Building Regulations

NHBC Standards – 7 1 Flat roofs and balconies

Chapter 7.1 This Chapter gives guidance on meeting the Technical Requirements and recommendations for flat roofs and balconies, and pitched roofs with a fully supported continuous weatherproof membrane.

NHBC Standards do not cover aspects of health and safety relating to building operations and to the handling and use of certain building materials. Such matters are covered by statutory requirements.

This version of the Standards has been updated to include the Amendments to the Standards April 2004. Changes include the following:


The use of timber in the construction of balconies is now limited.  This is to address the possibilities of serious injury occurring when materials have been used which have proved not to be sufficiently durable. 

In future, timber should not be used for:

•        Gallows brackets supporting a balcony

•        Posts of columns supporting a balcony

•        Guard rails or their support

However, timber will still be permitted for secondary elements such as:

•        Open balcony constructions with timber decking.  The decking may be supported on solid timber treated joists which in turn are supported by materials or components other than timber

•        Ballustrading.

(NHBC Standards Extra, Issue 29, April 2004).

Flat roofs

How flat is a flat roof? For many years, NHBC Standards have recommended a 1:40 fall to flat roofs.

This figure has been amended to take account of British Standards and many BBA Certificates which refer to a finished fall of 1:80.  Particularly with flat roofs using timber joists, the design fall should be 1:40 to be reasonably certain that the finished fall will be at least 1:80. (NHBC Standards Extra, Issue 29, April 2004).

Previous versions of the standards can be accessed in the Archive section (below).

Section 7.1 Contents


•        Design Standard

•        Statutory requirements

•        Loadbearing structure

•        Principles of design

•        Flat roof decking

•        Thermal insulation

•        Weatherproofing and surface finishes

•        Rainwater drainage

•        Guarding to balconies

•        Access for maintenance

•        Provision of information


•        Materials standards


•        Sitework standards

•        In-situ reinforced concrete

•        Precast concrete

•        Timber

•        Joist hangers

•        Falls

•        Decking

•        Thermal insulation and vapour control layers

•        Weatherproofing

•        Guarding to balconies

•        Protection of materials from weather


•        Statutory references


•        Commonly used flat roofs


•        Surface treatments acceptable to NHBC


•        Construction details of flat roofs and balconies



Chapter 7.1 (2003)

Amendments to the Standards (2003)

Source: NHBC Standards

            April 2004

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