Cavity wall insulation and wall ties

Issue date December 2016


Cavity wall insulation

Cavities in new work should not be filled. Either an insulating block inner leaf or cavity batt which maintains a cavity should be used.

Blown fibre insulation should not be used in new work.

When using slab insulation the following points should be noted:

  1. All wall insulation systems require higher standards of workmanship and supervision.
  2. Reducing the cavity to less than 50mm can increase the risk of cavity bridging by mortar droppings and uneven placing of slabs. The safer option is the use of thinner high efficiency materials.
  3. Ensure that slabs are stored flat, and without bearers, as they may warp and be difficult to fix. Protect polystyrene boards from prolonged exposure to sunlight.

Wall ties

All wall ties specified are to be stainless steel to BS 1243. The type of wall tie specified is to be as follows:

  • For cavities 75mm or less - Double triangle, Type 2.
    Horizontal spacing - 900mm. Vertical spacing - 450mm.
  • For cavities 76mm to 150mm - Vertical twist, Type 3.
    Horizontal spacing - 750mm. Vertical spacing - 450mm.

Additional spacing requirements for wall ties are covered in BS 8000: Part 3: Clause

Length of wall ties to suit cavity width and to include bedding of at least 50mm into each masonry leaf.

The guidance above is for individual leaves exceeding 90mm thickness. For thinner leaves refer to reference documents listed below.

  • BS 1243: Specification of metal ties for cavity wall construction.
  • BS 5628: Code of Practice for use of masonry: Part 3 - Materials and components, design and workmanship.
  • BS 8000: Workmanship on building sites: Part 3 - Code of Practice for masonry.
  • The Building Regulations 2000.