Best Cavity Wall Replacement for Old UK Homes

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Is your old UK home cold and costly to heat? The problem might be in your walls. Homes built before 1980 often have empty cavity walls that let heat escape.

This guide shows how the right cavity wall insulation can cut your energy bills by up to 35%, stop dampness, and protect your home’s brickwork.

Why Cavity Wall Insulation Matters for Older UK Properties

More than 6 million UK homes built before 1980 have no cavity wall insulation installed. These are cavity spaces between the inner and outer brick layers. They were meant to keep rain out, but now they let heat escape.

Here’s why this matters:

33% of your home’s heat escapes through a lack of insulation material in cavity walls
You could save about £405 each year by filling these gaps
Proper insulation cuts the risk of dampness by 68%

If you’re wondering about the cost of cavity wall insulation in 2025, we break it down in this guide. Older homes have special cavity wall insulation needs:

Their cavities are wider (75-100mm vs. 50mm in newer homes)
They often have lime mortar as insulation material that needs to breathe
Their timber parts can rot if the wrong type of insulation is used

A real success story: A 1920s home in Bristol saved £488 per year after getting polystyrene bead insulation. The original bricks still look great too.

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7 Types of Cavity Wall Insulation: 2025 Best Cavity Wall Replacement

Cavity wall insulation material used throughout the insulation process varies as per the household needs. Below are some of the best cavity wall insulation materials suggested for different insulation types, mineral wool insulation, spray foam insulation, and mineral fibre insulation are also discussed.

1. Expanded Polystyrene (EPS) Beads

Cost: £18-£22 per square meter
Heat resistance: 4.0-4.5 per inch
Best for: Homes with odd-shaped cavities or damp issues

These small foam balls are pumped into the cavity space. They fit around corners and fill gaps well. They don’t soak up water, which makes them ideal for wet areas.

If you’re concerned about potential issues, this guide on cavity wall insulation problems and fixes explains how to avoid common mistakes with EPS beads and other materials.

In 2025, about 62% of UK homes choose EPS beads for cavity wall insulation. They last over 50 years and don’t sink down over time.

2. Mineral Wool (Rock/Slag)

Cost: £14-£20 per square meter
Heat resistance: 3.0-3.7 per inch
Best for: Fire safety and cutting noise

Made from melted rock, one of the top cavity wall insulation is mineral wool that won’t burn. It lets water vapour pass through, which works well with lime mortar walls. Insulation performance was better for mineral wool than other cavity wall insulation types.

It cuts noise by up to 52dB, but it’s about 15% less warm than EPS beads. If fire safety or noise are big issues for you, mineral wool is the best type of insulation material and worth thinking about.

3. Polyurethane Spray Foam (Wall Insulation to Avoid Dampness)

Cost: £30-£40 per square meter
Heat resistance: 5.5-6.5 per inch
Best for: Maximum warmth

Spray foam expands to fill every gap, making a tight seal. This spray foam cavity insulation keeps in more heat than other different types of cavity wall insulation.

But it must be put in by experts. If done wrong, it can trap dampness against your inner walls. Good installers prevent 92% of damp problems.

4. Cellulose (cavity wall insulation for newly built homes)

Cost: £15-£25 per square meter
Heat resistance: 3.2-3.7 per inch
Best for: Eco-friendly homes

Made from 85% recycled paper with added fire and mould blockers, cellulose is kind to the planet. It breathes well, which suits older building styles.

The downside? It doesn’t work as well in very damp areas. For most inland UK homes, though, it’s a good green choice.

5. Rigid PIR Boards

Cost: £25-£35 per square meter
Heat resistance: 6.0-7.2 per inch
Best for: New builds & part-fills

These stiff boards keep heat in very well when cut to fit the cavity space. They work best in new builds or when you can take exact measurements.

For older homes with odd-shaped gaps, rigid insulation boards might leave air spaces that cause cold spots. They’re not ideal for Victorian or Edwardian homes with uneven walls.

6. Glass Wool Batts

Cost: £10-£15 per square meter
Heat resistance: 2.2-2.7 per inch
Best for: Budget projects

These cavity batts are the cheapest option. They can be placed in the cavity during building work.

Watch out though – they can sag over time and hold water in damp settings. If you live in a rainy area, this type of cavity wall insulation might not be best.

7. Sheep’s Wool

Cost: £28-£35 per square meter
Heat resistance: 3.5-3.8 per inch
Best for: Green heritage homes

This natural insulation material helps control dampness by soaking up and releasing moisture without losing heat. It’s one of the most eco-friendly insulation options.

You need at least 75mm of cavity width for sheep’s wool, so it won’t work in all homes. For Victorian houses with wider cavities, it’s a great choice that lets walls breathe.

What's the Best Cavity Wall Insulation for Damp-Prone Homes?

