It's an open and shut case

The sash window is a design classic that dates from the 17th century. In the 21st century, it comes in security glass and self-cleaning versions, too

(Sash Window)

Sash windows are a design classic. They've been around since the 17th century and they've changed very little since their earliest days. The two glazed sashes, which slide vertically in a timber frame, are supported by cords that are balanced with metal weights. The first examples were clunky affairs with thick glazing and heavy frames, but by the 18th century, it was possible to produce thinner, larger sheets of glass and thus the more elegant Georgian-style sashes. Then, in the 1850s, along came plate glass; and glaziers never looked back. In theory, those original Georgian, Victorian and Edwardian examples should still be going strong; properly and regularly maintained, a sash window should last pretty well indefinitely.

Sash windows are a design classic. They've been around since the 17th century and they've changed very little since their earliest days. The two glazed sashes, which slide vertically in a timber frame, are supported by cords that are balanced with metal weights. The first examples were clunky affairs with thick glazing and heavy frames, but by the 18th century, it was possible to produce thinner, larger sheets of glass and thus the more elegant Georgian-style sashes. Then, in the 1850s, along came plate glass; and glaziers never looked back. In theory, those original Georgian, Victorian and Edwardian examples should still be going strong; properly and regularly maintained, a sash window should last pretty well indefinitely.

The trouble, as most owners of period homes will know, is that over the decades, and indeed centuries, most original windows have suffered from periods of neglect. If the weather has managed to get to exposed wood, or thick coats of heavy paint have been applied on top of each other without any preparation, a sash window goes from being an appealing and efficient feature to a complete nightmare. Restoration is, of course, a solution. But it's also possible to fit brand-new sash windows, in the best tradition of the originals - with all the benefits of modern window technology.

One issue that traditional sash-window makers have had to get to grips with is double glazing. Current building regulations state that all new or replacement windows, including sashes, have to be double-glazed, except in listed buildings. "We can do it discreetly, making the sealed units as slim as possible," says John Rose, founder of the Original Box Sash Window Company. "We accept that keeping original features is the way to maintain the value of your home, and to do that, we need to make windows that are as near as possible to the originals."

So the Welsh craftsmen at the Original Box Sash Window Company joinery in Merthyr Tydfil are now quite happily fitting the most modern hi-tech sealed units into their traditionally made frames. The company also offers a security glass option; or the possibility of self-cleaning glass. Self-cleaning glass is coated on the outside in such a way that dirt can't cling; it breaks down and is washed away by rain; so, hooray, chuck out the bucket and chamois (in a drought, you simply hose it down).

The Original Box Sash Window Co covers the south-east of England from its Windsor base, and John Rose reckons on an average budget of £15,000 to refit a whole house, or £10,000 for a couple of large bays; doing a number of windows at a time is more cost-effective, he explains.

While the glass itself is 21st century, traditional sash-makers stick to a distinctly lo-tech material for their frames: wood. Ken Franklin of the London-based Original Double Glazed Sash Window Replacement Company reckons he has made around 5,000 sash windows since he started in the business. Timber, says Ken Franklin, is a far better choice in the long run than the now-ubiquitous UPVC. "UPVC is horrible stuff; it produces toxic fumes if there's a fire. You have to keep replacing it, and it can't be reused or recycled, so huge dumps of it are piling up in the third world."

UPVC is certainly cheaper to install initially; but it has a limited lifetime of perhaps 10 years. Timber, properly looked after, will last indefinitely. The latest water-based microporous paints allow the wood to breathe and, properly applied, will last for at least 10 years before needing a new coat, says Ken Franklin. "We paint all our windows in our workshop before installation, so that the bits that are buried in the brickwork are properly prepared and no rot can get in. We use hardwood sills, as well; the Georgians and the Victorians didn't expect their windows to last as long as they have, so they tended to use soft wood." He also uses efficient modern glues, rather than the boiled-hide glue that a craftsman would have used 100 years ago. Franklin, who is based in London, says that for most of the projects he takes on, a complete window costs between £1,500 and £1,800; very large, highly ornamental or curved windows cost more.

Planning regulations can be draconian when it comes to windows, says Ian Hall, a partner in Harmony Home Improvements Ltd. "In conservation areas, or for listed buildings, often window frames can only be replaced with timber. A lot of conversions, from the Eighties in particular, put in monstrosities that changed the character of the building; much of our work involves taking those out and putting original-style windows back." As well as traditional wooden sashes, Harmony, which covers London and the Home Counties, also offers "lookalikes" that tilt and slide, or that resemble sashes but open like casements. "The reason is cost," explains Hall. "It can cost £1,500 for one hardwood sash; a mock can cost half that."

The popularity of the traditional sash is confirmed by the fact that the big national glazing companies also now offer their own versions. Everest's timber sashes, for example, are made from European redwood with solid-brass fittings, and are available in a traditional vertical sliding style or an "easy-clean, dual-turn version".

If cost is a sticking point, there is always the dreaded UPVC. However, there's UPVC and UPVC, at least from the aesthetic point of view. Hall recommends a brand called Rehau, which has been approved by English Heritage. "From 10 yards away it's difficult to see the difference between Rehau and wood," he says. "It's maintenance free, and permitted in some conservation areas." Pickier councils, he says, might allow timber windows at the front of the house and Rehau at the back. "It comes in at around two-thirds to three-quarters of the price of replacing in timber," says Hall. "If cost is an issue and conservation and planning allow it, Rehau is the best pound-for-pound option."

Everest, 0800-010 123, www.everest.co.uk; Harmony HomeImprovements, 0800-093 2813, www.capital-sash.co.uk; The OriginalBox Sash Window Company, 01753 858196, www.boxsash.com; The Original Double Glazed Sash Window Replacement Company, 020-7435 0367, www.origdgsash.co.uk.

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