Publishing and copyright information

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© The British Standards Institution 2025

Published by BSI Standards Limited 2025

ISBN 978 0 539 18556 0

ICS 91.010.01; 13.200; 91.120.99

The following BSI references relate to the work on this document:
Committee reference CB/501
Draft for comment 24/30441030 DC

Foreword

Publishing information

This British Standard is published by BSI Standards Limited, under licence from The British Standards Institution, and came into effect on 31 March 2025. It was prepared by Technical Committee CB/501, Flood risk and watercourses. A list of organizations represented on this committee can be obtained on request to the committee manager.

Supersession

This British Standard supersedes BS 85500:2015 , which is withdrawn.

Information about this document

This is a full revision of the document, and introduces the following principal changes:

makes reference to, and is consistent with, the CIRIA Code of practice for property flood resilience [1];
includes a comprehensive list of the impacts of flood water on all materials and building elements;
includes more detailed guidance, supported by engineering drawings for new and retrofit resilient designs; and
benefits from the increased attention to property resilience promoted by the Property Resilience Roundtable.

This publication can be withdrawn, revised, partially superseded or superseded. Information regarding the status of this publication can be found in the Standards Catalogue on the BSI website at knowledge.bsigroup.com, or by contacting the Customer Services team.

Where websites and webpages have been cited, they are provided for ease of reference and are correct at the time of publication. The location of a webpage or website, or its contents, cannot be guaranteed.

Use of this document

As a guide, this British Standard takes the form of guidance and advisory recommendations. It is not to be quoted as if it were a specification or a code of practice.

Presentational conventions

The guidance in this document is presented in roman (i.e. upright) type. Any recommendations are expressed in sentences in which the principal auxiliary verb is “should”.

Additional commentary, explanation and general informative material is presented in smaller italic type.

Where words have alternative spellings, the preferred spelling of the Shorter Oxford English Dictionary is used (e.g. “organization” rather than “organisation”).

Contractual and legal considerations

This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

This publication is provided as is, and is to be used at the recipient’s own risk.

The recipient is advised to consider seeking professional guidance with respect to its use of this publication.

This publication is not intended to constitute a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

Introduction

National and local planning policies discourage inappropriate development in areas at risk of flooding. This British Standard does not promote development in flood risk areas but provides guidance on reducing the potential consequences where buildings are located in an area at risk of flooding.

This British Standard is intended to help manage residual risk after other measures or approaches, such as avoiding risk, locating development in an area of low risk or raising floor levels, have been implemented.

1 Scope

This British Standard gives guidance on how to improve the resilience of buildings through the consideration of resistance and recoverability to reduce the impacts of flooding from all sources, using suitable materials and construction details. Specifically, it provides guidance on:

assessing options for flood resilient measures, following a comprehensive flood hazard assessment and building survey; and
the design and specification of flood resilience for new buildings, extensions, conversions and retrofits.

The guidance covers the main types of building construction in the UK, for which experiential and other evidence is available. This British Standard is intended to be consistent with and complementary to the CIRIA Code of practice for property flood resilience [1] (see 4.2 ). It necessarily cannot cover all construction types and materials, and so additional guidance would need to be sought for any examples not covered in this British Standard.

It is not applicable to:

the detailed structural engineering;
the site layout of buildings;
the specification, fixing and deployment of flood resistance products, which are covered by other standards and documents, such as the BS 851188 series and Delivering benefits through evidence: Temporary and demountable flood protection guide [2];
the design of watertight concrete, which is specified in BS EN 1992‑1‑1 ;
amphibious or floating properties;
properties on stilts; or
avoidance measures outside the perimeter (footprint) of the building, such as local land raising above the predicted flood level.

2 Normative references

3 Terms and definitions

4 Resilient design process

4.1 Definition of resilience

4.2 CIRIA Code of Practice scheme delivery process

4.3 Flood characteristics and hazard assessments

4.4 Building surveys and design reviews for new builds

5 Impacts of flooding on buildings

5.1 General

5.2 Flood characteristics

5.3 Building characteristics (form and elements)

5.4 Impact of flooding on building materials

6 Design strategies

6.1 General

6.2 Opportunities for incorporating flood resilience

6.3 Planning policy and other statutory requirements

6.4 Other factors

6.5 Site layout and wider environmental factors

6.6 Factors for including resistance

6.7 Factors for including recoverability

7 New build

7.1 Detailed design

7.2 Detailed design considerations of new build elements affected by flooding

8 Retrofit

8.1 Retrofit construction details

8.2 Detailed design guidance

9 Doors, windows and air vents

9.1 General

9.2 External doors

9.3 Internal doors

10 Fixtures and fittings

11 Services

11.1 General

11.2 Pipework

11.3 Drainage services

11.4 Electrical services

11.5 Heating systems

11.6 Communications wiring

12 Other issues

12.1 Workmanship

12.2 Sustainability

Bibliography

BS 85500:2025

Flood resilient construction. Improving the flood performance of buildings. Guide

Current

Published:

27 Mar 2025