Architectural Heritage Protection: Guidelines for Planning Authorities

1. Page 111

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   Architectural Heritage Protection Guidelines for Planning Authorities 109 CHAPTER 7 CONSERVATION PRINCIPLES 7.8 Respecting Earlier Alterations of Interest 7.8.1 Alterations and additions to a structure can themselves be an irreplaceable part of a unique history. Different periods of alteration can inform the social and architectural history of the built heritage. For example, the subsequent addition of porches, balconies, shopfronts and returns can say much about changing fashions in architectural design and social aspiration, as can alterations or embellishments such as the addition of bargeboards, window and door surrounds or dormer windows. 7.8.2 In order to appreciate the integrity of a structure, it is important to respect the contribution of different stages of its historical development. Concentration on whether or not various parts of a building are ‘original’ can obscure the fact that later alterations and additions may also contribute to the special interest of the structure. Of course there may be alterations or additions which have not contributed to the special interest of the building, and which may in fact have damaged it. 7.8.3 Where new alterations and additions are proposed to a protected structure, it should be remembered that these will, in their turn, become part of the structure’s history and so it is important that these make their own positive contribution by being well designed and constructed. Alterations of different periods may contribute to a knowledge and appreciation of the history of a structure. The application of plaster hood-mouldings to earlier buildings was fashionable at the end of the nineteenth century. While they may now appear anachronistic, they can also be seen as part of the unique history of that building The conversion of this 1762 Charter School nursery to a store in the nineteenth century involved partially blocking the window openings, thereby altering its character. Restoring the openings would be possible using surviving evidence in the fabric and employing historically accurate detailing. This approach is appropriate where the character of an architectural composition can be restored by undoing later alterations of little interest New alterations – as in this conference room with tiered balconies constructed within a mediaeval castle tower – should respect their context and be of high-quality design and specification. In time, such interventions will contribute to the history of the structure

2. Page 112

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   Architectural Heritage Protection Guidelines for Planning Authorities 110 CHAPTER 7 CONSERVATION PRINCIPLES 7.9 Repairing Rather than Replacing 7.9.1 It should be the aim of good conservation practice to preserve the authentic fabric which contributes to the special interest of the structure. Good repair will arrest the process of decay of a structure and prolong its life without damaging its character and special interest. Where a damaged or deteriorated feature could reasonably be repaired, its replacement should not be permitted. 7.9.2 Many historic structures date from a time when the majority of building materials were wrought by hand. These materials have a variety and vitality that cannot be matched by machine-made materials. Tooling and chisel marks on stonework, undulations in blown-glass panes, and adze marks on timber elements supply a wealth of irreplaceable information about the people and the times that produced these structures. Also, through time, a structure and its components acquire a patina of age that cannot be replicated. The unnecessary replacement of historic fabric, no matter how carefully the work is carried out, will have an adverse effect on the character of a building or monument, seriously diminish its authenticity and will significantly reduce its value as a source of historical information. Replacing original or earlier elements of a building with modern replicas only serves to falsify the historical evidence of the building. 7.10 Promoting Honesty of Repairs and Alterations 7.10.1 To promote good conservation practice in line with the recommendations of international charters, repairs to a protected building or structure should generally be carried out without attempt at disguise or artificial ageing. This does not mean that the repair should be obtrusive or that inappropriate materials should be used in order to contrast with the historic fabric. A good repair, carried out with skill, leaves an interesting record of works done. Deliberately obscuring alterations confuses the historical record that is the building. New repairs should not detract from the visual integrity of the structure but should be discernible on closer inspection. The careful repair of a damaged feature such as a cast iron balustrade contributes much to preserving the character of a structure (shown here before and after repair). Where elements are not capable of repair, the new work should accurately reproduce the detail of the original. Entire sections should not be replaced if only a part is damaged Good conservation practice encourages the honesty of repairs and alterations which may be discernible to the expert eye but not visually obtrusive. This new hopper head was designed to match the style of the structure but is recognisable, on close inspection, as a new element from its 1999 date

