Architectural Heritage Protection: Guidelines for Planning Authorities

1. Page 141

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   Architectural Heritage Protection Guidelines for Planning Authorities 139 CHAPTER 9 ROOFS 9.2.6 Proposals to alter the shape of the roof of a protected structure or of a structure within an ACA will have a potential impact on the character of the structure and its surroundings. It should not be permitted without careful consideration of the circumstances. 9.2.7 Roofs of protected structures should retain their original form and profile and not be radically altered, for example, to provide extra accommodation in the form of a mansard roof. The insertions of lift-motor rooms, plant rooms and dormers can also materially alter the character and profile of a historic roof and should be carefully scrutinised. Similar alterations to other structures in an ACA should only be permitted after careful consideration of any effect that the alteration could have on the character of the ACA or on the setting of adjacent protected structures. 9.2.8 Where the original shape of the roof has been previously unsympathetically altered, the opportunity could be taken to reinstate the earlier form of the roof, thus restoring the integrity of the structure. However, any such restoration should be based upon firm evidence of the original state. Where a new roof is proposed, the design of the replacement should be sympathetic to the character and special interest of the building and not detract from the overall appearance. 9.2.9 Where a roof or its components have been removed, poorly repaired or altered inappropriately, the reversal of unsatisfactory later work could be undertaken. However, any such restoration work should be based upon firm evidence of the original state of the roof or element using old photographs, drawings, or other reliable information. Where it is proposed to re-roof a ruinous structure, the applicant should use expert advice to identify fabric or other evidence of the previous roof construction. Care should be taken that this evidence is not lost in the restoration works and is either recorded in detail or preferably retained in situ. A new roof should be appropriate to the character of the protected structure but this need not necessarily preclude the use of modern materials providing these do not damage the fabric or appearance of the building. Inappropriate alterations to roof shapes and details detract from the character of a structure; in this case the new roof has overhanging eaves with uPVC fascias, soffits and rainwater goods - an incorrect design using inappropriate materials on this former Board of First Fruits church The placing of service plant and lift overruns on roofs that are visible from either near or far can seriously detract from the character of a protected structure or of an ACA The original roof of this eighteenth-century dovecote was lost; however sufficient evidence survived to design a new roof which complements the structure

2. Page 142

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   CHAPTER 9 ROOFS Architectural Heritage Protection Guidelines for Planning Authorities 140 9.3 Cladding Materials 9.3.1 The type and nature of the cladding materials used on a roof have a significant impact on the appearance and special interest of a building. There are a number of types of roof cladding commonly found on historic buildings. The most common ones are described below. 9.3.2 The retention of traditional roofing materials and the development of new sources of these materials should be encouraged. The dismantling of other buildings for salvage materials, such as slate, should however be discouraged as this promotes the destruction of old buildings. 9.3.3 Any proposals that involve the removal, partial removal or alteration of the roof cladding materials of a protected structure will require careful scrutiny. The insertion of large areas of glazing or numbers of openable rooflights into prominent slopes of roofs is generally not appropriate. The covering of historic roofs with waterproof membranes such as bitumen or tar should not be permitted, except to those roofs originally covered with such materials. Slates IDENTIFYING SPECIAL FEATURES FOR PROTECTION 9.3.4 Slate is the most common covering material found on older roofs in Ireland. From the beginning of the eighteenth century until the mid-twentieth century, it was used on most buildings of consequence. Eighteenth-century slates that survive in situ are increasingly rare. Where they exist, these slated roofs contribute to the character of the building and are usually worthy of protection. 9.3.5 In the nineteenth century, the design of slate roofs became more elaborate with patterns formed in different colour variegated slates or courses of clipped or scalloped-edged slates. Such elaborate uses of slate are found on many churches and houses. Where such patterning is found, it should be identified, assessed and retained. 9.3.6 Slate roofs that have been laid in diminishing graduated courses should also be identified, as should the existence of unusual or large-sized slates. Valentia slate, famed for its qualities during the nineteenth century and again being quarried on a commercial basis, is here used on a conservation project. The use of regional slate types can be an important aspect of local distinctiveness and research indicates that slate native to a region generally performs best in the climatic conditions of that area. When undertaking restoration works to important roofs, the feasibility of reopening a local quarry to supply new slate should be investigated

