6.10 Light steel framed walls and floors


This Chapter gives guidance on meeting the Technical Requirements and recommendations for light steel framed walls and floors.


6.10 - D1 Design standards
6.10 - D2 Statutory requirements
6.10 - D3 Steel and fixings
6.10 - D4 Loadbearing walls
6.10 - D5 Non-loadbearing walls
6.10 - D6 Moisture control and insulation
6.10 - D7 Exterior cladding
6.10 - D8 Floors
6.10 - D9 Services
6.10 - D10 Acoustic performance
6.10 - D11 Control of fire
6.10 - D12-D13 Provision of information
6.10 - D14 Certification

6.10 - D1

Design shall meet the Technical Requirements

Design that follows the guidance below will be acceptable for external and internal walls, and floors using light steel framing.

This Chapter only applies to light steel framing, typically 0.45 to 3.2mm thick, as described and illustrated. Construction should be 'warm frame' with sufficient insulation outside the steel envelope to ensure that condensation does not fall within the depth of the light steel members.

For dwellings that incorporate loadbearing light steel framed walls and/or floors, both system and project certification will be required in accordance with Appendix 6.10-A.

For the purpose of this Chapter, non-loadbearing walls are those not designed to carry the principal dead and imposed loads or provide the overall stability for the building. In some circumstances (e.g. external infill walls) they will carry wind loads.

If the light steel framing is of a novel construction, not shown in this Chapter, NHBC will require assessment in accordance with Technical Requirement R3.

This Chapter does not apply to light steel framed external walls used in basements.


6.10 - D2
Design shall comply with all relevant statutory requirements

Design should be in accordance with relevant Building Regulations and other statutory requirements.


6.10 - D3
Steel and fixings shall be suitable for the design and adequately protected against corrosion

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 with the concepts of BS EN 10326.

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

(b) compatibility

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

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

(c) connections

Light steel components should be securely fixed together by bolting, welding, riveting, clinching, crimping, screwing or nailing.

Connections using these techniques should be justified either by design to BS EN 1993-1-3 or an appropriate test acceptable to NHBC.


6.10 - D4
Loadbearing walls incorporating light steel members shall be designed to support and transfer loads to foundations safely and without undue movement

Items to take into account include:


The structural design of loadbearing steel framed walls should be in accordance with BS EN 1993-1-3.

design loadings

The building should be designed to resist loadings in accordance with BS EN 1991-1-1, BS EN 1991-1-3 and BS EN 1991-1-4 including:

  • dead loads
  • imposed loads
  • wind loads.
  • snow loads
structural elements

Individual studs should not be less than 36mm wide, spaced at not more than 600mm centres, unless agreed with NHBC and other support is provided for wall boards and fixings.

A lintel should be provided to any opening in loadbearing panels where one or more studs is cut or displaced to form the opening. A lintel is not required where an opening falls between studs.

Lintel above window opening

Additional studs may be required at openings for fixing ties or supports for the cladding.

Multiple studs should be included to support multiple joists unless otherwise specified by the designer.

Lintels should be securely fixed to supporting studs to ensure that loads are transferred properly.

Where panels are diagonally braced with flat strip it should be fixed to each stud at the intersection to minimise the bow in the bracing member.

joints between panels and other elements

The design should detail how wall panels are to be securely fixed:

  • to the substructure
  • to adjacent panels
  • to the floor and roof framing.

Account should be taken of uplift forces and, where necessary, proper holding down devices should be provided to resist uplift. The anchorage for holding down devices should have sufficient mass to resist the uplift forces.

Timber wall plates should be fixed to the head rail of wall panels onto which timber roof trusses bear. The timber wall plate and head rail should be sized to permit single timber trusses to be positioned at any point between studs.


Wall panels may provide resistance to racking forces using one or more of the following techniques:

  • internal bracing
  • crossed flat bracing
  • internal sheathing board
  • external lining board
  • rigid frame action.

