....no, it's not J-Lo. I've discovered a worrying crack in the party wall
on the top floor of my new house. It's near to the outside wall, about
3ft long and 1-2mm wide. Goes at a steep diagonal starting about 6" from
the outside wall up to about 2' from the outside wall. Looking along the
outside wall, I can see that it appears to have bowed out slightly,
which is I presume the cause of the crack. The bowing appears to be
limited to the upper part of the wall.

Not sure how to proceed now. Just bought the place so I'm reluctant to
get the insurers involved as they may well decide it started with the
previous occupants and start a battle with previous insurers. Also, it's
a party wall so that could make things complicated.

What could cause this, and how would it be treated? I imagine what will
need to be done is one of those big metal X things on the outside wall
to hold it all together. Is that an expensive job, or even a DIY job?
I'm slightly tempted to plaster it up and keep an eye on it for 6
months, but that's obviously a bit risky.

Any ideas?

John