External masonry walls


Cladding shall satisfactorily resist the passage of moisture and be of the quality, type and dimensions required by the design. Issues to be taken into account include:

  1. masonry cladding to framed structures
  2. joints
  3. moisture barriers
  4. materials for cladding
  5. vertical tile or slate cladding
  6. stone veneer cladding.

Masonry cladding to framed structures

Allowance should be made for differential movement between cladding and the frame. The following precautions should be taken to prevent buckling and fracturing of masonry panels:

  • Flexible movement joints should be provided at the underside of each horizontal support member.
  • The masonry outer leaf should have a minimum two-thirds of its width supported securely by the concrete frame or a metal angle.
  • Vertical movement joints should be provided at corners.
  • The inner leaf should be adequately tied to the structural frame.


Joints between claddings and adjacent materials should:

  • be detailed to be watertight under the particular exposure conditions of the site
  • have provision for differential movement, where necessary.

Moisture barriers

Moisture barriers should be:

  • provided between walls of solid masonry and any boarding, slating, tiling or other similar claddings (unless specifically not required for a proprietary cladding)
  • roofing underfelt or equivalent.

Vapour control layers, such as polyethylene sheet, are not an acceptable moisture barrier.

Materials for cladding

Table 8: Materials for cladding

Tiles and slatesBS 402, BS 473, BS 680Clay tiles for tile hanging, concrete tiles for tile hanging, slates for vertical slating.
Timber boardingBS 1186Timber should:
comply with, and be class 3 or better
be a naturally durable species or pretreated with preservative.
Underfelt behind claddingBS 747Type 1F felt is acceptable as an underfelt behind cladding.
BattensBattens should be:
of the size specified in the design
pretreated with preservative.
Proprietary cladding systems
Technical Requirement R3

Timber cladding should be in accordance with Chapter 3.3 ‘Timber preservation (natural solid timber)’

Vertical tile or slate cladding

Vertical tile or slate cladding should:

  • have each tile or slate fixed with two nails
  • be fixed using aluminium, copper or silicon bronze nails
  • be finished with an under-course and tilting batten at the bottom edges.

Stone veneer cladding systems

Stone veneer cladding systems should be in accordance with:

  • BS 8298 when mechanically fixed
  • Technical Requirement R3 when adhesive fixed
  • Chapter 6.9 when used as a brick slip / rainscreen system.