3. Page 113

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   Architectural Heritage Protection Guidelines for Planning Authorities 111 CHAPTER 7 CONSERVATION PRINCIPLES 7.11 Using Appropriate Materials and Methods 7.11.1 Only appropriate materials and methods should be used in works to a protected structure. In early restoration works of the past, untested materials and techniques, such as the use of cement repointing and of some surface consolidants, actually resulted in the accelerated decay of the building fabric on which they were applied as part of conservation works. The use of modern materials and techniques should only be permitted where their appropriateness is supported by firm scientific evidence or where they have proved themselves over a sufficient period and where traditional alternatives cannot be sourced. 7.11.2 When dealing with planning applications for works to a protected structure, materials, details and specifications for works should be approved by the planning authority prior to the commencement of any works. 7.12 Ensuring Reversibility of Alterations 7.12.1 The use of processes which are reversible, or substantially reversible, when undertaking works to a protected structure is always preferable as this allows for the future correction of unforeseen problems, should the need arise, without lasting damage being caused to the architectural heritage. For example, filling structural voids with concrete would be an irreversible process while a loose fill could easily be removed at a later stage. Similarly, scribing new partitions around an existing cornice or skirting allows for the earlier work to remain intact, possibly to be re-exposed at a future time. 7.12.2 Not all works can be made reversible and a judgement will have to be made by the planning authority where irreversible works are proposed. Ideally, permitted works which affect the character and special interest of a protected structure should be reversible and such works considered temporary, to be reversed when circumstances allow. Such works might include the subdivision of important rooms or spaces within the interior of a protected structure. 7.12.3 The reversibility of proposals is an important conservation principle but should not be used to justify inappropriate interventions. 7.13 Avoiding Incremental Damage 7.13.1 Thought must be given by the planning authority to the potential cumulative impact of minor works to the character of protected structures and of ACAs. The quality and character of both can be damaged by incremental alterations. In the case of protected structures this applies to both internal and external works. 7.13.2 In an ACA, this principle can apply to a street or area where a precedent becomes established for the removal of architectural features or the addition of extensions. For example, the proposed alteration of the external railings of an individual house and the conversion of its front garden to accommodate car parking may at first appear minor and acceptable. However, the planning authority must consider the effect on the character of an ACA and the setting of other protected structures should substantial numbers of properties also alter historic railings and lose their gardens. Similarly, proposals to demolish existing returns to replace them with larger extensions should be treated with caution. Alterations, particularly those which impact on important elements of a protected structure, should as far as possible be reversible. Internally this can be achieved by scribing partitions around cornices, dado rails and skirting boards. However, the reversibility of a proposal should not be used to justify inappropriate works The restoration of the pioneering cast- and wrought-iron glasshouses at the National Botanic Gardens was preceded by technical and scientific research to ensure that the proposed ironwork repairs would be appropriate in terms of materials and construction

4. Page 114

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   Architectural Heritage Protection Guidelines for Planning Authorities 112 CHAPTER 7 CONSERVATION PRINCIPLES 7.13.3 It can sometimes be difficult to refuse permission for minor works, but a point may be reached when the combined impact of all the small alterations will be considerable and detract substantially from the architectural quality and character of the building or of an area. 7.14 Discouraging the Use of Architectural Salvage from Other Buildings 7.14.1 In granting planning permission for works to historic buildings, including all protected structures, the planning authority should not encourage the use of architectural salvage from other buildings for two reasons. Firstly, the re-use of architectural features from elsewhere can confuse the understanding and appreciation of a building, casting doubt on the authenticity of even the untouched parts of the fabric. Secondly, creating a market for salvaged building materials promotes the dismantling of other old buildings, for example the removal of slates or cut-stone elements from a building for reuse elsewhere. 7.14.2 The planning authority could use the planning process to discourage the use of architectural salvage from other buildings. Promoting the use of newly produced materials such as stone or wrought iron could help to keep them in production or encourage the revival of the craftsmanship associated with these materials. There may be occasions where suitable traditional materials are no longer in production and their production cannot be revived. In such cases, the use of salvaged materials may be appropriate after their provenance has been ascertained. 7.15 Complying with the Building Regulations 7.15.1 The Building Regulations are designed to secure the health and safety of people in and around buildings. The Regulations are set out in twelve parts (Parts A - M, excluding I). They are expressed in performance terms and are backed up by relevant Technical Guidance Documents (TGDs) which give guidance regarding compliance. Apart from a limited number of exemptions, they apply to all works involving new construction, extensions to buildings, material alterations to existing buildings and material change of use of such buildings. This salvaged portico is obviously not a part of the structure it now fronts. However it is not clear if it survives from a previous building on this site or was imported from elsewhere. This has the effect of blurring the historical record. The use of salvaged items can promote the practice of dismantling of other structures capable of repair and it is important to establish the provenance of salvaged material before use It can often be difficult to resist proposals for minor works which seem of little consequence such as the replacement of windows, doors and roof coverings or the conversion of front gardens to parking bays. However the cumulative effect of such alterations can be destructive to the special interest of a protected structure or of an ACA

