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What are non-standard cavities?

Non-standard cavities

Following the publication of the Department of Business, Energy & Industrial Strategy report on non-standard cavities and lofts in Great Britain which was prepared by the Energy Saving Trust we thought it would be useful to talk about what they were and how at Isothane we can help to improve the thermal efficiency of properties which have them.

the Definition of Non-Standard Cavities

In the report non-standard cavities are defined into two broad categories:

  • Non-standard construction cavity wall – the construction type is non-traditional or has a narrow or irregular cavity.
  • Standard cavity walls with issues – a standard masonry cavity but with issues such as height, access, exposure or faults that make insulation more expensive.

There are many types of non-standard cavity highlighted in the report but we’d like to concentrate on just a few of them.


These are masonry cavities where the minimum distance between the inner leaf and the outer leaf is less than 50mm. These types of cavities fall into the non-standard category because the energy savings can be smaller due to the width of the cavity and the amount of insulation required to fill it and the potential for moisture penetration from outside due to the reduced distance between the exterior and interior of the wall, particularly in exposed locations.


These walls have exterior courses made from stone and may have through stones. The inside of the cavity may be irregular which can affect how evenly certain insulation materials are distributed when installed.


These cavities are often found in high rise flats. Concrete floors at various stories protrude into or through the cavity to the outer leaf of the building. Whilst the support of the floor structure can make the cavity easier to insulate than in most high rise buildings the floor creates a thermal bridge which diminishes potential savings.


Walls with rigid insulation board filling part of the width of the cavity were common in constructions built during the 1980s and later.


These are dwelling where the outer face is damaged e.g. faulty pointing or missing/defective damp proof courses. These faults can lead to water penetrating into the cavity which can cause issued if insulated with the wrong type of material.


Some cavity walls appear from external inspection to be solid walls. Without closer inspection these homes could be assumed to have solid walls when in fact they are cavity walls. These walls can be insulated but would require a longer injection nozzle to reach the cavity void.


In some cases construction rubble is present within uninsulated cavities. This rubble can be cleared out allowing insulation to be injected however this does add cost to the process.


Finlock gutters are built-in concrete gutters that sit above the cavity. These gutters often leak moisture into the cavity especially if the lining of them is poor quality or has deteriorated over time.  They are also likely to cause a cold bridge through the concrete into the cavity, or bypassing the top of the cavity wall which reduces the savings achieved by the insulation. It is important the insulation chosen is unaffected by moisture.


Not all insulation work as well above a certain height. The height restrictions the insulation options to specific materials.


Properties in areas which are exposed to wind driven rain may be effected by water migrating across the cavity and to the inner leaf wall when inappropriate insulation materials are used.


Properties in flood risk areas should not be insulated with blown mineral wool as this can lead to water being held in the cavity after flooding. The insulation will no longer be providing the thermal benefits once it is wet and it also leads to damp issues in the property.  Polyurethane foam cavity wall insulation is a solution to this issue and can provide flood resilience to the properties. Polyurethane foam doesn’t need to be removed following flooding and maintains its thermal performance. 

If you want to read the full report it can be found at


Isothane produce a cavity wall insulation and stabilisation product, Technitherm® which can be used many non-standard cavities. Improving the thermal performance of the building whilst taking into account the reasons the cavities have been classed as non-standard.  The product is a closed cell polyurethane foam, injected into cavities as a liquid meaning that it can fill non uniform cavities such as those found in stone built properties. It has a better thermal conductivity value than some “standard” cavity wall insulation products meaning it can achieve the improved thermal performance even when the amount of material required is less, such as in properties with narrow cavities.

It has passed the BRE (British Research Establishment) Flood Resilience Test and meet their requirements for use in walls with defective or missing damp proof courses. The product can be found in the BRE’s Flood Resilience House which was launched in 2016. Its closed cell properties mean it can be used in properties which are in exposed locations.

For more information on how we can help to insulate non-standard cavities please contact our technical team.

Flood Resilience House    Non-standard cavities - stone Non-standard cavities - flood risk Non-standard cavities - exposed locations


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