Property: The secrets hidden in your attic: Old roofs are often the best roofs, beautiful, functional, built to last. David Lawson meets an expert builder who knows all about eaves

MOST OF us know next to nothing about that most crucial asset, the roof over our heads. And unless there is water dripping through the bedroom ceiling, we are unlikely to give it much thought. As a result we are vulnerable to cowboy builders, who suck their teeth, shake their heads and tell us: 'The whole lot'll 'ave to come off, guv.'

Clive Whitby is not in that game, however. He will not only fix your roof, but will also tell you when it was made, who put it on, how the materials were chosen and why he refuses to use cheap plastic tiles.

Crouching in a dusty attic under one of the most historic roofs in London, he fulminates against ill-informed experts, cowboys, mass-manufacturers and volume builders who, he reckons, are destroying our heritage and storing up problems for a rainy day. The George Inn, just south of London Bridge, was old long before Charles Dickens dropped by in search of characters for his novels. One fragment of the roof dates back centuries.

Mr Whitby is advising on a renovation by the National Trust, which owns this Grade I building. 'Just look at this swept valley,' he says. 'This sort of detail is being lost every day.'

A swept valley, it seems, is a rainwater gulley at the angle where roof faces meet. Craftsmen once cut tiles and slate to a broad U-shape, but most tiles today are preformed, destroying the old detail.

Architects are under constant pressure from manufacturers to use such materials rather than reproduce the old craftsmanship, Mr Whitby says. More than a sense of history is being lost. Swept valleys are thoroughly practical, dispersing water gradually, whereas the V-shape in many new homes and renovations can send water cascading down walls.

The average buyer cares little about such esoteric qualities, however. In fact, to most of us, an old roof immediately suggests expense, although the reverse can be true. 'At one time roofs were constructed by building craftsmen,' Mr Whitby says. 'The mortaring and slates were done by bricklayers, the battens by carpenters and the lead work by plumbers. They were all working in materials they knew intimately, and they built to last - perhaps for more than a century.'

Today's product has a guaranteed life of a mere 30 years. One set of workers will do the lot, often with no specialised training. 'Anyone can call himself a roofer,' he says.

To calculate the age of a roof, he goes up to the attic. If there is no felt, he will figure that the roof is likely to be more than 50 years old. 'Most surveyors would automatically see that as a need for replacement. That is how we lose so many small period details. Yet an old roof may be more sound than a recent replacement,' he says.

'After the 1987 hurricane I had 23 calls from former customers saying my roofs had not moved an inch. That was because I use traditional techniques.' This passion runs in the family. Mr Whitby's father, George, was a leading architect in the City of London, responsible for such landmarks as the Old Bailey extension. He died young, and Clive Whitby worked as a roofer during school holidays to boost the family income. He was taught by an elder brother, who now lives in Wales and works on historic buildings.

Mr Whitby was inspired by a book on the traditions of building crafts by Nathanial Lloyd. 'It is the only work I know that deals with the historic detail that went into roofs around the country.' When the author's sons, Christopher and Quentin, asked Mr Whitby to repair the family home, Great Dixter, in Sussex, another National Trust property, it represented a major challenge. More nerve-racking was the fact that the 16th-century building had been renovated by Edwin Lutyens in the Twenties. How do you invisibly mend the work of a great architect? Lloyd's book proved a godsend, however, as it draws on his close relationship with Lutyens and is illustrated with many of his methods.

The average roofer, for instance, might not merely have lost the carefully shaped swept valleys, but also have bedded them in modern mortar. The originals were set in material made from the ashes from steam engines, so Mr Whitby raided the local railway preservation society to ensure continuity. Ordinary homes deserve similar treatment, he says.

Every village in the country has its own character because of local materials and skills, but this is being destroyed by modern building methods.

Housebuilders who create a variety of roof types and shapes on each estate are his bete noire. 'Think of the Cotswolds, or of the south of France. Their charm comes from consistent colour and materials. Anything else sticks out like a sore thumb.'

Only large towns, such as Birmingham and London, have variety, because tile and slate from many places was used as ballast in ships and barges. Yet even here Mr Whitby tries to be consistent, although that can be difficult. 'On one house, I was trying to replace slate that came from Spain. But I was told some blaster overdid the explosive and wiped out the complete modern supply.

'If you are going to repair or replace a roof, look around for neighbouring properties still in their original coating,' he says. 'Talk to local builders, who will have access to the right tiles. They may even have put the roof up in the first place.

'And do not automatically think a roof needs to go just because a few slates or tiles are missing,' he says. You may be throwing away a slice of history, as well as faithful protection against the rain.

Contact Clive Whitby on 0850 779697.

(Photograph omitted)