Ministerial guidelines
Architectural Heritage Protection: Guidelines for Planning Authorities
Protected structures, architectural conservation areas, curtilage, and works to historic buildings.
Department of Arts, Heritage and the Gaeltacht · 2011 · 267 pages
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- Architectural Heritage Protection Guidelines for Planning Authorities 159 CHAPTER 10 OPENINGS Doors and Windows steps and landings which it is necessary to repair, the existing stone can be redressed by a skilled mason or indented with compatible stone. The maximum amount of the original stonework should be conserved. However, damaged steps and landings should not be built up in cement screed or similar inappropriate artificial compounds as this would alter their appearance. 10.3.22 Where there is a weathering problem connected with entrance steps and landings, specialist advice should be sought to overcome this. It should not be solved by covering the stone steps and landings with any waterproof coating material which would adversely affect their fabric or appearance. 10.4 Windows IDENTIFYING SPECIAL FEATURES FOR PROTECTION 10.4.1 The design of windows and the materials used in their construction make a significant contribution to the appearance and special character of a structure. Windows have historically been subject to changing fashions and advancing technology of glass manufacture so that an old building may exhibit a variety of window sizes and glazing patterns. Where different window types are important evidence of the building’s history and contribute to its character and interest, no attempt should be made to standardise the fenestration. Surviving original proportions of glazing patterns should always be respected, even if these now differ from the adjoining buildings of similar style and date. 10.4.2 While most windows in older buildings are made of timber, windows are also found dating from the late-eighteenth century onwards made wholly of iron or which incorporate iron or brass frameworks. The traditional use of lead-based paints and the quality of the close-grained timbers used in the eighteenth and nineteenth centuries have ensured the survival of many historic windows. Many are well suited to being carefully repaired. Generally, paint is the correct finish for external joinery on buildings over fifty years old and for all historic metal windows, including fanlights. Staining and varnishing are rarely traditional finishes for external surfaces although scumbling (or wood-graining) is occasionally found. There may be rare cases where external joinery was originally unpainted, generally oak or mahogany, and where this is so it should be identified and protected. Bootscrapers and other entrance features add character to the structure and are of social interest in themselves. Many have interesting design details and, like other handcrafted items, may be particular to a single street or area The indenting or redressing of decayed or damaged step nosings may occasionally be necessary. Such work should be carried out by an experienced mason. In cases of minor damage, and providing there is no threat to the safe use of the steps, it may be sufficient simply to smooth broken edges and avoid major intervention Coating stone steps in a waterproof material in an attempt to solve damp problems in the room below is rarely a successful solution. Apart from the unsightly nature of such work, it may cause the stone to decay from condensation from within the building or from moisture ingress through cracking of the coating
- CHAPTER 10 OPENINGS Doors and Windows Architectural Heritage Protection Guidelines for Planning Authorities 160 10.4.3 A variety of window types will be found in protected structures and buildings in ACAs. Some of the common types are listed below. In all types of windows, where regional characteristics exist, these should be identified and retained. The internal joinery associated with window openings is discussed in Chapter 11 below. Sash windows 10.4.4 Vertically sliding timber sash windows are probably the most common type of window found in older buildings in Ireland. Many original sashes and frames survive which are over two hundred years old and still give good service. The quality of the original materials and craftsmanship of these windows means that they are usually capable of repair and, if so, this should be encouraged. 10.4.5 Examples of horizontally sliding sash windows are now rare and any survivals should be retained in situ. Sash windows were used in Ireland for most building types from the end of the seventeenth century until the middle of the twentieth. In general the glazing pattern, the profile of the sash bars and the materials used reflect architectural fashions, the social status of the building (or its builder) and the available materials. The high quality and density of the timber available in the eighteenth and nineteenth centuries means that most of these historic windows are still capable of repair The majority of sliding sash windows found in this country slide vertically and sashes that slide horizontally are rare; they are usually, but not exclusively, found in smaller structures such as cottages Clues to the different phases of a building’s development can often be found on subsidiary elevations; this house retains a very early eighteenth-century sash window on the top right of this photograph; the differences in opening sizes and sash details of the other windows are the result of several later phases of work
