What is Affordable Warmth Scheme?

A Northern Ireland scheme for owner-occupiers and private tenants on lower incomes, run with the NI Housing Executive.

A perforated brick that ventilates a suspended floor void or room. Air bricks must stay clear when a cavity is filled; sleeves are fitted through the cavity where needed.

What is Area-based scheme?

A council-led energy efficiency programme in Scotland that targets particular streets or estates.

Expanded polystyrene beads coated with a binder as they are blown into a cavity, so they set into a free-draining fill.

A small camera on a flexible or rigid probe, pushed through a hole in a wall to see inside the cavity.

What is Building notice?

A notice to building control that notifiable work, such as cavity wall insulation in England, is being carried out.

Cavity Wall Insulation Glossary | Terms Explained

Affordable Warmth Scheme: A Northern Ireland scheme for owner-occupiers and private tenants on lower incomes, run with the NI Housing Executive.
Air brick: A perforated brick that ventilates a suspended floor void or room. Air bricks must stay clear when a cavity is filled; sleeves are fitted through the cavity where needed.
Area-based scheme: A council-led energy efficiency programme in Scotland that targets particular streets or estates.
Bonded bead: Expanded polystyrene beads coated with a binder as they are blown into a cavity, so they set into a free-draining fill.
Borescope: A small camera on a flexible or rigid probe, pushed through a hole in a wall to see inside the cavity.
Building notice: A notice to building control that notifiable work, such as cavity wall insulation in England, is being carried out.
Building standards: Scotland's equivalent of building regulations, set out in the Technical Handbooks.
Building warrant: Scottish permission needed for most building work. Insulation within a wall is listed as not needing one, but must still meet the standards.
Cavity: The gap between the outer and inner leaves of a cavity wall. In houses built from the 1920s onwards it is often 50mm to 75mm in older homes and wider in newer ones.
Cavity barrier: A barrier fitted in the cavity at a party wall or other boundary to stop fill passing into a neighbour's wall and to limit fire spread.
Cavity tray: A damp-proof membrane bridging the cavity above openings or abutments, directing water outwards.
CIGA: The Cavity Insulation Guarantee Agency, which provides 25-year guarantees for cavity wall insulation installed by its registered installers.
Cold bridge: A part of a wall that conducts heat out faster than its surroundings, such as a lintel or uninsulated reveal; also called a thermal bridge.
Competent person scheme: A government-authorised scheme that lets registered installers self-certify that their work meets the Building Regulations.
Condensation: Water that forms when warm, moist indoor air meets a cold surface. A common cause of mould that can be mistaken for penetrating damp.
CWISC: Cavity Wall Insulation Self Certification, CIGA's competent person scheme run with the BBA.
Damp-proof course (DPC): A horizontal barrier near the base of a wall that stops ground moisture rising. Ground or paving should stay below it.
Density: How tightly a blown fill is packed. Each certified system specifies a density range; too loose can settle, too tight can bridge moisture.
Driving rain: Rain carried sideways by wind against a wall. Exposure to driving rain is a key test of whether a wall can be filled.
ECO4: The fourth Energy Company Obligation, which requires larger energy suppliers to fund measures for eligible households in Great Britain. Extended to 31 December 2026.
Energy-saving materials relief: The VAT relief that zero-rates installation of insulation in homes until 31 March 2027, then 5%.
EPC: Energy Performance Certificate: a rating from A to G of a home's energy efficiency, with recommendations.
EPS: Expanded polystyrene, the material of bead cavity fills.
Exposure zone: A grading of how much driving rain a location receives, used to decide which walls and insulation systems are suitable.
Extraction: Removal of cavity insulation, usually by lifting bricks and vacuuming the fill out.
Fill pattern: The spacing and positions of drill holes for injecting a cavity fill, set by the system's certificate.
Full fill: Insulation that fills the whole cavity width, as with retrofit blown fills and some new-build batts.
GBIS: The Great British Insulation Scheme, which closed as planned on 31 March 2026.
Inner leaf: The inside wall of a cavity wall, usually blockwork in houses from the 1950s onwards.
Leaf: One of the two walls that make up a cavity wall.
Lintel: A beam over a window or door opening. Steel lintels in cavity walls often incorporate a cavity tray.
Making good: Filling drill holes and repairing any disturbed finishes after work, matched as closely as practical to the existing.
Mineral wool: Glass or stone fibre insulation. Blown into cavities as water-repellent loose wool, or used as batts in new walls.
Mortar droppings: Mortar that falls into a cavity during building. Where it collects, it can bridge the cavity.
Nest: Warm Homes Nest, the Welsh Government's scheme of free home energy improvements for eligible low-income households.
Notifiable work: Building work that must be notified to building control or self-certified, such as cavity wall insulation in England.
Outer leaf: The outside wall of a cavity wall, usually facing brick. It gets wet in rain and is designed to shed water down the cavity face.
Partial fill: Insulation boards fixed to the inner leaf leaving a clear residual cavity, used in new walls.
Party wall: A wall shared between two buildings. Separating walls between houses are often cavity walls.
Party wall bypass: Heat loss caused by air moving up an unfilled party wall cavity and out through the loft.
PAS 2030 / PAS 2035: Publicly available specifications for installing and coordinating energy efficiency retrofit, required for government-funded work.
Penetrating damp: Water getting through a wall from outside, often through defects such as failed pointing or cracked render.
Perpend: A vertical mortar joint between bricks.
Pointing: The mortar finish in the joints between bricks. Failed pointing is a common route for rain into a wall.
Remedial wall tie: A replacement tie, usually stainless steel, fixed through the joints to reconnect the two leaves of a cavity wall.
Render: A cement or lime coating on an outer wall. Cracked render can trap water behind it.
Retrofit: Improving an existing building, as opposed to building new.
Rising damp: Ground moisture rising through a wall, usually where the damp-proof course has failed or been bridged.
Spalling: Flaking or crumbling of brick faces, often from frost or salts. Spalled bricks let more water into a wall.
Stretcher bond: Brickwork with every brick laid lengthways, typical of cavity walls.
Thermal imaging: Using an infrared camera to show surface temperatures and reveal heat loss patterns.
Top-up: Adding fill to parts of a cavity that were missed or have settled.
U-value: A measure of how fast heat passes through a building element. Lower is better.
UF foam: Urea-formaldehyde foam, an older cavity fill no longer in mainstream use. Some foams need formaldehyde emission assessment under the Building Regulations.
Wall tie: A metal tie bridging the cavity to hold the two leaves together. Older galvanised ties can corrode.
Warm Homes Plan: The UK government's plan, published January 2026, for home energy upgrades, including low-income support and consumer protection reform.
Warm Homes: Local Grant: An England scheme delivered through councils for low-income households in homes rated EPC D to G.
Warmer Homes Scotland: A Scottish Government scheme, accessed through Home Energy Scotland, that can fund insulation for eligible households.
Weep hole: A gap in the outer leaf's mortar, usually above a cavity tray or at the base, that lets water out of the cavity.

Cavity wall glossary