Home Insulation in the UK: Complete Guide
Insulation is the single most cost-effective way to reduce energy bills and improve your home’s EPC rating. A well-insulated home loses far less heat through walls, roofs, and floors — cutting heating costs by 25–45% and making heat pumps and solar panels work more efficiently.
Loft insulation costs as little as £300–£500 and pays for itself in 1–2 years. Cavity wall insulation costs £500–£1,500. Both are available free via ECO4 and the Great British Insulation Scheme for eligible households.
Last updated March 2026
Fact-checked by John Rooney, Solar Energy Editor. Editorial policy
Quick Answer
Loft insulation costs £300–£500, cavity wall insulation £500–£1,500, and external wall insulation £8,000–£13,000. Both loft and cavity wall insulation are available free via ECO4 and GBIS for eligible households. Insulation is the best first step before installing solar panels or heat pumps, cutting heating bills by 25–45%.
Where does your home lose heat?
An uninsulated UK home loses heat through every surface. Understanding where heat escapes helps you prioritise which insulation to install first.
| Area | Heat Loss | Solution | Typical Cost |
|---|---|---|---|
| Roof / Loft | 25–30% | Loft insulation (270mm mineral wool) | £300–£500 |
| Walls | 30–35% | Cavity wall or external wall insulation | £500–£13,000 |
| Windows & Doors | 15–20% | Double/triple glazing, draught-proofing | £3,000–£8,000 |
| Floor | 10–15% | Underfloor or suspended floor insulation | £500–£1,500 |
| Draughts | 5–10% | Draught-proofing strips, chimney balloons | £50–£200 |
Source: Energy Saving Trust. Percentages are approximate for a typical uninsulated semi-detached house.
Types of home insulation
The right insulation depends on your home’s construction. Cavity walls (most homes built after 1930) are cheapest to insulate. Solid walls (older homes) cost more but benefit most.
Loft Insulation
The cheapest and most effective insulation upgrade. Mineral wool rolls (glass or rock wool) are laid between and over the joists to a depth of 270mm. If your loft has less than 100mm, topping up is the best place to start.
- Cost: £300–£500 (professional)
- DIY cost: £100–£200 (materials only)
- Savings: £200–£300/year
- Payback: 1–2 years
- Often free via ECO4 or GBIS
Cavity Wall Insulation
Homes built after 1930 typically have two layers of brick with a gap (cavity) between them. Insulation is injected through small holes drilled in the outer wall. The holes are filled and repointed afterwards.
- Cost: £500–£1,500
- Savings: £300–£500/year
- Payback: 1–3 years
- Materials: mineral wool, EPS beads, or polyurethane foam
- Often free via ECO4 or GBIS
External Wall Insulation (EWI)
Boards of insulation are fixed to the outside of the wall, then covered with render or cladding. Best for solid-wall homes (pre-1930) where cavity wall insulation isn’t possible.
- Cost: £8,000–£13,000
- Savings: £400–£700/year
- Payback: 12–20 years (without grant)
- Also refreshes the exterior appearance
- May require planning permission
Internal Wall Insulation (IWI)
Insulation boards or stud wall with insulation are fitted to the inside of external walls. Cheaper than EWI but reduces room size slightly (50–100mm per wall).
- Cost: £4,000–£8,000
- Savings: £350–£600/year
- Payback: 8–14 years (without grant)
- No planning permission needed
- Can be disruptive (redecoration required)
Floor Insulation
Suspended timber floors can be insulated from below (through the crawl space) using mineral wool or rigid board. Solid concrete floors can be insulated on top, but this raises the floor level.
- Cost: £500–£1,500 (suspended floor)
- Savings: £60–£120/year
- Payback: 5–12 years
- Concrete floor insulation: £1,500–£3,000+
Room-in-Roof Insulation
If your loft has been converted into a room, insulation must go between the rafters rather than on the loft floor. Rigid insulation boards or spray foam are used between and below the rafters.
