there i.e. mice, snakes, cats, small children, etc.

If you're worried about ventilation, then put some mesh type vents in.