One of my clients has a beautiful Grade II listed summerhouse, the back of which is troubled by excessive ivy.
Periodically I am sent round to the back to pull the ivy off, a job which is at once hateful (I detest working with ivy as the dust makes me sneeze, I invariably get bits in my eyes, in my hair, and down my neck; it takes a long time to do a decent job, and the wretched stuff invariably grows back, so it always feels like a lot of effort for not much result) and satisfying, as I really, really dislike ivy, and take pleasure from pulling it down.
Every time I do it, I comment that without digging out the roots, it will just grow back again: but often there isn't the time to spend digging out roots, when there are a hundred more important jobs to get on with.
Last year, I resorted to cutting across the stems, pulling off as much as I could both upwards and downwards, then spraying the base with glyphosate.
Now, at this point I will digress into that urban myth that cutting ivy stems will not kill off the upper part, but that the ivy will somehow take moisture from the air and will continue to live.
I have done a significant amount of research into this subject, and I am happy to report that this is not true: ivy uses walls/trees etc for support, not for nutrition. The problem rises where the aerial roots find an alternative source of water, ie on the "other" side of the wall. In that case, if you cut it across lower down, the upper part can still find water and can re-grow a new root system.
This does not apply to modern houses - mostly to old houses with very soft mortar (and no cavity insulation), or to elderly outbuildings or garden walls made of just one layer of bricks, so that the aerial roots can go through to the other side, and find a source of water over there.
But on a modern building, if you chop across the stems at ground level, or at knee height, and remove a section of the stem completely, then the upper part will die.
It will, however, take 3-10 years to rot enough to fall down of its own accord... the other urban myth, the one which says "leave the upper part to die, it's easier to remove" is also untrue. The tiny aerial roots actually harden when they die, so they become even more work to remove. The best time to remove the upper part seems to be 2-3 weeks after cutting the stem - time enough for the plant to start to wilt, but not time for the tiny roots to start to harden.
So, going back the the one I did last year, before I learned about the hardening of the aerial roots:
I chopped across at ground level, and pulled off as much as I could reach at the time. As you can see, the upper part is stubbornly still attached to the wall.
I had another go at pulling it down, and now the dead stems are brittle, so instead of being able to pull of great long streamers of it, it snaps off in short lengths, which is maddening.
At some point I am going to have to climb up and scrape it off.
So, if you have ivy growing on a wall, don't delay, chop it down NOW before it gets out of hand.
In fact, I think after ten years of professional gardening, I can't find any good reason to allow ivy to grow up walls. Not one single reason. Grow something else! Grow roses, grow pyracantha, paint the wall, anything rather than grow ivy up it!!