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Out of interest, is this in London or elsewhere?
Whilst I don't know, it wouldn't surprise me if some of the housing stock in London is lower quality compared to places which perhaps didn't have the pace and quantity of development at that time.
The other thing about much of London's Victorian housing stock is that it's built on clay soils with very shallow foundations, resulting in varying degrees of movement / subsidence being common. That and residual bomb damage.
Ok, I guess we'll agree to disagree here.
Most Victorian houses were knocked up out of whatever was to hand, with minimal concern for life expectancy or integrity.
I've lived in them all my life. I've worked on them. I've seen what they are made of.
Yes, you could (and ideally should) keep it going with period correct materials, I just don't think it's a practical proposition for most home owners who pick up one of these places like 6th or 7th or maybe even 38th hand.