Kensington and Chelsea conservation architects

The Borough’s townscape is unique in its high quality, finely grained, historic built environment and has a strong sense of identity and character. The Council has a reputation of upholding high standards of conservation and design. The character and appearance of the Borough are highly valued, locally, nationally and internationally.

The Borough’s townscape is rich in detail. Paying attention to detail, as well as to matters such as form and mass, is therefore important in ensuring new high quality development.

Development proposals should heed their local context. Analysing and responding to context is important in good design. The extent of the relevant context depends on the development.

The Borough has considerable residential densities but surprisingly modest building scales. For example, Victorian terraced housing in the Borough is typically of four storeys, providing 700 habitable rooms per hectare (hrh); Edwardian terraced mansion blocks at six storeys provide 970hrh. In North Kensington, the typical postwar estates are five and six storeys, providing 500hrh, much lower than in the Victorian period.

The Borough is a good example of how high density development can be completely compatible with a high quality environment. The design of a development must take into account the character and scale of the area, the need to foster good design and the Council’s and community’s aspirations for the site and area. The density of the development should be the outcome of this design process rather than the starting point. The density matrix in the London Plan needs to be considered in this context.

A comprehensive approach should be taken towards site redevelopment to make the best use of the land and improve the appearance of the area. Where appropriate this should include an assessment of the development potential of nearby sites to avoid piecemeal and uncoordinated development.

Backland sites – sites surrounded by other development with limited or no street frontage – may be difficult to difficult to integrate into the surrounding context.

The many mews streets in the Borough form an integral part of the 19th Century pattern of development of this area of London. They are an effective form of development for making good use of the space within larger perimeter blocks. Indeed, the mews as a feature of the townscape is one of the factors that distinguish London from other cities. Whilst their origin as stable blocks for large houses means that they are generally of modest design, they do have a distinct character based on their consistency, simplicity and unity.

Artists’ studios represent a distinctive building type that emerged in the middle of the nineteenth century. They are characterised by a number of features including large windows and expanses of studio space behind. They exist in many forms from grand studio houses commissioned by famous artists of the day, to more modest and utilitarian speculatively built groups. There are significant numbers in the Borough, which make an important contribution to its character and appearance. There is considerable pressure both for the introduction of new uses and the carrying out of alterations. This pressure is threatening the essence and character of these studios and consequently, undermining the artistic traditions of the Borough.

The Council will require all development to respect the existing context, character and appearance, taking opportunities available to improve the quality and character of buildings and the area and the way it functions, including being inclusive for all.
To deliver this the Council will:
a. require development to contribute positively to the townscape through the architecture and urban form addressing matters such as scale, height, bulk, mass, proportion, plot width, building lines, street form, rhythm, roofscape, materials and historic fabric as well as vistas, views, gaps, and open space;
b. require development to respond to the local context;
c. require the density of development to be optimised, sensitive to context;
d. require riverside and canalside development to enhance the waterside character and setting, including opening up views and securing access to the waterway;
e. require development within the Thames Policy Area to protect and improve the strategic importance and iconic role that the Thames plays in London;
f. require a comprehensive approach to site layout and design including adjacent sites where these are suitable for redevelopment, resisting schemes which prejudice future development potential and/or quality;
g. require the development of backland sites to ensure vehicular and pedestrian access is properly integrated into the surrounding street network and that the scale and massing respect the hierarchy of the existing urban block so as to enhance the character of the area;
h. ensure that, in carrying out alterations and extensions, the characteristics of the type of building, such as mews, terrace or mansion block, is preserved and enhanced;
i. resist the demolition of, and inappropriate alterations and extensions to, artists’ studios.

The Council will require all development to be of the highest architectural and urban design quality, taking opportunities to improve the quality and character of buildings and the area and the way it functions.
To deliver this the Council will:
a. require development to be:
i. Functional – fit for purpose and legible;
ii. Robust – well built, remain in good condition and adaptable to changes of use, lifestyle, demography and climate;
iii. Attractive – pleasing in its composition, materials and craftsmanship;
iv. Locally distinctive – responding well to its context;
v. Sustainable – in the use of resources, including energy, in construction and operation;
vi. Inclusive – accessible to all;
vii. Secure – designs out crime.
b. require an appropriate architectural style on a site by-site basis, in response to:
i. the context of the site;
ii. the building’s proposed design, form and use;
iii. whether the townscape is of uniform or varied character.

