Green roofs are a rapidly expanding business for Greenfix. Its managing director, Mike Cottage, explains how they work and why the future is actually brown roofs.

Greenfix, founded in 1998, has a UK turnover of about £2m. Green roofs represent a growing part of its business, which also includes soil stabilisation and erosion control. Laid over independent load-bearing structures, these multi-layered roofs contain live organic materials. The company’s 13 employees are based mainly in Cheltenham but the biodegradable materials used for each job are sourced locally, where possible. We speak to managing director Mike Cottage.

The basic ingredients of a green roof, from the top down, are: a pre-grown sedum blanket and a sedum substrate (including soil), which we provide; and a filter fabric and a drainage layer, which we buy in. But there are many variations.

Sedum is a bit like cactus. It stores water in its leaves and is highly durable. It can grow in numerous settings and can go six weeks without water. We also exploit its ability to support all sorts of flora and fauna. But its overriding function is for water absorption, storing and release.

People find us in a number of ways. We have relationships with waterproofing companies who recommend us, and some architects find us directly from adverts or the internet.

Once we’ve been commissioned, we ask what the customer wants to do with the roof. We’ll then work together to find a solution. Sometimes architectural specifications can be very detailed; sometimes we’ll talk to a client who has no concept at all and we’ll help them come up with a design. In all cases, we’ll get involved very early on and we’ll do all the relevant calculations, including those for substrate and drainage. The architect might ask for significant changes, which we’re usually able to accommodate. Value engineering might come into the equation, as cost is a primary concern but it’s unusual for customers to suggest different suppliers’ components. It’s not unknown, though, and it can be handy if we’re led to a good new supplier.

Once we’re ready to go on site, we can be there for anything from three days to three months. The size of area to be covered is the biggest determining factor. The green roof arrives in different components. Some of it comes in panels, the substrate is in bags and the sedum blanket comes in rolls. All of it can be easily handled, which is important when working at height. Although it’s light enough to carry up ladders and scaffolding, we’ll often use cranes and hoists.

One of our most technically challenging contracts was the Adnam’s brewery at Southwold in Suffolk, which was worth £200,000 to us, and was incorporated onto a metal standing-seam roof. We had to work at the height of summer. We didn’t envisage the extremes of hot weather. This was a problem because live materials in heat can suffer after they’ve been uprooted and transported from one environment to another. We had to replace some material.

We’re just about to start work on a large roof for developer Berkeley First in Isleworth, west London. Taylor Woodrow is the main contractor and it made contact with us through an architect. The project is for a block of flats and will include decking, paths, trees and a more durable layer to cope with the extra loading.