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Insulation for Masonry Partial Fill Cavity Walls

Insulating a cavity wall insulates a building without impacting on internal living space.

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Masonry cavity walls comprise of an outer skin of brick or blockwork, and an inner skin of masonry. In new buildings, the inner skin is usually blockwork. Between the two masonry leafs is an air cavity, into which thermal insulation is installed to meet building performance targets. A partial fill cavity features rigid insulation boards secured to the inner leaf masonry, leaving an air cavity behind the outer leaf.

Partial fill external walls can contribute to a whole-building solution that meets the energy efficiency target for new-build construction. They are particularly well suited to extensions of existing buildings, where the U-value targets tend to be less onerous.

What Celotex products are suitable as partial fill cavity insulation?

Offered specifically for partial fill cavity wall applications, Celotex CW4000 is sized specifically to fit standard wall tie spacing requirements. No cutting is required, so it can be installed quickly and easily as the brick and blockwork courses progress.

CW4000 offers a low thermal conductivity, keeping the insulation thickness - and therefore the overall wall construction - to a minimum. This is helped by a low-emissivity foil facing, which can improve the thermal resistance of the cavity space and contribute to meeting the required U-values.

High performance, partial fill insulation offers the following benefits:

  • Easy to fit between wall ties using cavity tie clips for retention.
  • Reliable long-term energy savings for buildings.
  • Low emissivity foil facers improve thermal performance of air cavity.
  • Excellent dimensional stability.

Why is partial fill cavity construction so common?

Using rigid insulation boards in conjunction with a minimum 50mm air cavity is a tried and tested solution familiar to designers, specifiers, contractors and building inspectors alike. It is a popular method for constructing external walls in the UK, and has been used on building sites for the last hundred years.

The clear cavity between the outer leaf and the insulation acts as a barrier to external moisture, stopping it from reaching the inside of the building. Most commonly, the outer skin of the cavity wall is constructed from brick. Blockwork is also used, clad or rendered to provide the desired finish. 

Natural or artificial stone can also be used, which has implications for the design of the wall. Cut stone can achieve a consistent thickness, but variation in the thickness of natural stone is likely to impact on how the clear cavity is maintained, and it is recommended to seek specialist advice in order to achieve the best results.


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Celotex products to consider

1200 x 450mm
0.022 W/mK

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