Use of reinforcement to concrete toppings above beam and block floors - pragmatic guidance and extended transitional provisions

The use of beam and block suspended concrete floors in residential construction has become common practice. More recently, in order to achieve adequate levels of thermal insulation, the use of EPS/XPS blocks together with a reinforced concrete topping or screed has grown.

In Technical Extra 15, published in October 2014, we included guidance on acceptable uses of this type of construction. Technical Extra 20, dated April 2016, reinforced the guidance and re-stated our position. However, it's become apparent that further clarity is required on the use of fibre reinforced concrete toppings when used in this location as it would appear that the guidance previously provided has not been fully implemented.

As part of an industry-wide collaboration on suitable structural toppings British Precast have prepared a draft Application Guide for the design and installation of beam and block suspended ground floors. The Guide (to be published shortly) includes in its draft form descriptions of concrete reinforcement products for various applications; polypropylene micro-fibre for non-structural applications and polypropylene macro-fibre, steel fibre and welded steel fabric for structural applications, in line with NHBC's 'Guidance on the use of reinforcement to concrete toppings above beam and block floors', which can be found on our website via the link, below.

Concurrently, beam and block floor manufacturers' 3rd party certificates are being amended to include the output from the industry collaboration, including suitable fibre reinforced concrete topping specifications that can be justified by acceptable design methodology

This work is nearing completion, although the supporting documentation has not yet been published and is therefore not available for use. But in recognition of this work moving forward and applying a pragmatic approach NHBC has agreed to extend the transition period until 1 October 2017 to enable this work to be completed in line with the agreed schedule for publication of the design and application guides by the concrete industry.

As previously, during this extended transition period remedial work necessary to comply with NHBC Standards will only be required where there are visible defects in construction. NHBC building inspectors will however be strongly encouraging the use of the guidance below and 'observation' notes will be entered into Site Record Books to confirm discussions of this nature with site managers.

Issued 4 July 2017

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