Methods adopted should be justified either by design to BS EN 1993-1-1 or tested to BS EN 594.


6.10 - D5
Non-loadbearing walls incorporating light steel members shall have adequate strength and support

Items to take into account include:

(a) construction

The following form of construction is acceptable:

  • light steel partitions using studs, head and base rails from sections not smaller than 43mm x 32mm x 0.45mm
  • stud spacings to suit the thickness of plasterboard, as follows:
    - not more than 450mm spacing for 9.5mm boards
    - not more than 600mm spacing for 12.5mm or thicker boards.

(b) movement joints

Non-loadbearing walls should not bridge movement joints in the main structure.

A joint should be constructed between the frame and any chimney or flue to prevent load transfer onto the chimney or flue.

(c) support

Non-loadbearing walls should be supported from the structural floor, not by a floating floor that incorporates a compressible layer, unless the floating floor is specifically designed for that purpose.

Allowance should be made for the possible deflection of floors at the head of non-loadbearing walls to prevent the wall becoming loadbearing.

Support where wall is parallel and between joists

Support where floor or beam is above wall


6.10 - D6
Wall designs shall ensure that the structure is adequately protected from the effects of moisture

Items to be taken into account include:

provision of dpcs and dpms

Dpcs should be installed beneath and for the full width of the lowest section of framing (e.g. all ground floor walls and internal partitions) to protect the steel from corrosion due to moisture. The dpc should be wide enough to lap with the dpm.

Dpcs and trays should be provided at openings to prevent rain penetration.


Breather membranes and other barriers, where provided, should be lapped so that each joint is protected and moisture drains outwards.

cavities in external walls

A clear cavity should be provided to reduce the risk of rain penetrating to the frame. The following minimum cavity widths, measured between the claddings and sheathings, should be provided:

Cladding Cavity width
Masonry 50mm nominal
Render on backed lathing 25mm nominal
Vertical tile hanging without underlay No vertical cavity required when a breather membrane is provided
Other cladding* 15mm nominal

* see Chapter 6.9 'Curtain walling and cladding'

The cavity should extend at least 150mm below the dpc and be kept clear to allow drainage. Weep holes or other suitable means of drainage should be provided where necessary to prevent water build up in the cavity.

insulation and interstitial condensation

The BRE Report 'Thermal insulation: avoiding risks' discusses aspects of insulation relevant to external light steel framed walls. In England and Wales account should be taken of Accredited Details for Part L.

A vapour control layer should be provided unless a condensation risk analysis in accordance with BS 5250 shows that one is not necessary. The vapour control layer should be fixed on the warm side of the wall insulation.

The vapour control layer should cover the external wall including base rails, head rails, studs, lintels and window reveals.

Vapour control layers should be of 500g polyethylene or vapour control plasterboard.

Insulation should continue 150mm below the base rail of the steel wall to minimise thermal bridging.

Insulation with an integral facing on one side only, e.g. a foil facing, should have the facing on the cavity side. The facing should not be used as the vapour control layer.

Service pipes, conduits, etc within walls should be on the warm side of the insulation.


6.10 - D7
Exterior cladding shall be compatible with the steel frame

Items to be taken into account include:

(a) wall ties

Wall ties for masonry claddings should be:

  • of a type which accommodates differential movement between the light steel frame and the cladding - see clause D7(c) below
  • fixed through to the studs, not the sheathing
  • installed at a minimum density of 3.7 ties/m2 e.g. spaced at a maximum of 600mm horizontally and 450mm vertically (see Sitework clause 6.10 - S5)
  • spaced at jambs of openings a maximum of 300mm vertically within 225mm of the masonry reveal. Additional studs may be needed to achieve this
  • inclined away from the light steel framing.

(b) masonry claddings

Soft joints should be provided to allow for differential movement. A gap of 1mm per metre of masonry should be provided at openings and soffits.

