Publishing and copyright information

The BSI copyright notice displayed in this document indicates when the document was last issued.

© The British Standards Institution 2025

Published by BSI Standards Limited 2025

ISBN 978 0 539 29851 2

ICS 91.060.20

The following BSI references relate to the work on this document:
Committee reference B/546
Draft for comment 25/30484498 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 December 2025. It was prepared by Technical Committee B/546, Flexible sheets for waterproofing and water vapour control. A list of organizations represented on this committee can be obtained on request to the committee manager.

Supersession

This British Standard supersedes BS 6229:2018, which is withdrawn.

Relationship with other publications

This British Standard is intended to be read in conjunction with BS 5250, BS 8000‑4 and BS 8233.

Information about this document

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

roof falls to achieve drainage;
thermal performance of inverted warm roof systems; and
fire performance, including fire classification of roof system.

Product certification. Users of this British Standard are advised that when selecting materials to consider the desirability of third-party certification of product conformity to this British Standard.

This publication can be withdrawn, revised, partially superseded or superseded.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 code of practice, this British Standard takes the form of recommendations and guidance. It is not to be quoted as if it were a specification. Users are expected to ensure that claims of compliance are not misleading.

Users may substitute any of the recommendations in this British Standard with practices of equivalent or better outcome. Any user claiming compliance with this British Standard is expected to be able to justify any course of action that deviates from its recommendations.

It has been assumed in the preparation of this British Standard that the execution of its provisions will be entrusted to appropriately qualified and experienced people, for whose use it has been produced.

Copyright is claimed on the data in Table A.2. Copyright holders are Met Office (2019): Met Office MIDAS Open: UK Land Surface Stations Data (1853-current). Centre for Environmental Data Analysis, Cited December 2025. http://catalogue.ceda.ac.uk/uuid/dbd451271eb04662beade68da43546e1

Presentational conventions

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

Commentary, explanation and general informative material is presented in smaller italic type, and does not constitute a normative element.

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.

1 Scope

This British Standard gives recommendations for the design, construction, care and maintenance of roofs with a flat or curved surface, at a pitch not greater than 10° to the horizontal, with a continuously supported flexible waterproof covering. The supporting structure of such roofs is either dense and heavy (such as a concrete slab), or consists of framing members supporting a lightweight deck of metal or of timber-based material.

NOTE Provided that the design conditions are similar, many of the recommendations contained in this code of practice apply to roofs at pitches greater than 10° and to those designed with multi-functional finishes.

This British Standard is intended for use by surveyors, architects, system designers, principal contractors, contractors and clients.

This British Standard does not apply to cold stores where the roof is directly over the conditioned space and high temperature enclosures.

2 Normative references

3 Terms and definitions

3.3 Boards

3.5 Condensation

3.9 Fall(s)

3.11 Flat roof

3.12 Gutter

3.14 Layers

3.21 Support(ing) structure

4 Design

4.1 General design considerations

4.2 Types of flat roof system

4.3 Structure

4.4 Roof falls to achieve drainage

4.5 Rainwater disposal

4.6 Thermal performance

4.7 Control of condensation

4.8 Sound attenuation

4.9 Fire safety

4.10 Surface protection of the waterproof layer

4.11 Rooftop components and installations

5 Materials

5.1 General

5.2 Roof slab/deck materials

5.3 Screeds

5.4 Waterproof layers

5.5 Thermal insulation

5.6 Air and vapour control layer(s) (AVCL)

5.7 Breather membranes (Vapour permeable membranes)

6 Exchange of information and project schedule

6.1 Exchange of Information

6.2 Project schedule

7 Workmanship

8 Care and maintenance

8.1 Owner's building information manual

8.2 Inspections

8.3 Maintenance procedures

8.4 Renewal/modification/change of use

Bibliography

BS 6229:2025

Flat roofs with continuously supported flexible waterproof coverings – Code of practice

Current

Published:

16 Dec 2025