6.10 Light steel framed walls and floors

MATERIAL STANDARDS

6.10 - M1	Materials standards
6.10 - M2	Steel and fixings
6.10 - M3	Damp-proof courses
6.10 - M4	Wall ties and fixings
6.10 - M5	Sheathings
6.10 - M6	Breather membranes
6.10 - M7	Thermal insulation
6.10 - M8	Vapour control layers
6.10 - M9	Plasterboard
6.10 - M10	Cavity barriers and fire-stops
6.10 - M11	Floor decking

Materials that comply with the design and the guidance below will be acceptable for external and internal walls, and floors using light steel framing.

Materials for external and internal walls and floors using light steel framing 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).

STEEL AND FIXINGS

Items to be taken into account include:

(a) steel

Steel should be grade S280 or S350 to BS EN 10326. Grade S390 steel may be used if it has a nominal yield strength of 390N/mm² and meets the concepts of BS EN 10326.

To provide adequate protection against corrosion due to condensation and the environment, the steel should be pre-galvanised in accordance with BS EN 10326 to provide a minimum zinc coating of 275g/m².

Light steel floor joists and ring beams in ground floors should be galvanised to 460g/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 300mm adjacent to the support or ring beam.

(b) compatibility

Where two metals are to be joined they should be compatible and not cause bimetallic corrosion in that environment. Alternatively the two metals should be isolated from each other.

The choice of fixings needs to take account of bimetallic corrosion which can occur when two dissimilar metals are in contact.

(c) connectors

The following connectors are acceptable:

• zinc plated bolts should be in accordance with BS 4190
• countersunk bolts should be in accordance with BS 4933
• screws should be in accordance with BS 5427
• rivets should be in accordance with the manufacturer's recommendations
• self-piercing rivets should be in accordance with the manufacturer's recommendations
• ring shank nails should be in accordance with BS EN 10263
• welded connections should be in accordance with BS 5135. The welding wire should be in accordance with BS 2901.

Cleats should comply with the requirements of BS 5950.

(d) holding down devices

Holding down devices should be manufactured from mild steel with zinc coating to BS 729 or BS 1706 and be suitable for the environment they will be exposed to.

Holding down devices manufactured from stainless steel to BS EN 10095 will be suitable in any environment.

DAMP-PROOF COURSES

Materials which are acceptable for use as dpcs include:

• polyethylene to BS 6515
• bitumen to BS 6398
• proprietary materials assessed in accordance with Technical Requirement R3.

WALL TIES AND FIXINGS

For masonry claddings wall ties should be of austenitic stainless steel, phosphor bronze or silicon bronze. Materials for wall ties should be compatible. Stainless steel, phosphor bronze and silicon bronze are compatible with each other.

For other claddings, ties and fixings should be assessed in accordance with Technical Requirement R3.

SHEATHING

Cement bonded particle board sheathing should be in accordance with BS EN 634 and BS EN 13986.

Plywood sheathing should be:

• in accordance with BS 5268 Part 6
• WBP to BS EN 636
• at least 5.5mm thick
• appropriate to the exposure of the building.

Oriented strand board should be OSB3 to BS EN 300 and be at least 8mm thick.

Proprietary sheathing materials should be assessed in accordance with Technical Requirement R3 and used in accordance with the assessment.

BREATHER MEMBRANES

Breather membranes should be:

• vapour resistant to less than 0.6MNs/g when calculated from the results of tests carried out in accordance with BS 3177 at 25°C and relative humidity of 75%
• capable of resisting water penetration
• self-extinguishing
• durable
• adequately strong when wet to resist site damage
• Type 1 to BS 4016 in areas of Very Severe exposure.

THERMAL INSULATION

Insulation materials should be inert, durable, rot and vermin proof and should not be adversely affected by moisture or vapour.

The following materials are acceptable:

• mineral wool to BS EN 13162
• FR (flame retardant) grade expanded polystyrene to BS EN 13163
• FR (flame retardant) grade extruded polystyrene to BS EN 13164
• rigid polyurethane foam and polyisocyanurate to BS EN 13165
• phenolic foam to BS EN 13166
• cellular glass to BS EN 13167.

Other insulation materials should be assessed in accordance with Technical Requirement R3.

VAPOUR CONTROL LAYERS

Minimum 500 gauge polyethylene sheet or vapour control plasterboard should be used.

Vapour control products manufactured from recycled materials should be assessed in accordance with Technical Requirement R3.

PLASTERBOARD

Plasterboard should be to BS 1230. Plasterboard thickness should be not less than:

• 9.5mm for stud spacings up to 450mm
• 12.5mm for stud spacing up to 600mm.

To provide fire-resistance, fire-rated boards should be used and installed in accordance with the manufacturer's instructions.

CAVITY BARRIERS AND FIRE-STOPS

Materials specified in statutory requirements are acceptable.

Suitable fire-stopping materials include:

• mineral wool
• glass wool
• cement mortar
• gypsum plaster
• intumescent mastic or preformed strip
• proprietary sealing systems (particularly those designed for service penetrations) assessed in accordance with Technical Requirement R3 to maintain the fire resistance of the wall.

FLOOR DECKING

The following materials are acceptable:

• moisture-resistant chipboard Type P5 to BS EN 312
• oriented strand board Type OSB3 to BS EN 300
• plywood in accordance with BS EN 636.

Fixings and supports should be as recommended by the manufacturer.

Floor decking materials not covered by a British Standard should be assessed in accordance with Technical Requirement R3.