3. Page 143

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   Architectural Heritage Protection Guidelines for Planning Authorities 141 CHAPTER 9 ROOFS CONSIDERATION OF PROPOSALS AFFECTING SLATES 9.3.7 In principle, sound slates should be carefully retained in situ. The stripping of traditional slate roofs should be discouraged because of the resulting loss of historic material such as the slates themselves, associated timberwork and parging (a lime mortar coating applied to the underside of slates). An applicant should be required to justify proposals by providing evidence of widespread failure of fixings or the poor condition of slates, battens or structural elements before stripping the roof. Where the work is permitted it should be carried out by experienced craftsmen, in order to maximise the preservation of the original material. Breakages can be minimised by good work practices such as the avoidance of double handling and by keeping slates in proximity to the work. As many as possible of the removed slates should be re-used on the more prominent slopes of the roof, with matching new materials on other, concealed slopes. The roof should be photographed prior to commencement of works to allow for its correct reinstatement. Where the existing slates are laid in patterns or in diminishing courses, such features should be retained. Any repairs should be carried out with care. 9.3.8 New cladding materials used in repair works should be compatible with the existing ones in terms of colour, size, texture, thickness and durability. The use of concrete tiles and fibre-cement tiles (sometimes referred to as ‘artificial slate’) should not be permitted in conjunction with, or as a replacement for, natural slate as the weathering characteristics, durability and appearance of these materials are very different from those of natural slate. Thatch IDENTIFYING SPECIAL FEATURES FOR PROTECTION 9.3.9 There are two distinct forms of historic thatched roof: the vernacular thatched roof, now most often found on traditional cottages, and the architectdesigned, cottage-orné thatched roof. The vernacular thatched roof was common throughout the country until the early twentieth century, but is now becoming increasingly rare. While many thatched roofs have been replaced in other materials, others have been simply covered over with corrugated iron sheeting above the thatch. Where there is a possibility that a building was thatched, care should be taken to identify, record and protect evidence of the original roof-covering. Regional slate varieties, by reason of their colours and distinctive sizing differences, contribute to the character of their structures, and indeed whole areas, although they are becoming increasingly rare. The unnecessary disturbance or comprehensive stripping of a slate-clad roof should be avoided as such works can result in breakages which may be difficult to replace. Exceptional circumstances may require the stripping of a slate roof such as failure of the roof structure due to rot, or if the roof is ‘nail sick’ Bands of different colour slate, variegated patterns or the use of decorative clipping of slates in diamond or fishscale shapes contribute to the character of a roof Parging, a traditional method of sealing and securing the underside of slates using a coating of lime mortar, is inevitably lost when a roof is stripped. In advance of any proposals to repair or renew a slate roof, the roof should be surveyed internally and externally to identify the types of slates used and existence of details such as parging, and to ascertain areas of local failure of the covering and of the structural elements

4. Page 144

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   CHAPTER 9 ROOFS Architectural Heritage Protection Guidelines for Planning Authorities 142 9.3.10 Thatch was a pervasive feature of the Irish landscape, as it provided a plentiful locally available roofing material. The traditional thatched roof has become symbolic of the vernacular heritage and is considered to be the indigenous roofing material. 9.3.11 Although the predominant material used was straw, there are regional variations in thatching style and materials used. Wheat straw, a farming by-product of food production, was used wherever it was produced. Rye is to be found on the Aran Islands, Co. Galway. Flax was used in Ulster. Heather, oats, potato hulm and marram grass are also to be found. Reed is used in particular locations where there were supplies from nearby riverbanks and lake margins. 9.3.12 In the vernacular tradition, thatched roofs are detailed functionally to withstand the elements and to make efficient use of scarce resources. The roof structure is often of unwrought wood. In coastal or other exposed locations, the roof structure was not a simple ‘A’ frame (which would necessitate a sharp ridge and excess concentration of wind pressures), but was truncated and made of four members to create a rounded profile. In these areas too, netting from ridges to eaves was employed as a restraint, as well as ropework tied back to pegs at the top of the wall and ridge scallops. In midland, eastern and southern areas, hipped- or half-hipped roofs replaced the gables to avoid excessive wind pressure. The roof structure often supported sods of earth, into which the thatch was fixed. When rethatching, it was expedient only to replace the upper layers, and lower layers can thus represent an important record of agricultural life in an area and retain features such as old varieties of straw and older fixing techniques. Scallop-thatching used wooden rods to fix the straw, and thrust thatching required the knotted straw bundle being forced tightly into the layer below. 9.3.13 The cottage-orné style of thatching differs greatly from the vernacular tradition, having a separate language of detailing featuring verandas, elaborate cresting to the ridge and patterned eaves fixings together with a sculptural treatment of chimney stacks and windows to attic rooms. CONSIDERATION OF PROPOSALS AFFECTING THATCH 9.3.14 Thatch presents special conservation issues, for two reasons. As a material it has a relatively short life, requiring to be renewed on a ten to thirty-year cycle. Secondly, thatch tends to be found on modest buildings whose accommodation may be inadequate for modern expectations. Hence there Irish vernacular thatching is simple in its construction and detailing, addressing, in the choice of roof profile, structure, materials and weathering details, the prevailing climatic conditions and available materials Unwrought or partially-wrought roof structures, however simple or slight they may seem, are part of the historic vernacular fabric. Repairs should aim to support the existing structural elements with new timbers rather than replace them Thatched roofs can decay quickly once neglected. Therefore it is important to make their repair a priority if grant assistance is available and to ensure that a thatcher, experienced in methods traditional to the region, is employed

