Light steel framing

6.10.20Cladding, lining and sheathing boards

Cladding panels, lining and sheathing boards shall be suitable for their intended purpose. Issues to be taken into account include:

  1. external cladding
  2. sheathing
  3. internal lining boards.

External cladding

The design and construction of the external walls should fully consider:

  • cavity drainage
  • differential movement
  • restraint
  • fire resistance.

In external walls, a clear cavity should be provided between the external insulation and the cladding. The cavity should:

  • be drained
  • have cavity trays and weep holes installed where the cavity is not fully maintained, e.g. at cavity barriers
  • be kept clean, free of obstructions and capable of draining freely
  • have drainage at its base, equivalent to 500mm2/m run, e.g. for masonry, one open perpend every 1.5m
  • have drainage openings placed to prevent the ingress of rain.

Masonry cladding should:

  • be constructed in accordance with Chapter 6.1 ‘External masonry walls’
  • not be supported by the LSF walls unless designed in accordance with Technical Requirement R5
  • be tied to the LSF walls with flexible wall ties fixed through to the studs
  • include movement joints as appropriate (e.g. a 1mm gap per continuous metre of vertical clay masonry should be provided at openings and soffits) to allow for differential movement due to thermal expansion, shrinkage (in concrete masonry) and moisture expansion (in clay) in accordance with PD 6697. The brick/block manufacturer’s advice should be sought on the level of movement to be expected.

Lightweight cladding should be:

  • in accordance with Chapter 6.9 ‘Curtain walling and cladding’
  • compatible with the LSF system construction
  • supported by systems assessed in accordance with Technical Requirement R3 which ensure that cladding design loads are effectively transferred to the building structure.


Sheathing boards should be:

  • of a suitable strength and quality
  • compatible with the steel frame
  • attached using suitable quality fixings.

Sheathing boards contribute to meeting many of the critical performance issues described in Table 7 and cannot be easily replaced, so they should be specified in accordance with the design life of the building.

Sheathing boards should be appropriate for the exposure of the building and suitable for use in humid conditions.

Table 10: Requirements for sheathing board materials

MaterialRelevant standardsMinimum thickness (mm)
Cement bonded particle boardBS EN 13986
BS EN 634
BS EN 12467
By design
Oriented strand board (OSB3 required)BS EN 3008.0
PlywoodBS EN 13986
BS EN 636
Proprietary materialsTechnical Requirement R3Technical Requirement R3

Fixings used to apply sheathing boards should be selected in accordance with the board manufacturer’s instructions and be suitably specified for strength and long-term durability in the anticipated exposure condition.

Sheathing boards should be adequately protected from weather during construction. This can be done through a combination of:

  • the use of water resistant boards with accredited proof of performance in accordance with Technical Requirement R3
  • the use of sealed jointed water resistant insulation to reduce water penetration
  • the application of a breathable membrane to the sheathing board
  • sequencing construction to minimise daily exposure with fully waterproof temporary coverings overnight and during inclement weather.

For all sheathing board types, junctions between adjacent boards, and at interfaces with other building elements, should be sealed and/or taped in accordance with the manufacturer’s recommendations.

A breather membrane should be used to provide protection to the building during and after construction in areas of very severe exposure to wind-driven rain.

Internal lining boards

Internal lining boards should be:

  • fixed in accordance with the design and the manufacturer’s recommendations
  • attached to light steel studs using self-drilling, self-tapping screws at a maximum of 300mm centres.

In addition to the general guidance for internal lining boards, plasterboard should:

  • be shown to provide adequate fire resistance where required
  • comply with BS EN 520 and be in accordance with Chapter 9.2 ‘Wall and ceiling finishes’
  • be a minimum of 9.5mm for stud spacing up to 450mm
  • be a minimum of 12.5mm for stud spacing up to 600mm.