- Architectural Heritage Protection Guidelines for Planning Authorities 161 CHAPTER 10 OPENINGS Doors and Windows 10.4.6 The number, arrangement and proportion of panes, the details of the glazing bars and frames and the presence or absence of horns, are important features of sash windows that should be respected, as should the opening methods. In many early windows, only the lower sash was weighted and the upper fixed. Where early examples of sash windows with exposed sash boxes survive they should be retained and not replaced with rebated windows. Late eighteenth and early nineteenth century Georgian-Gothic sash windows in pointed arched openings often had curvilinear glazing bars to the upper sash. Where these survive they should be retained. Later styles included the use of smaller glazed panes to the edges of the sashes called ‘margin lights’. The margins are often, but not always, glazed with coloured or patterned glass. Where these survive, they are of interest whether or not they are original to the building or to the opening. Casement windows 10.4.7 Early lead-glazed casement windows, predating the arrival of the sash window in the late seventeenth century, are extremely rare in Ireland and every effort should be made to retain surviving examples in situ. The use of casement windows was revived in the nineteenth century and examples are to be seen in late-Georgian, Victorian and later buildings with timber or metal frames. These are often glazed with small diamond or square quarry panes. French windows are a version of a casement window where the casements are carried down to the floor level and open like doors. Where casement windows are original or early replacements of quality, they should be retained, and repaired where necessary. Blocked, blind and dummy windows 10.4.8 Blind or dummy windows are a feature of many important buildings and structures. These are imitation window openings, usually the size and shape of adjacent openings and with similar head, sill and reveal details. They were used as a decorative device to give symmetry to the façade of an asymmetrically planned building. The blind or dummy window may contain a plain rendered, brick or stone panel. More elaborate versions can contain fully glazed fixed timber sashes set in the masonry panel. Where blind or dummy windows exist, they are usually an integral part of the elevational design and should be retained. 10.4.9 Blocked-up window openings are of historical interest particularly in informing an understanding of previous uses or forms of the building. Where they exist their presence should be recorded and analysed. Fully-glazed blind windows such as this example are rare; they may be deliberately designed to ensure symmetrical fenestration (for example, where the plan form did not permit a window), or could represent later blocking of openings. It is commonly thought that openings were blocked to avoid paying window tax, which was in force between 1799 and 1851, however in Ireland there is little evidence to support this theory The use of arched openings and the arrangement of glazing bars in decorative patterns helps to enliven facades and adds character to a structure Casement windows, although widely used in many countries, were seldom used in Ireland after the arrival of the sash window in the late-seventeenth century. Eighteenth- and nineteenthcentury casement windows, whether of timber or metal, generally open inwards, excepting French windows, which open out onto terraces or balconies
- CHAPTER 10 OPENINGS Doors and Windows Architectural Heritage Protection Guidelines for Planning Authorities 162 Mullioned windows 10.4.10 Mullions can be found in conjunction with transoms in cross-windows or as the vertical dividers in tripartite or bipartite windows or in bay windows. These mullions can be of stone, rendered brickwork or of timber, sometimes decoratively treated. The lights can be fixed, casement or sash. The proportioning of the subdivisions of mullioned windows is an important element in the overall design of a building and should be conserved. Metal windows 10.4.11 Seventeenth-century leaded lights were glazed into wrought iron frames and are now extremely rare. Cast-iron windows first appeared in Ireland in the early nineteenth century. These are commonly glazed with diamond quarries in casement or pivot lights, although wholly cast-iron sash windows are also occasionally found. 