5. Page 145

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   Architectural Heritage Protection Guidelines for Planning Authorities 143 CHAPTER 9 ROOFS are economic barriers to the conservation of this roofing material. Planning authorities should bear this in mind, and give consideration to any assistance that it may be possible to offer. 9.3.15 Re-thatching should, according to best practice, follow regional characteristics of materials, form and detail. Permission should not normally be granted for replacement of thatch with other materials, or of one type of thatch material with another. Complete stripping of thatch is rarely required and defective thatch should only be removed to a sound base. It is acceptable for a roof to have a variegated appearance following repair. Where anti-fire devices are introduced for thatch, they should be visually acceptable. 9.3.16 Proposals to reinstate thatch, on a roof that is known to have been thatched, should be carefully assessed. Surviving evidence from the building itself and information provided by old photographs and other records should be used to ensure accurate reinstatement of features. 9.3.17 Re-thatching a simple traditional vernacular roof using elaborate ridge or eaves details from the cottage-orné style is not appropriate. When rethatching a cottage-orné roof, however, it is important that the original detailing is respected. Where a thatched roof has been covered, for example with corrugated metal sheeting, the opportunity to re-expose the traditional material could be taken. There are local variations in thatching techniques and some details are particular to individual thatchers. In areas of the country, chickenwire is a traditional cover over thatch; whether over the entire roof or over vulnerable details requiring extra protection. Here a wire covering is about to be applied to finish off the ridge

6. Page 146

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   CHAPTER 9 ROOFS Architectural Heritage Protection Guidelines for Planning Authorities 144 Metal sheeting IDENTIFYING SPECIAL FEATURES FOR PROTECTION 9.3.18 Lead and copper were traditionally used on buildings of quality for flat roofs, roof-walks, gutterlinings or cladding for domes and cupolas. Both materials, together with zinc, were also used extensively for flashings. Dates or inscriptions can be found carved into lead. Where these exist they are often important features which should be preserved and, if possible, incorporated into the new roofcovering. 9.3.19 Corrugated-iron and profiled steel, zinc or aluminium sheeting is also to be found on a variety of buildings and it should be noted where they are likely to be the original cladding material. CONSIDERATION OF PROPOSALS AFFECTING METAL SHEETING 9.3.20 Lead and copper roofs should, where possible, be repaired rather than replaced. A correctly detailed and well-executed lead or copper roof can last for several hundred years without problems. There are examples, however, where the design of the original roof may have had inherent faults. These were most often caused by the use of overlarge sheets of the material or incorrect fixings that can lead to cracking of the sheets. Where there is an inherent design fault, the roof covering will require replacement to an improved design. Cracks should not be repaired with solder or with sealant, as these repairs will often cause further problems at a later stage. In addition, repairing metal sheeting with solder creates a fire hazard as most metal sheeting is supported by timber below. Stone ‘slates’ 9.3.21 So-called stone ‘slates’ are in fact thin slabs of limestone or sandstone dressed simply to rectangular shapes and used in a manner similar to slates. Stone ‘slates’ were usually laid in diminishing courses. There are very few remaining examples of stone ‘slates’ in Ireland and any examples should be preserved in situ with a minimum amount of disturbance. Clay tiles 9.3.22 Clay tiles were rarely used traditionally in Ireland after the middle of the eighteenth century and are now usually only seen in buildings of the late nineteenth or twentieth century. They can be found as flat tiles, pantiles or profiled interlocking tiles. Clay tiles should be retained on buildings or additions where they are the original roof-covering. Examples of clay roof tiles predating the twentieth century are Lead or copper sheeting were traditionally used on flat roofs or as a cladding to domes or cupolas. Lead, if properly specified and laid, can last several centuries in situ. Lead flashings can sometimes be cut with decorative finishes. Leadwork may have dates or inscriptions scratched on as graffiti, which is now of historical interest Clay roof tiles, though widely used in other countries, in Ireland rarely date from before the latter half of the nineteenth century. Either flat or profiled (pantiles) they can be decoratively shaped, as in this instance Corrugated iron sheeting may degrade through cracking or rusting (caused for example by sea spray in maritime areas) to a point where replacement is necessary. This recently-reclad harbour-master’s office has replaced the original, but rusting, corrugated iron with a modern profiled metal sheeting Moher ‘slates’, a regional type of roof cladding once common in Co. Clare, are in fact thin slabs of limestone dressed as slates. Stone ‘slates’ are rare survivors and, wherever possible, should be maintained in place with minimum intervention

