Jim wrote:

"Mary Fisher" wrote
In January 1993 we paid something over £300 for cavity wall insulation,

I am not familiar with this term. In the US, I have always used
paper-faced rolls of fiberglass stapeled between the wall studs. What is
CWI? The same? Sprayed foam/cellulose?

Firstly it's worth noting that building construction is very different in the
UK. We still use a lot of traditional brick for building (at least for exterior
walls) together with building block.

Homes made of wooden stud construction are rare in the UK.

Older buildings like mine dating from the Victorian era are typically made of
brick 2 layers thick (solid 9 inch walls). More recent buildings have a cavity
wall which consist of an internal wall made of building block tied to a single
layert outer wall made of brick. The air gap provides additional insulation.

More recently it's become the norm to install insulation material in that air
gap, either fron new or retrospectively with blown or foamed insulation to
improve the thermal properties further.

Graham