Most of the inhabitable regions of the Earth were originally covered by forests, grasslands and wetlands. These carbon-grabbing, biodiverse, spongy landscapes have been largely replaced by agriculture and urban development, which is drier, which is releasing carbon, which is losing its soils, and which has lost most of its wildlife. Indeed, biodiversity declines continue.

 apace.

Cities, and buildings in particular, are designed and maintained in ways where vegetation is omitted, removed or simplified so that the benefits of having vegetation close by are limited or lost.  Concrete, glass and other impervious surfaces that

 shed water, kills migrating birds and exacerbate the urban heat island effect, have been the essence of architecture for decades now.

There is now a huge and growing body of evidence that green infrastructure or green-blue infrastructure, that is soil, vegetation and water, that provides the setting for our cities, provides us with a range of benefits (also described as ecosystem services), including reduction in flooding, purification of air and water, summer shade and cooling, better health and wellbeing, places to relax and mingle, food and habitat for wildlife.

Having begun to appreciate the benefits of putting green infrastructure onto buildings, architects, engineers, horticulturalists and others have developed techniques to do this. The conventional building has horizontal and vertical surfaces, which keep out the weather. Relatively lightweight coverings of vegetation can be placed onto the horizontal surfaces (extensive green roofs) and vertical surfaces (green walls). Where there is the strength in the roof structure more substantial gardens can be created on roofs of course, although roof gardens have a long history.

Roofs (flat and occasionally sloping roofs) have been successfully greened, led by pioneers in Germany, who have produced relatively lightweight extensive green roof systems. The first guidance was published in Germany in 1982 as the extensive green roof market took hold. A recent example of a biodiverse extensive green roof, designed by the Green Infrastructure Consultancy is on the David Attenborough Building in Cambridge.

Vertical surfaces can also be vegetated with the range of irrigated plastic modules, fabric pockets and metal cassettes that are available. These products contain compost, substrate, or in some cases  stone wool. The range of species used is being expanded all the time and irrigation systems can be monitored and controlled remotely. The Rubens at the Palace Hotel green wall by Green Infrastructure Consultancy is an example.