Wandsworth, London
Basement impact assessments in Wandsworth
Wandsworth writes its basement limits into the local plan as numbers: one storey, half the rear garden, a metre of soil on top and flood-zone restrictions. A basement impact assessment in Wandsworth therefore starts by testing your idea against those lines. We coordinate the report on a fixed quote after a free constraints check.
Fixed quote after a free constraints check
- MCIAT chartered
- £2m PI insured
- LABC Partnered
- Fixed fees, VAT included
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How we work on basement impact assessments
Seven steps from first call to approval.
Enquiry and constraints check
We check the property against conservation areas, listed status, Article 4 directions, tree preservation orders, flood zone and planning history. We choose the right route and send a fixed quote.
Measured survey
We survey the house on one datum: rooms, levels, boundaries, drains, trees and the neighbours' windows that the 45° and 25° tests depend on.
Design options
We model the house in Revit and show you options in 3D and plan, with the planning strategy and the precedents in your street.
Design frozen
You choose an option in writing. Nothing changes after this without your say.
Independent check
A second chartered technologist checks every sheet against the council's validation checklist and the policy. A senior review signs it off before anything is submitted.
Submission
We prepare the forms, certificates, fee and documents and submit through the Planning Portal.
Officer liaison
We answer the planning officer and make any amendments within five working days, at no charge until approval.
Free redraws until approval. Every drawing set is checked independently, and the checker is never the person who drew it.
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Basement impact assessment in Wandsworth: the limits one by one
The Wandsworth Local Plan 2023-2038, adopted in 2,023, puts the basement test in its design policy. The rule in one line is: 1 storey; 50% garden; 1 m soil + 200 mm drainage layer. Spelled out, a new basement or an extension to one is allowed only if it is no more than a single storey, sits under no more than half the existing rear garden or other undeveloped garden area, and leaves naturally draining soil and a drainage layer above any part beneath a garden.
Two further tests follow. In a conservation area a lightwell must keep at least half of the original front garden depth, or a fixed minimum depth if that is greater. The scheme must also not increase flood risk, and a positively pumped device or equivalent has to guard against sewer flooding.
These are tests we can check before the engineer is appointed, which is why the free check includes a measured look at the garden. A plot that fails the half-garden line on a map will not pass because the report is long.
Local figures for Wandsworth
| Measure | Value | Period | Source |
|---|---|---|---|
| LP6: a new basement or basement extension is permitted only where it is no more than one storey; residential basements extend under no more than 50% of the existing rear garden or other undeveloped garden area; lightwells in conservation areas keep at least 2 m or 50% (whichever is greater) of original front garden depth; at least 1 m of naturally draining permeable soil plus a 200 mm drainage layer sits above any part under a garden; no increase in flood risk; and a positively pumped device (or equivalent) guards against sewer flooding. | 1 storey; 50% garden; 1 m soil + 200 mm drainage layer | — | wandsworth.gov.uk, Wandsworth Local Plan 2023-2038 (adopted 19 July 2023), LP6 criteria A.1-A.8, printed p.294 (PDF p.296); paras 14.43-14.45, printed p.294-295 |
| LP12 Table 15.2: basements are restricted by flood zone and breach hazard; in Flood Zone 3b basements are not permitted. Where acceptable, access thresholds and staircases must be at least 300 mm above the 1 in 100 fluvial level including climate change allowance, and basements in surface-water risk areas need mitigation such as raised thresholds or storage. | 300 mm above 1 in 100 + climate change level | — | wandsworth.gov.uk, Wandsworth Local Plan 2023-2038 (adopted 19 July 2023), LP12 Table 15.2, printed p.311-313 (PDF p.313-315) |
| Local plan | Wandsworth Local Plan 2023-2038 | — | wandsworth.gov.uk |
| Conservation areas | 46 named conservation areas published by the council | — | planning.data.gov.uk |
| Listed building entries | 312 list entries (Historic England, within the LPA boundary) | — | planning.data.gov.uk |
| Households living in a house | 31.4 % of households living in a house or bungalow (detached, semi-detached or terraced) | Census 2021 | nomisweb.co.uk |
| Domestic gardens share of land (GLUD 2005) | 21.5 % of land that is domestic garden (GLUD 2005) | 2005 | data.london.gov.uk |
| Householder applications granted | 91.9 % | 1 July 2025 - 30 June 2026 | assets.publishing.service.gov.uk |
| Borough CIL residential rate | £1,031.39/m² (Nine Elms Residential Area A); £475.34/m² (Nine Elms Residential Area B); £0 (Roehampton Charging Area); £448.43/m² (all other areas) | rate for 2026 (schedule rates £575 / £265 / £0 / £250) | wandsworth.gov.uk |
| Party Wall etc. Act 1996 s6(1): excavation within 3 m horizontally of an adjoining owner's building or structure and deeper than the bottom of its foundations | 3 m | — | legislation.gov.uk |
A blank value means the figure has not been published, not that there are none. Check your own address with the council.
