How much does loft insulation cost in 2026?

For a standard semi-detached house, loft insulation using 270mm glass wool typically costs between £300 and £600. This investment can save approximately £150-£200 per year on energy bills.

What is the difference between internal and external solid wall insulation?

External solid wall insulation involves fixing insulation boards to the outside of your home and rendering over them, costing £8,000-£13,000. Internal insulation involves fitting rigid boards to the inside walls, which is cheaper (£4,000-£8,000) but slightly reduces floor space.

Am I eligible for free insulation grants in the UK?

Under the ECO4 scheme and the Great British Insulation Scheme, households on low incomes, receiving certain benefits, or in council tax bands A-D with low EPC ratings may be eligible for free or heavily subsidised insulation.

How long does it take for cavity wall insulation to pay for itself?

With an average cost of £500-£1500 and annual savings of around £200, cavity wall insulation typically pays for itself within 3 to 7 years, making it one of the most cost-effective energy upgrades.

Can I install loft insulation myself?

Yes, laying rolls of mineral wool in an accessible loft is a common DIY task. However, care must be taken not to compress the material or block ventilation, and protective gear is essential due to skin irritation.

What is the best material for underfloor insulation?

For suspended timber floors, mineral wool batts or rigid foam boards supported by netting are common. For solid concrete floors, rigid PIR boards placed on top (before a screed) are standard, though this raises floor height.

Does insulation cause damp?

Correctly installed insulation should not cause damp. In fact, it often reduces condensation by keeping surfaces warmer. However, poor ventilation or installing insulation in unsuitable cavities (e.g., exposed to driving rain without protection) can lead to moisture issues.

Home Insulation Cost Guide

By Mustafa Bilgic | Published: Jan 1, 2025 | Updated: Feb 20, 2026

Energy prices remain a significant concern for UK households in 2026. With heating accounting for over half of standard energy bills, preventing heat loss is the most effective way to reduce costs. This comprehensive guide details the costs, savings, and payback periods for loft, cavity wall, solid wall, and floor insulation.

Why Insulate Your Home in 2026?

An uninsulated home loses heat at an alarming rate. Approximately 25% of heat escapes through the roof, 35% through the walls, and 10% through the floor. By addressing these thermal bridges, you not only lower your carbon footprint but also secure substantial financial savings.

In 2026, the cost of materials and labour has stabilised compared to previous years, yet the return on investment (ROI) remains high due to sustained energy tariffs. Furthermore, government initiatives like the ECO4 scheme continue to support homeowners in improving their Energy Performance Certificate (EPC) ratings.

1. Loft Insulation Costs and Savings

Loft insulation is often the "low-hanging fruit" of home energy efficiency. It is relatively inexpensive, effective, and often suitable for DIY installation.

Cost Breakdown

For a standard semi-detached home in the UK, professional installation of 270mm mineral wool insulation typically costs between £300 and £600. If you choose to do it yourself, the material cost can be as low as £200-£300.

Savings & ROI

Since around 15% (up to 25% in older homes) of heat is lost through the roof, insulating an empty loft can save between £150 and £200 per year on energy bills. This results in a payback period of approximately 2-3 years.

Material Options

Glass Wool: Most common, cost-effective, and easy to roll out.
Rock Wool: Better soundproofing and fire resistance than glass wool.
Spray Foam: Significantly more expensive (£50/m²) but provides superior airtightness. Note: Check with mortgage providers before installing spray foam as it can affect valuation.

2. Cavity Wall Insulation

Most homes built after the 1920s have cavity walls—two layers of brick with a gap in between. If this gap is empty, you are losing around 35% of your heat through the walls.

Installation & Costs

Cavity wall insulation must be installed by a professional. The process involves drilling small holes in the external brickwork and injecting insulation material. The cost for a semi-detached house ranges from £500 to £1,500, depending on the wall area and material used.

Types of Fill

Mineral Wool: The standard option.
Polystyrene Beads: Better for narrower cavities and preventing moisture transfer.
Polyurethane Foam: Best thermal performance but most expensive.

Savings

You can expect to save roughly £200 per year on heating bills, offering a payback period of 3-7 years.

3. Solid Wall Insulation

Homes built before the 1920s typically have solid walls with no cavity. Insulating these is more expensive and disruptive but yields the highest energy savings.

