Extending Listed Buildings

Principles and Practice

Richard MacCullagh


  Ulster Museum facade showing intergration of original and 1960s extension  
Ulster Museum, Stranmillis, Belfast – Frances Pym 1962-4 A brutalist cantilevered masterpiece added to the front facade of James Cumming Wynne’s 1929 building. Some extensions break all the rules and still work. The part Heritage Lottery Fund funded 2006-9 refurbishment and remodelling has been criticised for dramatically altering the internal character of the 1960s museum. 

The historic environment has evolved and will continue to evolve over time through natural processes and human interventions. As a society we have come to collectively value and protect elements of this inheritance and these are now described in the most recent United Kingdom national planning policies as ‘heritage assets’. These assets include historic buildings, monuments, sites, places and landscapes of significance that merit special consideration in planning decisions because of their heritage interest. Heritage assets include those that are designated, such as listed buildings, scheduled monuments and conservation areas; and undesignated assets, such as local lists of buildings of local interest. This article considers the principles and practice of extending buildings which have been designated as heritage assets by being listed for their special architectural or historic interest.

Most historic buildings reflect the cumulative changes of different ownership and uses and these in themselves can add to the special interest of a listed building, reflecting social and individual values and needs. Unlike today, such decisions were historically made without the constraints of planning authorities but may have been controlled by other factors. While listing introduces a much greater degree of control, it does not mean a historic building should be frozen in time but calls for well-informed and intelligent management of changes so the listed building can sustain its heritage value. This applies as much to the decision-making body as to the owner, architect or heritage consultant who develops any proposed scheme.

Any works of alteration, extension or demolition will require listed building consent (LBC) if they affect its character and in determining this the local planning authority or secretary of state ‘shall have special regard to the desirability of preserving the building or its setting or any features of special architectural or historic interest it possesses’.[1] If the listed building is in a conservation area then there is also a duty to ensure that ‘special attention shall be paid to the desirability of preserving or enhancing the character or appearance of the conservation area’.[2]

  West Down Conference Centre - exterior with modern extension West Down Conference Centre - section of original facade
  West Down Conference Centre University of Winchester – Feilden Clegg, 2001. This Grade II listed building was on the Buildings at Risk Register with a very uncertain future when it was acquired by Winchester University. Feilden Clegg was commissioned to turn it into a conference centre with student accommodation and studio space for the university’s performing arts school. A fairly nondescript wing was removed to make way for a glazed foyer, staircase and lift linking the original 1880 Thomas Stopher preparatory school to the 1905 Arts and Crafts hall and chapel by John Simpson. New flat-roofed dormers were added to the front elevation of the main building. This is a successful contemporary interventionist approach that still conserves much of the building’s original character and gives it a new lease on life.

Most extensions will also require planning permission and statutory government guidance will apply. In England the current guidance is contained in the new National Planning Policy Framework (NPPF) which provides a presumption in favour of sustainable development.[3] It states that one of the 12 core principles that underpin both plan-making and decision-taking is that planning should conserve heritage assets in a manner appropriate to their significance, so that they can be enjoyed for their contribution to the quality of life of this and future generations. It also says that account should always be taken of: the desirability of sustaining and enhancing the significance of heritage assets and putting them to viable uses consistent with their conservation; their potential to contribute to sustainable communities; and the desirability of new development making a positive contribution to the historic environment’s local distinctiveness. Significance, as defined by the NPPF glossary ‘includes archaeological, architectural, artistic or historic interest. Significance derives not only from a heritage asset’s physical presence, but also from its setting’.

North of the border, Scottish Historic Environment Policy (SHEP, 2010) contains similar policies to England’s NPPF. Significance, for example, is a major theme in both SHEP and the NPPF, but the concept does not appear in the Welsh equivalent, Planning Policy Wales. This refers to the ‘character’ of listed buildings and the need to ‘safeguard’ their ‘special architectural or historic interest’. Nevertheless, differences are generally in emphasis rather than substance.

As well as national planning policy, every planning authority has a local plan and the policies in this will be a material consideration in determining a planning application. The local plan will have relevant policies on design and the historic environment and may have some more detailed design guidance in the form of supplementary planning documents.

