Does Your Home Have an Unfilled Cavity?
Cavity wall construction became standard in the UK from around 1920 onwards. Most homes built between 1920 and 1995 have two skins of brickwork with a 50-75mm gap — the cavity — between them. This cavity was left unfilled in the original construction, and many were never insulated in the subsequent decades.
The simplest way to check is to measure the thickness of an external wall. If it is 260-300mm (typically 102mm brick + 75mm cavity + 102mm inner skin, or similar), you likely have a cavity. You can also look at the brick pattern from outside: a stretcher bond (all bricks laid lengthways) usually indicates a cavity wall. Flemish or English bond (alternating headers and stretchers) usually indicates solid wall construction. If in doubt, a professional survey — which we offer free of charge — will confirm this with a physical probe through a small drill hole.
What Cavity Wall Insulation Involves
Cavity wall insulation is injected into the existing cavity through small holes drilled in the mortar joints of the outer wall. The most common material is mineral wool (blown in as loose fibre) or EPS (expanded polystyrene) beads. The process takes a day for a typical semi-detached property, leaves no visible marks on the interior, and causes minimal disruption. Holes are re-pointed after injection and are barely visible once the mortar has cured.
The insulation permanently fills the cavity, reducing heat loss through the walls by up to 35%. This typically translates to annual savings of £200-£400 depending on property size, current heating costs, and the proportion of the external wall area that is wall (versus windows). The insulation has a design life of 25 years and requires no maintenance.
Costs for Cambridgeshire, Norfolk and Suffolk Homes
Self-funded cavity wall insulation in East Anglia typically costs £600-£1,500 for a mid-terraced or semi-detached house, and £800-£2,000 for a detached property. The variation reflects the amount of accessible wall area, access complexity (scaffolding may be needed for properties with inaccessible upper floors), and the fill material specified.
With a payback period of 3-5 years for most properties, cavity wall insulation is one of the best-value energy efficiency upgrades available — rivalled only by loft insulation top-ups. Unlike some measures, the savings are relatively straightforward to calculate: lower heating bills, year after year.
Getting Cavity Wall Insulation Free Through ECO4
The ECO4 scheme (Energy Company Obligation, Obligation 4) funds energy efficiency improvements in lower-income and fuel-poor households. Eligible households can receive cavity wall insulation — and often loft insulation — completely free. Eligibility is means-tested, based on income and benefit receipt, and property EPC rating (currently D, E, F, or G).
Across Cambridgeshire, Norfolk, and Suffolk, ECO4 funding is delivered through local area coordinators and approved installers. We work with ECO4 area coordinators to assess eligibility during our free surveys. If your property qualifies, we can arrange fully funded insulation — often alongside other measures like loft top-ups — through the scheme. Contact us to check eligibility for your East Anglia property.
When Cavity Wall Insulation is Not Suitable
Not all cavity walls are suitable for insulation. Properties in very exposed coastal locations (particularly along the Norfolk and Suffolk coasts) may have cavities that serve a drainage function — water blown in from heavy rain exits through the cavity rather than reaching the inner wall. Filling these cavities can cause damp problems. We check this during surveys using moisture meters and review of the exposure rating for the location.
Cavities contaminated with construction debris, cavities that are partially bridged, or properties that have had previous failed or degraded insulation injected also require careful assessment before treatment. Our surveyors use a borescope (a fibre-optic camera on a thin probe) to inspect the cavity condition before any commitment is made. If the cavity is not suitable for insulation, we will advise on alternative wall performance options including internal wall insulation overlays.
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