“No 26 has previously been the subject of substantial extension at existing basement level on two occasions…. These historic basement extensions comprise ‘basement’ development under the [Council’s] basement policy definitions because they were built below the prevailing ground level of No 26 at the street front and garden rear.”
“The Policy applies to all basement proposals: extensions, and new developments, across all land uses. ‘Basement’ means one or more floor levels substantially below the prevailing level of the back gardens. Lower ground floors are not regarded as basements in this context. A basement will not be allowed where a property already has an existing basement.”
“It is acknowledged that the definition of basement needs more clarity and text will be altered as appropriate.”
“Comment The distinction between lower ground floors and basements is not made clear. At what stage does a lower ground floor become a basement? Both usually involve the entire bottom floor being situated below ground level, so that the problems that arise when further excavation takes place are similar for both. Accordingly, the policy should treat existing lower ground floors as basements, and prohibit excavation beneath floors which are below ground, whether or not they might be considered as basements or lower ground floors. Council’s response It is acknowledged that the definition of basement needs more clarity and text will be altered as appropriate. The suggestion would put a stop to most basement proposals in the Borough. The policy is not intended to stop basement development. The proposed policy would allow people to extend their homes and help minimise their impacts.”
“This policy applies to all new basement development. For the purposes of this policy, basement development is the construction or extension of one or more storeys of accommodation below the prevailing ground level of a site or property.”
“34.3.47 Basements are a useful way to add accommodation to homes and commercial buildings. While roof extensions and rear extensions add visibly to the amount of built development, basements can be built with much less long term visual impact – provided appropriate requirements are followed. This policy sets out these requirements. 34.3.48 Basement development in recent years has been the subject of concern from residents. Basements have given rise to issues about noise and disturbance during construction, the management of traffic, plant and equipment, and concerns about the structural stability of buildings. These concerns have been heightened by the growth in the number of planning applications for basements in the Royal Borough…. The vast majority of these are extensions under existing dwellings and gardens within established residential areas. 34.3.49 In the Royal Borough, the construction of new basements has an impact on the quality of life, traffic management and the living conditions of nearby residents and is a material planning consideration. This is because the borough is very densely developed and populated. It has the second highest population density and the highest household density per square km in England and Wales. Tight knit streets of terraced and semi-detached houses can have several basement developments under way at any one time. The excavation process can create noise and disturbance and the removal of spoil can involve a large number of vehicle movements. 34.3.50 A basement development next door has an immediacy which can have a serious impact on the quality of life, while the effect of multiple excavations in many streets can be the equivalent of having a permanent inappropriate use in a residential area. There are also concerns over the structural stability of adjacent property, character of rear gardens, sustainable drainage and the impact on carbon emissions. Planning deals with the use of land and it is expedient to deal with these issues proactively and address the long term harm to residents’ living conditions rather than rely only on mitigation. For all these reasons the Council considers that careful control is required over the scale, form and extent of basements. 34.3.51 The policy therefore restricts the extent of basement excavation to no more than under half the garden or open part of the site and limits the depth of excavation to a single storey in most cases…. 34.3.52 ‘Garden’ or ‘open part of the site’ is the private open area to the front, rear or side of the property. A ‘single storey’ is one that cannot be subdivided in the future to create additional floors. It is generally about 3 to 4 metres floor to ceiling height but a small extra allowance for proposals with a swimming pool may be permitted. 34.3.53 Restricting the size of basements will help protect residential living conditions in the borough by limiting the extent and duration of construction and by reducing the volume of soil to be excavated. Large basement construction in residential neighbourhoods can affect the health and wellbeing of residents with issues such as noise, vibration and heavy vehicles experienced for a prolonged period. A limit on the size of basements will reduce this impact. … 34.3.58 Where a basement has already been implemented following the grant of planning permission or through the exercise of permitted development rights, the policy does not allow further basement floors or basement extensions that would exceed 50 per cent of the garden or open part of the site. This is to ensure consistency of approach.”
“70. Given my findings above on CL7(a) and (b), it logically follows that additional basement floors which might follow on after an extant or implemented permission or after the implementation of permitted development rights should be prevented. Otherwise CL7(b) would not be effective or reasonable or fair. For the same reasons, this criterion should also be subject to the recommended monitoring and review modifications in order to be sound. 71. The Council said that this would not apply where a property already had an existing basement before the need for planning permission came into effect with the 1947 Planning Act. The Council said this would be ‘fair’, which I take also to mean ‘reasonable’ and ‘proportionate’, and that it would be consistent with national planning legislation in Development Orders when restrictions on development rights are introduced. I agree. Unfortunately, the policy at 34.3.58 does not say this and so is not sound. Modification MM6 rectifies this unsoundness. I have slightly altered the Council’s wording to make clear that both originally constructed and later added basements must have taken place before1 July 1948 . 72. I conclude that with the above modification CL7(c) is justified, effective and consistent with national policy.”
“Where a basement has already been implemented following the grant of planning permission or through the exercise of permitted development rights, the policy does not allow further basement floors or basement extensions that would exceed 50 per cent of the garden or open part of the site. This provision would not apply to a basement which forms part of the original property or to a later addition which were constructed prior to1 July 1948 . This is to ensure consistency of approach.”
“If regard is to be had to the development plan for the purpose of any determination to be made under the planning Acts the determination must be made in accordance with the plan unless material considerations indicate otherwise.”
“basement floors”, and simply “basement”
“The proposed basement would be constructed below the existing lower ground floor level, and would be the first subterranean addition to the property.”
“I remain satisfied that the original lowest floor level of the property has not been lowered in order to facilitate the erection of the rear closet wing.”