Concrete Toppings

Structural concrete topping

The concrete topping thickness and reinforcement specification shall be determined in accordance with BS EN 1992-1-1⁸ by a qualified structural engineer

The concrete topping shall be according to BS 8500-1¹¹, BS 8500-2¹² and BS EN 206¹⁰, manufactured in plants covered by the QSRMC scheme (Quality Scheme for Ready Mixed Concrete) and laid by personnel with the appropriate skills and experience;

The specifications in Table 2 are suitable for single-family self-contained dwelling units and communal areas in blocks of flats with the characteristic imposed loads defined in Table 4;

The concrete specifications in Table 3 are suitable for commercial buildings with the characteristic imposed loads defined in Table 5.

*NOTE: NHBC do not accept micro-fibre structural concrete toppings

Table 2 – Concrete topping specifications for single-family self-contained dwelling with the characteristic imposed loads given in Table 4

Overall concrete thickness above the services (mm) Grade Maximum aggregate size (mm)

Type

See also NHBC
Guidance note³⁵

Reinforcement Specifications³⁰
65-75 C28/35 10 Self-compacting micro-fibre*  (Class I) Fibrin XT Ultra (0.9 kg/m³), Fibrin 23 (0.9 kg/m³); or similar approved
65-75 C28/35 10 Self-compacting macro-fibre (Class II) Durus S400 (4.0 kg/m³)  Novomesh B&BA (macro, 3.33 kg/m³), Durus Easy Finish (3.0 kg/m³); or similar approved
65-75 C25/30 20      Standard        micro-fibre* (Class I) Fibrin XT Ultra (0.9 kg/m³), Fibrin 23 (0.9 kg/m³); or similar approved
65-75 C25/30 20    Standard      macro-fibre (Class II) Durus S400 (4.0 kg/m³)  Novomesh B&BA (macro, 3.33 kg/m³), Durus Easy Finish (3.0 kg/m³); or similar approved
65-75 C25/30

 

C28/35

          20            Standard

 

10 Self-compacting

Conventional 1 layer of A142 steel mesh to BS 4483 with a characteristic yield strength of (fyk) 500 N/mm²; nominal cover to reinforcement shall be 35 mm
65-75 C25/30

 

C28/35

         20            Standard

 

10 Self-compacting

Steel Fibre Adfil SF86 (13.33 kg/m³), Novomesh B&BA (steel, 15.0 kg/m²); or similar approved

Table 3 – Concrete topping specifications for commercial buildings with the characteristic imposed loads given in Table 5

Thickness (mm) Grade Maximum aggregate size (mm) Type Reinforcement
65-75 C25/30 10 Self-levelling self-compacting concrete Steel mesh1)
65-75 C28/35 20 Conventional Steel mesh1)

1) Structural mesh should be sized and designed according to BS EN 1990⁵, BS 1991-1-1⁷ and BS EN 1992-1-1⁸ and their UK National Annexes

Table 4 – Imposed and partition loads for concrete topping reinforced with macro-polymer fibres and steel mesh A142 (kPa)

Description Characteristic value of loads for single-family dwellings Characteristic value of loads for communal areas in blocks of flats
Imposed uniformly distributed load (kPa) 1.5 3.0
Imposed concentrated load (kN) 2.0 4.0
Line load partition, parallel and perpendicular to the beam (kN/m) 4.0 5.0
Allowance for moveable partition (kPa) 1.0 1.0

Table 5 – Imposed and partition loads for commercial buildings and concrete topping reinforced with steel mesh

Description Characteristic values of loads
Imposed UDL (kPa)
Imposed concentrated load (kN)
5.0
4.5
Line load partition parallel and perpendicular to the beam (kN/m) 5.0
Allowance for moveable partition (kPa) 1.0
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