On Oct 5, 9:19*pm, S R wrote:
I'm getting the existing poor quality double glazing replaced
next summer, but I am also considering cavity wall insulation.

In what way is it poor quality?

I ask because as long as it is a) not rotten b) seals work c) no
howling gales through it d) windows not broken or steamed-up (which
can be fixed) then windows are windows and the money may be better
spent elsewhere...

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.

.... such as after finding out you do not have a usable cavity wall
(sufficient depth, free from obstructions etc) that you could insulate
on the inside via sticking insulation on the walls or building a free-
standing timber frame inside into which you stuff insulation and
dryline (plasterboard).

The reason I say that is double glazing is quite expensive (payback
period is 50-100yrs over single glazing and even longer if you already
have double glazing), and insulating solid walls on the inside is also
rather expensive. If you DIY it will still be costly re materials,
redecorating etc - but the difference is you reduce your heating bill
really quite significantly. If you are spending £800/yr on heating-
alone now, it is quite conceivable you could reduce that to £300 as
well as feeling somewhat warmer. Payback period would be quite long
even though.

You can insulate on the outside, but unless that is rendered it can
significantly change the character and may be prohibited if a Gr-II
listed building etc. If possible, however, you can the thermal mass of
the inside as long as you can stuff enough heat into it in the first
place. You would use polystyrene stuck to the wall with plastic pegs,
with an expanding mesh, and a render coat over the top - or something
along those lines.