On Wed, 07 Jan 2009 20:29:29 +0000 The Natural Philosopher wrote :
What I would do is to lift the floor, nail battens to the joists to
support the insulation, at the right height to bring the celotex panels
flush with the joist tops, and then tape over the joists and panels with
celortex foil tape.

With a six foot void, make an access and work from below is probably
easier.

--
Tony Bryer, 'Software to build on' from Greentram
www.superbeam.co.uk www.superbeam.com www.greentram.com