Terraced houses on Blackhorse Road in Walthamstow with white rendered fronts, two-storey bay windows and low brick front walls
Floor plan drawings, pencil sketches of a house, a scale rule and a protractor spread across a desk
Photo: Tima Miroshnichenko / Pexels

Flood risk assessment · London Borough of Waltham Forest

Flood risk assessment in Waltham Forest, from £375 fixed

Waltham Forest's Policy 91 asks for a flood risk assessment in Flood Zones 2 and 3, and in Flood Zone 1 where the site has critical drainage problems or the use becomes more vulnerable, as in a house split into flats. It also wants sustainable drainage aiming at greenfield run-off, so we cover both.

Flood risk assessmentfrom £375
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A red clad outbuilding with a white window standing in brown floodwater among bare trees
Flood-resistant materials are specified to a height above the estimated flood level. Photo: Serge Lavoie / Pexels.

What Waltham Forest Council asks of a flood risk assessment

From the council's Local Plan Part 1, Policy 91 (Managing Flood Risk) (adopted 29 February 2024).

  • Policy 91 requires a site-specific flood risk assessment for all development in Flood Zones 2 and 3, and in Flood Zone 1 for sites of 1 hectare or more, changes of use to a more vulnerable class, or areas identified as having critical drainage problems. (source, checked 29 October 2026)
  • Assessments must give enough detail to assess the risk of flooding to and from the development from all sources, now and in the future, and should be proportionate to the expected degree of flood risk. (source, checked 29 October 2026)
  • The assessment must include flood-resistant design and construction, sustainable drainage, safe management of residual risk and emergency planning. (source, checked 29 October 2026)
  • Proposals should include sustainable drainage aiming for greenfield run-off rates, and where those rates cannot be achieved a payment in lieu will be secured to mitigate flood risk. (source, checked 29 October 2026)

What Waltham Forest flood risk assessment drawings have to show

In Waltham Forest the flood zones follow the River Lea and smaller rivers such as the Ching, but a critical drainage problem can bring an assessment anywhere. A house converted to flats counts as a change to a more vulnerable use, which also triggers one in Flood Zone 1.

We keep the assessment proportionate, as the policy asks, and show the drainage for the new roof and hard surfaces on the plans, since the council looks for run-off as close to greenfield as the site allows.

PS2 · at a glance

Waltham Forest: 771 householder decisions

Waltham Forest
Approvals, prior approvals included81.5%

628 of 771 granted. London: 85.8%.

Decided within 8 weeks90.1%

585 of 649 applications, prior approvals excluded.

Source: MHCLG PS2, 1 July 2025 to 30 June 2026. Dark tick: London.
Two hands holding a printed floor plan over a desk of drawings, with a pen and notebook beside it
Checking the drawings with you before anything goes to the council. Photo: Tima Miroshnichenko / Pexels.

What it costs in Waltham Forest

  • Flood risk assessment: from £375.

Flood risk assessment across London · Waltham Forest planning rules · every price

Flood risk assessment · Waltham Forest

What happens next in Waltham Forest

We check your address on every map the council uses, take the flood level with climate change, set the floor level and resilience measures, and mark them on the drawings.

Photo: Helena Jankovičová Kováčová / Pexels

Answers

Waltham Forest flood risk assessment questions

Do I need a flood risk assessment to convert a house to flats in Waltham Forest?
Possibly, even in Flood Zone 1. Policy 91 requires one for a change of use to a more vulnerable class, and in any area with critical drainage problems, as well as for everything in Flood Zones 2 and 3. Whether a particular conversion counts depends on its use class, which we check before quoting.
What does Waltham Forest expect on drainage?
Policy 91 says proposals should include sustainable drainage that aims for greenfield run-off rates, managing water as close to its source as possible. Where those rates cannot be achieved, the council secures a payment in lieu to mitigate flood risk, so we show the drainage approach on the drawings.

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Existing drawingsThe building as it stands
£175
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Proposed drawingsYour scheme, revised until right
£225
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Total, planning application£795
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