6.2 External timber framed walls

Also see:

6.2.15 Insulation

Insulation shall be correctly installed and provide suitable performance.

Insulation should be:

  • breathable, eg mineral wool (rock or glass), or
  • assessed in accordance with Technical Requirement R3 for use in timber frame wall panels.

Insulation should generally be placed within the stud void and cover the whole wall area between studs. No gaps should be left:

  • at corners
  • at junctions with partitions
  • against studs, rails or noggings
  • behind services and pattresss panels.

Water and heating services within walls should be on the warm side of the insulation.

Where insulation is to be installed to the external/cavity face of the frame:

  • it should be assessed in accordance with Technical Requirement R3 as an integral part of the wall system
  • a clear cavity should be provided, based on the dimensions set out in Table 2 in Clause 6.2.10, between the outer face of the insulation and the external cladding
  • a breather membrane should be installed to protect the timber frame wall and sheathing. A secondary breather membrane to protect the external insulation may be necessary depending on insulation manufacturer’s installation instructions and independent technical approval
  • stud locator marks should be transferred onto the outer face of insulation/external breather membrane (dependant on wall tie type and order of works)
  • wall ties should transfer loads directly to the timber frame studs and not via the insulation
  • the installation of lightweight cladding systems should be designed by a structural engineer to ensure adequate load transfer to the structural frame
  • cavity barriers should be installed to fully close the cavity, ensuring their performance is unlikely to be made ineffective by failure of the insulation.

Where insulation, either in the form of insulated plasterboard or a separate continuous layer, is to be installed to the inside face of the frame, the fire resistance of the wall should be in accordance with Clause 6.2.9 with appropriate supporting evidence.

Last updated: 2nd January 2024

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