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Last edited 13 Mar 2018
Basements in buildings
A basement is part of a building that is either partially or completely below ground level.
Approved document B of the UK building regulations, Fire Safety, Volume 1 Dwelling houses, defines a ‘basement storey’ as ‘a storey with a floor which at some point is more than 1,200 mm below the highest level of ground adjacent to the outside walls.’
The term ‘basement’ is sometimes used interchangeably with the term ‘cellar' and may refer to any sort of below ground space used to provide accommodation, storage, car parking, services spaces, and so on.
However, Approved Document F, 'Ventilation' suggests that, in relation to dwellings, a basement: '...is a dwelling or a usable part of a dwelling (i.e. a habitable room), that is situated partly or entirely below ground level.' Whereas a cellar '... is part of a dwelling which is situated partly of entirely below ground level, and is distinct from a basement in that it is used only for storage, heating plant or purposes other than habitation.'
 Recent history
During Victorian and Edwardian times, with cheap labour available, basements were commonly constructed below buildings, but with the onset of the First World War, building rates fell dramatically. After the war the number of houses with servants fell so the requirement for additional accommodation was greatly reduced.
In the 1920s and 30s, with an improvement in public transport, more building land became available and therefore the need to construct basements below the ground almost disappeared.
It is now estimated that less than 2% of new properties are being constructed with basements. However, in cities, such as London, due to the demand for housing, the price of land and the cost of moving, basements are being constructed or converted for living space. This is causing concern in some areas where very large, multi-storey basements are begin constructed, which can cause significant disruption to neighbours over a long period.
See Planning (Subterranean Development) Bill and the Basement Excavation (Restriction of Permitted Development) Bill for more information.
 Benefits of basements
The potential benefits of basements include:
- An increase in floor area without an increase in the size of the footprint of a buildings or a significant impact on the size of the garden.
- An increase in space to support growing families without the need to move house.
- Semi-basements can make good use of sloping sites since constructing a basement will negate the requirement for levelling the site.
- If an existing house is located in a sensitive area, for example an Area of Outstanding Natural Beauty, where there are restrictions on development, the construction of a basement can allow the addition of extra space that would otherwise not be allowed.
- Houses with basements can have improved energy efficiency since the basement will have fewer exposed external walls.
 Downsides of basements
- The significant cost of excavation, working below ground in confined spaces and waterproofing.
- Disruption caused by excavation works.
- Difficulty providing natural lighting, ventilation, drainage, access and means of escape.
- There is the potential that waterproofing can fail, which can be difficult and costly to fix.
- It may be difficult to find consultants and contractors as they may be concerned about potential future litigation if the basement was to fail.
If there is an existing basement that is to be converted into residential space, it is unlikely to require permission. This is assuming that it is not separate to the main dwelling, the usage isn’t significantly changing and a light well is not being introduced.
If a new basement is to be created through excavations involving major work, the creation of separate accommodation or if the external appearance is altered, planning permission is likely to be required.
For works to a listed building, consent is likely to be required.
For any works to basements or the construction of new basements, building regulations are applicable and will cover areas including ventilation, drainage, ceiling heights, damp proofing, electrical wiring, water supplies, means of escape and so on. See building regulations for more information.
 Party Wall Act 1996
Where properties adjoin, there may be a mutual right of support for both land and buildings. This can apply to buildings that are joined, buildings that rely on the support of adjacent land, and to the land itself. This means that if works are carried out to land, buildings, retaining walls, excavations and so on, or if structures are demolished, the right of support of adjoining properties must be maintained.
See Right of support for more information.
Concerns about the disruption caused by the construction of basements, and the trend for ever larger 'iceberg' basements in cities such as London have resulted in attempts to introduce restrictions, such as the Basement Excavation (Restriction of Permitted Development) Bill and the Planning (Subterranean Development) Bill.
In August 2016, the City of Westminster introduced a new code of construction practice with an average levy of £8,000 on the construction of basements and a new ‘subterranean squad’ to help reduce the impact of basement construction works.
Deputy leader Robert Davis, said: “We are sticking up for local residents, many of whom have found the explosion of basement development in recent years hellish. It is right that those who want to build basements should contribute to this new service, which will work to help mitigate the negative impacts. Westminster City Council supports the right kind of growth and is not against all basement development, but they must be carried out in a way that is considerate to local residents and the environment.”
 Related articles on Designing Buildings Wiki.
- Basement excavation.
- Basement Excavation (Restriction of Permitted Development) Bill.
- Basement v cellar.
- Basement waterproofing.
- Building an extension.
- Building regulations.
- Crawl space.
- How to build a garage.
- How to build a porch.
- Planning (Subterranean Development) Bill.
- Planning permission.
- Right of support.
 External references
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