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:
- structural elements
- timber separating walls
- timber quality.
6.3.5.1 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.
6.3.5.2 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.
6.3.5.3 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 2025