Size and height come first: more storeys, more staircases, more risers and more flat entrance doors mean more time on site, and time is most of the cost. Layout complexity matters almost as much, which is why a sprawling converted building can cost more to assess than a taller purpose-built block of flats. Assessment type is the other big lever: a non-destructive Type 1 inspection of the common parts is the default, while wider scopes add destructive sampling or work inside flats and are priced accordingly; the FRA types overview explains all four.
Then come the quieter drivers. Poor access, meaning locked risers, missing keys or no responsive site contact, adds visits and therefore cost. Thin records force the assessor to reconstruct basics such as door inspection history or the evacuation strategy from scratch. Volume cuts the other way: portfolio clients booking many buildings at once usually pay less per building than a one-off instruction, because travel and administration are shared across the programme.