Not sure about size not measured. Surveyor said nothing can be done, builder said maybe wall ties but was not sure about stairs where there is nothing to tie into.
They didn't know but they never looked in loft, could it be weight of roof? I am having gutters replaced and repairs as water coming in, could be that? There is old structural movement.
Thanks been searching internet, had builder and surveyor look but they didn't know anything. It's a small 3 bed semi, bulge is about inch and a half where stairs run along, built 1928.