they can not be done buy wfp
ladders
jerry
they can be done by wfp just push the brush head through the bars. not easy and standard poles not long enough but still possible with the right equipment.
I agree I do 2 blocks (24 flats, 3 storey) some have balconies. I also have some houses with balconies. I do them all WFP, you have to angle the brush straight to go through the bars, it takes a bit longer, but is quite possible.