I have a bungalow with a very shallow (6 degree) felted roof and an old
sloping ceiling attached to the underneath of the roof timbers. There
is no loft access to most of it.

I am building a new, flat ceiling under the old one (gap of 2 to 20"
between them). I don't think the old ceiling is insulated so I will put
loft insulation over my new ceiling.

Do I need to use vapour-barrier plasterboard to stop condensation
forming in the space above the insulation? There is no ventilation here.
Or is it better to use ordinary board so any moisture can get out?

I am hoping to just paint the plasterboard. Do I need to tape the joins
or just use filler?

I will be putting 9W CFL spotlights in the ceiling. Can one cover a low
energy CFL spot with insulation or should this be avoided to stop it
getting too hot?

Thanks

Roger