What does the Insulation Calculator do?

Compare loft, cavity wall, solid wall and floor insulation costs, savings and payback periods. All calculations are performed in your browser using official UK rates and thresholds.

Does this include waste allowance?

Yes. Most building material calculations include a standard 10% waste allowance. You can adjust this figure depending on the complexity of your project and cutting requirements.

Material prices are indicative estimates based on average UK prices. Actual costs vary by region, supplier, brand and current market conditions. Always get quotes from local suppliers.

Insulation Calculator

Compare loft, cavity wall, solid wall and floor insulation costs, savings and payback periods.

Last updated: April 2026 · Source: Energy Saving Trust — Insulation

Insulation Type

Area to Insulate (m²)

Installation Cost

£400.00

Annual Saving

£355.00

Payback

1.1 years

10yr Net Saving

£3,150.00

Disclaimer

This calculator is provided for informational purposes only and should not be considered as financial or tax advice. All calculations are performed locally in your browser — no personal data is collected or sent to our servers. Rates and thresholds are sourced from HMRC and GOV.UK and are updated for the current tax year. Always verify results with HMRC or consult a qualified professional before making financial decisions.

How It Works

Insulation is one of the most cost-effective energy efficiency improvements for UK homes. Loft insulation to the recommended 270mm depth costs £300-£600 and saves approximately £180-£250 per year. Cavity wall insulation costs £500-£1,500 and saves £150-£300 per year. These short payback periods make insulation an excellent investment.

Solid wall insulation (internal or external) is more expensive at £4,000-£14,000 per property but saves £200-£400 per year. Floor insulation costs £500-£1,000 for a timber floor and saves £40-£70 per year. Draught-proofing windows and doors costs £100-£300 and saves £30-£60 per year.

Government schemes may help cover the cost. The Great British Insulation Scheme provides insulation measures free or at reduced cost to eligible households. This calculator estimates the materials needed, installation cost and annual savings for each insulation type based on your property's characteristics.

Example: 1960s 3-bed semi, no loft or cavity wall insulation

Loft insulation (270mm): £450 installed
Annual saving: £220
Payback period: 2 years
Cavity wall insulation: £800 installed
Annual saving: £280
Payback period: 2.9 years
Combined annual saving: £500

Source: Energy Saving Trust — Insulation

Frequently Asked Questions

What does the Insulation Calculator do?: Compare loft, cavity wall, solid wall and floor insulation costs, savings and payback periods. All calculations are performed in your browser using official UK rates and thresholds.
Does this include waste allowance?: Yes. Most building material calculations include a standard 10% waste allowance. You can adjust this figure depending on the complexity of your project and cutting requirements.
Are prices accurate?: Material prices are indicative estimates based on average UK prices. Actual costs vary by region, supplier, brand and current market conditions. Always get quotes from local suppliers.