Internal walls

Also see:

6.3.5Load-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:

  • individual studs, sills and headplates 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
  • lintel and cripple studs should be provided to each opening, except when the stud spacing is unaffected
  • multiple joists should be supported by multiple 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, e.g. by the use of a continuous top binder.

Timber separating walls

The type and spacing of wall ties and straps should limit sound transmission across the cavity in accordance with building regulations.

Wall ties 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 should be of a suitable grade and specified according to the strength classes in BS EN 338, e.g. C16 or C24. When graded to BS 4978:

  • the species should be included in accordance with BS EN 1912 or the class strength specified
  • BS EN 338 can be used to determine strength class.

Timber should have a maximum moisture content of 20%.

Structural softwood for internal use should be:

  • dry graded to BS 4978
  • marked ‘DRY’ or ‘KD’.

Timber for walls which are to be dry-lined should be regularised and comply with BS 8212. Finger joints should comply with BS EN 15497.