- Cost: £1,500–£4,000
- Savings: £300–£500/year
- Payback: 4–8 years
- Critical for converted lofts and dormer rooms
Insulation costs in the UK (2026)
Costs vary by insulation type, house size, and region. The table below shows typical costs for a 3-bed semi-detached house.
| Insulation Type | Cost (3-bed semi) | Annual Saving | Payback | Free via Grant? |
|---|---|---|---|---|
| Loft (0 to 270mm) | £300–£500 | £200–£300 | 1–2 years | ECO4 / GBIS |
| Loft top-up (100mm to 270mm) | £200–£350 | £50–£100 | 2–4 years | GBIS |
| Cavity wall | £500–£1,500 | £300–£500 | 1–3 years | ECO4 / GBIS |
| External wall (EWI) | £8,000–£13,000 | £400–£700 | 12–20 years | ECO4 |
| Internal wall (IWI) | £4,000–£8,000 | £350–£600 | 8–14 years | ECO4 |
| Floor (suspended timber) | £500–£1,500 | £60–£120 | 5–12 years | ECO4 |
| Room-in-roof | £1,500–£4,000 | £300–£500 | 4–8 years | ECO4 |
Source: Energy Saving Trust, 2026. Savings based on gas heating at typical domestic tariff. Actual savings depend on home size, heating usage, and fuel type.
Free insulation grants (2026)
Two government-backed schemes provide free or heavily subsidised insulation for eligible UK households. You do not need to apply separately — an approved installer handles the application.
ECO4 (Energy Company Obligation)
The main scheme for free insulation and heating upgrades. Large energy suppliers fund improvements for low-income and fuel-poor households. Runs until March 2026.
- Free loft, cavity wall, external wall, and floor insulation
- Free first-time central heating and boiler upgrades
- Free solar panels (in some cases)
- Eligibility: receiving qualifying benefits OR via LA Flex
- Home must have EPC rating of D, E, F, or G
Great British Insulation Scheme (GBIS)
Targets homes with poor insulation regardless of income. Broader eligibility than ECO4 — you may qualify based on your home’s EPC rating and council tax band alone.
- Free loft insulation and cavity wall insulation
- Covers loft top-ups (from 100mm to 270mm+)
- Eligibility: council tax bands A–D in England and Wales
- Or: receiving qualifying benefits (any band)
- Home must have EPC rating of D, E, F, or G
Apply through an approved installer or your energy supplier.
| Scheme | Eligibility | Measures Covered | Runs Until |
|---|---|---|---|
| ECO4 | Low income / benefits / LA Flex | All insulation types, heating, solar | March 2026 |
| GBIS | Council tax band A–D (or benefits) | Loft and cavity wall insulation | March 2026 |
| HUG2 (Home Upgrade Grant) | Low income, off-gas-grid homes | Insulation, heat pumps, solar | March 2025 (closed) |
How much can insulation save on energy bills?
The savings depend on your home’s size, fuel type, and current insulation level. The figures below are based on Energy Saving Trust data for a typical gas-heated 3-bed semi-detached house.
| Measure | Annual Saving (Gas) | Annual Saving (Oil) | Annual Saving (Electric) |
|---|---|---|---|
| Loft insulation (0→270mm) | £250 | £310 | £475 |
| Cavity wall insulation | £395 | £475 | £745 |
| External wall insulation | £540 | £650 | £1,020 |
| Floor insulation | £85 | £105 | £160 |
| Loft + Cavity (combined) | £645 | £785 | £1,220 |
Source: Energy Saving Trust, 2026. Figures for a 3-bed semi-detached house. Savings for detached homes are approximately 30–50% higher.
What insulation should I install first?
Prioritise the cheapest measures with the fastest payback first. This order works for most UK homes:
Loft insulation (or top-up)
If you have less than 270mm, top up. The cheapest measure and often free via GBIS. Saves £200–£300/year. Can be DIY if your loft is accessible.
Cavity wall insulation
If your home has unfilled cavity walls (most post-1930 homes). Quick to install (half a day), often free via ECO4 or GBIS. Saves £300–£500/year.
Draught-proofing
Seal gaps around doors, windows, letterboxes, and chimneys. Very cheap (£50–£200) and often DIY. Saves £60–£100/year.
Floor insulation
Suspended timber floors can be insulated from below. Worth doing if you have accessible crawl space. Moderate savings.
Solid wall insulation (EWI or IWI)
The biggest saving but most expensive measure. Consider if your home has solid walls (pre-1930) and you’re eligible for ECO4 funding. Otherwise, do this when you’re already having external work done.
