I live in a wooden house, which is kind of ideal yes. You say brick, which isn't actually that bad, if you reference the classic NIST report [1].
And even in a brick house a lot of the interior walls are still just plywood or drywall, even in the UK AFAIK.
What is interesting though is that OP said it is sufficient with one AP per floor plus one outside. So apparently propagation within one floor is fine, but between floors or to the exterior is not. In that case, it has to be a building where the interior walls are mostly just drywall, and the exterior walls and floor slabs are reinforced concrete with little in terms of openings. Which sounds more like an apartment building than anything else?
I think it depends largely on age - “new builds” (1980s onwards) often have a brick partition wall down the middle and the rest plaster/wood stud. The last couple of houses (significantly older) I’ve lived in have been pretty much all brick walls.
We’ve got 3 UniFi APs downstairs here, 2 up. There are still things on the periphery that only just cling on, and when you’ve got stuff like that it takes a lot of airtime.
