How to design a flood resilient building


Accounting for flood risk in the design stage of a development project is imperative.

Six of the ten wettest years on record in the UK have occurred in the last 25 years and half of 2022’s top ten most fatal natural disasters were floods.

As a result of the ongoing acceleration of greenhouse gas emissions, we are experiencing a climate breakdown that is engendering heavier rainfall patterns and rising sea levels – both of which are big contributors to increased flood risk.

Adapting to more extreme conditions can only be achieved through forward-thinking design which finds proactive solutions to improve a development’s flood resilience.

Why should architects use flood risk assessments?

Assessing the flood risk of a site is one of the most important stages of the planning process.

If the proposed development is located within flood zones 2 or 3, or on sites of 1 hectare or greater in flood zone 1, a flood risk assessment must be carried out to identify how the building and occupants will be impacted and how the building will impact the flood risk in the surrounding area, with mitigation measures suggested to reduce risks to an acceptable level. 

These reports are critical to designing flood resilient structures; they take climate change factors into account and suggest measures to manage the different types of flood risk affecting a site.

Given the uniqueness of each location, the insight supplied by these reports will also ensure technical drawings are tailored to the topography which surrounds the building.

How do sustainable drainage systems improve flood resilience?

With flood risks identified, the next stage of planning is to determine how they will be mitigated in the building’s design.

This will depend on what variant of flood risk(s) is impacting the site – areas affected by coastal flooding will require a different approach to those susceptible to groundwater or river flooding.

One of the most effective and agreeable measures to manage flood risk is the incorporation of sustainable drainage systems (SuDS).

Beneficial to the development, local communities and the environment, SuDS are increasingly the go-to measure for controlling flooding and will become a mandatory inclusion for new developments in 2024, following the government’s implementation of Schedule 3.

When it comes to designing a flood resilient building, this is the first water exclusion strategy architects should consider; SuDS are capable of absorbing or storing water from different flood sources before it can even reach the property.

A sustainable drainage report will help architects to evaluate what type of SuDS suit the site and whether they can discharge water into nearby watercourses or sewers.

The outcomes of this report can be reinforced with a detailed drainage design which will provide calculations and drawings of pipe dimensions and levels and gradients to illustrate how appropriate SuDS can be included.

Additional measures for flood resilient design

In instances where a site is located in a flood zone 2 or 3, SuDS may not sufficiently reduce flood risk alone and the building itself may require adaptation to prevent the introduction of flood water.

This is a vital consideration given the extensive harm flooding can cause.

In his acclaimed publication, Retrofitting for Flood Resilience: A Guide to Building & Community Design (RIBA, 2020), architectural expert Edward Barsley outlines how flood water often swells, distorts and delaminates materials as well as irreparably damaging electrics and wiring.

“The hydrostatic and dynamic loads in these contexts can [also] cause structural failure, particularly when supplemented with impact from debris,” the specialist in environmental design in architecture added.

“Scouring and erosion can undermine foundations, and buoyancy forces can cause whole properties to be displaced.”

So, what can be done to mitigate these possible outcomes?

Depending on the level of flood risk, site topography and planning authorities, there are several measures which can be taken. These include:

  • Reinforcement of doors and windows
  • Elevation of property off the ground
  • Use of flood resistant materials
  • Basement tanking
  • Installation of sump pumps or foundation vents
  • Build permanent flood defences

How can GeoSmart support flood resilience?

Flood risk assessments, sustainable drainage strategies and detailed drainage designs are pivotal to the design process and will support the development of safer, flood resilient buildings.

To request one of our reports or speak to a member of our specialist team, get in touch