5. Page 115

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   Architectural Heritage Protection Guidelines for Planning Authorities 113 CHAPTER 7 CONSERVATION PRINCIPLES 7.15.2 Works carried out in accordance with the guidance in the TGDs will, prima facie, indicate compliance. However, the adoption of an approach other than that outlined in the guidance is not precluded, provided the relevant requirements of the Regulations are complied with. Parts of the Building Regulations which are particularly relevant to works in relation to historic buildings include Part A (Structure), Part B (Fire Safety), Part L (Conservation of Fuel and Energy) and Part M (Access for People with Disabilities). However, some parts of the Regulations do not apply to a material change of use, for example the requirement in Part A dealing with disproportionate collapse or the requirements of Part K dealing with stairways, ladders, ramps and guards. 7.15.3 Alterations, extensions and material changes of use affecting historic buildings may present particular problems, and approaches other than those contained in the TGDs may be appropriate in order to ensure compliance while protecting the character of the building. The difficulties that may arise in the application of the Building Regulations to existing buildings is acknowledged in the preamble to each TGD, where it is stated: In the case of material alterations or changes of use to existing buildings, the adoption without modification of the guidance in this document may not, in all circumstances, be appropriate. In particular, the adherence to guidance, including codes, standards or technical specifications, intended for application to new work may be unduly restrictive or impracticable. Buildings of architectural or historical interest are especially likely to give rise to such circumstances. In these situations, alternative approaches based on the principles contained in the document may be more relevant and should be considered. 7.15.4 In the interest of conserving the character of buildings of outstanding architectural and historical importance, the enhanced thermal performance requirements introduced in the 2002 amendment to the Building Regulations do not apply to works (including extensions) to existing buildings which are protected structures or proposed protected structures under the Planning and Development Act 2000. In that amendment it is also acknowledged that the application of this part may pose particular difficulties for habitable buildings which, although not protected structures or proposed protected structures may be of architectural or historical interest, and the following guidance is included in the TGD: Works such as the replacement of doors, windows and rooflights, the provision of insulated dry-lining and damp-proofing to walls and basements, insulation to the underside of slating and provision of roof vents and ducting of pipework could all affect the character of the structure. In general, the type of works described above should be carefully assessed for their material and visual impact on the structure. Historic windows and doors should be repaired rather than replaced, and dry-lining and dampproofing should not disrupt or damage historic plasterwork or flagstones and should not introduce further moisture into the structure. Roof insulation should be achieved without damage to slating (either during the works or from erosion due to condensation) and obtrusive vents should not affect the character of the roof. In specific cases, relaxation of the values proposed may be acceptable if it can be shown to be necessary in order to preserve the architectural integrity of the particular building. 7.15.5 Specific issues in relation to Parts B and M of the Regulations are dealt with respectively in other chapters of these guidelines. Provision is also made in the Building Control Act for the granting of a dispensation or relaxation in relation to specific works or materials by a Building Control Authority where the case for such dispensation or relaxation is accepted by the authority.

