01Barnet, London
Basement drawings to Barnet's extension guidance
Barnet gives basements numbers: single storey; 3 m / 3.5 m / 4 m; 50% of garden length. Front lightwells are limited to 1 m deep; half the width. We draw to those limits from £1,995 including VAT, so the application is checked against the guidance before it reaches the council.
From £1,995 (VAT included)
- MCIAT chartered architectural technologists
- £2m professional indemnity insurance
- LABC Partnered
- ICO registered
02The brief
The numbers in the extension guidance
The council's extension guidance, the Sustainable Design and Development Guidance SPD, Part 4: Guidance on residential extensions and alterations, sets the envelope for a rear basement: single storey; 3 m / 3.5 m / 4 m; 50% of garden length. The three figures are the projection beyond the rear wall for terraced, semi-detached and detached houses, and the last is the share of the garden length that may be excavated.
A semi-detached house therefore has a different limit from its terraced neighbour, which is why we measure the garden and the rear wall before sketching a plan.
03The record
Local figures for Barnet
| Measure | Value | Period | Source |
|---|---|---|---|
| Basements should be a single storey and project no more than 3 metres (terraced), 3.5 metres (semi-detached) or 4 metres (detached) beyond the rear wall, excavating no more than 50% of the rear garden length. | single storey; 3 m / 3.5 m / 4 m; 50% of garden length | No period | barnet.gov.uk, SDDG SPD Part 4 (extensions), p.27, paras 4.106-4.107, 4.111 |
| Front lightwells should be no more than half the width of the house and project no more than 1 metre from the front wall; a self-contained basement dwelling is unacceptable. | 1 m deep; half the width | No period | barnet.gov.uk, SDDG SPD Part 4 (extensions), p.27, paras 4.105, 4.108, 4.119 |
| Approved Document B Vol 1, para 2.16 | Basement storeys with habitable rooms need an escape window or external door, or a protected stair to a final exit | No period | gov.uk |
| Party Wall etc. Act 1996 s6(1), s6(2), s6(5) | Adjacent excavation notice at least 1 month before work: within 3 m and deeper than the neighbour's foundations, or within 6 m and cutting a 45° line from their foundations | No period | legislation.gov.uk |
| Householder: alterations/extensions to a single dwellinghouse, from 1 Apr 2026 | 548 GBP | No period | ribblevalley.gov.uk |
| Domestic gardens share of land (GLUD 2005) | 28.1 % of land that is domestic garden (GLUD 2005) | 2005 | data.london.gov.uk |
| Green Belt share of the council area | 28 % of council area covered by green-belt polygons | No period | planning.data.gov.uk |
| Listed building entries | 651 list entries (Historic England, within the LPA boundary) | No period | planning.data.gov.uk |
A blank value means the figure has not been published, not that there are none. Check your own address with the council.
04The streets
Householder applications by street in Barnet
| Street | Applications | Approved |
|---|---|---|
| Wolmer Gardens | 42 | 82% |
| Hampden Way | 36 | 86% |
| Oakleigh Park South | 36 | 77% |
| Marsh Lane | 35 | 91% |
| Millway | 34 | 93% |
| Sturgess Avenue | 34 | 94% |
| Uphill Road | 32 | 73% |
| Chanctonbury Way | 31 | 90% |
| Oakleigh Road North | 30 | 79% |
| Woodlands | 30 | 76% |
| Laurel Way | 29 | 76% |
| Mount Pleasant | 28 | 80% |
| Arlington Road | 27 | 80% |
| Berkeley Crescent | 27 | 100% |
| Longland Drive | 27 | 100% |
Counts of householder applications by street; no individual applications are shown. Streets with fewer than five applications are left out.
05The drawing
A basement in section
A house and garden over a single-storey basement. The lettered marks show the limits the legend gives.
- A Barnet: depth and garden share
- single storey; 3 m / 3.5 m / 4 m; 50% of garden length
- B Barnet: excavation depth
- 1 m deep; half the width
- C Party wall notice for excavation
- Adjacent excavation notice at least 1 month before work: within 3 m and deeper than the neighbour's foundations, or within 6 m and cutting a 45° line from their foundations
- D Escape from basement rooms
- Basement storeys with habitable rooms need an escape window or external door, or a protected stair to a final exit
06The detail
Front lightwells and self-contained basements
At the front the guidance says: 1 m deep; half the width. It also treats a self-contained basement dwelling as unacceptable, so a basement here is an extension of the house above, with internal access.
Escape is the other front-of-house question. Basement storeys with habitable rooms need an escape window or external door, or a protected stair to a final exit. We dimension the lightwell and the window or door that serves it.
Large gardens and where they meet other controls
Domestic garden makes up 28.1% of the borough's land in the GLA's Generalised Land Use Database. A long garden helps the garden-length test, but a house near the Green Belt, which covers 28% of the borough, is read against that setting too.
A basement under a listed house also needs consent, and the borough holds 651 list entries and 16 conservation areas. The listed building consent drawings for Barnet explain that route, and architectural drawings in Totteridge show how a conservation area and Green Belt combine.
Neighbours and fees
Excavation next to a neighbour's foundations needs a party wall notice. Adjacent excavation notice at least 1 month before work: within 3 m and deeper than the neighbour's foundations, or within 6 m and cutting a 45° line from their foundations. The council's householder fee is £548, separate from our fee.
A roof storey on the same house is a different application, covered by mansard roof drawings in Barnet. The basement conversion drawings hub lists the full route.
07The papers
What the drawings rest on
Party wall services
08Correspondence
Questions
How far can a basement extend beyond the back of a Barnet house?
The extension guidance sets single storey; 3 m / 3.5 m / 4 m; 50% of garden length. The distances differ for terraced, semi-detached and detached houses, so we confirm yours from the survey.
Can I have a lightwell at the front?
Yes, within the guidance limit: 1 m deep; half the width. If the front basement room is habitable, the lightwell often carries its escape window.
Can a basement become a separate flat?
Not under this guidance, which calls a self-contained basement dwelling unacceptable. A basement is an extension of the house above.
28.1%
of land that is domestic garden (GLUD 2005)
Domestic gardens share of land (GLUD 2005), Barnet, 2005. Source: data.london.gov.uk
09Further reading
Related pages
Other services in Barnet
10Sources
Sources and dates
- barnet.gov.uk, retrieved
- gov.uk, retrieved
- legislation.gov.uk, retrieved
- ribblevalley.gov.uk, retrieved
- data.london.gov.uk, retrieved
- planning.data.gov.uk, retrieved
- planning.data.gov.uk, retrieved
- barnet.gov.uk, retrieved
- planning.data.gov.uk, retrieved
Licences
- Contains public sector information licensed under the Open Government Licence v3.0.
- Contains OS data © Crown copyright and database right 2026.
- Contains Historic England data © Historic England 2026. Contains Ordnance Survey data © Crown copyright and database right 2026.
- GLA Planning London Datahub, householder applications. Contains public sector information licensed under the Open Government Licence v3.0.
Send us the address of your house.
We look up the conservation area, listing and Article 4 position, then reply with a fixed fee. A message before 3pm is answered the same working day.