I recently took over a house built in the 1980's during a building boom.
The quality of workmanship is poor. I was inspecting a part of the attic
which, up to now, was inaccessable. The builder forgot to put in
insulation!!! The heat escapes right through the plaster board ceiling and
out the house.

The ceiling plasterboards are nailed directly to the ceiling joists with no
vapour barrier installed. I'd like to insulate this attic space but can't
fathom how to apply a continuous vapour barrier to the existing structure
without ripping down all the ceilings involved. I've seen home renovation
programs like (Bob Vills'a Home Again and other similar programs) where
professionals spray an expanding insulation product, Polyicynene I think,
into new construction cavities without first applying a vapour barrier. Is
this a good way of getting the existing structure covered in a
moisture-proof barrier? Can I follow up the Polyicynene application with a
blown loose-fill cellulose or fibreglass batting insulation for greater
R-value and not worry about moisture problems like mould?