The Complete UK Home Insulation Guide 2025: Where to Start & What Works Best

Last updated: May 2025

If your home feels cold, costs a fortune to heat, or you’re simply looking to reduce your carbon footprint, insulation is the single most effective upgrade you can make. But with so many options—cavity wall, internal wall, loft insulation, and more—knowing where to start can feel overwhelming.

This comprehensive guide cuts through the confusion, showing you exactly which insulation upgrades to prioritise, what they cost, and how to access free funding through government schemes.

Quick Answer: Where Should You Start?

Based on decades of building science research and real-world retrofit data, here’s the optimal order for insulation upgrades:

1. Loft insulation (if less than 270mm) – £300-800, saves £150-250/year
2. Cavity wall insulation (if you have cavity walls) – £400-800, saves £150-300/year
3. Draught-proofing – £100-300, saves £50-90/year
4. Solid wall insulation (internal or external) – £2,000-15,000, saves £250-600/year
5. Floor insulation – £800-2,000, saves £60-150/year

Understanding Your Home’s Heat Loss

According to the Building Research Establishment (BRE) and Energy Saving Trust, the average uninsulated UK home loses heat through:

• 35% through walls (the biggest single loss)
• 25% through the roof
• 15% through draughts
• 15% through floors
• 10% through windows

This data makes it clear: walls and roofs should be your priority. But the best starting point depends on your home’s current insulation levels and construction type.

Loft Insulation: Your First Priority

Why Start Here?

Loft insulation offers the best return on investment of any insulation upgrade. Heat rises, and without proper loft insulation, it escapes straight through your roof. Most UK homes built before 1990 have inadequate loft insulation.

Current Standards

• Recommended depth: 270mm (about 11 inches)
• If you have less than 100mm: Upgrade immediately
• If you have 100-200mm: Top up to current standards

Cost and Savings

• DIY cost: £300-500 for materials
• Professional installation: £500-800
• Annual savings: £150-250
• Payback period: 2-5 years

Types of Loft Insulation

DIY vs Professional Installation

Note: If you’re on benefits or have a low income, you may qualify for free loft insulation through the ECO4 scheme. Our recommended provider, Blueape Renewables, can check your eligibility and arrange installation at no cost.

Wall Insulation: The Biggest Impact

First: What Type of Walls Do You Have?

Not sure? Check your Energy Performance Certificate (EPC) or measure the thickness at a door or window.

Cavity Wall Insulation

If you have unfilled cavity walls, this should be your second priority after loft insulation.

Solid Wall Insulation

For older homes with solid walls, you have two main options:

Internal Wall Insulation (IWI)

Cost: £2,000-4,000 (DIY) or £4,000-8,000 (professional)

External Wall Insulation (EWI)

Cost: £8,000-15,000

Modern Insulation Materials

Draught-Proofing: Quick Wins

Often overlooked, draught-proofing offers the fastest payback of any energy efficiency measure.

Where to Check

DIY Solutions

• Brush strips: £5-10 per door
• Foam strips: £3-5 per window
• Silicone sealant: £5-10 per tube
• Chimney balloons: £20-30
• Keyhole covers: £5-10

Total DIY cost: £100-200 for average home Annual savings: £50-90 Payback: Often under 1 year

Professional Draught-Proofing

For comprehensive draught-proofing, including difficult areas like suspended floors, consider professional help. Cost: £300-500.

Floor Insulation: Worth Considering

While not a priority for most homes, floor insulation can improve comfort and reduce heat loss.

When to Consider Floor Insulation

• During renovations
• If you have suspended timber floors
• If floors feel particularly cold
• When installing underfloor heating

Options and Costs

Accessing Free Insulation: ECO4 and Other Schemes

Blueape Renewables is our recommended ECO4 installer. They offer quick eligibility checks, professional surveys, and handle all paperwork on your behalf.

Common Insulation Problems and Solutions

Condensation and Damp

Problem: Insulation installed without proper ventilation Solution: Ensure adequate ventilation, use breathable materials

Settling Cavity Wall Insulation

Problem: Insulation settles over time, leaving gaps Solution: Top-up installation or cavity extraction and refill

Thermal Bridging

Problem: Cold spots where insulation is interrupted Solution: Continuous insulation layer, attention to details

Planning Your Insulation Journey

Year 1: The Basics

• Install loft insulation (£300-800)
• Draught-proof your home (£100-300)
• Apply for ECO4 funding

Year 2: Major Upgrades

• Cavity wall insulation (£400-800)
• Or begin internal wall insulation

Year 3+: Complete the Envelope

• Finish wall insulation
• Consider floor insulation
• Upgrade windows if needed

Insulation and Heat Pumps

If you’re considering a heat pump, insulation is essential. Heat pumps work most efficiently in well-insulated homes. Most installers recommend:

• Minimum 270mm loft insulation
• Filled cavity walls or insulated solid walls
• Good draught-proofing
• Double glazing

Finding Quality Installers

Blueape Renewables is our recommended ECO4 installer. They offer quick eligibility checks, professional surveys, and handle all paperwork on your behalf. Disclosure: We recommend Blueape Renewables as our trusted insulation partner. They’re TrustMark registered, offer comprehensive ECO4 support, and have excellent customer reviews. Using our link helps support this guide at no extra cost to you.

Frequently Asked Questions

Q: How do I know if my cavity walls are already insulated? A: Look for drill holes in the mortar (usually filled with matching mortar), check your EPC, or have a professional inspection with a borescope.

Q: Can I over-insulate my home? A: No, but you must maintain adequate ventilation. Modern buildings regulations ensure this balance.

Q: Will internal wall insulation cause damp? A: Not if installed correctly with proper vapour control and ventilation. Always use qualified installers.

Q: Is it worth waiting for new technology? A: No. Current insulation technology is mature and effective. The savings you’ll miss while waiting outweigh any future improvements.

Q: Can I get a grant if I’m not on benefits? A: Possibly. ECO4 Flex allows councils to set their own criteria. Some offer support based on income or health conditions.

Next Steps

Ready to start your insulation journey? Here’s what to do today:

1. Measure your loft insulation – Less than 270mm means it’s time to upgrade
2. Check your eligibility – Blueape Renewables offers free ECO4 eligibility checks
3. Book a survey – Professional assessment ensures you get the right insulation
4. Start saving – Every month you delay costs you money in wasted energy

Disclosure: We recommend Blueape Renewables as our trusted insulation partner. They’re TrustMark registered, offer comprehensive ECO4 support, and have excellent customer reviews. Using our link helps support this guide at no extra cost to you.

Additional Resources

• Energy Saving Trust Calculator – Calculate your potential savings
• Simple Energy Advice – Government advice service
• EPC Register – Check your home’s current rating

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This guide is updated regularly to reflect the latest standards, costs, and available support. For professional advice specific to your property, always consult qualified installers.

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→ Learn which UK grants might help fund your battery installation in our [Home Energy Grants Guide]

→ Optimise your battery for use with a heat pump — read our [2025 Heat Pump Update]