Insulation Calculator UK
Free Insulation UK | Home Insulation Cost calculator for the UK. Get instant, accurate results with our easy-to-use online tool. Updated for 2025/26 with...
Last updated: February 2026
Insulation Calculator
Calculate insulation materials needed for walls, loft, and floors. Get cost estimates and energy savings.
About This Calculator
This free insulation calculator helps UK residents make accurate calculations quickly and easily. All calculations are performed instantly in your browser - no data is stored or shared.
- 100% Free - No registration or payment required
- Instant Results - Calculate in real-time
- Mobile Friendly - Works on all devices
- Privacy Focused - All calculations done locally
- Updated 2025 - Latest UK rates and regulations
How to Use This Insulation Calculator
- Measure Your Space: Use a tape measure to determine the length and height of the area you want to insulate. For loft insulation, measure the floor area of your loft.
- Enter Dimensions: Input your measurements in metres. For irregular spaces, calculate separate sections and add them together.
- Select Material Type: Choose between Standard (mineral wool), Premium (PIR/PUR boards) or Budget (glass wool) options based on your needs and budget.
- Calculate: Click "Calculate Now" to see rolls needed, total cost and estimated annual energy savings.
- Review Results: The payback period shows how quickly your investment will be recovered through reduced energy bills.
UK Insulation Types & U-Values
UK Building Regulations Part L require specific U-values (thermal transmittance) for different building elements. Lower U-values mean better insulation. The table below shows common insulation types and their typical performance.
| Insulation Type | Application | Typical Thickness | Cost per m² |
|---|---|---|---|
| Mineral Wool (Glass/Rock) | Loft, walls, floors | 270mm (loft), 100mm (walls) | £4-8 |
| PIR/PUR Boards | Walls, floors, flat roofs | 50-120mm | £15-35 |
| Expanded Polystyrene (EPS) | External wall, floors | 100-200mm | £8-15 |
| Spray Foam | Loft, walls (professional only) | 100-150mm | £20-50 |
| Sheep's Wool | Loft, timber frame walls | 200-300mm | £12-25 |
| Wood Fibre | Walls, roofs (breathable) | 120-200mm | £25-45 |
UK Building Regulations U-Values (2025)
Building Regulations Approved Document L (Conservation of Fuel and Power) sets minimum thermal performance standards. These U-values apply to new builds and extensions in England and Wales:
| Building Element | New Build U-Value | Extension U-Value | Best Practice |
|---|---|---|---|
| Pitched Roof (Loft) | 0.11 W/m²K | 0.16 W/m²K | 0.10 W/m²K |
| Flat Roof | 0.11 W/m²K | 0.16 W/m²K | 0.10 W/m²K |
| Walls | 0.18 W/m²K | 0.28 W/m²K | 0.15 W/m²K |
| Ground Floor | 0.13 W/m²K | 0.18 W/m²K | 0.10 W/m²K |
| Windows | 1.2 W/m²K | 1.4 W/m²K | 0.8 W/m²K |
| Doors | 1.0 W/m²K | 1.4 W/m²K | 0.8 W/m²K |
Note: Scotland has separate Building Standards with slightly different requirements. Northern Ireland follows similar standards to England and Wales.
UK Government Insulation Grants (2025)
The UK government offers several schemes to help homeowners reduce insulation costs. Check your eligibility below:
ECO4 Scheme
Free insulation for low-income households and those receiving qualifying benefits. Covers loft, cavity wall, and solid wall insulation.
- Income Support, JSA, ESA, Universal Credit
- Working Tax Credit, Child Tax Credit
- Pension Credit Guarantee
- Child Benefit (income limits apply)
Great British Insulation Scheme
For homes with EPC rating D, E, F or G. Provides support for cavity wall and loft insulation regardless of income.
- Available to homeowners and landlords
- Properties with EPC D-G eligible
- Partial funding for most applicants
- Full funding for lower Council Tax bands
Boiler Upgrade Scheme
While primarily for heat pumps, this scheme works best with proper insulation. £7,500 towards air source heat pump installation.
- Valid EPC required (not older than 10 years)
- Loft insulation may be recommended
- Available until 2028
- Must use MCS certified installer
LA Flex (Local Authority Flex)
Local councils can extend ECO eligibility to households in fuel poverty, even without qualifying benefits.
- Low household income (varies by council)
- Health conditions worsened by cold
- Living in cold/damp conditions
- Contact your local council to apply
Typical Energy Savings by Insulation Type
Based on Energy Saving Trust data for a typical semi-detached home with gas heating. Actual savings depend on property size, current insulation levels, and energy prices.
| Insulation Measure | Annual Saving | Typical Cost (DIY) | Typical Cost (Pro) | Payback |
|---|---|---|---|---|
| Loft Insulation (0 to 270mm) | £315/year | £300-400 | £600-900 | 1-3 years |
| Loft Top-up (120 to 270mm) | £55/year | £150-200 | £300-400 | 3-7 years |
| Cavity Wall Insulation | £295/year | N/A (pro only) | £500-1,500 | 2-5 years |
| Solid Wall (Internal) | £395/year | N/A (pro only) | £8,000-12,000 | 20-30 years |
| Solid Wall (External) | £395/year | N/A (pro only) | £12,000-22,000 | 30-55 years |
| Floor Insulation | £110/year | £500-800 | £1,000-2,500 | 5-23 years |
| Hot Water Cylinder Jacket | £45/year | £15-25 | £25-50 | <1 year |
| Draught Proofing | £60/year | £50-150 | £200-400 | 1-7 years |
Source: Energy Saving Trust, 2025. Based on average UK energy prices of £0.245/kWh for gas.