External Wall Insulation (EWI)

This involves fixing insulation boards to the outside of the house and covering them with render or cladding. It changes the appearance of the property and may require planning permission.

Cost: £8,000 - £13,000
Pros: Does not disrupt the interior, improves weatherproofing, increases curb appeal.
Cons: Expensive, requires scaffolding.

Internal Wall Insulation (IWI)

Rigid insulation boards are fitted to the inner surfaces of external walls, or a stud wall is built and filled with mineral wool.

Cost: £4,000 - £8,000
Pros: Cheaper than external, can be done room-by-room.
Cons: Reduces floor space slightly, requires re-decorating and moving radiators/skirting boards.

4. Underfloor Insulation

Drafts coming up through floorboards can make a room feel significantly colder. Insulating the ground floor (upper floors don't usually need it) costs between £400 and £1,800.

For suspended timber floors, the process involves lifting floorboards and laying mineral wool between joists. For solid concrete floors, rigid insulation is laid on top, which will raise the floor level.

Calculate Your Payback Period

Use our simple tool below to estimate how long it will take to recover your investment.

Insulation Payback Calculator

Total Installation Cost (£):

Estimated Annual Savings (£):

5. Government Grants & Funding (ECO4)

The UK government continues to push for net-zero targets through schemes like ECO4 (Energy Company Obligation) and the Great British Insulation Scheme (formerly ECO+).

Who is Eligible?

You may qualify for free insulation if:

You receive means-tested benefits (e.g., Universal Credit, Pension Credit).
Your home has an EPC rating of D, E, F, or G.
You live in a Council Tax band A-D (for the Great British Insulation Scheme).

Major energy suppliers are obligated to fund these improvements. Contact your supplier or use the government's online eligibility checker to see if you qualify for full or partial funding.

Summary of Costs (2026)

Insulation Type	Typical Cost	Annual Savings	Payback Period
Loft Insulation (270mm)	£300 - £600	£150 - £200	2 - 3 Years
Cavity Wall	£500 - £1,500	£200	3 - 7 Years
Solid Wall (Internal)	£4,000 - £8,000	£250 - £400	15+ Years
Solid Wall (External)	£8,000 - £13,000	£250 - £400	20+ Years

Frequently Asked Questions

Is spray foam insulation worth the extra cost?

Spray foam offers superior air-sealing properties and expands to fill every nook, making it highly effective. However, it is significantly more expensive than mineral wool and can cause issues with mortgage lenders if not installed with the correct documentation and ventilation strategies. Always consult a surveyor before choosing spray foam.

How thick should loft insulation be in 2026?

Current building regulations recommend a depth of at least 270mm for mineral wool loft insulation. If you have existing insulation that is thinner (e.g., 100mm), you can top it up to reach the recommended depth, improving efficiency instantly.

Does insulation help in summer?

Yes. Insulation acts as a thermal barrier, slowing down heat transfer. Just as it keeps heat in during winter, it keeps radiant heat out during summer, helping to maintain a cooler internal temperature during heatwaves.

What is the 'fabric first' approach?

The 'fabric first' approach prioritises the insulation and airtightness of the building envelope (roof, walls, floors, windows) before investing in renewable technologies like heat pumps or solar panels. Reducing the heat demand of the property is the most logical first step in any retrofit project.

Can I insulate a flat roof?

Yes, flat roofs can be insulated from above (warm deck) or below (cold deck). A warm deck roof involves placing rigid insulation boards on top of the roof deck before the waterproofing layer is applied. This is generally preferred as it reduces condensation risks compared to cold deck roofs, where insulation is placed between joists.

How do I find a reputable installer?

Look for installers certified by the National Insulation Association (NIA) or the Cavity Insulation Guarantee Agency (CIGA). For government grant work, installers must be TrustMark accredited.

Are there eco-friendly insulation materials?

Absolutely. Sheep's wool, cork, wood fibre, and recycled cellulose (paper) are excellent sustainable alternatives to fibreglass or plastic-based foams. They are often breathable and have a lower embodied carbon, though they may cost slightly more.

About the Author: Mustafa Bilgic
Mustafa is the Lead Content Editor at UK Calculator, specialising in home economics, energy efficiency, and construction costs. With over a decade of experience in the UK housing market analysis, he helps homeowners make informed financial decisions.