I previously wrote on the wiki about how it's a good idea to grow climbing plants on the walls of your house because the shade and insulation keep the house cool in summer and warm in winter. It's cheap and it's easy to install (you just plant it!). However, I made a mistake in that I chose Parthenocissus tricuspidata (Boston Ivy) which isn't an ivy at all but a member of the grape family; meaning that it's deciduous and so not good for insulation in the winter.
So next I bought a real ivy plant, a plant of the genus Hedera. The shop only had Hedera colchica, so I got that. After a while I did a bit more research, and realized it wouldn't grow tall enough to completely cover the walls of my house!
My research said I needed to buy Hedera helix (Common Ivy), which can grow up to 20-30m high. I mentioned it to my Dad, and he said he had plenty. We dug some up and I've just planted it in my garden.
I should add that family (except my Dad), friends, professionals (and friends who are professionals) all think I'm mad to grow an ugly, invasive, poisonous weed that will rapidly destroy the fabric of my house while absorbing heavy metals from the atmosphere.