Which application your project needs
The usual route for a house; flats and listed buildings follow other rules.
- A · Lawful Development Certificate decision
- 8 weeks
- B · Prior approval decision
- 42 days
- C · Householder decision
- 8 weeks
Flood zones and the threshold height
The flood policy sets a second layer: 300 mm above 1 in 100 + climate change level. Basements are restricted by flood zone and breach hazard, and are not permitted at all in the functional floodplain. Where one is acceptable, the access threshold and staircase must sit above the design flood level, and basements in surface-water risk areas need mitigation such as raised thresholds or storage.
Low-lying streets near the river are where this bites. We read the flood map first and give you the answer before any survey costs are spent.
A borough of heritage and garden squares
Wandsworth has 46 conservation areas, 312 listed entries and 9 registered parks and gardens. Only 31.4 per cent of households live in a house, so basements are likely to sit beneath terraces and converted houses, and gardens cover 21.5 per cent of the land.
The council's Basement extensions guidance (non-statutory) sits beside the plan. Our planning drawings in Wandsworth show the lightwell depths and garden coverage against each criterion on the sheet.
Decisions, levy and party walls
The council decided 977 householder applications in its latest year, granted 91.9 per cent and decided 92.4 per cent on time. Levy depends on location: the borough schedule runs from £1,031.39/m² (Nine Elms Residential Area A); £475.34/m² (Nine Elms Residential Area B); £0 (Roehampton Charging Area); £448.43/m² (all other areas).
A party wall notice is required for excavation within 3 metres of a neighbour's building below its foundations, and within 6 metres on the diagonal test. Our structural calculations in Wandsworth page covers the engineering.
Testing a plot against the criteria
Our free check works as a test of the plot. We measure the rear garden, mark half of its undeveloped area, and draw a section that shows the soil over the roof of the basement and the drainage layer within it. We also draw the front garden with the depth a lightwell must leave, and mark the flood zone from the borough's mapping.
If the plan fails a criterion, we say which one and by how much, and offer a smaller version that passes: a shallower floor, a shorter footprint, or a basement stepped away from the garden. The aim is a design that can be reported on without asking the council to relax its own limits.
Cost and next steps
The scope depends on the flood zone, the garden and the depth, so there is no list price. The free check gives you a fixed quote, and we say plainly if a plan breaks one of the limits.
See architectural drawings in Wandsworth, compare Lambeth and Merton, or read the national basement impact assessment guide.
What you receive
Related pages
Other services in Wandsworth
Basement impact assessments nearby
Questions
How big can a basement be in Wandsworth?
One storey, under no more than half the existing rear garden, with naturally draining soil and a drainage layer above any part under a garden.
Can I build a basement in a flood zone in Wandsworth?
Restricted by zone and breach hazard, and not permitted in the functional floodplain. We check the flood map first.
What about the front lightwell in a conservation area?
It must keep at least half the original front garden depth, or a fixed minimum depth if that is greater.
How much does it cost?
A fixed quote after a free constraints check, because garden, flood zone and depth change the scope.
Sources and dates
- wandsworth.gov.uk, retrieved
- wandsworth.gov.uk, retrieved
- planning.data.gov.uk, retrieved
- planning.data.gov.uk, retrieved
- nomisweb.co.uk, retrieved
- data.london.gov.uk, retrieved
- assets.publishing.service.gov.uk, retrieved
- wandsworth.gov.uk, retrieved
- legislation.gov.uk, retrieved
- planning.data.gov.uk, retrieved
- wandsworth.gov.uk, retrieved
- legislation.gov.uk, retrieved
- legislation.gov.uk, retrieved
- legislation.gov.uk, retrieved
- Contains public sector information licensed under the Open Government Licence v3.0.
- Contains OS data © Crown copyright and database right 2026.
- Contains HM Land Registry data © Crown copyright and database right 2026. This data is licensed under the Open Government Licence v3.0.
- Contains Historic England data © Historic England 2026. Contains Ordnance Survey data © Crown copyright and database right 2026.
Tell us about your property.
We check the constraints, then send a fixed fee. Messages before 3pm get a reply the same working day.