6. Page 116

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   Walls and Other Structural Elements CHAPTER 8

7. Page 117

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   Architectural Heritage Protection Guidelines for Planning Authorities 115 8.1 Introduction 8.1.1 The structural system of a historic building and its elements play a major role in defining its character. Structural elements may include external and internal load-bearing brick or masonry walls, mud walls or timber-framed walls; columns of stone, cast iron or concrete; stone, brick or concrete vaults; timber, iron or steel beams, trusses, girders and many others. Structural elements may be important as early examples of the use of certain materials such as cast iron or concrete. Even where interesting structural elements are not exposed, they are nonetheless of significance and contribute to the character of the building. 8.1.2 The structure of the building may be clad externally and the type and appearance of the cladding materials used may also contribute to the character of the building. Common cladding materials include metal sheeting such as corrugated iron, slatehanging, tile-hanging, timber boarding and terracotta or faïence units. 8.1.3 Any finishes applied to the structure of a building may also be of importance. Rubble stone walls were often finished with a render coating. This may have been applied as a roughcast coat or with a smooth, trowelled finish sometimes ruled and lined to resemble ashlar blocks. Smooth or roughcast renders may have been limewashed, painted or self-finished. Small stones or other materials may have been pressed into the wet coating after application to provide a pebble-dashed finish. 8.1.4 When assessing the contribution of structural elements, including walls and associated features, to the character of a protected structure or of an ACA, the planning authority should ask: a) What is the original structural system of the protected structure? b) Has this been altered in the past? If so, are the alterations of interest or have they damaged the appearance or the structural integrity of the building? c) Are there early or original structural elements of particular interest? d) Are there likely to be any concealed elements of interest? e) Is the present structural material, cladding or finish original? f ) If not, is it of interest or does it conceal an original surface or earlier finish beneath? g) If there is an original surface or earlier finish beneath, should it be investigated or were there reasons why it was covered over, such as poor quality materials or unsightly alterations? h) If there is a later finish, is it causing damage to the earlier surface? If it is causing damage, would the process of removing this finish lead to further damage? For example, the removal of a strong cement-based render could take away parts of the earlier surface below. i) Is the structure part of a group or terrace of similar buildings? If so, would any alterations to one of the terrace affect the quality or character of the entire group, such as uncoordinated façade cleaning, painting or repointing? j) Is there any original architectural detailing such as string courses, pilasters, cornices or quoins? Are there any later embellishments or alterations of interest? How will these be protected and conserved during the works? k) Are there any elements such as balconies, verandas or balconettes attached to the walls? Do these contribute to the special interest of the building? l) Are there any other features or fixtures of interest attached to the walls such as plaques or fire marks? CHAPTER 8 WALLS AND OTHER STRUCTURAL ELEMENTS Structural elements, such as masonry walls, may play a major role in defining the character of the structure. Here the granite and brickwork wall retains its original pointing. This wall was never rendered, but where finishes were originally used they almost always contribute to the special interest of the structure

