The Building Conservation Directory 2021

112 T H E B U I L D I N G CO N S E R VAT I O N D I R E C TO R Y 2 0 2 1 C AT H E D R A L COMMU N I C AT I ON S REPLACING STEEL WINDOWS A guide for home-owners PETER CLEMENT R EPLACEMENT OF existing steel windows in a historic building might be considered for a number of reasons, the principal one being that the present windows, through age, neglect or both, have deteriorated to such an extent that repair or restoration, either in situ or off site, is not an option. Other common reasons include the need to reduce energy loss from single glazed metal frames, or a desire to remove inappropriate earlier replacements. Any proposal to replace windows in a listed building would require the owner to seek permission, as listed building consent is required for alterations to these buildings, and in practice any replacement will involve a degree of alteration. The need for planning permission may also apply if the building is unlisted but in an area designated for protection, such as a conservation area or area of outstanding natural beauty. (For further details of heritage protection requirements, see page 25). Depending on the listing and the historic or architectural significance of the property within its locality, securing permission can sometimes be a lengthy process. Consequently, it is sensible to discuss any plans for replacing windows with the planning authority at the earliest opportunity. Also consider seeking guidance from an experienced steel windows professional and a conservation architect or heritage consultant, who could approach the planners on your behalf to find out how they might respond to any proposed window replacement and what conditions might be imposed. These early meetings could save a great deal of time and money by avoiding window styles, types or patterns that never had a realistic chance of gaining approval. When considering an application, subject of course to the property’s status, planners will generally prefer to see a replacement which matches the existing as closely as possible. Some problems should therefore be expected where a proposal includes double glazing, since the addition of sealed units will inevitably affect the windows’ appearance when compared with the existing. Once you have received guidance from the planning department’s conservation team on what is and is not likely to succeed, this might be the time to approach a number of steel window manufacturers. Begin the process by discussing what product range they can offer and how close these are to what you and the planners are looking for. STEEL FRAMES We tend to think of steel windows as belonging to the mid 20th century, typified by those of the major steel window companies of the era such as such as Clement, Crittall, Hope's and Williams & Williams. However, before the introduction of standardised rolled steel window sections at the end of the First World War, steel windows were already popular in domestic architecture, particularly as a result of the fashion for leaded light windows in the late 19th century. These early examples include a wider variety of profiles and components, and may be mistaken for blacksmith-made wrought iron windows. Cast iron windows are also sometimes found in late 19th century houses, but they are readily distinguished from steel windows by their shape, and they often had more elaborate designs. Today the steel window replica replacement industry remains dominated by hot rolled steel windows whose profiles are close in appearance to those which have existed in a similar form since late Victorian times and the basic ‘Z’ pattern section used to create an opening light remains universal. Although there are now far fewer steel profiles available than there were, it is still possible that your manufacturer could find a suitable one from stock that either matches or is close to the hot rolled steel sections required. Failing this, those profiles that are available can in the hands of an enterprising manufacturer be milled down or engineered to suit. This may consist of welding on specific steel shapes and patterns, such as an ovolo or half round moulding, to get close to the original pattern. The small number of windows that are very highly decorated may prove to have been fabricated from cast iron, not steel, and it should be feasible, subject to expense, to have new castings made if the project warrants it. However, steel windows too can vary significantly, and sometimes a rare and unusual example of historic fenestration requires highly bespoke steel replicas. Should the project be of a size to justify the cost, new steel profiles can be rolled to order to replicate the originals precisely, and it is interesting to note that these one-off solutions are possible even on a smaller scale given sufficient desire and resources. Once made, the frames are hot dip galvanised to BS EN ISO 1461:2009 EN ISO 1461, weather stripped and if required have a surface coating of polyester powder paint to BS EN 13438. If the project requires a brush applied finish, it is helpful to inform the galvanisers who can then apply an acid etch to the steel surface to improve paint adhesion. W20 steel windows at The Comet Works, a former Victorian armaments factory in Birmingham (Photo: Silver Cloud Photography)