Compressible joint to be 1.0mm thick per metre of masonry to allow for vertical movement

(c) other claddings

For other claddings reference should be made to Chapter 6.9 'Curtain walling and cladding' (Design and Sitework).


6.10 - D8
Suspended floors shall be designed to support and transmit loads safely to the supporting structure without undue deflection

Items to be taken into account include:

dead and imposed loads

Floors should be designed to resist loading in accordance with BS EN 1991-1-1 including:

  • dead loads
  • imposed loads.

Information concerning balcony loading is given in Chapter 7.1 'Flat roofs and balconies' (Design and Sitework).

joist spacing

Steel joists should be spaced at centres not greater than 600mm.


The in-service performance of light steel joists should be controlled by four serviceability criteria:

Static criteria:

i) the maximum deflection for a single joist due to imposed load should be limited to span/450

ii) the maximum deflection for a single joist due to dead and imposed loads should be limited to the lesser of span/350 or 15mm.

Dynamic criteria:

iii) the natural frequency of the floor should be limited to 8Hz for dead load plus 0.2 x imposed load. This can be achieved by limiting the deflection of a single joist to 5mm for the given loading

iv) the deflection of the floor (i.e. a series of joists plus the floor decking) when subject to a 1kN point load should be limited to the following values:

Span (m) Max. deflection (mm)
3.5 1.7
3.8 1.6
4.2 1.5
4.6 1.4
5.3 1.3
6.2 1.2

The deflection of a single joist is dependent on the overall floor construction and the number of effective joists that are deemed to share the applied 1kN point load. The following table gives typical values:

Floor configuration Number of effective joists

Joist centres

400mm 600mm
Chipboard, plywood or oriented
strand board
2.5 2.35
Built-up acoustic floor 4 3.5


attachment to supporting structure

Light steel joists should be fixed to supporting walls by web cleats, direct attachment to wall studs, or by bearing onto the supporting structure. In the latter configuration, bearing stiffeners may be required.

prevention of roll

Floors constructed using joists with an asymmetric web (e.g. of 'C' or Sigma profile) can cause the floor to 'roll'. To avoid this, one of the following alternatives should be used where the span exceeds 3.5m for 'C' joists or 4.2m for Sigma joists:

  • a continuous line (or lines) of proprietary steel herringbone struts provided between the joists. The pairs of struts should have a physical gap between them so that they do not rub against each other at the cross-over point and create noise

    a continuous line (or lines) of proprietary steel herringbone struts provided between the joists

  • solid blocking provided to every third pair of joists with ties between them

    solid blocking provided to every third pair of joists with ties between them

  • joists alternately reversed and tied together in pairs

    joists alternately reversed and tied together in pairs

  • joists alternately reversed and continuous ties (e.g. resilient bar) fixed to the joist flanges.

    joists alternately reversed and continuous ties (e.g. resilient bar) fixed to the joist flanges

floor decking

The correct thickness of decking should be specified for the joist centres used.

The thickness should be not less than those shown in this table for normal domestic loads, i.e. an imposed load of 1.5kN/m2.

Floor decking
Thickness of decking [mm]

Joist centres

400mm 600mm
Chipboard 18 22
Plywood 15 18/19
Oriented strand board 15 18/19


Oriented strand board should be laid with the stronger axis at right angles to the supports. Other decking materials not listed in the table should comply with Technical Requirement R3. The above thicknesses may not be adequate to achieve a mass for floor decking of 15 kg/m2 for sound insulation requirements of floors in England & Wales.

The floor deck is generally used as a diaphragm and, to achieve this, floor boarding should be attached using self-drilling, self-tapping screws, ring shank nails or other approved fixings at 300mm maximum centres. T&g joints should be glued.


Suitably sized trimmers should be provided around floor openings.

notching and holing

The flanges of light steel joists should not be notched except to accommodate connections.

Drilling or punching through the web should only be carried out within recognised limits (see Sitework clause 6.10-S11).

ground floors

Light steel joists used in ground floor construction should have thermal insulation positioned to ensure that condensation does not form on the joists.

