Here is the roof space of a Victorian terraced house.
The roof slates forming the covering are typically not underlined with “sarking” felt and they are well supported by a traditional timber frame of down rafters and cross purlins.
It is quite common for roof spaces in properties of this age to be not fully separated resulting in an increased risk of fire spreading between neighbouring houses.
Here the gap has been infilled with modern concrete blocks. This is a satisfactory arrangement. It is now often a requirement of many mortgage lenders and insurance companies, and will be highlighted in your surveyors report.