Gardens - they're on the up

Your leaky flat roof could be transformed into a dramatic terrace – and it's never been easier
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Given the dead costs involved in moving house, more people are looking to make alterations rather than seek pastures new. There are some things that cannot be changed, however, and moving is the only option. The most frequent reasons that I come across for this are either looking for a different location or looking for more external space.

OK, so if you want to live in an entirely different place, you need to move. The question of external space, however, may not be as obvious. There may be little or no garden, but have you considered the roof?

Particularly in urban areas, where space is at a premium, the idea of using flat roofs as "outdoor rooms" is often considered, but rarely adopted. Now, however, things may be about to change.

Ken Livingstone, together with the architect Lord Rogers, has co-written a GLA planning document called "Living Roofs" promoting green roofs, roof terraces and roof gardens across London.

The document suggests that using our roofs more imaginatively "can deliver benefits throughout the city for individuals and for society as a whole, by creating new outdoor spaces, enhancing bio-diversity, reducing flood risk (by absorbing heavy rainfall), providing insulation and improving the appearance of our cityscape".

Sounds wonderful. I don't imagine for a moment that the majority of people would not agree with these sentiments and, certainly, I have a catalogue of past customers who have enthusiastically pursued such a possibility. But it is amazing how few actually come to fruition.

Generally, it is not technical or construction limitations that hold us back. While most flat roofs are not designed to carry more than a " maintenance" load, it is usually a relatively simple project to sufficiently strengthen the roof structure with deeper joists or in some cases some simple steelwork. The roof covering needs to be carefully considered, but flat roofs are not the leak-prone disasters of yesteryear – technology has moved on.

I am currently adding a flat-roofed extension to my own house and rather than the old boiling cauldrons of hot tar needed for an asphalt roof, we are using a wonderful roof material called EPDM. Imagine a very tough sheet of rubber – something like the inner tube of your bicycle wheel, but a bit thicker – that arrives in one rolled-up sheet, big enough for the whole roof. Rigid insulation is laid over a slightly sloping ply deck and the rubber sheet is just glued down in one go with no joints to worry about. To form a surface to walk on, we will make a "raft" of timber decking that lies on top without piercing the rubber layer.

So if we all think that roof gardens are such a good thing, why are we not doing it in more numbers already? Why do we need our city fathers to write inspirational documents to encourage us to do what we already agree is a good idea? The answer, I am sad to say, is that institutionally, we won't let each other.

The general principles of our planning permission system come from the broadly held views of the public at large. In short, planning policy reflects our society back in our faces, and all too often it is a pretty ugly view. As the GLA document points out, "the planning system assumes that privacy for existing residents is the paramount consideration. Roof gardens or terraces, it is often judged, might enable residents to overlook their neighbours or create noise, thereby blighting their lives."

Living in a city is not a particularly private business and blocking the use of so many wonderful garden opportunities just to prevent the chance of a neighbour's eye-line straying into a bedroom is quite simply mean. If you want privacy, draw the curtains! It is not as if people generally want to peep at each other, anyway. As the Livingstone/Rogers document concludes, such closed mindedness "misunderstands the nature of cities".

For small-scale projects, our planning system, which is supposed to facilitate development, leans far too far against change and I am delighted to see local authorities being pushed by positive guidance from the top. As the Mayor has it: "It's time to make our roofs places for life."

Hugo Tugman runs the design service Architect Your Home;

Project: roof gardens

How much will it cost?

The typical flat roof at the rear of an urban house can form a lovely outside space for a relatively small outlay. Even if joists need to be replaced and a new waterproof deck formed, a budget of £10K can cover decking, pots and planting. Be careful about balustrading – it needs to conform to regulations and if you get carried away with frameless glass, the costs can run away.

How much hassle is it?

Access is important to consider. If you need to form new French doors to your roof terrace, this will be messy and disruptive. Similarly, if ceilings below need to be replaced due to strengthening work, the mess will be significant. However, if the builders can access the roof without going through the house, you shouldn't find the works too intrusive. As yet, local planning policies are generally still biased against roof gardens, but hopefully (as explained) this looks set to change. To avoid wasting time and money, find out whether you will be allowed to use a roof as a terrace first. An architect or planning consultant will be able to advise you, or you could write to your local planning department (it's best in writing because you should get a written response), enclosing a site plan and some photographs. A view from Google Earth can help, too.