8. Page 118

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   CHAPTER 8 WALLS AND OTHER STRUCTURAL ELEMENTS Architectural Heritage Protection Guidelines for Planning Authorities 116 8.2 Alterations to Walls and Other Structural Elements 8.2.1 In identifying the important qualities of the walls and other structural elements of protected structures, all original architectural detailing should be respected, as should later additions, embellishments or remodelling of definite quality. There may be cases where alterations are of little interest in themselves or which positively detract from the architectural quality of the whole by reason of their poor design or their poor relationship to the rest of the building. Past alterations may also have damaged the structural integrity of the building or structure. In such cases, the planning authority may consider it desirable to encourage the reversal of unsatisfactory alterations that disfigure or conceal earlier work of greater merit or have caused physical problems or deterioration. This should only be done after careful consideration of all the consequences. Any works carried out on this basis should always be based upon firm evidence and an assessment of the original state and detailing of the structure. Structural Stability 8.2.2 The analysis of the structural stability of a historic building generally requires the skill and experience of a specialist structural engineer rather than one who is a general practitioner. Where an application is made to demolish or dismantle a protected structure (whether in whole or in part) based on reasons of structural instability, the onus is on the applicant to prove that the proposals are valid and all relevant matters have been properly addressed. In some cases, the planning authority may need to commission its own independent advice on structural matters. 8.2.3 Where alterations are proposed to walls or other structural elements of a protected structure, the planning authority should be satisfied that the proposals are based on a proper knowledge and understanding of the existing structure. Many old buildings suffer from minor structural defects but will continue to perform satisfactorily providing they are not subject to major disturbance. Alterations such as the creation of new openings, changes to the interior spaces or the installation of new services and equipment could overload an existing structural system and, where this is a possibility, the proposals should be reconsidered. In these circumstances, specialist advice may be required. 8.2.4 Repair works to a protected structure should generally be permitted only where they are low key and involve reinstatement or strengthening of the existing structure. It is preferable to repair rather than rebuild structural elements. But where it is considered acceptable to permit part of a structure to be taken down and rebuilt, the planning authority should make it a condition of the permission that the existing work be thoroughly recorded prior to any works taking place and that rebuilding incorporate as much of the original material as possible. Settlement 8.2.5 Proposals which have the potential to cause settlement in a historic building should be given careful consideration. Excavation or re-grading of ground levels adjacent to or within a protected structure could cause its foundations to settle or fail. The structural integrity of old foundations may also be undermined by previous inappropriate alterations or extensions, by the planting of certain types of tree close to the building or by the saturation of adjacent ground by poor drainage design. 8.2.6 Settlement of the foundations of a structure in the past may have resulted in loads being transferred onto previously non-load-bearing partitions. Therefore proposals to remove all or part of any walls of old buildings should be treated with great caution as these may adversely affect the structural integrity of the building. Intensification of use or seemingly minor alterations can cause settlement and have an adverse effect on the structural integrity of an old building. Evidence of minor structural defects such as cracking should be investigated but may be symptomatic of structural movement or settlement that happened long ago and may now have stabilised. Cracks should be monitored over a period of time to establish if movement is continuing and is sufficiently serious to warrant action

9. Page 119

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   Architectural Heritage Protection Guidelines for Planning Authorities 117 CHAPTER 8 WALLS AND OTHER STRUCTURAL ELEMENTS Works in connection with damp-proofing 8.2.7 Works in connection with damp-proofing may materially alter the appearance or character of a protected structure or have implications for its structural stability. Inappropriate works can lead to the unnecessary destruction of large amounts of fabric such as external render, internal plasterwork, panelling or flooring. Where there would be such an adverse effect on the structure, the proposals should be not be permitted. Likewise, any proposals which would involve the removal of large amounts of historic finishes, such as plasterwork, are not likely to be considered acceptable. 8.2.8 In assessing applications for planning permission involving damp-proofing works that could have an adverse effect, the applicant should show that the works are in fact necessary. There may be other solutions to the issue which should be first considered. The fabric of older buildings was usually designed to allow absorption of moisture from the ground or from rainwater and its subsequent evaporation from the surface. Later alterations or neglect may have interfered with the original drying-out process of the structure. Also, damp problems may be caused by condensation. 8.2.9 Reversing inappropriate later alterations may be sufficient to alleviate the problems of damp and are generally less destructive to the fabric of the building. Such works could include reopening blocked-up windows or vents, removing later impervious surface finishes from walls or floors, ensuring that ground levels around the building are appropriate, or locally re-grading the ground surrounding the building to ensure that surface water drains away from the external walls. The location of vapour-generating activities within a building such as cooking or showering should be carefully considered and, if necessary, relocated. 8.2.10 A proposal to install a new damp-proof course into a protected structure is likely materially to alter the appearance or character of the structure or have implications for its structural stability. If it has been determined that the installation of a damp-proof course is the only solution to problems in a protected structure, the method proposed should be carefully considered. The insertion of a continuous lead, slate or other damp-proof course is probably the most effective method but only if a complete physical barrier can be achieved. This may not be possible without unacceptable disruption or damage to the fabric of the structure and the added possibility of settlement-cracking in the future. This method is usually only successfully achieved in walls of coursed stone or brickwork. 8.2.11 The planning authority should be aware that the injection or infusion of a chemical damp-proof course will require injection holes drilled into the walls which may be visually unacceptable in an historic wall and can often be ineffective. The efficacy of electro-osmotic systems is doubtful. Furthermore, such systems may involve the use of metals, such as iron or copper, which are likely to rust or to stain the fabric of the building. Adding flashings 8.2.12 Lead flashings can be provided to prolong the life of decayed projecting features but should generally only be used where this can be achieved unobtrusively. New flashings should not visually distort the proportions of important mouldings or other features. Surface treatments 8.2.13 The covering of walls of a protected structure with a water-repellent coating should not normally be permitted. Traditional buildings were designed to ‘breathe’, that is, to absorb a certain amount of ground or atmospheric water, allowing it to evaporate at a later stage rather than to repel all water from an impervious surface. Damp problems arise more often from poor maintenance or poorly-executed repair works than from inadequate original detailing. The injection of a damp-proof course may result in visually obtrusive pockmarks on the external walls of the building and is unlikely to be fully effective in rubble walling

