Cavity Wall Insulation With Polyurethane Foam (PU foam)

Cavity wall insulation involves the injection of a suitable insulant, using a specified and approved system designed to ensure a complete fill of the cavity wall area.

Composition & Durability

Injected PU foam is a two-component chemically modified polyurethane foam which achieves superior U-value and air-permeability results.

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The materials are produced under strict quality control to ensure compliance with the performance requirement of the appropriate British Board of Agreement Certificate.

The installation must be carried out in accordance with the relevant BBA Certificate, their surveillance scheme, the System Suppliers installation manual.

Once installed, PU Foam in the cavity will remain an effective insulant for the life of the building and will require no further maintenance.


Injected PU foam can be used in cavities for a superior performing insulation which also helps to bond the inner and outer leaves providing strength to the building.

PU foam is often the most cost effective solution for the following properties:

  • With hard-to-treat cavity, or with structural or defective/corroded wall ties,  
  • Those unsuited to external wall insulation due to planning restrictions,
  • Those where internal wall insulation would disrupt tenants,
  • Homes in high wind or severe wind driven rain exposure conditions including the 5.2M properties at risk of flooding in the UK.

Thermal Conductivity: For standard construction 65mm cavity u-values of 0.33 W/m2K can be achieved and in a 100mm standard construction cavity the U-value can be down to 0.22 W/m2K.

Density:  Approx 40Kg/m3

Water: Closed cell polyurethane foam provides an extra layer of resilience against the ingress of wind driven rain and flood water through the cavity


Survey: A pre-installation assessment is carried out to determine the suitability of the property for cavity wall insulation.

Preparation: Internal and external checks are carried out by the Technician prior to installation. Injection holes are drilled in the external wall of the cavity as specified by the relevant BBA Certificate and System Suppliers manual. Holes are drilled in the mortar between the bricks or stones. Each elevation is completely filled including any gable peaks.  The cavity at any party wall line is sealed with a by injecting a column of PU Foam.

Installation: PU Foam is injected into the cavity via an injection gun in a specified sequence to ensure a complete fill of the cavity.

Making good: Following the installation the injection holes are made good to match the original wall surface as closely as possible.

Post Installation Check: All fuel-burning appliances and their flues or source of air supply are checked to confirm their effectiveness.

There is also a 25 year insurance backed guarantee available for PU Foam.

Cavity Wall Insulation

Cavity Wall Insulation stores the heat within the inner walls, bouncing it back into the room and holding it for longer.

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Spray Foam Insulation

Polyurethane (PU) Foam helps to reduce heat loss so reducing your energy bills & making your home feel more comfortable.