I live one floor up and the ivy working its way up the outside wall had started to cover air vents and windows. A simple problem surely? 'I'll just get some weedkiller to get rid of it'
Well my research so far suggests that no substance on earth (with the possible exception of Polonium-210) harms ivy. It's often said that after the inevitable nuclear holocaust only a few insects will survive. Well if so they will have my ivy to nest in.
Giving up on chemical warfare (but open to suggestions for future attacks) I got some secateurs and proceeded to cut across the bottom just six inches from the ground. That wasn't easy as the thickest parts were inches across, but I made it. I stood back and admired my handiwork... and couldn't see any change. I still can't see a change a month later. It looks perfectly happy there on the wall with no contact with the earth.
As merry said "it must make a difference eventually or why would ivy have roots to begin with'
...to be continued
Many plants all but shut down during the winter so severing the stems now will have less of an effect than if it were done in summer. Once spring starts in earnest then I would expect it to start to wilt and eventually die. But if it flowered last autumn there will be countless seeds ready to drop off by now and start it all over again.
We sometimes have to cut ivy off walls at work and we always cut a four or five inch gap away, on the advice of our tree surgeon. That way it can't heal over. And even then it can take up to a year before it has died back to the point where it can be removed. And sometimes the dratted stuff seems to have got roots into the wall and be taking nutrients from that. Or from the air, I sometimes think. Tough stuff! 
Good luck, hope yours dies back soon.
Eccles, I suppose it will have dropped seeds since it's well established and it will grow again from them. In any case I couldn't kill the base of it so that part will grow too. I shall have to keep cutting it back.
Rosie, this has indeed put roots (tendrils?) into the wall. You can see strands as thick as a pencil disappear and reappear inches away. It's amazing stuff really. I wonder how deep into the wall it grows? If it goes right through the wall it will encounter the main power lines and perhaps that will discourage it 
Anyway if it's going to die back later in the year that's good enough I guess. I just want to keep it from covering windows etc. It was starting to remind me of Day of the Triffids
Could you lean out the window with a blow torch and burn it to death.
I wouldn't be too sure about the power lines. It is more likely that the ivy will discourage the power lines, I think.
Not very easily as it's the window over the bath. I did think about leaning out, tieing a rope to it and going down to tie the other end to a car 
I doubt it would work, but would be fun to see.
You don't want to kill the ivy Pani as that means all in money in your house dies with it - if you are superstitious anyway! 
Ps If you just cut the branchy bits off you get about 10 more in place of that single 1 - I know as there was ivy growing in my garden up the house wall when I came here - 24 years ago - and I now rue the day that I decided to nuture it as now I can't get rid of it! 
Babs, the money will be no use if I can't get out the door
Well I have no hope of actually killing the ivy, but I hope to control it well enough to keep it away from my windows etc. The parts above the cuts I made are just begining to look a little ragged now so it's starting to affect it. The areas further along that I didn't touch have grown up into the guttering which is another potential problem. I think I had better cut those too before it blocks it or pulls it off the wall.
I think, without any fear of contradiction, that Pani is not superstitious. And since he is skint it doesn't matter anyway.
Well it's finally started to make a real difference. In the last week or so the ivy has begun to go brown and dead. It has a way to go yet and even longer before the remnents of it disappear. I don't see any sign of it actually falling down so I guess it will go one leaf and twig at a time.
Originally I only cut the bit nearest to me (in case others wanted to keep it) but the contract gardeners must have got the hint from my efforts and went round cutting a 2ft gap in all the ivy. I think they cheated and used a power tool of some kind since theirs was cut much neater than mine.
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