The Council will require development to preserve and to take opportunities to enhance the cherished and familiar local scene.
To deliver this the Council will:
a. require development to preserve or enhance the character or appearance of the conservation area and protect the special architectural or historic interest of the area and its setting;
b. resist the change of use of any building where the current use contributes to the character of the surrounding area and to its sense of place;
c. resist substantial demolition in conservation areas unless it can be demonstrated that:
i. in the case of substantial harm or loss to the significance of a heritage asset it is necessary to achieve substantial public benefits that outweigh that harm or loss;
ii. in the case of less than substantial harm to the significance of a heritage asset, that the public benefits, including securing the optimum viable use, outweigh that harm;
iii. the building or part of the building or structure makes no positive contribution to the character or appearance of the area;
d. require full planning applications in conservation areas.

The Council will require development to protect the heritage significance of listed buildings, scheduled ancient and sites of archaeological interest.
To deliver this the Council will:
a. require all development and any works for alterations or extensions related to listed buildings, scheduled ancient monuments and sites of archaeological interest,
to preserve the heritage significance of the building, monument or site or their setting or any features of special architectural or historic interest;
b. resist the demolition of listed buildings in whole or in part, or the removal or modification of features of architectural importance, both internal and external;
c. require the preservation of original architectural features, and later features of interest, both internal and external;
d. i. take opportunities to reinstate internal and external features of special architectural or historic significance, commensurate with the extent of proposed development;
ii. take opportunities to remove internal and external features that harm the architectural or historic significance of the asset, commensurate with the extent of proposed development;
e. resist the change of use of a listed building that would materially harm its character;
f. require any work to a listed building to sustain the significance of the heritage asset and as such strongly encourage any works to a listed building to be carried out in a correct, scholarly manner by appropriate specialists;
g. require desk based assessments and where necessary archaeological field evaluation before development proposals are determined, where development is proposed on sites of archaeological significance or potential.

The Council will require that alterations and additions do not harm the existing character and appearance of the building and its context.
To deliver this the Council will resist small-scale development that:
a. harms the character or appearance of the existing building, its setting or townscape;
b. results in a cumulative effect which would be detrimental to the character and appearance of the area;
c. is not of high quality form, detailed design and materials or is not discreetly located.

The Council will require roof alterations and additional storeys to be architecturally sympathetic to the age and character of the building and group of buildings.
To deliver this the Council will:
a. permit additional storeys and roof level alterations where the character of a terrace or group of properties has been severely compromised by a variety of roof
extensions and where infilling between them would help to reunite the group;
b. resist additional storeys, and roof level alterations on:
i. complete terraces or groups of buildings where the existing roof line is unimpaired by extensions, even when a proposal involves adding to the whole terrace or group as a co-ordinated design;
ii. buildings or terraces that already have an additional storey or mansard;
iii. buildings that have a roof structure or form of historic or architectural interest;
iv. buildings that are higher than surrounding neighbours, or where they would detract from significant skylines or profiles;
v. buildings or terraces where the roof line or party walls are exposed to long views from public spaces, and where they would have an intrusive impact on that view or would impede the view of an important building or open space beyond;
vi. buildings that, by the nature of the roof construction and architectural style, are unsuitable for additional storeys, e.g. pitched roofs with eaves;
vii. mansion blocks of flats where an additional storey would add significantly to the bulk or unbalance the architectural composition;
viii. terraces that are already broken only by isolated roof additions.

The Council will require extensions and modifications to existing buildings to be subordinate to the original building, to allow the form of the original building to be clearly understood, and to reinforce the character and integrity of the original building, or group of buildings.
To deliver this the Council will resist proposals for extensions if:
a. the extension would extend rearward beyond the existing general rear building line of any neighbouring extensions;
b. the extension would rise above the general height of neighbouring and nearby extensions, or rise to or above the original main eaves or parapet;
c. the extension would spoil or disrupt the even rhythm of rear additions;
d. the detailed design of the addition, including the location or proportions or dimensions of fenestration or the external materials and finishes, would not be in character with the existing building;
e. the extension would breach the established front building line;
f. an important or historic gap or view would be blocked or diminished;
g. the architectural symmetry of a building, terrace or group of buildings would be impaired;
h. the original architectural features on a formal flank elevation would be obscured;
i. access to the rear of the property or of those adjoining would be lost or reduced;
j. a conservatory is proposed to be located at roof level, significantly above garden level or on a corner site.