Insulation and your EPC rating
Insulation has the biggest impact on your EPC rating of any single measure. Adding loft and cavity wall insulation to an uninsulated home can improve your rating by 1–2 bands (e.g. E→C or D→B).
| Measure | Typical EPC Impact | SAP Points Gained |
|---|---|---|
| Loft insulation (270mm) | +5 to +10 points | Can move up 1 band |
| Cavity wall insulation | +10 to +15 points | Can move up 1–2 bands |
| External wall insulation | +15 to +25 points | Can move up 2+ bands |
| Floor insulation | +3 to +5 points | Minor improvement |
| Loft + Cavity (combined) | +15 to +25 points | Often enough for 1–2 band jump |
This matters for rental properties — landlords in England and Wales must achieve a minimum EPC E rating. From 2026, an EPC C target is expected for new tenancies. Insulation is the cheapest way to reach these thresholds.
A note on spray foam insulation
Spray foam insulation has become popular for loft rafters and underfloor use, but it comes with risks. Some mortgage lenders refuse to lend on homes with spray foam applied to roof timbers because it can mask structural issues and prevent timber inspection.
Frequently Asked Questions
How do I know if my walls are cavity or solid?
Homes built after 1930 usually have cavity walls. You can check by measuring the wall thickness — cavity walls are typically 27–30cm thick, solid walls are 23cm or less. Alternatively, look at the brick pattern: if all bricks are uniform (stretcher bond), it's likely a cavity wall. If you see alternating long and short bricks (Flemish bond or English bond), it's solid. A surveyor or insulation installer can confirm.
How do I check if I already have cavity wall insulation?
Your EPC certificate will state your wall insulation status. You can also have an installer drill a small inspection hole to check. If your home was built after 1995, it may already have cavity wall insulation as it became a building regulation requirement.
Is loft insulation a DIY job?
Yes, laying mineral wool rolls in an accessible loft is a straightforward DIY job. You'll need 270mm total depth (two layers: 100mm between joists, 170mm across joists). Use a dust mask, gloves, and knee boards. Budget £100–£200 for materials. Professional installation costs £300–£500 and is often free via GBIS.
Will insulation make my home too airtight?
No. Insulation reduces heat loss but does not eliminate ventilation. UK building regulations require adequate ventilation. If you significantly improve airtightness (e.g. with external wall insulation), an installer may recommend trickle vents or a mechanical ventilation system (MVHR) to ensure good air quality.
Can I get free insulation if I'm not on benefits?
Yes. The Great British Insulation Scheme (GBIS) is available to homeowners in council tax bands A–D in England and Wales, regardless of income. You don't need to be on benefits. Your home must have an EPC rating of D or below. The scheme covers loft insulation and cavity wall insulation.
Does insulation help with heat pumps?
Absolutely. Heat pumps run at lower temperatures than gas boilers, so good insulation is essential. Most heat pump installers carry out a heat loss calculation and may require insulation upgrades before installing a heat pump. Insulating first can also reduce the heat pump size (and cost) needed.
How long does insulation last?
Mineral wool loft insulation lasts 40+ years if undisturbed. Cavity wall insulation (blown mineral wool or EPS beads) lasts 25+ years. External wall insulation systems typically last 30+ years with the render coating needing maintenance every 15–20 years. Spray foam insulation lasts 25+ years.
Will insulation increase my property value?
Yes. Insulation improves your EPC rating, which directly affects property value. Research from the Department of Energy suggests that moving from EPC band E to C can add £10,000–£16,000 to a property's value. Even without selling, insulation reduces energy bills from day one.
Related Guides
ECO4 Scheme
ECO4 eligibility, free measures, how to apply, and common scams to avoid.
EPC Upgrades
Improve your EPC rating. Costs, grants, and property value impact.
Heat Pumps
Air source & ground source heat pumps: costs, BUS grant up to £7,500.
Whole-House Retrofits
Whole-house energy upgrades with ECO4 and HUG2 schemes.
Sources
John Rooney is the founder of Solar Info and has been covering the UK solar energy market since 2023. He fact-checks all content against official MCS and Ofgem data and maintains relationships with MCS-certified installers across the UK.