Home Insulation Types and Costs Compared
Loft, cavity wall, and solid wall insulation costs per square metre, energy savings, and which upgrades deliver the best return for your home.
Insulation is the single most cost-effective way to reduce energy bills, improve comfort, and boost your EPC rating. Yet millions of UK homes remain under-insulated - costing their owners hundreds of pounds every year in wasted heat. Whether you're tackling a draughty Victorian terrace or upgrading a 1970s semi, understanding which insulation to prioritise makes the difference between money well spent and money wasted.
Insulation Priority Order
Not all insulation delivers equal value. Here's the order most UK homeowners should follow:
| Priority | Insulation Type | Cost | Annual Saving | Payback |
|---|---|---|---|---|
| 1 | Loft insulation (270mm) | £300–£600 | £150–£300 | 1–3 years |
| 2 | Cavity wall insulation | £500–£1,500 | £150–£400 | 2–5 years |
| 3 | Draught-proofing | £100–£300 | £30–£60 | 1–3 years |
| 4 | Hot water cylinder jacket | £20–£50 | £30–£80 | Under 1 year |
| 5 | Floor insulation | £500–£1,500 | £50–£100 | 5–15 years |
| 6 | Solid wall insulation | £5,000–£15,000 | £300–£600 | 10–25 years |
Always start at the top. There's no point spending £10,000 on wall insulation if your loft has 50mm of insulation and your hot water cylinder is bare.
Loft Insulation
The Basics
The recommended depth is 270mm of mineral wool (glass or rock wool). Many UK homes have some loft insulation, but often only 100–150mm - well below current standards.
| Scenario | Cost | DIY Possible? |
|---|---|---|
| Top-up from 100mm to 270mm | £200–£400 | Yes |
| New installation (0 to 270mm) | £400–£800 | Yes |
| Loft room insulation (between and over rafters) | £1,500–£3,000 | Professional recommended |
DIY tip: Mineral wool rolls from B&Q or Wickes cost £5–£8 per m². For a 50m² loft, materials cost £150–£300. Lay the first layer between joists, the second at right angles across the top.
Loft Boarding Considerations
If you want to board your loft for storage after insulating, use loft legs (stilts) to raise the boards above the insulation. Compressing insulation by laying boards directly on top defeats the purpose - compressed mineral wool loses its thermal performance.
- Loft legs and boarding: £30–£50 per m² installed
Cavity Wall Insulation
How It Works
An insulation material is injected through small holes drilled in the external brickwork, filling the cavity (typically 50–75mm wide) between the inner and outer walls.
| Material | Cost (3-bed semi) | Thermal Performance | Notes |
|---|---|---|---|
| Mineral wool (blown) | £500–£1,000 | Good | Most common, well-proven |
| EPS beads (polystyrene) | £500–£1,200 | Good | Better for narrow or uneven cavities |
| Polyurethane foam | £800–£1,500 | Excellent | Best performance, highest cost |
Is Your Home Suitable?
Cavity wall insulation works well in most homes, but isn't suitable for:
- Solid walls (no cavity to fill - see below)
- Walls with severe damp problems that need resolving first
- Properties in very exposed locations where driving rain penetrates the outer leaf
- Walls where the cavity is less than 40mm wide
A reputable installer will survey your property and advise on suitability before quoting.
Solid Wall Insulation
Pre-1930 UK homes typically have solid walls (a single thickness of brick or stone) with no cavity. These walls lose heat 2–3 times faster than insulated cavity walls. Solid wall insulation is the most expensive but highest-impact upgrade for these properties.
External Wall Insulation (EWI)
Rigid insulation boards are fixed to the outside of the house and covered with a protective render finish.
| Item | Cost |
|---|---|
| Insulation boards (100mm EPS or mineral wool) | £30–£50 per m² |
| Render finish (silicone or monocouche) | £40–£70 per m² |
| Scaffolding | £1,000–£2,500 |
| Window reveals, sills, and detailing | £1,000–£3,000 |
| Total (3-bed semi, ~80m² wall area) | £8,000–£15,000 |
Pros: No loss of internal space, dramatic EPC improvement (10–20 SAP points), new external appearance
Cons: Changes the building's appearance (check planning in conservation areas), expensive, scaffolding required
Internal Wall Insulation (IWI)
Insulated plasterboard is fixed to internal walls, either on battens (with insulation between) or as laminated boards bonded directly to the wall.
| Method | Cost per m² | Thickness Added | Notes |
|---|---|---|---|
| Insulated plasterboard (dot-and-dab) | £35–£55 | 40–60mm | Simplest, some cold bridging |
| Battens + PIR insulation + plasterboard | £45–£70 | 60–90mm | Better performance, more space lost |
| Aerogel blanket + plasterboard | £80–£120 | 25–40mm | Thinnest option, most expensive |
Total for a 3-bed semi: £5,000–£10,000
Pros: Cheaper than EWI, no external change, can be done room by room
Cons: Reduces room sizes by 50–90mm per insulated wall, disrupts skirting boards, window reveals, sockets, and radiator positions. Requires replastering and redecoration.
Floor Insulation
Suspended Timber Floors
Many pre-1950 UK homes have suspended timber ground floors with a ventilated void beneath. These can be insulated from below (if there's crawl space) or from above during floor replacement.
| Method | Cost | Notes |
|---|---|---|
| Insulation from below (mineral wool between joists) | £500–£1,500 (professional) | Requires crawl space access |
| Insulation from above (rigid board between joists) | £20–£35 per m² | Done during floor renovation |
| Draught-proofing floorboards only | £100–£300 | Fills gaps, stops draughts |
Solid Concrete Floors
Insulating a solid floor means laying rigid insulation boards on top, then a new screed or floating floor. This raises the floor level by 75–100mm.
- Cost: £30–£50 per m² (insulation + new floor)
- When practical: During a major renovation, extension, or garage conversion when the floor is being relaid anyway
Grants and Funding
| Scheme | What It Covers | Eligibility |
|---|---|---|
| Great British Insulation Scheme | Cavity wall, loft, solid wall, flat roof insulation | Council tax bands A–D (England), or qualifying benefits |
| ECO4 | Insulation, heating upgrades, ventilation | Low-income households on specific benefits |
| Boiler Upgrade Scheme | Heat pumps (not insulation directly) | Homeowners with valid EPC |
| Local authority grants | Varies by council | Check your council's website |
These schemes can reduce costs by 50–100% for eligible households. The Energy Saving Trust provides up-to-date guidance on available grants. Always check eligibility before paying full price.
Insulation and Your EPC
| Improvement | Typical SAP Points Gained | EPC Band Impact |
|---|---|---|
| Loft insulation (0 → 270mm) | 5–10 | Can move up one band |
| Cavity wall insulation | 5–15 | Often moves up one band |
| Solid wall insulation | 10–20 | Can move up 1–2 bands |
| Floor insulation | 2–5 | Minor improvement |
For more on how insulation affects your property value and EPC rating, see our EPC guide.
Next Steps
- Check your loft - measure existing insulation depth. Under 200mm? Top it up.
- Check your walls - cavity or solid? Filled or unfilled? Your EPC report tells you.
- Check grant eligibility - you may qualify for free or subsidised insulation
- Get a professional assessment - an energy assessor can prioritise improvements (£60–£120 for an EPC)
- Get quotes - use our repair calculator for insulation cost estimates
- Read about which improvements add most value to prioritise spending
- Check our glossary for terms like U-value, PIR, mineral wool, and thermal bridging
Frequently Asked Questions
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