On Sun, 18 Nov 2007 05:46:29 -0800 (PST), a particular chimpanzee,
randomly hit the keyboard and produced:

Part of our kitchen has a sloping ceiling; plasterboard nailed to the
sloping roof rafters.
This section is not insulated.
What is the best, and what is the easiest way to do it? Should I
take off the plaster, lower the ceiling by 3 inches, and pack between
the joists and the extra space with fibre - a relatively big job....
or could I successfully take an easier route; drill holes and inject
something - expanding foam maybe?

Neither.

The best; remove the plasterboard, install 25mm PIR foam boards
(Kingspan, Celotex, etc) between the rafters, leaving a 50mm
ventilated space over, then 120mm PIR under, then a polythene vapour
barrier, then plasterboard.

The easiest; an insulated plasterboard under.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have you strayed?"