10.4.12 Most examples of steel-framed windows in Ireland date from the first half of the twentieth century. Steel-framed windows with horizontally proportioned panes were characteristic features of buildings of, or influenced by, the Modern Movement in architecture. When these window frames are removed and replaced with frames of different materials, proportions or sectional profile, much of the architectural character of the building is lost. Where metal-framed windows are important to the character and quality of a structure that is protected, they should be repaired or, if beyond repair, their replacement on a like-for-like basis should be encouraged. Window ironmongery 10.4.13 Original sash fittings include meeting rail catches, weights and pulleys, or quadrant catches where weights were not used. Casement latches, hinges and fasteners, where they survive, are features of interest. They should be identified and retained in situ. If security issues arise, existing window ironmongery could be augmented with sensitively placed modern locks rather than replaced. Balconettes, window boxes, external blinds 10.4.14 Wrought or cast-iron balconettes, window boxes and sill guards are important architectural elements contributing to the interest of a building and should be retained. Other features such as early or original external shutters, blind boxes and window canopies should be identified and retained. The design of Modern Movement windows represented a clean break with the past; often favouring horizontal lines and thin steel frames. Such windows are an integral part of the original design of an early or mid twentieth-century structure and replacing them in other materials and to different profiles almost always detracts from the character of the structure Mullions, sometimes together with transoms, were used to divide larger openings into manageablysized sashes or casements. As with these Arts and Crafts style leaded casements, mullioned windows were usually designed consciously to contribute to the appearance of the structure Cast-iron sash, casement, pivot and fixed windows were often designed more for function than beauty, but occasionally cast-iron windows of subtle elegance are found and where this is so, they may be the most important element of the façade Original and early window furniture and mechanisms can provide information about the history of the window. As fixtures of interest, they may be included in the protection of the building so that, even if they have been – or are about to be – supplanted they should be retained in situ Balconettes and other external fixtures associated with windows were often more ornamental than practical, designed as part of the aesthetic of the structure or added later. Even where not in use they should be retained as part of the original design or as evidence of a subsequent fashionable alteration
- Architectural Heritage Protection Guidelines for Planning Authorities 163 CHAPTER 10 OPENINGS Doors and Windows CONSIDERATION OF PROPOSALS AFFECTING WINDOWS 10.4.15 The visual impact of alterations to the windows of a historic structure can be significant. Proposals to remove, replace or otherwise alter historic windows should be given close attention. Where repairs are proposed, these should preferably be specified on a window-by-window basis as the extent of repair can vary widely depending on weathering and other factors. 10.4.16 Repair and repainting of historic windows should be carried out with due care for the joinery or metalwork and any original or early glass and for the appearance and character of the structure. Where proposals are made to paint windows, care should be taken to establish the original finish before applying paint to unpainted joinery. Methods and specification of repainting should be approved by the planning authority before works commence. It is rarely appropriate to remove paint from historic timber windows by immersion (see 11.3.9 below) or to remove paint from glazed lights using a heat gun. 10.4.17 Replacement of sashes or entire windows should only be permitted where the existing windows are missing; are verifiably decayed beyond repair; or are themselves inappropriate recent replacements. Replacement windows should be of appropriate material, design and detail and approved by the planning authority prior to any work commencing. The complete replacement of such elements in historic buildings should rarely be permitted where they are capable of repair. 10.4.18 Plastic and aluminium are inappropriate materials for replacement windows in historic buildings (unless these materials can be proved to have been used originally). 10.4.19 It is of importance to the character and appearance of a structure that fenestration patterns are protected. Where replacement windows are permitted, the materials, glazing divisions and sectional profile of the new windows should be appropriate to the date of the protected structure or to the date when the opening was made. If the latter, the design should be judged on its contribution to the protected structure. While windows are vulnerable to the impact of the weather, it is rare that a whole window is affected to the extent that complete replacement is necessary. Repair by splicing and piecing is a traditional method of prolonging the life of timber windows, and many joiners still specialise in this work (this window is shown after repair). The high quality of the timbers used historically means that it makes economic sense to leave unaffected elements in place, as they have proven their longevity, having withstood centuries of use While the recent sash windows on the upper floor of this house seem reasonably accurate at first glance, the joiner or designer did not base the detailing on the surviving original sashes on the ground floor. The replacement windows are made to a thicker profile and have horns which the original sashes do not. The inclusion of horns is a common error made in fabricating new sashes. In this case the original windows predate the use of horns, which did not become standard until the second quarter of the nineteenth century
