How much does cavity wall insulation cost?

Professional cavity wall insulation typically costs £500–£1,500 depending on the size and type of property. A mid-terrace house costs around £400–£600, a semi-detached £600–£900, and a detached house £800–£1,500. The work usually takes 2–3 hours and is minimally disruptive — small holes are drilled in the outer wall, insulation is injected, and the holes are filled. Many households can get cavity wall insulation for free or at reduced cost through government schemes like ECO4 and the Great British Insulation Scheme.

How much can cavity wall insulation save on energy bills?

According to the Energy Saving Trust, cavity wall insulation can save approximately £295 per year for a detached house, £185 for a semi-detached, and £110 for a mid-terrace. Savings depend on the property type, existing insulation, energy efficiency, and heating system. The payback period is typically 2–5 years if you pay for it yourself, making it one of the best investments in home energy efficiency.

Can I get free cavity wall insulation?

Yes — cavity wall insulation is one of the most commonly funded measures under government energy efficiency schemes. ECO4 provides free insulation for households on certain benefits or low income. The Great British Insulation Scheme targets homes in lower council tax bands that are less energy-efficient. In Scotland, Home Energy Scotland offers grants. Contact your energy supplier or local council to check eligibility. Many installations are fully funded.

How do I know if my house has cavity walls?

Most homes built from the 1920s onwards have cavity walls (two layers of brick with a gap between them). Homes built before 1920 typically have solid walls (a single thick layer). You can check by looking at the brickwork: if you can see a regular pattern of alternating long and short bricks, it's likely a solid wall. If all bricks are the same length, it's likely a cavity wall. Your EPC (Energy Performance Certificate) will also state whether you have cavity walls and if they're insulated. You can also measure the wall thickness — cavity walls are usually 27–30cm (11–12 inches) thick.

Cavity Wall Insulation Costs UK 2026 — Prices, Savings & Grants | PocketWise

Cavity wall insulation is one of the cheapest and most effective ways to reduce your energy bills. Here’s what it costs and what you’ll save.

At a Glance

Feature	Detail
Homes with cavity walls	Most UK homes built from the 1930s onwards
Cost	£500–£1,500 (professional installation)
Installation time	2–3 hours
Annual savings	£110–£295 depending on property
Payback period	2–5 years
Free/subsidised available	Yes — ECO4, Great British Insulation Scheme
Lifespan	25+ years (most last the lifetime of the building)
EPC improvement	Can improve by 1–2 bands

Costs by Property Type

Property type	Typical cost	Annual saving	Payback
Mid-terrace	£400–£600	~£110	~4 years
End-terrace	£500–£800	~£145	~4 years
Semi-detached	£600–£900	~£185	~4 years
Detached	£800–£1,500	~£295	~3.5 years
Bungalow	£500–£1,000	~£200	~3 years

Savings source: Energy Saving Trust estimates

How It Works

Step	Detail
1	Surveyor checks walls are suitable (cavity present, no damp, no damage)
2	Small holes (about 22mm) drilled in the outer wall at regular intervals
3	Insulation material pumped/injected into the cavity through the holes
4	Holes filled and made good
5	No internal disruption — all work done from outside

Insulation Materials

Material	Type	Notes
Mineral wool (glass/rock)	Blown fibre	Most common, good thermal performance, breathable
Polystyrene beads	Bonded beads	Good for exposed or wet locations
Polyurethane foam	Injected foam	Highest insulation value but less breathable — can cause damp issues in some walls

Is Your Home Suitable?

Suitable	NOT suitable
Cavity walls (usually 1930s onwards)	Solid walls (pre-1920s typically) — need external or internal wall insulation instead
Cavity at least 50mm wide	Very narrow cavities
No significant damp or water penetration	Walls with existing damp problems
Brick, block, or rendered walls	Timber-framed walls (different insulation method)
Walls in reasonable condition	Damaged or deteriorating mortar/brickwork

How to Check if You Have Cavity Walls

Method	Detail
Brick pattern	All bricks the same length (stretcher bond) = cavity. Alternating long/short = solid
Wall thickness	Measure at a window or door opening. 27–30cm = cavity. 22–23cm = solid
Year of build	Pre-1920 = usually solid. 1920s–1990s = usually cavity. Post-1990s = usually already insulated
EPC certificate	States wall type and whether insulated
Borescope inspection	Installer drills a small test hole to check

Available Grants

Scheme	Who qualifies	What’s covered
ECO4	Low-income households, certain benefits (UC, Pension Credit, Child Tax Credit, etc.)	Free cavity wall insulation
Great British Insulation Scheme	Homes in council tax bands A–D (England), or A–E if on qualifying benefits	Free or subsidised insulation
Home Energy Scotland	Scotland residents	Grants + interest-free loans for energy efficiency
Nest (Wales)	Wales residents on low income/benefits	Free home energy improvements
Local council schemes	Varies by area	Check with your council
Energy supplier schemes	Via your energy company	May offer funded insulation

How to Get Free Insulation

Step	Action
1	Check your eligibility on Simple Energy Advice (gov.uk)
2	Contact your energy supplier to ask about ECO4
3	Contact your local council for local schemes
4	In Scotland: call Home Energy Scotland on 0808 808 2282
5	In Wales: call Nest on 0808 808 2244

Problems With Cavity Wall Insulation

Problem	Cause	Solution
Damp patches on internal walls	Insulation bridging moisture from outer to inner wall	Remove insulation from affected area; may need full extraction
Cold spots	Gaps or voids in insulation (poorly installed)	Re-inject or top up insulation
No improvement in energy bills	Other heat loss sources (roof, windows, draughts)	Address other insulation gaps
Insulation settles over time	Some materials can settle, creating gaps at the top	Top-up injection

Cavity Wall Insulation Extraction

Detail	Information
When needed	If insulation is causing damp, is defective, or was incorrectly installed
Cost	£1,500–£4,000+ depending on property size
Process	Insulation is mechanically removed or extracted by suction
Who does it	Specialist extraction companies (not the same as installers)
Guarantee claim	If poorly installed, you may be able to claim against the installer’s CIGA guarantee

CIGA Guarantee

Feature	Detail
What it is	The Cavity Insulation Guarantee Agency provides a 25-year guarantee
Coverage	Defects arising from the installation of cavity wall insulation
Who’s covered	Homeowners of properties insulated by CIGA-registered installers
How to claim	Contact CIGA: ciga.co.uk / 01onal 2478 3024
Check your guarantee	You can search by postcode on the CIGA website

Cavity Wall Insulation vs Other Insulation

Insulation type	Cost	Annual saving (semi)	Payback
Cavity wall	£600–£900	~£185	~4 years
Loft (0 to 270mm)	£400–£600	~£355	~1.5 years
Solid wall (external)	£8,000–£15,000	~£365	~30+ years
Solid wall (internal)	£4,000–£8,000	~£365	~15+ years
Floor insulation	£500–£1,500	~£80	~10 years

Cavity wall and loft insulation are by far the best value.

Cavity Wall Insulation Costs UK 2026 — Prices, Savings & Grants