How to install partial fill cavity wall insulation

The guidance provided in this post is based on the expertise of Kingspan Insulation, it is intended to provide general guidance on partial fill cavity wall insulation installation.

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Partial fill cavity wall insulation is a popular method of insulating in new build cavity wall construction.

This method involves filling only a portion of the cavity with insulation, as opposed to a full fill.

The insulation is placed against the inner leaf of blockwork and is held in position by wall ties, which are used to tie the two skins of masonry together.

The key to a successful installation is proper positioning of the wall ties.

Positioning Wall Ties

When installing wall ties in the inner leaf, they should be placed at 600mm horizontal centres.

  • For solid concrete floors, wall ties should start at either one course of blockwork below the damp proof course or, depending on your location, a specified distance below the top surface of the ground floor perimeter insulation upstand.
  • For suspended timber floors, wall ties should start a minimum of 200mm below the top surface of the ground floor perimeter insulation upstand.

As you continue constructing the inner leaf, the next course of wall ties should be positioned at regular horizontal centres.

Extra wall ties should be positioned at jambs for all openings.

The next course of blockwork should then be installed to secure the ties.

Installing Insulation Boards

After raising each section of the inner leaf, and before installing the insulation board, excess mortar should be removed and mortar droppings cleaned from exposed edges of the installed insulation boards.

The first row of insulation boards should now be installed between the two rows of wall ties, ensuring each insulation board is retained tight against the inner leaf and joints are butted.

Secure each board at a minimum of three points. Additional ties may also be required to satisfy structural requirements or to ensure adequate retention of boards or cut pieces.

Next, build the outer leaf to the level of the top of the boards and repeat the process.

If finishing at a gable, insulation boards should be continued 200mm beyond the height of the top storey ceiling and a cavity tray installed above the insulation.


In conclusion, proper positioning of wall ties is crucial for a successful cavity wall insulation installation.

By following the guidelines outlined in this blog post, you can ensure that your insulation is securely in place, providing you with improved energy efficiency and cost savings on your heating and cooling bills.

The guidance provided in this blog post is based on the expertise of Kingspan Insulation, a leading manufacturer of insulation products. We recommend watching their 2-minute video on cavity wall insulation installation for a detailed visual guide on the process.

If you're looking for an insulation solution for partial fill cavity walls, we highly recommend the Kooltherm K108 Cavity Board. This advanced product has a thermal conductivity of just 0.019 W/mK, which means it can achieve the same wall U-value as alternatives, but with a much thinner profile. This not only maximizes usable internal floor space, but it also allows for more natural daylight to flood into your building. Additionally, the Kooltherm K108's clear cavity design resists moisture penetration, making it a perfect choice for any construction project.

Kingspan Insulation's products and technical support team are available to help ensure a successful installation and improve the energy efficiency of your home. Visit their website or contact them directly for more information

Frequently Asked Questions

  • Where should the insulation be placed when installing partial fill cavity insulation?

Partial fill cavity insulation should be placed on the inner leaf of the wall and in the appropriate residual cavity of the outer leaf, as per the guidelines outlined in section 6.1.7 of the NHBC Standards for Thermal Insulation.

  • Why is partial fill insulation foil backed?

Partial fill insulation is foil backed in order to reflect radiant energy back into the cavity space, helping to reduce the amount of cold air that enters in the winter and reflecting heat back into the cavity during the summer. This allows the ventilated space to be used more efficiently as part of the overall building structure.

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