I'm currently bricking up two doorways in a 4" party wall between two
terraced houses, as part of a project to reinstate the original
dwellings. I did the first one using medium density blocks, which I
lugged back from Wickes myself, nearly stuffing both my back and the
car suspension in the process... a joiner who later surveyed my
handiwork said I could/should have used the much lighter aerated type
instead. Is that right? If so I could at least use those for the
second doorway!

When we had an extension built a few years ago, with a cavity wall, I
remember the builder used heavy blocks for the outer wall and much
lighter ones for the inner - I assumed I'd need the heavier ones for
the doorway.

I've just noticed in the latest Wickes catalogue (page 36) both types
of block are described as "3.5N" - would that be their load rating?

Thanks
David