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For Tenants, Homeowners, and Landlords in the United Kingdom.

This page outlines the insulation measures currently available under the Energy Company Obligation (ECO4) scheme. The information is intended for tenants, homeowners, and landlords who are eligible for energy efficiency upgrades under ECO4.

The purpose of each insulation type is to reduce energy loss, enhance internal thermal comfort, and extend the efficiency of heating systems in residential properties. Each entry includes an explanation of the method, its application, installation timeframes, material components, and expected lifespan.

Internal Wall Insulation (IWI)

Internal Wall Insulation refers to the application of thermal insulation on the inside surface of a building’s external walls. This measure is typically applied to older homes built using solid brick or stone, which do not contain a cavity between wall layers.

System Overview:
To install IWI:

  • Insulated plasterboard or a stud wall framework is affixed to the internal side of the external wall.
  • Insulation materials—such as rigid foam boards, mineral wool, or multi-layer composite panels—are placed behind the plasterboard or within the frame
  • The installation is completed with a plastered or boarded finish suitable for decoration.

This process reduces the flow of heat out of the home and limits cold surfaces that can cause condensation.

Suitability:
Recommended for solid wall properties where cavity wall insulation is not an option.

Installation Duration:
Approximately 3–5 days, depending on the number of external walls treated and the size of the property.

Expected Lifespan:
30–40 years.

Cavity Wall Insulation (CWI)

Cavity Wall Insulation involves filling the gap (cavity) between the external and internal walls of a property with insulating material. This is suitable for properties constructed with cavity walls, generally built after the 1920s.

System Overview:
The procedure includes:

  • Drilling small holes in the outer wall.
  • Injecting insulation material (mineral wool, polystyrene beads, or polyurethane foam) into the cavity.
  • Sealing the drilled holes after injection.

The insulation traps heat within the home by preventing air movement within the wall space.

Suitability:
Applicable only to properties with uninsulated cavity walls. A pre-installation assessment, often involving a borescope inspection, confirms suitability.

Installation Duration:
2–4 hours for a typical semi-detached property.

Expected Lifespan:
25 years or more. Installations are typically covered under a CIGA (Cavity Insulation Guarantee Agency) warranty.

Loft Insulation

Loft Insulation is applied to the floor of a loft (attic) space, between and over the horizontal wooden beams known as joists. This prevents warm air from escaping through the roof of the property.

System Overview:
The process typically includes:

  • Placing insulating rolls (commonly mineral wool) between joists.
  • Adding a second layer across the joists to the recommended depth.
  • In some cases, rigid boards or natural insulation materials such as sheep’s wool may be used.

This is one of the most cost-effective insulation methods available.

Suitability:
Effective for all homes with accessible loft space and no existing or insufficient insulation.

Installation Duration:
Approximately 2–4 hours.

Expected Lifespan:
Over 40 years.

Room in Roof Insulation

Room in Roof (RIR) Insulation refers to the insulation of converted loft spaces used as bedrooms or living areas. The measure targets heat loss through sloped ceilings, vertical walls, and flat ceilings within the room.

System Overview:
The procedure involves:

  • Fixing insulated plasterboards or mineral wool batts between and across rafters.
  • Applying insulation to vertical gable or party walls and dormer windows.
  • Finishing the interior with plasterboard.

Materials used include polyisocyanurate (PIR) boards, mineral wool, and multi-layer reflective insulation.

Suitability:
Ideal for dormer bungalows, attic conversions, and any property with a habitable loft room.

Installation Duration:
1–3 days depending on complexity.

Expected Lifespan:
More than 40 years.

Flat Roof Insulation

Flat Roof Insulation involves adding a thermal barrier above or below the flat roofing structure. The choice between warm roof (above) or cold roof (below) depends on property construction and accessibility.

System Overview:
There are two main methods:

  1. Warm Roof: Insulating boards are placed above the roof deck and under the waterproof membrane.
  2. Cold Roof: Insulation is installed between the ceiling joists underneath the roof deck.

Common materials include PIR insulation boards, mineral wool batts, or spray foam insulation. Each method reduces heat loss and mitigates condensation.

Suitability:
Applicable to properties with flat or low-pitched roofs, often found in extensions or apartment buildings.

Installation Duration:
1–3 days, depending on roof area and construction type.

Expected Lifespan:
25–30 years.

Each of these measures is approved based on suitability, cost-effectiveness, and compliance with government retrofit standards. If you are interested in applying for ECO-funded improvements, use The Consumer Rights’ free ECO4 eligibility checker