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 300mm adjacent to an external wall support or ring beam.

resistance to ground moisture

Provision should be made to prevent ground moisture affecting light steel floors.

This can be achieved by either:

  • 50mm concrete or 50mm fine aggregate on a polyethylene membrane laid on 50mm sand blinding, or
  • 100mm concrete.

Where necessary, oversite concrete should be protected against sulfate attack by the use of a polyethylene sheet dpm, not less than 1200 gauge (0.3mm) (or 1000 gauge if assessed in accordance with Technical Requirement R3), properly lapped.

ventilation of underfloor voids

A minimum ventilation void of 150mm should be provided below the floor.

On shrinkable soils where heave could take place, an allowance for movement should be added to the underfloor ventilation requirement to determine the minimum dimension of the floor void. The allowance for movement relates to the shrinkage potential of the soil as follows:

  • high potential - 150mm
  • medium potential - 100mm
  • low potential - 50mm.

Voids should be ventilated by openings providing not less than either 1500mm2 per metre run of external wall or 500mm2 per m2 of floor area, whichever gives the greater opening area.

Every part of the void under the floor should be thoroughly ventilated through openings on at least two opposite sides.


6.10 - D9
Services shall be adequately protected from damage

Cutting of service holes on site should be avoided since badly cut edges can have an adverse affect on the durability of the frame and may cause damage to pipes and cables.

Grommets should be used around the edge of service holes to protect electrical cables and reduce the risk of bimetallic corrosion. Swagged holes for electric cables and plastic piping do not require grommets.

Service mains and service outlets should be designed to ensure the fire resistance of walls and floors is not impaired.

In Scotland, services are not permitted within framed separating walls.


6.10 - D10
Internal walls and floors shall be designed to adequately resist the passage of sound

Designs should be in accordance with relevant Building Regulations and other statutory requirements.


6.10 - D11
Walls and floors shall resist the spread of fire

All structural elements should have adequate fire resistance.

Items to be taken into account include:

(a) ceilings

Ceilings should provide the necessary fire protection to floors constructed with light steel joists. Either one or two layers of plasterboard are required and at least one of these should be fire-rated. When two layers of board are used, joints should be staggered between layers. Boards should be attached using self-drilling, self-tapping screws.

(b) cavity barriers

Cavity barriers should be provided in accordance with relevant Building Regulations.

Horizontal cavity barriers (except under eaves) should be protected with a dpc tray. The tray should have a minimum upstand of 100mm. Alternatively polyethylene encased cavity barriers providing a minimum upstand of 100mm should be used.

(c) fire-stops

Fire-stops should be provided in accordance with relevant Building Regulations.


6.10 - D12
Designs and specifications shall be produced in a clearly understandable format and include all relevant information

For light steel framed walls and floors, the following information should be available:

  • relevant drawings
  • materials specification
  • fixing schedules
  • fixing details
  • manufacturers' recommendations relating to proprietary items.

The information should be in a form suitable for the use of site operatives and be available on site before and during construction.

Assembly instructions should allow for every structural connection made on site including fixing details for framing, wall ties and should show as appropriate:

  • number and spacing of bolts, screws and rivets
  • size and type of each fixing type, including corrosion protection.
6.10 - D13
All relevant information shall be distributed to appropriate personnel

Ensure that design and specification information is issued to site supervisors and relevant specialist subcontractors and/or suppliers.

Where proprietary products are to be used, manufacturers usually have specific requirements for fixing and/or assembly of their products. This information should also be made available for reference on site so that work can be carried out satisfactorily in accordance with the design and specification.

Copies of the assembly instructions should be given to the person doing the job.


6.10 - D14
Design of the superstructure shall be checked by an NHBC steel frame certifier

The specific project details should be checked by an NHBC steel frame certifier so that a certificate can be issued in accordance with Appendix 6.10-A. The project certificate should be made available on site for inspection by NHBC.