  Winchester College Dormitory extension - exterior Winchester College Dormitory extension - interior of glazed link
  Winchester College Dormitory – Seymour and Bainbridge, 2007. A successful 3-storey addition to a 17th century dormitory which adjoins the 14th century St Mary’s Chapel and uses a combination of solid flint walls and large frameless corner windows, together with copper butterfly roof and glazed atrium next to Chambers. The glazed link enables minimal alterations to the existing fabric and adds interest to the transition from old to new internally. The result is a delight to behold!


Given the great variety of historic building types and their individual characteristics, design advice shouldn’t be too prescriptive as what might work for one site may not necessarily work for another. Some listed buildings will be much more sensitive to change than others, so each case should be considered on its individual merits. A good starting point, however, is to develop a thorough understanding of the significance of the listed building and its setting. Only by going through this process will one be able to make value judgements about what survives and its capacity for change. The NPPF requires an applicant to describe the significance of any heritage assets affected, including any contribution made
by their setting. It states that: ‘the level of detail should be proportionate to the assets’ importance and no more than is sufficient to understand the potential impact of the proposal on their significance’.[4] This will normally involve both desktop and historic building analysis and in some cases careful opening up of building fabric may be required (with the agreement of the planning authority). It is essential to use appropriate heritage expertise in this assessment.

  London town house - facade London town house - side and rear
  London Town House – Waugh Thistleton Architects, 2011. This Grade II listed early Victorian townhouse was in a very dilapidated state. The design proposals were informed by a heritage significance statement and included a side extension to first and second floors and an elegant contemporary double-height glass infill extension to the rear. The historic cellular floor plan was retained, and cornices, staircase and architectural joinery were repaired or reinstated. A contemporary approach was taken in the basement and it was possible to provide a small subterranean extension to the side and rear wing, which had to be underpinned anyway.

It is as important to understand the historic plan form of a listed building as its external envelope, so that any addition can be added without compromising the special interest of a historic interior. A value judgement must be made regarding the significance of what is opened up or covered over by the extension. An appreciation of the building’s setting and context is also essential as in many cases the extension will be visible in the public realm and may also impact on other historic buildings.

Listed buildings are often the product of more than one period. In some cases it may be relatively easy to add a further addition provided it is sensitive to the scale and detail of the existing fabric. Others may already have been extended to such a degree that a further extension would harm their character, or the site might be too tightly constrained by its boundary. In some cases it might be desirable to remove recent additions of low quality and replace them with a better-designed extension. However, later additions can be difficult to evaluate. For example, alterations made to a Georgian building in the Victorian period are more likely to be considered part of the building’s history than those made in the 1960s, but there are exceptions in both cases and many grey areas between. Some listed buildings present bigger challenges for adding extensions than others because of their sensitivity to change. For example, in the case of a church built in one single-phase or one that enjoys a degree of architectural completeness, it might be preferable to place facilities inside as part of an internal re-ordering or provide a freestanding building (both solutions will present challenges). It is also possible that archaeological resources survive within or beneath the listed building’s curtilage and decisions will be required regarding preservation in situ or recording. Others such as gate lodges and tollhouses present challenges of scale due to their diminutive size but may need an extension to keep them in viable use.

  Three-storey glazed infill extension - exterior Extension interior with timber floor
  London Town House – Found Associates, 2010. A six-storey Grade II listed early 19th-century townhouse in Belgravia Conservation Area. The proposals involved demolition of poor quality first floor additions and the construction of a three-storey glazed infill extension and a first floor extension over the closet wing, both in a contemporary style. There was also extensive internal remodelling and refurbishment including removal of a poor quality reproduction staircase and panelling, installation of a new staircase in the closet wing and introduction of air-conditioning and underfloor heating.

Pre-application consultation with the planning authority’s conservation and planning officers is important. The statutory heritage body should be consulted where the building concerned is listed at the highest grade (eg English Heritage for Grade I and II* buildings) [5] as they will be commenting on the planning and LBC applications. In more challenging schemes or ones that are likely to be contentious, it is worth considering wider public consultation or contacting relevant national or local amenity societies. The quality of response can vary but consultations are useful if all parties are prepared to engage constructively.

Planning decisions should not ‘stifle innovation, originality or initiative’ (NPPF para 60), and planners are required to be objective in their deliberations. Many conservation officers are not themselves from a design background and benefit from seeking the views of design professionals. In some local authorities they have access to a panel of architects and designers, and this can prove beneficial particularly on larger or more challenging schemes.

Acknowledging the above caveats, most listed buildings can be altered or extended sympathetically to some degree to accommodate continuing or new uses. Some will present the opportunity to promote a design intervention that would not have been possible without the listed building to inspire it. Such high quality work can delight and add to the historic building’s interest.

