NHBC Standards 2006

6.4 Timber and concrete upper floors

MATERIALS STANDARDS

6.4 - M1Materials standards
6.4 - M2-M4Timber floors
6.4 - M5Joist hangers and restraint straps
6.4 - M6Strutting
6.4 - M7Floor decking
6.4 - M8Sound insulation
6.4 - M9Structural steelwork in floors
6.4 - M10Concrete and reinforcement
6.4 - M11Proprietary systems

6.4 - M1
All materials shall:
(a) meet the Technical Requirements
(b) take account of the design
 

Materials that comply with the design and the guidance below will be acceptable for timber and concrete upper floors.

Materials for timber and concrete upper floors should comply with all relevant standards, including those listed below. Where no standard exists, Technical Requirement R3 applies (see Chapter 1.1 'Introduction to the Standards and Technical Requirements').

References to British Standards and Codes of Practice include those made under the Construction Products Directive (89/106/EEC) and, in particular, appropriate European Technical Specifications approved by a European Committee for Standardisation (CEN).

TIMBER FLOORS

6.4 - M2
Structural timber shall be of the appropriate grades and sizes to support the imposed loads
 

Structural timber should be specified according to the strength classes in BS 5268-2. It is insufficient to specify timber using the BS 4978 (incorporating the requirements of BS EN 518) grading rules (eg GS or SS) unless the timber species is also specified so that the strength class can be determined.

Finger joints should comply with BS EN 385.

Where possible, regularised timber should be used for joists.

I-joists and metal web joists should be assessed in accordance with Technical Requirement R3.

6.4 - M3
Structural timber shall be of suitable durability, particularly in conditions where it could become damp
 

Timber that is built into solid external walls or embedded should be pre-treated with preservative. Reference should be made to Chapter 2.3 'Timber preservation (natural solid timber)' (each section) for recommended methods of preservative treatment.

Any timber treated with preservative and cut after treatment should be given two liberal applications of a suitable colour tinted preservative to the cut surfaces.

6.4 - M4
Structural timber shall have a suitable moisture content
 

Structural softwood for internal use should be dry graded to BS 4978 or BS EN 519 and marked 'DRY' or 'KD'.

JOIST HANGERS AND RESTRAINT STRAPS

6.4 - M5
Hangers and straps shall be of appropriate types and strength and shall have adequate durability
 

Joist hangers to BS EN 845-1 are acceptable. It is important that joist hangers are the correct size for the timber joist or trimmer.

Where joist hangers are required to resist tensile forces, a joist hanger complying with the requirements of BS 5628-1 Appendix C or proprietary joist hangers that have been assessed in accordance with Technical Requirement R3 should be used.

Restraint straps should have a cross-section of at least 5 x 30mm or be proprietary restraint straps assessed in accordance with Technical Requirement R3 and be protected in accordance with the requirements of BS 5628-3. Tables 1 and 2 of Appendix 6.4-B list suitable materials and protective finishes. The size of nails or screws should be specified for fixing restraint straps to joists.

STRUTTING

6.4 - M6
Strutting shall ensure adequate rigidity of the floor structure
 

Timber strutting should be either:

  • herringbone strutting at least 38mm x 38mm, or
  • solid strutting at least 38mm thick and at least three-quarters the depth of the joist.

Proprietary metal strutting should have been assessed in accordance with Technical Requirement R3.

Thin metal strip is not acceptable as strutting.

FLOOR DECKING

6.4 - M7
The type and thickness of the decking material shall have adequate strength and moisture resistance
 

The following materials are acceptable:

  • softwood boarding in accordance with BS 1297
  • moisture-resistant chipboard, Type P5 to BS EN 312. Ring shank nails (length 2½ x decking thickness) or screws should be specified for fixing chipboard
  • oriented strand board Type OSB3 to BS EN 300
  • plywood in accordance with BS EN 636. Fixings and support should be as recommended by the manufacturer
  • floor decking materials not covered by a British Standard should have been assessed in accordance with Technical Requirement R3.

Some decking materials require their joints to be glued together and glued to joists (see Sitework clauses 6.4 - S19 and S20).

SOUND INSULATION

6.4 - M8
Materials and systems for floating floors, including insulation materials, shall be of a type that will provide adequate sound insulation
 

Details of materials and systems for floating floors should be in accordance with Chapter 8.3 'Floor finishes' (each section).

Materials and systems should comply with relevant Building Regulations.

STRUCTURAL STEELWORK IN FLOORS

6.4 - M9
Steelwork shall be suitably durable and be of the appropriate section to support the imposed loads
 

Structural steel should be in accordance with Chapter 6.5 'Steelwork support to upper floors and partitions' (each section), or be designed by an Engineer in accordance with Technical Requirement R5.

Steel beams should be protected by a suitably durable paint coating as detailed in Chapter 8.5 'Painting and decorating' (each section). Intumescent paints should be compatible with paints providing corrosion protection.

CONCRETE AND REINFORCEMENT

6.4 - M10
Concrete shall have appropriate reinforcement and be of a mix design that is suitable for the location and intended use
 

For guidance on the specification and use of concrete, concrete additives and reinforcement, reference should be made to Chapter 2.1 'Concrete and its reinforcement' (each section).

PROPRIETARY SYSTEMS

6.4 - M11
Proprietary concrete flooring systems shall have adequate strength and durability
 

Proprietary concrete flooring systems should be designed in accordance with BS 8110, or should have been assessed in accordance with Technical Requirement R3.