Rare orchids and bees are thriving on London’s green rooftops as city eyes up cooling solutions

Green roofs bring great biodiversity benefits, but have one key drawback as a cooling solution according to a new study.

Transcript

00:00All roofs, the principle is that the energy that is coming from the sun is reflected back

00:16straight to the atmosphere and to space, right?

00:19So this energy that is coming in the first place is simply not accumulated in the city,

00:25in the buildings, in the streets, etc.

00:30The heat that is stored in the soil on which the plants are will be released in this form

00:35of sensible heat that you can feel, and they will heat up the air at night, which is what

00:41we found in our study too.

00:43Basically green roofs do decrease air temperature, or are expected to do, but on average throughout

00:49the day, because they heat up also the air at night, you get this kind of null average

00:55decrease in temperature.

01:01This is quite a massive green roof, there is a lot of weight that is added to the building

01:05below it, and behind me you see a roof from another building just across the street, and

01:14this building, for example, could not withhold such a green roof as of now.

01:20So it means that it offers very little options in terms of interventions.

01:26Whitening its roof would actually reflect part of the solar energy again, and reduce

01:30temperature within the building and also in its surroundings probably, but as you can

01:35see behind me, the problem with whitening of roofs, and it's often a cost that has to

01:40be added to it, is the fact that it gets sanded, it gets dirty, and so its reflective

01:45capacity is lowered, and so you have to make sure to maintain it always as white as possible.

01:51I think the more green roofs that we can get, especially in these highly urban areas, the

01:57better.

01:58We do have some orchids here on the roof, some very rare orchids, I believe one of them

02:03is very rare and it's the only one currently known in the UK.

02:09In an environment like this where it is remote, you don't have a lot of footfall, it does

02:13give an opportunity for some of these rare species to thrive.