10. Page 120

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    CHAPTER 8 WALLS AND OTHER STRUCTURAL ELEMENTS Architectural Heritage Protection Guidelines for Planning Authorities 118 8.2.14 The inappropriate use of surface consolidants prevents the evaporation process. Any cracks which develop in the surface layer will allow the entry of water trapping moisture and salts against or behind the wall surface, so promoting decay and endangering the character and fabric of the protected structure. Such treatments, where permitted, should only be carried out by experts after detailed consultation. Cladding in synthetic materials 8.2.15 Permission should not normally be granted for the cladding of any part of a protected structure in synthetic materials, such as artificial stone. 8.2.16 The addition of external insulation to historic buildings should not be permitted where this would adversely affect important features. 8.3 Walling and Other Structural Materials Stonework IDENTIFYING SPECIAL FEATURES FOR PROTECTION 8.3.1 There is a wide variety of building stones to be found in Irish buildings, usually locally produced limestone, granite and, to a lesser extent, sandstone. In addition, imported stones such as Portland stone, red sandstone and marble were often used in architecturally significant buildings. 8.3.2 Cut stone, or ashlar, was used extensively in construction. Many prominent buildings are entirely faced in finely worked ashlar, while even humbler buildings can include cut-stone elements such as sills, string courses, copings or quoins. Other buildings and many boundary walls were constructed of rubble stonework, which was often finished in plain or roughcast render. 8.3.3 The original ashlar surface was often tooled or polished and this distinctive texture should always be respected as a part of the building’s character. Carved work, where it exists, should be identified and protected. Masons’ marks, where found, should also be protected. These are symbols or initials incised into stonework by the mason originally responsible for executing the work. CONSIDERATION OF PROPOSALS AFFECTING STONE WALLING Specification of repair works 8.3.4 Stone is generally a very durable material but inappropriate repairs and poor workmanship can accelerate its decay. It may be better that masonry be left untouched rather than allow proposals which could result in incorrect treatment and consequent damage. 8.3.5 Stonework repairs require detailed specification and the applicant should be required to supply all necessary information to allow an assessment of the proposals. In some cases, the planning authority may need specialist advice to satisfy itself that due care has been exercised and that all relevant matters have been properly addressed in the application. 8.3.6 Where repair works are proposed to stone walls, particularly ashlar walls, of a protected structure the information required as part of a proposal could include: Architectural detailing, tooling, masons’ marks and carving – ranging from lettering and vermiculation to bas-relief sculpture– should always be noted and protected Even durable stones such as granite and limestone can be irreparably damaged by inappropriate works. The cement mortar used in repointing this wall is stronger than the stonework. As a result, structural movement in the wall could not be absorbed by the mortar and instead the stone has fractured. The impermeability of the mortar may cause future additional damage, as any water entering the wall through this fracture will be unable to escape

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.