Building Regulations

NHBC Standards – 6 4 Timber and concrete upper floors

Chapter 6.4 This Chapter gives guidance on meeting the Technical Requirements and recommendations for the construction of timber and concrete upper floors (in houses) and separating floors (in flats).

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. The standards were originally written in 1992 when solid timber joists were the norm.  They now reflect the rise in popularity of l-joists and metal web joists. (NHBC Standards Extra, Issue 29, April 2004).

There have been issues with certain proprietary joists used over long spans, typically over 4.5m. where a floor may feel ‘bouncy’ when walked on.  Although there is no question of the floor being structurally inadequate, it can feel uncomfortable to a homeowner and not what they expected in their new home.  After discussions with representatives of the joist manufacturers, NHBC has decided to impose a limiting deflection of 0.003 times the span with a maximum of 12mm if strutting is not provided or 14mm if it is. (NHBC Standards Extra, Issue 29, April 2004).

Although this is in excess of what the British Standard design code currently says, NHBC have made representations to the BSI Committee responsible and is hopeful that the code will be amended with the same requirement. (NHBC Standards Extra, Issue 29, April 2004).

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

Section 6.4 Contents


•        Design Standard

•        Statutory requirements

•        Upper floor design

•        Structural timber

•        Trimmer joists

•        Strutting of floor joists

•        Joist hangers

•        Joist support at separating walls

•        Restraint strapping

•        Structural steel in floors

•        Fire spread

•        Floor decking

•        Concrete floors

•        Floors between dwellings

•        Provision of information


•        Materials standards

•        Timber floors

•        Joist hangers and restraint straps

•        Strutting

•        Floor decking

•        Sound insulation

•        Structural steel in floors

•        Concrete and reinforcement

•        Proprietary systems


•        Sitework standards

•        Timber floors

•        Joist hangers

•        Trimmed and trimming joists

•        Multiple joists

•        Strutting

•        Notching and drilling

•        Restraint strapping

•        Overlapping and butted joists

•        Floor decking: general

•        Softwood boarding

•        Chipboard flooring

•        Oriented strand board flooring

•        Plywood flooring

•        Other floor decking

•        Floors between dwellings

•        Concrete floors

•        In-situ concrete

•        Precast concrete

•        Firestopping


•        Statutory references


•        Span tables for timber floor joists


•        Protection from corrosion of metal components embedded in masonry



Chapter 6.4 (2003)

Amendments to the Standards (2003)

Source: NHBC Standards

            April 2004

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