46 C O N T E X T 1 6 2 : N O V E M B E R 2 0 1 9 Further reading Historic England (2012) Glass and Glazing: practical building conservation series. London: Routledge Many thanks to Malcolm Starr (Historic England) and Rupert Harris Conservation for sharing their material. Sophie Godfraind, a building conservation advisor in the technical conservation teamof Historic England, is co-editor of the Historic England Practical Building Conservation volumes on Metals and Glass and Glazing. Steel windows in storage, showing the cavetto (curved) moulding A side view of steel windows in storage, showing assembly detailing Corps buildings on a first-world-war aerodrome. It saw brief use between 1916 and 1919, and was then abandoned for military purposes. The majority of the first-world-war buildings remain. Most of them are of single-skin brick- work on minimal foundations or footings, with steel-framed windows. Although displaying good levels of craftsmanship, they were not designed to last. Because of their exceptional rarity and architectural interest, all 22 remaining buildings are listed Grade II* (under a single list entry). Although a repair programme is under way, the site remains on Historic England’s buildings- at-risk register. More than 100 windows are suffering from corrosion and distortion, and need repair. This is a major issue to make the buildings weather tight. When conservation work first started on the site about 10 years ago, the metal windows were assumed to be cast iron and the site managers at the time assumed that they were beyond repair. Windows in three of the buildings were replaced, some with cast aluminium and others in new cast iron, none of which have the same moulding profile as the originals. The trust now managing the site is seeking a more sustainable approach, preserving the historic windows and their detailing, in keeping with the approach applied to the rest of the site and building fabric in general. Earlier this year, Historic England commissioned a survey by Geoff Wallis Conservation to reassess conserva- tion options. Close inspection showed that the frames are riveted together, and the glazing bars are tenoned through them and riveted over – evidence that they were assembled from individual rolled-steel components, not cast in iron as a single unit as had been previously thought. The sections comprising the fixed frame (including the glaz- ing bars) carry cavetto mouldings, derived from the sections used inVictorian cast-iron windows. The weathering seal is poor, as the mouldings on the fixed frames have not been dressed off where they face the casement: this detail was improved in later windows designs. The condition survey found that the steel frames and casements were rusting generally, but many sections were capable of repair and could be retained. Where corrosion is most severe (particularly at low level on the fixed frames and on the casements), affected sections will need to be renewed. Several casements are so badly corroded that they must be completely replaced; any serviceable sections will be sal- vaged and used to repair other casements. All replacement will follow the original moulding profiles and construction methods. The quoted costs for refurbishment and limited replacement using matching sections are lower than for wholesale replacement (with a profile different to the original) quoted for by current windows manufacturers. This case study illustrates the importance of commissioning the right specialist to survey and assess conservation options, based on an understanding of the original metal frames and their present condition. With the right advice and skilled workmanship, these rare windows can be given a new lease of life.