External timber framed walls

6.2.12Vapour control layers

Vapour control layers shall be installed correctly and restrict the passage of water from within the home to the timber frame.

Vapour control layers should be:

  • 500 gauge (125 micron) polyethylene sheet, vapour control plasterboard or a product assessed in accordance with Technical Requirement R3
  • adequately fixed to the warm side of the insulation and frame (framing timbers should have a moisture content of less than 20%)
  • placed to cover the external framed wall area, including rails, studs, reveals, lintels and sills
  • fixed at 250mm centres to the top and bottom of the frame, at laps and around openings
  • lapped with the DPC
  • made good where damage has occured.

Joints in vapour control membranes should:

  • have 100mm minimum laps
  • be located on studs or noggings.

Where vapour control plasterboard is used, joints should be:

  • positioned on studs or noggings
  • filled, taped and finished
  • cut with care to avoid displacing the vapour control material.