- CHAPTER 10 OPENINGS Doors and Windows Architectural Heritage Protection Guidelines for Planning Authorities 164 Where clues survive as to the correct detailing of a replacement window they should be followed in order to fabricate a historically-accurate new window. In the case illustrated here, evidence of the detailing of the original central sashes existed in the blind side lights but was ignored From the middle of the nineteenth century a hierarchy of glazing within a single building became common: newly-available, but expensive, plate glass was used on the principal floor with smaller paned windows at the basement and upper floors. This arrangement was often original to the building and should be respected and plate glass sashes not mistakenly ‘restored’ as small-pane windows
- Architectural Heritage Protection Guidelines for Planning Authorities 165 CHAPTER 10 OPENINGS Doors and Windows 10.4.20 Replacement windows should replicate the opening method of the original windows. Top- and bottomhung or pivot windows are not suitable replacements for sliding sashes or side-hung casements. Their use will disrupt the visual integrity of a historic building and its setting and can be detrimental to the character of an ACA. 10.4.21 Where replacement of existing windows has become necessary, the opportunity may arise to consider the replacement of later, inappropriate or damaging alterations and allow for the installation of new windows whose design is more appropriate to the structure, or to the ACA. This is particularly relevant in unified terraces of buildings where inappropriate replacement windows have damaged the character of the entire group of buildings. However, such restoration should always be based upon firm evidence of the original design of the window using old photographs, drawings, or other reliable information, such as surviving original windows in the neighbouring buildings. Caution should be exercised as some past alterations may contribute to the cumulative historical interest of a building and should not be erased without due consideration of all the consequences. For example, improvements in glass-making technology led to a fashion in the latter part of the nineteenth century for replacing small-paned sashes with single panes of plate glass. These single-paned sash windows can now be seen as part of the historical record of the building and should only be permitted to be replaced after careful consideration by the planning authority. 10.4.22 The reopening of blocked windows may be appropriate in cases where this re-establishes the elevational design of the building. But an assessment needs to be made as to whether or not the blocked opening was part of the original design, such as a blind window, or part of alterations to the structure where the earlier opening may no longer relate to the present form of the building. Previously blocked openings should not be opened up where it would lead to the disturbance or destruction of later interior work of quality. 10.4.23 The erection of new external blinds and canopies should generally not be permitted where there is no evidence that they previously existed and when their effect on the appearance of the building and its setting may be considered damaging. The removal of redundant blind boxes should generally not be permitted where they contribute to the character of the structure or area. 10.5 Glass and Glazing IDENTIFYING SPECIAL FEATURES FOR PROTECTION 10.5.1 All old surviving glass is important to the character and quality of a historic building. Historic plain glass types include blown cylinder glass, blown crown glass and blown or cast plate glass. Decorative uses of glass include stained glass, painted glass, coloured glass or old glass. Old glass may have early, etched inscriptions on it, adding to the importance of the glazing. By its delicate nature, thinly blown historic glass is vulnerable to damage, making it remarkable that so much survives. The irregular surfaces of plain glass, naturally highly polished, contort reflections and add considerable character to the buildings and streets where historic glass is found
- CHAPTER 10 OPENINGS Doors and Windows Architectural Heritage Protection Guidelines for Planning Authorities 166 Crown and other plain glass 10.5.2 The irregularities and imperfections of handmade glass cannot be replicated with modern float glass and are essential to the quality of the historic window. Where crown, cylinder or early polished plate glass survives, its existence should be recorded. All original or early glass should be protected and retained. Stained and painted glass, decorative zinc-framed or leaded glass 10.5.3 Individual pieces of stained, painted or coloured glass set in lead or zinc cames (used in H- or T- section strips respectively which hold the pieces of glass in place) are usually associated with church architecture. There are, however, many fine examples of stained, painted or coloured glass decorative panels in public buildings and in doors, fanlights and windows of houses, often within margin lights. The windows of many late Georgian churches and other buildings were glazed with leaded panels or cast-iron glazing bars containing clear glass quarries. CONSIDERATION OF PROPOSALS AFFECTING GLAZING Crown and other plain glass 10.5.4 Where old or interesting glass has been identified in a protected structure or in another building, such glass should be retained and protected