We're replastering our lounge and having removed the old cracked &
blown plaster, we've found a fair sided crack running diagonally in
the interior brick wall between the lounge and the old kitchen.

The crack starts at the top corner where the wall joins the inner skin
of the exterior wall and extends downward at approx 45 degrees then
meanders a bit. There are no major visible cracks on the outer skin of
the exterior wall, although one or two bricks have cracks through them
but not in any sort of 'connected' way. The exterior extension walls
(see below) have no visible cracks at all.

The house was built in the 1930's and the lounge has an extension, put
in about 15 years ago by the previous owners, with the opening going
through the exterior wall - RSJ put in above the window and the wall
below the window removed. There is approx 70cm between the inner
wall/outer wall corner and the opening.

We've got a builder coming round this afternoon to have a look at the
crack, but I'm pretty worried about this and I'm hoping that someone
can provide some reassuring words of wisdom & tell me it's common and
not going to cost a fortune to put right.

Perry