There are various definitions of good design, but the criterion set by Vitruvius over 2,000 years ago, that architecture should be functional, durable and attractive, [6] has stood the test of time and can be applied equally to any building, object or designed space, at any scale. Architectural style is less important than how the extension relates to the existing building and its context in terms of scale, mass, form, siting, proportions, details and materials.


The design and construction of the extension should:

  • show an understanding of the heritage significance of the listed building and its setting
  • seek to minimise any harm to the listed building’s heritage value or special interest
  • normally play a subordinate role and not dominate the listed building as a result of its scale, mass, form, siting or materials
  • fulfil a function that is in the listed building’s long-term interest
  • sustain and add value to the listed building’s significance by being of high quality design, craftsmanship and materials.


It is important for new work to acknowledge the old and in Extensions (see Recommended Reading) Historic Scotland has produced useful guidance on five different approaches to contextual design:

  • restoration
  • replication
  • complementary addition
  • deferential contrast
  • assertive contrast.


This involves well-documented reconstruction of missing elements and, in some cases, the removal of later additions – for example where an original frontage has become hidden behind later extensions. However, if later extensions have special interest and contribute to the significance of the building, then the presumption is normally to retain them.


New work is designed specifically to match the original building and does so in all respects, replicating not only materials but also style.

Winchester College Music School facade showing juncture of old and new elements Winchester College Music School - extension  
Winchester College Music School – Nugent Vallis Brierley, 2004. An architectural tour de force providing much needed studio space to ES Prior’s 1904 Arts and Crafts building. The distinctive roof design provides optimum acoustics and creates an interesting skyline feature, which complements the original architect’s very individual design.

Complementary addition

This takes design cues from the profile, massing, bay rhythm, scale and proportion of the existing building, but without the replication of details. Quite substantial extensions can be added to some buildings without detracting from the character of the original. The same additions to other buildings would result in imbalanced design or straggling composition. In those cases, a well-designed modern addition that will not read as part of the original building will affect its appearance less radically.

Deferential contrast

This is where the new becomes a modest backdrop against the old. Even if it is large, it seeks not to be assertive. It might be achieved by reflective glass, for example.

Assertive contrast

This means affirmation of the new as a more or less equal partner to the old. New and old combined should be of greater lasting value than either on its own.

As the examples illustrated here show, extending listed buildings can be challenging but it often inspires delightful, purposeful and enduring designs which add to the vitality and interest of the original building. There is clearly a need to understand and respect the original building’s character and significance, but good design is a creative process and needs to be considered objectively on an individual basis. Good judgement and quality in both design and execution are the keys to producing results that will be appreciated both now and for many years to come.



Recommended Reading

Managing change in the historic environment: Extensions, Historic Scotland, 2010 (www.historic-scotland.gov.uk/ extensions.pdf)


1 Sections 16 and 66, Planning (Listed Buildings and Conservation Areas) Act 1990, and Sections 14 and 49, Planning (Listed Buildings and Conservation Areas) (Scotland) Act 1997

2 Section 72, Planning (Listed Buildings and Conservation Areas) Act 1990, and Section 64, Planning (Listed Buildings and Conservation Areas) (Scotland) Act 1997

3 Scotland, Wales and Northern Ireland have their own planning policy documents.

4 The equivalent policy in Scotland states: 'In general the more extensive the intervention which is proposed, the more supporting information applications should provide'. (SHEP 3.43.) No comparable advice is given in Welsh and NI planning policy documents, but varying the level of information according to the nature of the proposal reflects good practice.

5 Historic Scotland, Cadw or the Built Heritage Directorate of the Northern Ireland Environment Agency should be consulted where appropriate on their higher graded buildings.

6 Vitruvius proposed that architecture should display three qualities: utilitas, firmitas and venustas. These were elegantly rendered into English as ‘commodity, firmness and delight’ by Sir Henry Wotton in 1624. However, the message grows more obscure with the evolution of language, and ‘functional, durable and attractive’ would perhaps be a more fitting translation for the 21st century.


The Building Conservation Directory, 2013


RICHARD MacCULLAGH MRTPI IHBC BA(Hons) MSc DipTP is principal of RMA Heritage, a historic environment consultancy, which is based in Hampshire. He previously managed the conservation and design team at Winchester City Council and has worked in Scotland, Northern Ireland and Dublin.

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