On 05/10/2010 21:19, S R wrote:
My house is a semi built in 1873, from Yorkshire stone.

It is a devil of a job heating it and keeping the heat in.

I'm getting the existing poor quality double glazing replaced next
summer, but I am also considering cavity wall insulation.

I'm not sure how effective CWI is in house such as mine, and also the
effect it has on resisting or promoting damp penetration.

If your walls are two feet thick then they are almost certainly rubble
filled. Such walls have voids but AIUI cavity wall insulation is not
effective. Two feet of wall is a better insulator than 9 inches of wall
but it is not comparable with a modern insulated wall.

If the wall is substantially thinner you will need to establish what
there is between the inner and outer courses. 1873 is early for proper
cavity walls in brick built houses. I would have thought a cavity would
be unlikely in a stone built house of that age but I could be wrong.