How much does cavity wall insulation cost in the UK?

Cavity wall insulation typically costs £500-£1,500 for a standard semi-detached house (around 60-80m² of wall area). The cost depends on the property size, cavity width, and insulation type. Blown mineral wool is generally cheapest, while foam injection is more expensive but may last longer.

How much can I save with cavity wall insulation?

According to the Energy Saving Trust, a typical UK semi-detached house can save £180-£295 per year on heating bills after cavity wall insulation. Detached houses save more (up to £300+), while mid-terrace houses save less (around £100-£150) as they have fewer external walls. Try our heat loss calculator (/insulation/heat-loss-calculator/) to see how insulation affects room-level heating demand.

Is my house suitable for cavity wall insulation?

Most UK houses built after 1920 have cavity walls (two layers of brick or block with a gap between). Houses built before 1920 typically have solid walls. A surveyor can confirm by drilling a small hole or using a borescope. Cavities in exposed locations or with existing damp may not be suitable for all insulation types.

What types of cavity wall insulation are available?

The three main types are: blown mineral wool fibre (most common and cheapest), blown polystyrene beads (EPS, good for damp areas), and injected polyurethane foam (best thermal performance but most expensive). All are installed by drilling small holes in the outside wall and injecting the material under pressure.

Does cavity wall insulation cause damp?

When installed correctly in suitable properties, cavity wall insulation should not cause damp. However, in properties with existing damp issues, severely exposed locations, or damaged brickwork, cavity fill can sometimes create a moisture bridge. A proper survey before installation is essential to identify any risks.

Cavity Wall Insulation Calculator — Cost, Area & Savings Estimator UK

Cavity Wall Insulation Calculator \u2014 Area, Cost & Savings

Calculate the wall area to insulate, estimated cost and potential annual energy savings from cavity wall insulation for UK homes.

Wall Dimensions

Wall Height

External wall height (eaves to ground)

Total Wall Perimeter

Total length of all external walls

Deductions

Total Window Area

Combined area of all windows

Total Door Area

Combined area of all external doors

Insulation Details

Cavity Width

Typical UK cavities are 50-75mm

Insulation Type

Cost Per m\u00B2 (optional)

Enter installer quote per m\u00B2 for cost estimate

How We Calculate This

This calculator estimates the wall area that needs insulating by calculating the gross external wall area and subtracting windows and doors. It then provides an estimated annual energy saving based on typical UK figures from the Energy Saving Trust.

The formula

Net wall area = (Wall height × Wall perimeter) - Window area - Door area

The wall perimeter is the total length of all external walls measured around the outside of the building. Typical UK houses have a perimeter of 25-40 metres.

Energy savings estimates

Savings are based on Energy Saving Trust data for typical UK homes, scaled to your property size. A typical semi-detached house with around 80m² of external wall area saves approximately £100-£300 per year depending on the insulation type and your current energy costs.

UK Building Regulations

Under Part L of the Building Regulations, cavity wall insulation should achieve a U-value of 0.55 W/m²K or better for existing buildings. For new builds, the target is 0.30 W/m²K. Cavity wall insulation is often installed under the ECO scheme (Energy Company Obligation) which may provide free or subsidised installation for eligible households.

Frequently Asked Questions

Last updated: February 2026

All calculations are estimates. Verify with your supplier.

Cavity Wall Insulation Calculator \u2014 Area, Cost & Savings

Wall Dimensions

Deductions

Insulation Details

How We Calculate This

The formula

Energy savings estimates

UK Building Regulations

Frequently Asked Questions

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