On 15/08/2020 09:32, Martin Brown wrote:
On 14/08/2020 22:44, H Poules wrote:
Hello. I have a back-to-back red brick mid terrace house in the UK.
There is a large crack in an internal wall on the 2nd floor. The wall
between the bathroom and the bedroom. The crack runs diagonally up in
a step pattern from the bottom corner where the wall joins the
external wall. The crack is visible on both sides of the wall. It is

Two obvious questions a

Is it in an old coal mining area? Or on a heavy clay soil?

Is there a wall on the ground floor underneath where the upstairs wall
that has cracked is or was there one in the past?

I recall someone in my youth who decided to DIY knock out the central
ground floor wall between front room and dining room when open plan was
very fashionable (but without putting in an RSJ in to take the load). It
did not go well but was entertaining for onlookers!

An RSJ that isn't quite up to the job might explain it.

An RSJ that IS up to the job sometimes doesn't help if the point
loading onto the foundations makes the latter fail, whereas previously
the weight was evenly supported along the whole foundation.

Any BCO doing the job properly would insist on an excavation to
check the foundations and widen/deepen them if necessary.

Andrew
no more than 5mm wide at its widest parts. I cants see signs of
cracks on the walls below. Can this be due to the support of the 2nd
floor weakening? Or is the wall bowing. Please can anyone help me work
out what is happening and what might need doing to fix it
please

You definitely need a surveyor to look at it in person and probably to
put some tell tales on it to see if it is still moving and how fast.

Advice on Usenet may be worth less than you have paid for it.