Cavity walls, partial fill insulation

Why is it important?

Brick and block is a popular construction type and generally involves a cavity wall construction. Building Regulations can be achieved by part or full fill insulation, depending upon preferred construction type.

How is it installed?

When complying with current Building Regulations and looking to build a traditional partial fill cavity wall, the construction should consist of an external skin of 102.5mm facing brick with a 100mm cavity partially filled with Celotex CW4050 50mm cavity insulation, leaving a residual cavity of 50mm and then an internal skin of 100mm Celcon Standard aerated blocks.

Insulation should be retained with a minimum of 3 clips over each board’s perimeter.

Above windows and doors install insulated cavity lintels. Cavity trays should then be installed with weep vents incorporated within the external skin at 450mm centres.

Cavities should be closed around windows and doors and at the top of walls with proprietary insulated cavity closers.

Hints & Tips

  • Ensure cavity insulation boards are kept clean and dry during construction and any mortar that may fall on them is cleaned off.

  • Ensure blockwork is kept clean and free from deviations on the cavity side, to allow insulation to sit flush against the back of the blocks.

  • To further reduce the transfer of heat away from the inside of the building it is recommended that below the DPC the cavity is fully filled with 100mm insulation, reducing thermal bridging.

  • Ensure correct positioning and quantity of wall ties are incorporated within the wall construction.

  • The insulation boards within the gable walls should always be taken up to ridge level to future proof the property for the possibility of the roof void being used as a habitable space.

  • If the cavity is closed at or below DPC level the first row of insulation boards should be mechanically fixed to the blockwork.