Picking the wrong insulation for a damp home can cause big problems. Three Insulation materials stand out for wet areas:

1. EPS Beads: The Moisture Expert

Doesn’t soak up water
Let water drain away
Stops water from wicking through walls
Best for: Coastal homes, basements, and houses with damp issues

2. Hydrophobic Mineral Wool: The All-Rounder

Has added water-repellent
Keeps working even when slightly damp
Let water vapour pass through
Best for: Homes with minor damp or seasonal wet issues

3. Phenolic Foam Boards: The High-Performance Choice

The closed-cell design keeps water out
Excellent heat resistance (7.5 per inch)
Needs expert fitting
Warning: Avoid standard fibreglass in damp areas—it traps water against inner walls and can rot timber

Mineral Wool vs Polystyrene Beads: Which Works Better?

When choosing between these popular options, think about:

Feature	Mineral Wool	EPS Beads
Heat Resistance	3.4 per inch	4.3 per inch
Fire Safety	Won’t burn	Melts at 100°C
Sound Proofing	52dB less noise	38dB less noise
Damp Resistance	Fair	Excellent
Eco-Friendly	Can be recycled materials	Can’t be recycled

Real-world examples show their strengths:

A London terrace used mineral wool to cut street noise by 60%
A Cornish cottage fixed rising damp problems with EPS beads

Choosing the right material depends on your property and goals. This comparison of DIY vs. professional cavity wall insulation replacement can help you decide the best approach for your home.

How to Avoid Dampness When Insulating Older Cavity Walls?

To prevent damp problems, follow these steps:

Step 1: Check Your Cavity First

Before adding any insulation, use a camera to look for:

Existing damp patches
Cracked mortar
Rusty wall ties (common in pre-1970 homes)

Step 2: Plan for Moisture Control

Fix problems before insulating:

Use breathable membranes with EPS beads in risky areas
Try foil-backed boards in very damp spots
Replace rusty wall ties (costs £12-£18 each)

Step 3: Check After Insulating

Make sure it worked:

Use thermal cameras to find cold spots
Place damp meters in problem rooms
Look for leaks during heavy rain

Pro Tip: Don’t block air vents. Old homes need airflow to stay dry.

Eco-Friendly Options: Sustainable Cavity Wall Insulation

If you care about the planet, try these green options:

1. Recycled Denim

Made from 90% recycled jeans
Heat resistance: 3.5 per inch
Best in drier areas
Keeps textile waste out of landfills

2. Hempcrete

Actually removes CO₂ from the air
Heat resistance: 2.5 per inch
It needs wider cavities (at least 100mm)
It helps control moisture and air quality

3. Cork

Harvested from living trees
Naturally resists mould and pests
Costs more (£40-£50 per square meter)
Great for sound and heat

2025 Money Help: The ECO4 scheme offers £1,500-£5,000 grants for green insulation in older homes.

2025 Cost Guide: Materials, Install & Payback Times

Insulation Material	Cost per m²	80m² Home	Payback Time
EPS Beads	£20	£1,600	3.1 years
Mineral Wool	£17	£1,360	4.3 years
Spray Foam	£35	£2,800	5.9 years
Cellulose	£22	£1,760	4.7 years

Based on gas at £0.12/kWh and normal UK heating patterns

Key Tips for Successful Cavity Wall Insulation

Warning: Don’t use standard fibreglass in damp cavities—it traps moisture and damages walls
Safety First: Mineral wool is safest for terraced homes where fire spread is a concern
Damp Control: EPS beads work best in wet climates and coastal areas
Measure First: Check your cavity width before the insulation material you choose —Victorian homes often have wider gaps
Get Experts: Use only certified installers who know your type of property

Final Thoughts

The right cavity wall insulation injected into the cavity does more than cut your energy bills. It makes your home more comfortable and healthier while protecting its structure for decades.

Understanding your home’s needs and picking the best type of cavity wall means investing in comfort, value, and helping the planet.

For personal advice and professional installation, talk to certified insulation installers who know your type of property. The best solution balances heat retention, moisture control, and structural needs—giving you insulation that’s perfect for your unique home.

Frequently Asked Questions

Can cavity wall insulation cause dampness?

Poor installation can lead to dampness if:

Insulation Materials trap moisture
Wall problems aren’t fixed first
Airflow is blocked

Choose breathable insulation material options like EPS beads or treated mineral wool to reduce risks.

How do I know if my home has cavity walls?

Look for these signs:

Brick pattern (stretcher bond means cavity walls)
Wall thickness (solid walls are usually over 22cm)
The build date (most UK homes after 1920 have cavity walls)

If unsure, a professional can drill a small test hole to check.

Is cavity wall insulation OK for listed buildings?

For Grade II listed homes, cavity wall insulation is usually allowed as it doesn’t change how the building looks. Always check with your conservation officer first. Grade I and II* listings may need special permission.

How long does cavity wall insulation last?

Life spans vary:

EPS Beads: 50+ years
Mineral Wool: 25-30 years
Spray Foam: 20-25 years
Cellulose: 20-30 years

Good installation helps any material last longer.