The Council adopted Policy CL7: Basements on 21 January 2015 and it forms part of the Local Plan. The policy is based on a robust and extensive evidence base. The Inspector’s report on the policy acknowledged the special character of the Royal Borough and the issues relating to basement development. The Borough has seen an increasing number of basement planning applications. It is largely residential with a dense built environment, very high property values and a high quality historic environment.

Policy CL7 is the first of its kind in setting limits on the extent of development. The policy preparation and its adoption took over two years with a very lengthy examination process for a single policy. The examination hearings took over four and a half days which reflects the controversial nature and the level of interest in the policy.

The policy sets out a number of criteria which seek to manage the impact of basement development on residents, the environment and on the character and appearance of the Borough. One of the main objectives of Policy CL7 is to bear down on the volume of excavation in order to curtail not only the individual but also the cumulative effect of basement development on living conditions. Map 1 demonstrates the great number of planning applications relating to basement development between 2001 and 2015. Whilst the mapping is over a long time period, it still serves to demonstrate the importance of considering cumulative impacts. The impacts relate to the whole Borough, and the intention of the policy is therefore to mitigate the cumulative impact across the whole Borough. In considering each application and appeal it is therefore important not just to limit consideration to the properties either side of the application site or even the street but apply the policy consistently. A ‘case by case’ analysis of each site negates the very basis of the policy as such an approach fails to consider the cumulative impacts that the policy is designed to mitigate. The policy does include some exceptions for ‘large sites’ as set out later in this document.

The policy criteria and reasoned justification make it very clear that construction impacts are a material planning consideration in this Borough. These cannot be adequately dealt with by a planning condition. The full proposal regarding mitigating these issues needs to be submitted with the planning application to be considered properly and comply with the policy.

Given the complexity and the issues surrounding basement development in the constrained urban environment in this Borough, it is necessary to provide further guidance on the adopted Policy CL7.

1. Engage with the Council and obtain pre-application advice
“The Council offers a pre-application advice service for applicants. Detailed information on the planning advice service is available on the Council’s website. As set out in the NPPF (paragraph 188), “Early engagement has significant potential to improve the efficiency and effectiveness of the planning application system for all parties. Good quality pre-application discussion enables better coordination between public and private resources and improved outcomes for the community.”

2. The 50% rule
“As stated in the policy the 50% maximum extent will be measured separately for each garden within the site e.g. front, back or side. An existing lightwell with no built structure below should be regarded as forming part of the ‘garden’ or ‘open part’ of the site. The Royal Borough is characterised by terraced houses and in most cases the front and back gardens will be clearly separate and the measurements straightforward as shown in figure 1.”

3. Be careful with the design of all external elements
“CL7 (g) – not introduce light wells and railings to the front or side of the property where they would seriously harm the character and appearance of the locality, particularly where they are not an established and positive feature of the local streetscape;”
“CL7 (h) – maintain and take opportunities to improve the character or appearance of the building, garden or wider area, with external elements such as light wells, roof lights, plant and means of escape being sensitively designed and discreetly sited; in the case of light wells and roof lights, also limit the impact of light pollution;”

4. Basements in the curtilage of Listed Buildings
““CL7 (e) – comply with the tests in national policy as they relate to the assessment of harm to the significance of heritage assets;”
“CL7 (f) – not involve excavation underneath a listed building (including vaults);”
3.13 Criterion (f) of the policy precludes excavation underneath a listed building. However, it may be possible to construct a basement in the garden of a listed building subject to a number of considerations. Criterion (e) of Policy CL7 makes it clear that such proposals would need to comply with the tests in the national policy; in particular the advice outlined in paragraphs 132 to 134 of the NPPF. The Council’s general duty in relation to listed buildings is set out in section 66 of the Planning (Listed Buildings and Conservation Areas) Act 1990. This is to “have special regard to the desirability of preserving the building or its setting or any features of special architectural or historic interest which it possesses.”.