Light steel framed walls and floors

6.10

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:

external cladding
sheathing
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

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

Material	Relevant standards	Minimum thickness (mm)
Cement bonded particle board	BS EN 13986 BS EN 634 BS EN 12467	By design
Oriented strand board (OSB3 required)	BS EN 300	8.0
Plywood	BS EN 13986 BS EN 636	5.5
Proprietary materials	Technical Requirement R3	Technical 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.