I run livingroofs.org, which is the UK's only independent green roofs association. We promote "vegetated roof structures" in urban and rural regeneration.

I'm not a hippy. I come from a community theatre background. I got involved because I'm keen on nature conservation and birdwatching. A lot of rare invertebrates used to be common on poorer agricultural land and you don't see much of that any more, so they moved into urban wasteland. But now, all that's disappearing because of urban development, so a green roof is the perfect habitat for them to move into.

Green roofs are usually flat. You have waterproofing and insulation, then some kind of geotextile layer. Then you have your substrate - crushed bricks, mainly - and then your plants. You can have grass but you don't need it. Grass on a roof is high maintenance and weight. It's better to have alpines, and cliff-top plants, ones that don't need many nutrients - a good one is sedum. With these, you don't have to go up there and weed and mow.

If you look at the bigger picture, many places are getting into green roofs. Toronto, Portland, Chicago are developing policies where every flat-roof building should have a green roof. It cuts the need for air conditioning because the rooms underneath are cooler. It also traps water, where it evaporates instead of going into the drainage system. Why isn't the UK doing this? We have a mountain of aggregates such as building rubble, that you can't put in landfill any more and is perfect green roof material. There's 24 times the size of Richmond Park in flat roofs in London, which could be green tomorrow. You have all those buildings in out-of-town shopping developments which are grey, dead sheds - they should have green roofs. That's where you would get your nature conservation.

Getting Barclays to put a green roof on top of their tower was a highlight for me. It's the highest green roof designed for nature conservation in the world. It's 160 metres up and I can take people up there to look at it, and you can see right across London. Which is something for a geezer from Deptford.

Dusty Gedge, The Guardian