Home Insulation Guide UK 2025: Types, Costs, and Grants
Nobody gets excited about insulation. It's not like solar panels or a shiny new heat pump. It hides behind walls and under floors. You can't show it off to visitors.
But here's what the energy industry knows that homeowners often miss. Insulation upgrades frequently deliver the fastest payback of any home energy improvement. Faster than solar. Faster than heat pumps. And it makes everything else work better.
Why Insulation Matters More Than You Think
The average UK home loses 25-35% of its heat through poor insulation. Your boiler or heat pump works constantly to replace energy that's literally escaping through walls, roof, and floors.
Adding insulation is like plugging a leak. You're not generating more heat—you're keeping what you've already paid for.
The numbers are straightforward:
- Loft insulation upgrade: £300-£600
- Annual savings: £200-£350
- Simple payback: 1-3 years
Compare that to heat pumps with 15-20 year paybacks. Insulation often wins on pure economics.
Real Homeowner Experiences
David, Leeds (1930s semi-detached): "Our cavity walls had never been filled. The house was always freezing despite running the heating constantly. We got cavity wall insulation through the ECO4 scheme—completely free because we're on Pension Credit. The difference was immediate. Our heating bills dropped by about £280 a year, and the house just feels warmer. Should have done it years ago."
Claire, Cardiff (Victorian terrace): "Solid walls are expensive to insulate, so we started with the loft and draught-proofing. My husband did the loft himself over a weekend—cost us about £250 in materials to get to 300mm depth. Combined with proper draught excluders on all the doors and windows, our gas bills dropped noticeably. We're saving around £350 a year now."
Tom, Glasgow (1970s bungalow): "We had the Great British Insulation Scheme do our loft and cavity walls last summer. The whole thing was free because of our EPC rating and Council Tax band. The installer was in and out in a day for the cavities, then came back for the loft. Our house went from EPC E to C. That made us eligible for the heat pump grant, which we're now looking into."
Where Heat Escapes
Roof and Loft: Up to 25%
Heat rises. In winter, it rises right through your ceiling and into your loft, then out through your roof. Up to a quarter of your home's heat can escape this way.
Loft insulation is usually the cheapest and easiest fix. If you have less than 270mm depth, adding more is almost always worthwhile.
Walls: Up to 35%
Exterior walls account for the biggest heat loss in many homes. The solution depends on your wall type:
Cavity walls: Built after 1930, with a gap between inner and outer layers. This cavity can be filled with insulation relatively cheaply.
Solid walls: Built before 1930, typically a single layer of brick. These need insulation added to the inside or outside—much more expensive and disruptive.
Floors: Up to 10%
Ground floors can lose significant heat, especially in older properties with suspended timber floors and gaps around the edges.
Windows and Doors: Up to 25%
Single glazing, draughty frames, and gaps around doors all contribute. Double or triple glazing and proper draught-proofing help considerably.
Types of Insulation
Mineral Wool (Glass or Rock Wool)
The fluffy stuff you picture when someone says "insulation."
Pros:
- Cheapest option
- DIY-friendly for loft floors
- Fire-resistant
- Widely available
Cons:
- Irritating to handle (wear proper protection)
- Can compress over time, reducing effectiveness
- Doesn't air seal
Cost: £5-£15 per square metre for materials
Blown-In Insulation
Loose-fill material blown into cavities or loft spaces.
Pros:
- Fills irregular spaces and gaps
- Good for topping up existing insulation
- Less disruptive than other methods
Cons:
- Requires professional equipment
- Can settle over time
- Not suitable for all cavity walls
Cost: £15-£25 per square metre installed
Spray Foam
Liquid foam that expands and hardens. Available in open-cell and closed-cell varieties.
Pros:
- Air seals as it insulates
- Fills irregular spaces perfectly
- Long-lasting
Cons:
- Expensive
- Can cause issues with roof tiles and moisture if installed incorrectly
- Some mortgage lenders don't like it
- Difficult to remove
Cost: £25-£50 per square metre installed
Warning: Spray foam in lofts has caused mortgage problems for some homeowners. Lenders worry about roof ventilation and timber condition. Get proper advice before proceeding.
Rigid Board Insulation
Foam boards (PIR, EPS, XPS) used for walls, floors, and flat roofs.
Pros:
- High insulation value for thickness
- Structural strength
- Moisture-resistant (depending on type)
Cons:
- More expensive than mineral wool
- Needs careful installation to avoid gaps
- Flammable (requires proper fire barriers)
Cost: £15-£40 per square metre for materials
Costs for Different Insulation Projects
| Project | DIY Cost | Professional Cost | Annual Savings |
|---|---|---|---|
| Loft insulation (top-up to 270mm) | £200-£400 | £300-£600 | £200-£350 |
| Cavity wall insulation | N/A | £500-£1,500 | £150-£300 |
| Solid wall insulation (internal) | N/A | £5,000-£10,000 | £250-£450 |
| Solid wall insulation (external) | N/A | £10,000-£25,000 | £250-£450 |
| Floor insulation | £300-£600 | £600-£1,500 | £50-£100 |
| Draught-proofing | £50-£150 | £200-£400 | £50-£100 |
Grants and Funding
ECO4 (Energy Company Obligation)
Major energy suppliers must help low-income and vulnerable households improve energy efficiency. This can include free or heavily subsidised insulation.