7. Page 147

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   Architectural Heritage Protection Guidelines for Planning Authorities 145 valuable historical and architectural survivals and should be retained in situ. Clay and terracotta are however found extensively in ridge tiles. Glazed tiles 9.3.23 A distinctive feature on some roofs of the midtwentieth century is glazed tiling. Glazed tiles should be retained on buildings or additions of that period where they are the original roof-covering. Concrete tiles 9.3.24 Concrete tiles were used on roofs of the late twentieth century and should be retained on buildings or additions of that period where they are the original roof covering. Shingles and shakes 9.3.25 Shingles are thin, sawn or cleft pieces of timber used as roof, and sometimes wall, cladding. Shakes are shingles which are split on at least one face. Shingles and shakes were rarely used as a roofcovering in Ireland after the end of the seventeenth century and where examples are found they should be identified and are generally worthy of protection. In addition to their use as roof cladding, shingles and shakes are sometimes found as cladding to roof lanterns and similar features and as cladding to walls. Shingles and shakes were usually made of cedar, but chestnut and oak are among the timbers also used. 9.3.26 Where shingles and shakes are found, they should be retained. Where replacement shingles or shakes are required, these should match the original ones on a like-for-like basis, while allowing it to be clear on close inspection which is the original material. Asphalt, bitumen and other membranes 9.3.27 Where this is the original type of covering it should be retained, but, if necessary, replaced with a like material, as membranes can be difficult to repair effectively. 9.4 Roof Details 9.4.1 The architectural detailing of roofs is often of importance not only to the individual building, but can also contribute to the character of a town or surrounding countryside. CHAPTER 9 ROOFS Glazed roof tiles are part of the architectural design of some mid twentieth-century structures. They are unusual and should be retained where found. In this example, the purple colour of the glazed tiles contrasts strongly with the green copper cladding of the dormer surrounds and the creamy colour of the faïence wall cladding to make a strong architectural statement The use of shingles and shakes is rare in Ireland. Where it is necessary to replace parts of a shingled roof or wall cladding, the new shingles should match the original and should not be lighter in weight to the originals. Both shingles and shakes need ventilation to their undersides and roofs and walls clad in these materials should not be altered to include felt underlays

8. Page 148

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   CHAPTER 9 ROOFS Architectural Heritage Protection Guidelines for Planning Authorities 146 A visually interesting roof, such as this one with multiple gables, decorative stacks, turrets, cresting, finials and elaborate dormers, is a very important feature not only of the structure itself but may also act as a landmark in the local townscape or landscape Decorative and functional details of roofs that contribute to its character should be protected. In this instance, the original crenellated parapet, in place until recent years, has been removed, significantly detracting from the character of a rare late-mediaeval townhouse 9.4.2 Architectural details are important features of the roofscape and their removal should rarely be permitted where they are in good condition or are capable of repair. The removal of details of interest will have implications for the special interest of the structure, as they contribute to the quality and character of a roof. Where the structure forms part of a unified terrace, the alteration or removal of roof details from one structure will affect the character of the entire group and this should be borne in mind when considering a proposal for planning permission. 9.4.3 Where inappropriate earlier changes have been made, the reinstatement of missing features in replica may be appropriate, where there is sufficient evidence for their original form, or otherwise with an appropriate new design. Evidence for the original design might be found in adjacent buildings, for example, where the building is part of a terrace.

