6.3 Internal walls

Also see:

2.16.29.2

6.3.5 Load-bearing timber walls

Internal load-bearing timber walls shall be designed to support and transfer loads to foundations safely and without undue movement. Issues to be taken into account include:

  1. structural elements
  2. timber separating walls
  3. timber quality.

Structural elements#

Structural design of load-bearing timber walls should be in accordance with BS EN 1995-1-1.

When constructing structural elements:

  • the underside of the lowest sole plate should be positioned at or above internal finished floor level, see Figure 8
  • individual studs, rails and head binders should be 38mm x 75mm minimum, although larger sizes may be required to achieve an adequate level of fire resistance
  • studs should be spaced at a maximum of 600mm centres
  • mid height noggings should be installed when required for additional stiffness
  • lintels and cripple studs should be provided to each opening, except when the stud spacing is unaffected
  • multiple studs should be included to support multiple joists, beams, girder trusses and other point loads, unless otherwise specified by the designer
  • where a head binder is not provided, joists, roof trusses and other similar loads should bear directly over studs
  • framing joints should be secured with a minimum of two nails per joint
  • where internal walls are made up from panels, structural continuity should be maintained, eg by the use of a continuous head binder.

Twin leaf timber separating walls#

The type and spacing of wall straps should limit sound transmission across the cavity in accordance with Building Regulations.

Wall straps should:

  • be specified in accordance with the system designer’s recommendations
  • have a maximum cross-section of 40mm x 3mm
  • be fixed below ceiling level
  • be spaced a minimum of 1.2m horizontally.

Timber quality#

Timber should be of the appropriate grade, moisture content and size to support the imposed loads.

Structural timber components should be of a suitable strength class, as specified by the designer to BS EN 338. Solid structural timber should be:

  • machine graded to BS EN 14081, or visually graded to BS 4978 for softwoods or BS 5756 for hardwoods
  • assigned a strength class based on BS EN 1912 when visually graded
  • dry graded
  • marked in accordance with BS EN 14081.

Further guidance on strength classes for certain timber species can be found in PD 6693.

Engineered wood products such as I-section or metal-web studs should be assessed in accordance with Technical Requirement R3.

Timber should have a maximum moisture content of 20% at the time of dry lining to minimise shrinkage.

Last updated: 2nd January 2024

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