Flat roofs - a waste of space?

Let’s be honest here. When you look around, you can see flat roofs everywhere, all quietly doing a sterling job protecting the structures beneath them from the elements. Effective? Definitely. Uninspiring? Probably. But they can be so much more! From farms to apiaries, spaces for recreation to gardens for wildlife - if you have a flat roof, it can be transformed. And you’ll help to save the planet too.

It is commonly thought that the first flat roofs evolved in the Middle East where, due to lack of rainfall, a method was devised to collect what rainfall there was, via these flat roofs. Fast forward to today, and with the help of modern technology and products, these barren, under-utilised areas of our towns and cities are being converted to accommodate high-rise vegetable plots, nature reserves and outdoor recreational spaces bringing with them myriad benefits in terms of sustainability, water and air quality, and bio-diversity.

From truly awe-inspiring rooftop farms and gardens in the sky to the unassuming roof on the extension in the back garden, flat roofs can play their part in greening cities and enhancing lifestyles.

One of the largest green, flat roof projects in recent years has been Brooklyn Grange Farm in New York. Its total farming area, across all three of its rooftop farms combined, is 3.1 acres which produces a staggering 80,000 lbs of produce every year. Now, New York City alone has 14,000 acres of unused rooftop space – you do the maths!! That space, if utilised, could grow an incredible 361 million pounds of produce each year.

Closer to home, and on a smaller scale, rooftop farms have been set up on the roofs of a number of high end restaurants in London providing the freshest of home grown produce for their discerning clientele. No air miles and farm-to-fork in the blink of an eye.

According to Steven Peck of the Toronto-based non-profit Green Roofs for Healthy Cities, “The roofscapes of our cities are the last urban frontier—from 15% - 35% of the total land area.” With some thought and imagination, they can offer much more than just a pretty view.

The City of London’s latest addition to its existing 60 green roofs, and making it the largest roof top public space in the square mile, is ‘The Garden at 120’. It’s located at the top of the Fen Court office building at 120 Fenchurch Street and offers a peaceful retreat from busy City of London streets with fruit trees, Italian wisteria, seating, a water feature and a refreshment area - all this and views of some of London’s most recognisable landmarks – and 15 storeys up!

On a more micro scale, and within the price range of the general public, the flat roof above a house extension or even a garage could play host to a couple of productive beehives, be transformed into a sedum covered haven for wildlife or a comfortable and stylish sitting area with space to grow flowers, fruit and vegetables.

It is clear that rooftop gardens, large and small, have become an important element in sustainable architecture providing numerous environmental, economic, and social benefits, as well as increasing the habitat for local wildlife.

However, it’s important to note that at the centre of every green roof application there needs to be a robust membrane which will keep water out of the building below. And it is absolutely imperative to get the right waterproof membrane - because the consequences of its failure could be catastrophic. The ideal choice would be a seamless membrane which would negate the possibility of water leakage and root run through the seams. This is where Proteus’ green roof waterproofing system comes in employing its exclusive Cold Melt® membrane at the heart of its green roof build-ups. Cold Melt® is certified by the BBA to last for the design life of the building on which it is installed, and when combined with an advanced hybrid insulation and topped with soil and plantings, it ensures that all current building regulations are met and no leakages occur – strength and stability in one system.

There are two types of green roof to consider depending on needs and budget - the extensive or the intensive.

An intensive green roof allows complete gardens on rooftops with shrubs, climbers, perennials, bedding and even trees. These are usually container or raised bed gardens requiring at least 30cm (1ft) in depth of growing medium, a large proportion of which needs to be organic matter. Whereas the extensive green roof only requires an 8-15cm (3-6”) depth of growing medium, which can consist of mainly lightweight inorganic materials such as perlite leca, sand, rockwool and crushed tiles or concrete, to support green carpets of low maintenance creeping plants like sedums and native wild flowers. It’s your choice - there’s a green roof to suit all requirements – and it can offer incredible value for money, according to Proteus Waterproofing.

As with any construction process, cost is dependent on specification and consideration has to be made regarding many variants when it comes to specifying a green roof. It needs careful planning and the right build-up of components.