Curtain walling and cladding

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6.9.19Insulated render and brick slip cladding

Insulated render and brick slip cladding shall be designed and installed to ensure adequate in-service performance. Issues to be taken into account include:

  1. weather resistance
  2. thermal bridging and condensation
  3. air infiltration
  4. insulated render: reinforcement and render
  5. brick slip cladding: slips, carriers and joints.

Weather resistance

Timber and steel framed backing walls should have a cavity between the wall and the insulation which is:

  • a minimum of 15mm wide
  • drained and vented (for timber frame)
  • drained (for steel frame).

A cavity can increase the risk of damage from impact, especially at low level, around balconies and where cradle systems etc. can come into contact with the façade. Suitable precautions to resist impact damage should be provided e.g. by the provision of a rigid board behind the insulation whilst maintaining the cavity.

The following illustrations show typical interfaces and general design principles:

Movement joints in the backing wall should be:

  • continued through the insulated render system
  • formed in accordance with the manufacturer’s recommendations.

Thermal bridging and condensation

The system should:

  • be designed to minimise the risk of thermal bridging, surface and interstitial condensation
  • be assessed using a suitable condensation risk analysis
  • generally include a vapour control layer, fixed to the warm side of the wall insulation.

Air infiltration

Before installation of the system, the backing wall should be reasonably airtight with:

  • masonry walls jointed to a high standard, i.e. each joint filled
  • each joint taped or sealed on framed walls, including a rigid sheathing on the cavity face.

Insulated render: reinforcement and render

Reinforcement should:

  • be detailed in the design and be in accordance with the manufacturer’s recommendations
  • be formed with appropriate trim at openings, corners, angles, interfaces and movement joints
  • include additional mesh where there may be increased stress in the render system, i.e. at the corners of window or door openings
  • be lapped to a minimum of 100mm.

Render should:

  • not be applied where the surface has contamination, dust or loose particles
  • have the appropriate number and thickness of coats in accordance with the manufacturer’s recommendations
  • be mixed to ensure colour consistency where coloured pigments are specified
  • be specified and used with the appropriate trims to form corners, returns and features in accordance with the manufacturer’s recommendations.

Brick slip cladding: slips, carriers and joints

Brick slip systems, including proprietary carriers forming an integral part of the system, should:

  • be specified and fixed in accordance with the design and the manufacturer’s recommendations, taking account of relevant height restrictions
  • be set out and designed to ensure that excessive cutting of brick slips is avoided, i.e. in the storey heights, at corners and around openings
  • have coursing arranged to suit lintel heights.

Mortars, proprietary mortars and grouts should be specified:

  • to enable each joint to be adequately filled and appropriately struck
  • in accordance with the system manufacturer’s recommendations.