during the building works. Where repairs are necessary to the window frames, the panes can be carefully removed and reset by a specialist. If a window is decayed beyond repair, the original glass can be removed with great care and set aside for re-use in repair work elsewhere within the same building. Small corner cracks should not be used as a reason to remove early panes of plain glass. Badly-damaged panes of significance, such as bullseye panes or those with inscriptions, can be plated with a thin glass layer and retained in place. The use of ultraviolet protective film on historic glass should be avoided particularly where the glass is thin. 10.5.5 Where the loss of historic glass in a prominent location would significantly affect the character of a protected structure or an ACA, the planning authority could make it a condition that damaged panes are replaced with new handmade panes. Stained and painted glass, decorative zinc-framed or leaded glass 10.5.6 The repair and cleaning of artistically or historically important glazing, such as stained glass or painted glass panels, is the work of specialist conservators. Where it is proposed to carry out works to stained Most of the panes of this window, which will need maintenance as part of a larger project to repair the whole structure, are of cylinder sheet glass. Some are cracked while a few are missing. If timber repairs are necessary the glass should be carefully removed from the frames by one of several methods, securely stored and reglazed on completion, sealed with putty. Historic glass should always be adequately protected during general building works, even where no window repairs are proposed Historically, the aim of glassmakers was to create perfect, uniform glass panes which, until recently, was not achievable with the methods available to them. Modern float glass is perfectly uniform but, as a result, without character. It is the very imperfections of handblown glass such as bubbles, undulations or tints, once seen as faults, that are now prized. In fact, historic glass is irreplaceable. Crown glass is no longer made as the skills to blow and spin thin crowns have been lost, while few makers still produce cylinder sheet glass Stained glass comes in many forms, from finelydetailed floral patterns in a domestic building – as in this example – to illustrative panels by internationally important artists in public buildings
- Architectural Heritage Protection Guidelines for Planning Authorities 167 CHAPTER 10 OPENINGS Doors and Windows Decorative panels of stained, painted or etched glass should be retained in situ until repairs are specified and carried out by experienced stained glass conservators, as unnecessary removal or poorly-detailed restoration could cause damage and possibly devalue the artistic work. If necessary, the panels should be protected (outside and inside, but with adequate ventilation), and all broken pieces stored carefully until professional help can be obtained The insertion of new extract fans, louvres and the like should generally be confined to basements or minor elevations; however if the basement was designed as part of a principal elevation, as is the case in this structure, or is visible from the street or on the approach to the structure, then such additions should be avoided. The addition of items that would necessitate altering the frame or structural opening of a historic window should also be avoided, even on secondary elevations or painted glass windows, the applicant should show that the proposed work is necessary and will involve the minimum intervention and replacement of historic material. Re-leading of panels should not be seen as routine and the buckling of leaded windows is not, in itself, a conclusive indication of a need to undertake re-leading. The repair of leadedglass panels should preferably be carried out in situ. It is often acceptable to allow cracks in the glass to remain unrepaired and for small holes to be filled in situ. However, there may be cases where serious problems warrant the removal of the panel to an off-site workshop for repair. Before any works are carried out, the window should be recorded in situ with photographs, drawings or both. Alterations that involve the insertion of inappropriate modern panes into a window should not be permitted. Modern forms of glazing 10.5.7 The use of modern wired glass, obscured glass, tinted glass or louvred glass panels or the insertion of extract fans, air-conditioning units and similar devices on prominent elevations should generally not be permitted. 10.6 External Protection 10.6.1 New external protection may be proposed to protect historic or interesting glass from breakage or from damage by the elements. Where this is the case, this protection should be provided in a way which is reversible and as unobtrusive as possible. The protection should not be made or fixed in a way that will damage the fabric or appearance of the structure or window. For example, the rusting of metal grilles or run-off from copper or iron fixings could cause damage to the fabric. The creation of unventilated cavities behind external secondary glazing panels can encourage excessive and damaging heat build-up or allow condensation to occur on the face of the historic glass. Where secondary glazing is proposed, the applicant should indicate how the original glasswork is to be ventilated.
