Light steel framing

6.10.7Steel and fixings

Steel and fixings shall be suitable for the intended use. Issues to be taken into account include:

  1. steel grade
  2. protection against corrosion
  3. connections and fixings
  4. holes and notches.

Steel grade

Steel should be in accordance with BS EN 10346 and of any of the following grades:

  • S280
  • S320
  • S350
  • S390
  • S420
  • S450.

Protection against corrosion

All steel should be pre-galvanised in accordance with BS EN 10346 (minimum 275g/m2 zinc coating (Z) or 150g/m2 aluminium-zinc alloy coating (AZ)). Structural steel members should not be altered without the approval of the designer. Welded zones should be cleaned and treated with a zinc-rich paint to prevent corrosion.

The junction between the ground floor joists and their support should be designed to maintain the durability of the floor. Light steel floor joists and ring beams in ground floors should be galvanised to 450g/m2.

Alternatively, they can be galvanised to 275g/m2 with additional protection of a two-coat bitumen-based coating to BS 1070, BS 3416 or BS 6949, or have a two-coat liquid asphaltic composition applied. Ring beams to ground floors should be totally protected, and joists protected for a minimum of 300mm adjacent to an external wall support or ring beam.

Where steel is used less than 150mm above ground level, the guidance in Clause 6.10.16 should be considered.

Connections and fixings

Where two metals are to be joined, they should either be:

  • compatible and not cause bimetallic corrosion, or
  • isolated from each other.

Connections should be:

  • properly installed
  • securely made by clinching, crimping or by one of the methods detailed in Table 4
  • justified in accordance with BS EN 1993-1-3 or a test method acceptable to NHBC.

Table 4: Types of connections

Type of connectionRelevant standard
CleatsBS EN 1993-1-1
Countersunk bolts (tightened to the correct torque)BS 4933
Hot-dip galvanised fastenersBS EN ISO 10684
Rivets, including self-piercing rivetsManufacturer’s recommendations
ScrewsBS EN ISO 10666
BS EN ISO 15480
BS EN ISO 15481
BS EN ISO 15482
BS EN ISO 15483
(also see BS EN ISO 4042)
Welded connectionsBS EN 1011 and BS EN 1090
Zinc-plated boltsBS 7371-3

Holding-down devices

Holding-down devices should be suitable for the environment they will be exposed to, and manufactured from:

  • mild steel with zinc coating to BS EN ISO 1461
  • stainless steel to BS EN 10095 (suitable for most environments).

Holes and notches

Joists and studs should not be altered without the approval of the steel frame designer, and the drilling, cutting or punching through of members shall only be undertaken to an engineer’s design in accordance with Technical Requirement R5.

To prevent damage to services, holes and penetrations should be fitted with grommets or swaged under factory conditions.

End notching of light steel joists may be required for the interconnection of trimming joists and should be in accordance with the design. Notches elsewhere in the span are not acceptable.

Also see Clause 6.10.22.