Journal of Architectural Conservation

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Managing Editor: Jill Pearce

This is a major study under the general editorship of Michael Tutton and Elizabeth Hirst. In her Introduction Elizabeth Hirst states the general approach, that repair and preservation are always preferable to replacement, and that with windows of historic buildings they are often legally required. The various chapters are written by different specialists selected for their particular expertise. 

Hentie Louw surveys the development of windows under various headings, Daylight, Fresh Air and Ventilation, Views, Stylistic Expression and Construction, following a progression in each. Their requirements are often contradictory. He shows that glass did not achieve much transparency until the 1680s, and that this both stimulated the current concern with ‘prospects‘, and necessitated curtains to improve privacy. His ninety pages and more than a hundred illustrations cannot be adequately summarized here, but suffice it to say that his survey is masterly.

Window fittings are dealt with by Treve Rosoman. He illustrates various types of stays for early casements, suggests associations with particular regions, and shows how they were revived by the Arts and Crafts movement. Hinges go through the various phases, H-type, H-L type, butterfly and cockspur. From the nineteenth century he draws on extensive catalogue material. Sash windows and their pulleys, sash weights and securing devices, are richly illustrated.

David Martlew deals with the development of window glass. He describes the different production processes in detail, the tools used, and the qualities of the glass they produced. He describes the Normandy process as ‘the crown glass method’. He is particularly interesting about the various nineteenth-century processes, a subject which is difficult to explore elsewhere. He strongly advocates that original glass should be retained when the frame has to undergo major repair, even when less than a century old. Fanlights developed from tables of crown glass cut along a chord which just misses the central bullion.

Charles Brooking is familiar as the originator of the Brooking Collection of architectural components salvaged from demolished historic buildings, now part of Greenwich University. He provides no less than 82 photographs in colour and monochrome of datable windows in situ, from all historical periods right through to the 1950s. He illustrates only five examples of wrought iron windows, mostly from the Home Counties, although these survive in great numbers. Regrettably, he includes only one quadrant stay, so small as to be almost invisible, and that proves to be a revivalist example. (Another occurs later in the book, Figure 288). On wooden and cast iron windows his illustrations are more valuable and extensive.

On Principles and Policy Bob Kindred contributes a superb survey of recent legislation and official guidance, and points out that Historic Scotland’s ‘Memorandum of Guidance’ of 1998 is significantly more detailed and informative than anything produced by English Heritage. With the experience of 130 years of conscientious repairs (many of which have gone badly wrong later) he comes to the same conclusions in detail that William Morris proposed in outline in his famous manifesto of 1877 which launched the S.P.A.B., that frequent minor maintenance and minimal intervention using reversible materials has proved again and again to contribute best to the longevity and authenticity of historic buildings.

Michael Tutton and Robert Thorniley-Walker contribute a chapter on Surveying. From April 2007 the onus for complying with statutory safety procedures has been on the client; we should all remember this. They point out that ‘Historic buildings have been slow to take up the use of mast climbers’, and that substantial savings can be made with them. For those unfamiliar with them he provides a photograph. The general approach is that a thorough survey before undertaking conservation always saves trouble later, and can often indicate the cause of an underlying fault. There is an intriguing mention of divining rods, on which I would have liked more information.

Robert Thorniley-Walker writes on Structural Implications. He urges us to question the expert whenever possible, and not to be embarrassed about asking for a second opinion. He provides a valuable table of the causes of distress, with their relevance to windows expressed as percentages. Eaves spread is by far the commonest at 70%, and expansion of rusting iron fittings a close second at 50%.

Window Performance and Sustainability is covered by Mike Parrett. His case studies are fascinating. He points out that double glazing was recommended by no less an authority than Edwin Chadwick, and that secondary glazing inside the building has been used since the seventeenth century. He illustrates a mid-nineteenth-century Scottish example. The increasing emphasis on insulation standards and fuel efficiency cannot be expected to exclude listed buildings for ever. The abundant ventilation provided in early buildings with open fires solved many problems before they arose, but the substitution of central heating has created many more. I am puzzled that the architectural profession has devoted so little attention to the design of internal secondary glazing. It is the one significant omission in this otherwise comprehensive volume.

Of the various materials used for repair and conservation, Alan Lamb covers timber in fascinating detail. He shows that every repair can be executed on a limited scale, replacing like for like (including the quality of timber employed), and urges that every possible element of the original window should be retained.

The chapter on Diagnosis and Treatment of Timber Decay by Jagjit Singh is rather alarming to the non-specialist, and inevitably, it is not all specific to windows. A useful table on page 290 summarizes the diagnosis of the different biological agents which may be encountered. It is satisfying to read that ‘Timber window frames, if well maintained, will last indefinitely’.

The section on conserving and repairing metal windows by Eleni Makri and Rupert Harris is particularly strong on windows of cast iron and non-ferrous metals, and on appropriate paint coatings. They are less convincing when they stray into the history of windows, which Hentie Louw has already covered. I am sceptical of some of their historical information. ‘Crown glass first became available post-1684’? Certainly the name ‘crown glass’ was used from that time, but as E. S. Godfrey’s magnificent study of the early glass industry shows, window glass made in England by the Normandy process was abundantly available from the 1580s. Figure 322 illustrates a wrought iron casement dated here to the mid-seventeenth century, but I believe it is substantially earlier. Would one really expect to find diamond glazing and some pieces of the distinctive blue-green ‘forest’ glass so late? (Wrought iron windows recur on page 322, with four excellent illustrations). Their valuable practical advice is beyond praise.

The section on the conservation and repair of stone windows by Graham Abrey concludes that even seriously weathered stone is preferable to wholesale replacement, and that intervention can cause more problems than it solves. He too finds that faults are often traceable to structural movement, or to the rusting of iron fixtures. His tables of the properties of repair materials, and a detailed exploration of mortars, are particularly valuable.

Ruth Cooke’s chapter on Leaded Lights and Stained Glass stresses the need for ‘good housekeeping’, minimal intervention and the retention of all original material. Indeed, these principles recur over and over again throughout the book. The pigments of Victorian glass prove to be as vulnerable to environmental damage and to misinformed cleaning as medieval glass.

The subject of paints and coatings is allowed a chapter to itself by Karen Morrissey. A fascinating cross-section of the paint films on a window of the Radcliffe Observatory at high magnification shows 23 phases since construction, and the accompanying layers of dirt. Traditional lead-based paints come out well on all counts except toxicity. Morrissey uses contemporary paintings well to illustrate original colour schemes.

One author after another condemns uPVC windows. The only modern material which consistently finds favour is stainless steel. Rods of it concealed within the fabric of an historic building can sometimes solve structural problems efficiently and cheaply.

While general principles of conservation are laid down the approach is severely practical. Many authors state where the various specialized materials can be obtained. The book ends with a valuable bibliography of some 200 items, and an index. This is a book which deserves a place in the conservation library of every architectural practice. The price may be beyond most amateur enthusiasts, but they have a right to expect that it will be available in reference libraries.

John McCann