Mick6 wrote:
The walls of our 1930's house appear to be thinner upstairs than
downstairs, most obvious on the landing where there's a shelf / second
window sill:

http://tinyurl.com/3a8tuo

Our neighbour told me that, when she had cavity wall insulation
recently, the installers were only able to do downstairs. She wasn't
sure whether this was because upstairs was solid or a thinner cavity.

Has anyone come across this type of construction before? Is it more
likely that it's solid or just a thinner cavity? I'd have thought
that, if a cavity existed, it could be filled with the kind of blown
insulation that's used today.

Thanks.

As a CWI installer I came across this from time to time, and while not very
common, it's not a rarity neither - I think builders went through a short
spell of doing this as you say, around the 30's, and yes, the shelf on the
stairs is a feature of all of them.

With regards to having them insulated, they will only insulate the lower
part because while there may be a small cavity upstairs, an inch at most,
this isn't possible to insulate by injection, and even if it were, it would
be useless as mineral wool only works over 40mm in thickness, and you could
never get the correct density given that the inch cavity would be completely
solid in parts where debris has filled it