https://www.bbc.co.uk/news/articles/clyjpyxnlx9o
From Tizers Mystery Roof Question this happened a few days back in Notting Hill area of London
This style (in a way all show and no go) with the front parapet rooves are prone to problems. It looks like the end house has been rebuilt , possibly with a basement excavation. Surprisingly avoiding damage from WW2 similar , larger , houses continue much further north without the bay windows , but ran onto north kensington / ladbroke grove becoming demolished when declared "slums" in the late 1960s as the estate that has Grenfell Tower on it was constructed, The council ran out of money leaving other houses opposite that a mix of empty or cheap tenure with one family per floor , some early 1970s were sold , not exactly cheap and not exactly weatherthigh but have become very expensive now. The "invert valley gutter" style can sometimes be seen better from the rear on the pictured house style from passing trains when there are rail lines running behind, So far as I remember there are no downpipes to the fronts of the buildings , with a mid gutter to each house running to the rear and it is a pain to keep the gutter clear of leaves - any window in the roof slope could be opened to do a bit of maintenance if needed, so the hip of the roof met at each house adjoining the next one , or a half hip and high wall for end terrace ones. The parapet appears not to tie in to the roof structure - one would have thought there would be two bearing beams running aft to fore cemented into the brickwork as a tie - modern method would be some kind of bat u nail and screws resin bonded into the essentially decorative finish of a one brick? thick running course built all the way along the terrace frontage - if the end house lost the keying into the adjoining that too could weaken the run - as could taking out internal walls of one or more of the houses but its more likely vibration from increasingly heavy motor vehicles along roads that were designed in the days of the horse carriage and horse tram
It might be an ill wind but placing mansard rooves as replacements would add an extra storey - assuming foundations can support them