You may qualify if you receive certain benefits (Pension Credit, Universal Credit, Child Tax Credit, etc.) or live in a low-income area.
Contact suppliers directly or use the Simple Energy Advice service to check eligibility.
Great British Insulation Scheme
Aimed at middle-income households in less efficient homes (EPC D-G). Provides cavity wall and loft insulation at no cost or reduced cost.
Eligibility depends on Council Tax band, EPC rating, and sometimes income.
Local Authority Grants
Some councils offer additional funding for insulation. Search "[your council name] energy grants" to see what's available locally.
Scottish and Welsh Schemes
Scotland has Warmer Homes Scotland and Home Energy Scotland loans. Wales has Nest and ECO Flex. Northern Ireland has affordable warmth schemes. These often have different eligibility criteria than English schemes.
Prioritising Your Upgrades
If you're working with a limited budget, here's the typical priority order:
- Draught-proofing: Cheapest, quick payback. Seal gaps around windows, doors, floorboards, and letterboxes.
- Loft insulation: If you have less than 270mm, topping up is almost always worthwhile. Often pays back in 1-2 years.
- Cavity wall insulation: If you have cavities that aren't filled. Good payback, typically 3-5 years.
- Hot water cylinder jacket: If you have an uninsulated tank. Costs £15-£25, saves £20-£40 per year.
- Floor insulation: Especially if you have a suspended timber floor with draughts underneath.
- Solid wall insulation: Expensive but valuable if you're renovating anyway or have a very inefficient solid-walled home.
British Property Types and Insulation Challenges
Different eras of British housing present unique insulation challenges:
Victorian and Edwardian Terraces (pre-1919)
Solid brick walls, single-glazed sash windows, suspended timber floors. These homes can lose 40% or more of their heat through walls alone. Options are limited to internal or external wall insulation—both expensive and disruptive. Many owners start with loft insulation and draught-proofing, leaving walls for a major renovation.
Inter-War Semi-Detached (1919-1945)
Often cavity walls, but the cavity may be very narrow (50-75mm). Some were built with solid walls. Worth checking before assuming cavity fill is possible. These homes often have good roof access for loft insulation.
Post-War Council Housing (1945-1970)
Mixed construction. Concrete pre-fab, traditional brick, or early cavity walls. Some non-traditional builds have specific insulation requirements. Check with your council or a surveyor before proceeding.
1970s-1990s Estates
Standard cavity walls (typically suitable for filling), reasonable loft access, double-glazed replacements common. These homes often respond well to standard insulation upgrades.
Modern New Builds (2000+)
Built to increasingly stringent building regulations. Many already have adequate insulation. Focus on air-tightness and any areas missed during construction.
DIY vs Professional Installation
DIY-friendly:
- Loft insulation (roll-out mineral wool)
- Draught-proofing around doors and windows
- Hot water cylinder jacket
- Letterbox draught excluder
- Chimney balloon or cap
Professional only:
- Cavity wall insulation (requires specialist equipment)
- Solid wall insulation (complex installation)
- Spray foam (specialist application)
- Underfloor insulation on suspended floors
- Flat roof insulation
Finding a Reputable Installer
For professional work, look for:
- TrustMark registration: Government-endorsed quality scheme
- PAS 2030 certification: Required for grant-funded work
- CIGA guarantee: 25-year guarantee for cavity wall insulation
- Multiple quotes: Get at least three and compare like-for-like
- Surveyor inspection: Good installers survey before quoting
Frequently Asked Questions
Q: How thick should loft insulation be?
A: Current recommendations are 270mm minimum for mineral wool. Many older homes have only 100mm or less—topping up is almost always worthwhile.
Q: Can cavity wall insulation cause damp?
A: In exposed locations (driving rain), poorly installed cavity fill can lead to damp problems. A proper survey should assess exposure levels. West-facing walls in exposed areas may not be suitable.
Q: Is spray foam insulation worth it?
A: Spray foam offers excellent performance but has downsides. Some mortgage lenders won't lend on properties with spray foam in the roof. It can cause ventilation issues if installed incorrectly. Get independent advice before proceeding.
Q: Will insulation make my house too hot in summer?
A: Insulation keeps heat out as well as in. Well-insulated homes are often more comfortable in summer. Proper ventilation matters though—don't seal everything without considering airflow.
Q: How long does cavity wall insulation take?
A: Typically 2-4 hours for a semi-detached house. The installer drills small holes in the mortar joints, injects insulation, and fills the holes. Minimal disruption.
Q: Can I insulate a listed building?
A: Yes, but you may need listed building consent for visible changes. Internal insulation and loft insulation usually don't require consent. Check with your local conservation officer.
The Bottom Line
Insulation isn't glamorous, but it's often the smartest first step in home energy improvement. Better insulation makes every other system—your boiler, heat pump, or radiators—work more effectively.
If you're planning a heat pump, check your insulation first. The better insulated your home, the smaller the heat pump you need and the better it performs. Many installers won't fit a heat pump until insulation is sorted.
Start with an EPC assessment if you haven't had one recently. See where you're losing heat. Then tackle the cheapest, highest-impact improvements first—usually draught-proofing and loft insulation. Work your way up to more expensive measures as budget allows.
Don't forget to check grant eligibility before paying full price. ECO4 and the Great British Insulation Scheme have helped thousands of British homeowners get free or subsidised insulation. Your postcode and circumstances might qualify you for support you didn't know existed.