Use of reinforcement to concrete toppings above beam and block floors
The use of beam and block suspended concrete floors in residential construction has been common practice for over 25 years, particularly for low-rise residential buildings. Beam and block ground floor systems are typically constructed using EPS (polystyrene) or concrete blocks supported by pre-stressed concrete beams. EPS blocks can assist in achieving adequate levels of thermal insulation. Beam and block floor systems are completed with a concrete structural topping when non-loadbearing blocks are used, or non-structural screed where blocks are loadbearing.
As part of an industry-wide collaboration on suitable structural toppings British Precast have prepared a Design Guide and an Application Guide for beam and block suspended ground floors. The guides accord with NHBC's 'Guidance on the use of reinforcement to concrete toppings above beam and block floors', accessed via the link below.
Beam and block floors incorporating non-loadbearing blocks
Where non-loadbearing blocks are used (e.g. EPS grade R1 or concrete blocks with a compressive strength < 7.3N/mm2) floor systems require a structural concrete topping. Macro-polypropylene and steel fibres can provide suitable reinforcement to structural concrete toppings and may be considered as an alternative to traditional welded steel mesh, provided that the topping is designed in accordance either with acceptable third party assessment for the floor system, or with the design methodology and equations given in the British Precast Design Guide. In either case, fibres are to be used in accordance with the manufacturer’s instructions.
Beam and block floors incorporating loadbearing blocks
Where load-bearing blocks are used (e.g. EPS grade R2 or concrete blocks with a compressive strength ≥ 7.3N/mm2) floor systems can be finished using a non-structural screed to level the surface ready to receive a floor covering. Micro-polypropylene fibres may be suitable for use in non-structural screeds.
Micro-polypropylene fibres will not be acceptable for use as reinforcement in structural toppings on homes covered by NHBC warranty where the foundations are begun on or after 1 January 2018.
Between now and 1 January 2018, remedial work on suspended beam and block floors 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 Book to confirm discussions of this nature with site managers.
Issued 27 September 2017DOWNLOAD THE GUIDANCE (PDF)
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