From Wikipedia:
Around the mid-19th century, this form of housing was deemed unsatisfactory and a hazard to health. The passage of the Public Health Act 1875 (38 & 39 Vict. c. 55) permitted municipal corporations to ban new back-to-backs, replaced in the next phase of building by byelaw terraced houses. Leeds City Council opted not to enforce the ban, however; the popularity of back-to-back houses with builders and residents led to their continued construction in Leeds until the 1930
The term "back-to-back" should not be confused with "through" terraced houses, the backs of which face each other across an alleyway, and are thus not contiguous like a true back-to-back. Back-to-back houses can also be known as blind-backs,[3] particularly when built up against factory walls, or occasionally as a terrace of houses standing on its own.