Light steel framed walls and floors

6.10

6.10.11Moisture control

The structure shall be adequately protected from the effects of moisture. Issues to be taken into account include:

  1. cavities in external walls
  2. DPCs, DPMs and cavity trays.

Cavities in external walls

A clear cavity should be provided to reduce the risk of rain penetrating the frame.

The minimum cavity widths (measured between the claddings and sheathings) to suit the cladding type should be provided in accordance with Table 6.

Table 6: Minimum cavity widths

CladdingCavity width
Masonry50mm nominal
Render on backed lathing 25mm nominal
Vertical tile hanging without underlay No vertical cavity required where a breather membrane is provided
Other cladding(1)15mm nominal

Notes

1 See Chapter 6.9 ‘Curtain walling and cladding’

The cavity should:

  • extend at least 150mm below the DPC
  • be kept clear to allow drainage
  • be provided with weep holes or other suitable means of drainage where necessary.

DPCs, DPMs and cavity trays

DPCs, DPMs and cavity trays should:

  • be provided at openings to prevent rain penetration
  • be installed underneath the full width of the lowest section of framing, e.g. all ground floor walls and internal partitions, to protect the steel from corrosion due to moisture
  • be wide enough to lap with the DPM.

Materials acceptable for use as DPCs include:

  • BS 6515 polyethylene
  • BS 6398 bitumen
  • materials assessed in accordance with Technical Requirement R3.