Our (1906) terrace house was built in an era when the use of attic space for storage was decades in the future. Loft hatches (and insulation!) were not installed and there was a brick divider about every 10-12 houses.
One of our neighbours heard what he thought was rats or squirrels in his loft space. One weekend he knocked through from the landing ceiling and was surprised to find an enterprising neighbour (I won't mention his country of origin for fear of incurring the Mod's wrath) had boarded out at least four adjacent lofts and fitted the space out with mattress's, bedding and lighting. At a rough guess his three bed mid-terrace had sleeping space for forty!
Needless to say, full height brick partition's followed pretty quickly for everyone.