9. Page 149

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   Architectural Heritage Protection Guidelines for Planning Authorities 147 CHAPTER 9 ROOFS Ridges, ridge-combs, cresting, finials and weathervanes IDENTIFYING SPECIAL FEATURES FOR PROTECTION 9.4.4 Ridges were traditionally finished with clay, terracotta, lead or stone capping. In the latter part of the nineteenth century the treatment of the ridge became more elaborate with terracotta ridgecombs, finials or iron cresting being used. Original or early weathervanes are of particular interest and contribute to the character of the structure. CONSIDERATION OF PROPOSALS AFFECTING RIDGES, ETC. 9.4.5 Modern ridge tiles should not be permitted as a substitute for clay, terracotta, stone, lead or zinc. Where possible the original or early ridge details should be retained and repaired. Where replacement is considered appropriate they should be replaced to match. Original or early weathervanes should be retained and repaired as necessary. Associated masonry detail IDENTIFYING SPECIAL FEATURES FOR PROTECTION 9.4.6 The masonry details associated with a roof may include crowsteps, kneelers, scrolled springers, bellcotes, gargoyles, decorative water-spouts, eaves cornices, blocking courses, parapets, balustrades and other ornaments. CONSIDERATION OF PROPOSALS AFFECTING MASONRY ROOF DETAILS 9.4.7 Masonry details are important features of roofs and their removal should rarely be permitted where they are in good condition or are capable of repair. The repair and conservation of these details should be in accordance with the guidance notes given for stonework in Chapter 8 above. Domes, cupolas, lanterns, decorative roof-ventilators, spires and steeples IDENTIFYING SPECIAL FEATURES FOR PROTECTION 9.4.8 These roof features are not only important architectural features of the structure itself; the silhouette of such features contributes to the character of the surrounding landscape or townscape. CONSIDERATION OF PROPOSALS AFFECTING DOMES ETC. 9.4.9 The removal of domes, cupolas, lanterns, ventilators, spires or steeples, or their replacement with simpler forms, should generally not be permitted. Ridge tiles, finials, iron cresting and weathervanes are found on many structures and give a building its distinctive outline against the sky. Repairs should follow best practice for each particular material The visual impact of domes, lanterns, steeples and other prominent architectural features can extend well beyond their immediate setting and their removal may affect a wide area even where they are unused or unnecessary to the current use of the building Where it is proposed to ventilate roof spaces, important architectural details should be retained intact; in this example a pierced ceramic tile has been replaced by a new vent tile which disrupts the line of the ridge comb and damages its visual integrity Masonry details associated with roofs may be functional or not. Whether they are plain or decoratively detailed, they add character to a roof and, even if now redundant, should be retained

10. Page 150

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    CHAPTER 9 ROOFS Architectural Heritage Protection Guidelines for Planning Authorities 148 Chimneys, shafts and pots IDENTIFYING SPECIAL FEATURES FOR PROTECTION 9.4.10 Chimney stacks and pots are important elements of the roofline of a building. They can be indicators of the date of a building and of its internal planning. In Victorian buildings in particular, chimneys are usually an integral part of the architectural design. CONSIDERATION OF PROPOSALS AFFECTING CHIMNEYS 9.4.11 Chimney stacks or pots, finials, or cresting should usually be repaired and retained. Only if they are decayed to the extent of being dangerous, should their rebuilding or replacement be permitted. Even when they are perceived to have no further use, chimneys should be retained together with their pots where their appearance is important to the appreciation of the building as a whole. While their main purpose is to remove smoke from open fires, chimneys also function in providing permanent ventilation to the building and, particularly in older buildings, they serve, or may have come to serve, a structural function. They also contribute visually to the architectural composition and massing of a building. Redundant flues should be capped but never fully sealed. Eaves, verges and parapets IDENTIFYING SPECIAL FEATURES FOR PROTECTION 9.4.12 The architectural treatment of the edges of a roof often gives a distinctive character to the entire structure. The eaves may be flush, or almost flush, with the wall below or there may be a projecting stone or brick course at the head of the wall to support the eaves gutter. Alternatively, the eaves may overhang the wall supported on projecting, exposed rafter ends, or on boxed-in rafter ends. Projecting eaves may be supported on plain or decorative timber or metal brackets. 9.4.13 There may be a parapet wall that rises above eaves level with a concealed gutter behind. Parapets can be balustraded or plain. 9.4.14 The verges of the roof may be flush with the wall and the gaps between the slates or tiles filled with mortar. The wall may rise above the plane of the roof and form a gable parapet. Alternatively, the verge may overhang the wall in which case the edges may be trimmed with bargeboards. Bargeboards can be relatively plain timbers or elaborately carved or pierced. Curvilinear ‘Dutch-Billy’ or Queen Anne Revival style gable parapets are relatively uncommon in Ireland, especially elaborate terracotta examples such as this dating from the late-nineteenth century. These decorative elements make a contribution to the townscape as well as largely redefining this pair of Georgian houses Work to this chimneystack has included coating the stone cladding of the right-hand stack with render and adding a new clay pot. The new work contrasts badly with the original wellcrafted ashlar stack with chamfered sides and carved mouldings Chimneystacks, whether simple or elaborate, are integral to roofs of most periods and make a vital contribution to the silhouette of the structure. This terrace of early nineteenth-century cottages has simple stacks set diagonally in a revival of a Tudor detail

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