That was ours when I first bought it. The small extension to the 'rear addition' was a full single brick though with 3/3rds of it an inside bathroom (off the rear extension / kitchen) and the remaining 1/3rd the outside (and only) loo.
Now the 'new' ss extension is the only bit of the house with cavity walls.
I did re-render the main flank wall (internally, pre plastering) with a thermal render of some sort (that was supposed to help). It was quite 'aerated' so I can see how it might. We have since considered lining that with some Celotex but never got round to it.
But what if you have a single brick built house that is designed to 'breathe' through the brickwork to some degree and then you seal it up with (especially) external cladding?
Sometimes it's the right place to have them ... and I don't only mean when you are working in the garage / garden. ;-)
Cheers, T i m