"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Peter Crosland wrote:

Doing the work from within avoids
any potential problems with hidden pipes or wiring within the inner
wall or plaster.


A friend of mine, when he had cavity wall insulation installed, removed the
relevant panes of glass from his conservatory roof first, to save on the
cost of scaffolding (£500 I think). Meant the installers just used ladders.
Put glass units back afterward, job done.