Low Energy House

Low Energy House - What is Cavity Insulation?

Blown cavity insulation is the most economical way of insulating external walls. It is much cheaper than internal or external insulation systems. If it has been established that the external walls have been constructed with cavities then a registered cavity wall insulator should be consulted

Assessment of Dwelling for Cavity Insulation

The registered cavity wall insulator will send a trained surveyor or technician to undertake an assessment of the dwelling and confirm its suitability for cavity wall insulation.

Cavity Insulation - Blown Cavity Insulation - Image provided by Rockwool® LtdCavity Insulation - Wall Suitability for Insulation

The suitability of the walls for cavity fill will be based on several factors including:

  • The location of the house and the level of exposure to rainfall
  • The height of the walls
  • The state of repair of the structure
  • The width and general suitability of the cavity
  • The condition of the cavity ties
  • Flues and air vents in the wall
  • The heating system
  • The method of construction of any adjoining buildings

Cavity Insulation - Building Regulations

The Building Regulations specifically define cavity wall insulation as building work. If cavity wall insulation is to be installed in the home, it will be necessary to make an application to the Building Control Service and obtain approval. The appropriate requirements will be applied so as to ensure the walls and insulation materials are suitable.

Registered Cavity Insulation Installer

A registered cavity insulation installer must be employed to carry out the work. The contractor will usually make the Building Regulations application for the insulation project directly to the Local Authority. The registered installer will carry out the work using an approved insulation system and approved insulating materials. On completion of the work the installer will provide a 25 year guarantee

Cavity Insulation - Cavity Insulation -Injection Process - Image Provided by Rockwool® LtdInstallation Method

Cavity wall insulation involves the mechanical injection of a suitable insulation material into the existing cavity. Holes will be drilled into the joints of the outside brickwork and the insulation material will be blown into the cavity, via an injection nozzle, until it completely fills the void. When the injection process is finished the holes will be made good to match the existing mortar as closely as possible.

Cavity Insulation Materials

There are three different materials that can be used in cavity walls in the UK:

  • Mineral Wool - The mineral wool used for cavity fill insulation consists of mechanically spun glass mineral wool or rock mineral wool that is treated with a binder or water repellent during manufacture. Mineral wool is resistant to water penetration and will not transmit water across the cavity. It is not a vapour control layer and will allow the structure to breathe naturally.
  • Polystyrene Beads - The polystyrene beads used in cavity wall insulation are usually combined with a binding agent or adhesive at the time of injection. Polystyrene beads are resistant to water penetration and will not transmit water across the cavity. They do not form a vapour control layer and will allow the structure to breathe naturally.
  • Urea Formaldehyde Foam - urea formaldehyde foam is injected into the cavity in a wet foam state, 90-95 per cent pre-expanded, through holes drilled in the brickwork. It completes its expansion by moulding itself to the unique shapes within the cavity and sets to form a rigid insulation material. The cured foam is resistant to water penetration and will not transmit water across the cavity by capillary attraction. The foam is not a vapour control layer and will allow the structure to breathe naturally. Care must be taken before choosing urea formaldehyde foam as it is not suitable for use in high buildings or in exposed and elevated locations.

Checks After Installation of Cavity Insulation

After the installation has taken place, the cavity insulation installer must check that no air vents have been filled and that the flues and air supply vents to heating appliances are still effective.

To Determine Whether or Not Your External Walls Have a Cavity - Link to - Cavity or Solid Wall?

Up to 35 per cent of the heat inside a home is lost through the external walls. The householder may be eligible for a grant or, in certain circumstances, qualify for free installation

About Cavity Insulation - Insulated Cavity Wall - Home Insulation