Frequently Asked Questions
UK Building Regulations recommend 270mm of mineral wool insulation for lofts (or equivalent thermal performance). This achieves a U-value of approximately 0.16 W/m²K. If you have existing insulation, you may only need a top-up layer to reach 270mm.
Yes, loft insulation is one of the easiest DIY home improvement projects. Rolls of mineral wool are lightweight and simply laid between joists and over the top. Wear protective gloves, goggles and a dust mask. Avoid compressing the insulation and don't block roof vents or eaves. For boarded lofts, you'll need to lift boards first.
The best insulation depends on your application. For lofts, mineral wool (glass wool or rock wool) offers excellent value at £4-8 per m². For walls, cavity wall insulation is most cost-effective if you have a cavity. For solid walls, internal dry-lining with PIR boards is cheaper than external insulation but reduces room size.
Most UK homes built between 1930 and 1990 have cavity walls. Check the thickness - cavity walls are typically 25-30cm (10-12 inches) thick. You can also use a borescope through a drilled hole, or check your EPC certificate. Homes built before 1920 typically have solid walls. A professional surveyor can confirm definitively.
Spray foam can be effective but has drawbacks. Some mortgage lenders and surveyors view spray foam negatively as it can mask roof defects and make inspection difficult. Open-cell spray foam may cause moisture issues in cold roofs. Always use a reputable installer with guarantees, and check with your mortgage lender before installation.
External wall insulation (EWI) usually falls under permitted development rights, meaning no planning permission is needed. However, you'll need planning permission if your property is listed, in a conservation area, or if EWI significantly changes the building's appearance. Always check with your local planning authority before proceeding.
The main UK insulation grants in 2025 are: ECO4 Scheme (free insulation for those on qualifying benefits), Great British Insulation Scheme (for EPC D-G rated homes), and LA Flex (council-administered for fuel-poor households). Scotland has additional schemes like Warmer Homes Scotland. Check Simple Energy Advice (gov.uk) for eligibility.
Most insulation materials last the lifetime of the building (50+ years) if kept dry and undisturbed. Mineral wool doesn't degrade over time. However, insulation can become compressed, damaged by pests, or waterlogged. Spray foam may shrink over decades. Inspect your loft insulation every few years and top up if it has settled or become thin.
Expert Tips for Insulation
1. Double-Check Your Input Values
Ensure all values entered are accurate and in the correct units. Small input errors can significantly affect results. UK calculators typically use metric units (kg, cm) unless otherwise specified.
2. Understand the Calculation Method
This calculator uses standard formulas recognised in the UK. Results are estimates - actual values may vary based on individual circumstances not captured by general formulas.
3. Use Results as Starting Points
Calculator results provide guidance, not definitive answers. For important decisions involving money or health, consult qualified professionals such as financial advisors or NHS services.
4. Compare Multiple Scenarios
Try different input values to understand how changes affect results. This helps you make informed decisions and plan for various outcomes.
5. Save Important Results
Screenshot or note down significant calculations for future reference. This is especially useful for financial planning, health tracking, or comparing options over time.
6. Check Official Sources
While we strive for accuracy, always verify important information with official UK sources such as HMRC, NHS, or relevant regulatory bodies for current rates and guidelines.
7. Use on a Stable Internet Connection
For the best experience, use this calculator on a stable internet connection. Results calculate instantly in your browser without needing to submit forms or wait for server responses.
8. Provide Feedback
If you notice any issues or have suggestions for improving this calculator, please contact us. User feedback helps us maintain accuracy and usefulness.
Common Mistakes to Avoid
1. Entering Incorrect Units
Confusing kg with stones, or cm with inches, dramatically affects results. UK calculators typically expect metric inputs. Check unit labels carefully before entering values.
2. Rounding Input Values
Using rounded estimates (e.g., "about 70kg") instead of accurate measurements introduces errors. Where possible, use precise values for more accurate results.
3. Ignoring Important Variables
Not all factors may be captured by this calculator. Individual circumstances, exceptions, and special cases may not be reflected in standard formulas.
4. Treating Estimates as Exact
Calculator results are estimates based on typical scenarios. Your actual figures may differ based on factors not included in the calculation.
5. Using Outdated Information
UK rates, regulations, and guidelines change. While we update regularly, always verify critical information with official sources for current data.
6. Not Considering Context
Results should be interpreted within your specific situation. What applies generally may not apply to your particular circumstances.
7. Making Major Decisions Without Professional Advice
For significant financial or health decisions, calculator results should supplement - not replace - professional guidance from qualified advisors.
8. Assuming All Calculators Are Equal
Different calculators may use different formulas or assumptions. Results from our UK-specific calculator may differ from generic international tools.
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Expert Reviewed — This calculator is reviewed by our team of financial experts and updated regularly with the latest UK tax rates and regulations. Last verified: February 2026.
Last updated: February 2026 | Verified with latest UK rates
Pro Tips for Accurate Results
- Double-check your input values before calculating
- Use the correct unit format (metric or imperial)
- For complex calculations, break them into smaller steps
- Bookmark this page for quick future access
Understanding Your Results
Our Insulation Calculator provides:
- Instant calculations - Results appear immediately
- Accurate formulas - Based on official UK standards
- Clear explanations - Understand how results are derived
- 2025/26 updated - Using current rates and regulations
Common Questions
Is this calculator free?
Yes, all our calculators are 100% free to use with no registration required.
Are the results accurate?
Our calculators use verified formulas and are regularly updated for accuracy.
Can I use this on mobile?
Yes, all calculators are fully responsive and work on any device.
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