- CHAPTER 10 OPENINGS Doors and Windows Architectural Heritage Protection Guidelines for Planning Authorities 168 10.6.2 The installation of secondary glazing to the exterior of windows can be visually obtrusive and proposals should be given careful consideration. The appearance and character of the building will be harmed by the use of plastic sheeting that can surface-craze or become opaque through exposure to the elements. This sheeting is also highly flammable and its use should not be permitted near valuable glass where the exterior is accessible to vandals. The appearance of the external protection will be enhanced by requiring it to be formed to fit the shape of the opening and any tracery while allowing for sufficient ventilation. 10.7 Improving the Thermal Efficiency of Historic Openings Draught-proofing 10.7.1 Simple draught-proofing is usually the most acceptable method of improving the thermal efficiency of historic windows and doors. However, some caution should be exercised. Most draughtproofing systems have a shorter life-expectancy than the historic window or door frames themselves and so the installation of draught-proofing, which often requires routing out of sashes and frames, should not take place to the detriment of the existing joinery. 10.7.2 The installation of draught-stripping measures to openings should take account of the age, importance and suitability of the element for such work. The measures used should not compromise the condition of the fabric nor unacceptably alter the appearance of the element. Double-glazing and secondary glazing 10.7.3 The installation of double-glazing to protected structures is problematic and should generally not be permitted where original or early windows exist. The installation of double-glazed units into existing openings, even where the existing window frames are not of any special interest, may not be visually acceptable and can rarely be achieved without making unacceptable changes to the profiles of the frames arising from the depth of the double-glazed units. It also makes the sashes much heavier and could strain the joints. The use of false spacer bars or bars applied to the interior or exterior is usually visually unacceptable. Additional problems may arise as many old buildings suffer from condensation problems following the installation of airtight windows. In this case the external secondary glazing is shaped to fit each light, however two drawbacks arise: the adverse visual impact on viewing the structure and the potentially very serious physical damage to the glasswork arising from the lack of ventilation to the exterior. The warm micro-climate between glass and outer glazing can lead to the distortion of the lead matrix and damage to glass and paint from organic growth In this case, the external secondary glazing is shaped to fit each light; however its design has two serious drawbacks: the adverse visual impact on the structure and, the potential to cause physical damage to the glasswork arising from the lack of ventilation of the cavity between the historic glass and the new protective layer. The micro-climate created between glass and outer glazing by the lack of ventilation can lead to the distortion of the lead matrix and damage to glass and paint from organic growth This grille, possibly only intended as a temporary measure, is nevertheless damaging to the appearance of the window and the building as a whole and its fixings are starting to fail. If protection is indeed necessary – a question all custodians of stained glass should first ask themselves – the use of black coated stainless steel grilles would be preferable, shaped to fit each lancet and tracery light
Source Department of Arts, Heritage and the Gaeltacht: Architectural Heritage Protection: Guidelines for Planning Authorities (2011) · Licence the publisher's termsText read from the publisher’s PDF; tables, maps and drawings do not survive as text, and page numbers are the PDF’s (its first page is 1). Check the original before relying on a passage.