Never say never...We use to load a window screen (it was metal) with a 100 watt tube transceiver and an antenna tuner from a tank and talk to Germany on 20 meters from our 8th floor dorm room. There are several problems though.
1. rf burns if anyone touches it
2. very directional, the building will act as a reflector behind the railing.
3. with 5 watts you would probably be better off with an antenna made for limited space
4. more than 5 watts on 11 meters you run the possibility of all types of interference and distortion.
I'm afraid that no matter what you use if the antenna is not above the building # 2 will affect you.