If your home feels cold despite the heating being on, the problem is usually heat escaping through the roof, walls and floors. Home insulation is one of the most cost-effective upgrades in the UK: loft insulation for a typical semi-detached house costs around £900, while cavity wall insulation is usually around £2,700, and both can cut heating bills by hundreds of pounds a year.
The best insulation for your home depends on how it was built. Most houses from the 1930s onwards have cavity walls that can be filled quickly, older properties often have solid walls that need internal or external insulation, and almost every home benefits from a properly insulated loft. Choosing the right measures in the right order gives you the biggest energy savings for the least money.
Below we compare insulation prices and savings for each part of the house, show which upgrades pay back fastest, explain the insulation grants available to eligible households, and highlight the mistakes – especially around ventilation and damp – that can turn a good investment into an expensive problem.
Insulation prices and savings compared
The table below shows typical costs and yearly savings for a three-bedroom, semi-detached, gas-heated home, based on Energy Saving Trust estimates. Detached homes cost more but save more; flats and mid-terraces cost and save less.
| Measure | Typical cost | Typical yearly saving | Payback |
|---|---|---|---|
| Loft insulation (0–270mm) | £800–£1,000 | £200–£300 | Around 3–5 years |
| Cavity wall insulation | £2,000–£3,000 | £200–£300 | Around 7–10 years |
| Internal solid wall insulation | £8,000–£12,000 | £350–£500 | Long term |
| External solid wall insulation | £11,000–£18,000 | £350–£500 | Long term |
| Suspended floor insulation | £1,600–£2,900 | £80–£100 | Long term |
| Draught-proofing | £100–£300 (DIY less) | £50–£100 | 1–3 years |
One important detail: topping up a loft that already has around 100–120mm of insulation saves only a small amount each year. The big wins come from lofts with little or no insulation.
Loft insulation
In an uninsulated home, roughly a quarter of heat is lost through the roof. The recommended depth for mineral wool is at least 270mm, laid in two layers – one between the joists and one across them. If you want to use the loft for storage, raised loft legs and boarding keep the insulation from being squashed, which would reduce its effectiveness.
Loft insulation is one of the few measures that can be a DIY job in a simple, dry loft with easy access. Use gloves, a mask and goggles, and never cover electrical cables, light fittings or the eaves vents that let air flow through the roof space.
Cavity wall insulation
If your home has cavity walls – two layers of brick with a gap between them – an installer drills small holes in the outside walls, injects insulation into the gap and fills the holes. A typical house is done in half a day to a day, with no disruption inside.
Not every wall is suitable. Homes on exposed, wind-driven rain sites, walls with damp problems, or cavities narrower than about 50mm may need a different approach. A good installer will carry out a borescope survey first and should provide a 25-year CIGA guarantee once the work is done.
Solid wall insulation
Homes built before the 1920s usually have solid walls, which lose more heat than cavity walls. There are two options:
- Insulated boards fixed to the inside of external walls
- Cheaper, can be done room by room
- Reduces floor area slightly; sockets and skirting need refitting
- Insulation fixed outside, then rendered or clad
- No loss of indoor space, refreshes the exterior
- Higher cost; may need planning permission
The smart order: what to insulate first
- Draught-proofing: seal gaps around doors, windows, letterboxes and floorboards – cheap and instant.
- Loft insulation: the fastest payback in most homes.
- Cavity wall insulation: if your walls are suitable.
- Hot water cylinder and pipes: a cylinder jacket and pipe lagging cost very little.
- Floor and solid wall insulation: best combined with other renovation work to share the disruption.
Getting the basics right before installing a heat pump also means a smaller, cheaper system and lower running costs.
Ventilation and damp: the part people forget
A warmer, more airtight home holds more moisture. Without enough ventilation, insulation can lead to condensation, mould and damp. Keep these points in mind:
- Keep trickle vents in windows open and use extractor fans in kitchens and bathrooms.
- Do not block air bricks or loft eaves vents.
- Fix any existing damp before insulating walls or floors.
- Make sure your installer follows recognised standards (such as PAS 2035 on funded schemes), which include a ventilation assessment.
Insulation grants and free help
- Warm Homes: Local Grant (England): councils can fund insulation and other upgrades for low-income households, usually those with a household income of £36,000 or less or on certain benefits, in homes rated EPC D to G.
- Home Energy Scotland: grants and interest-free loans for insulation and heating in Scotland.
- Wales and Northern Ireland: each runs its own government-backed home energy support programme.
- Council schemes: some local authorities offer extra help for older or vulnerable residents.
Be wary of cold callers offering “free government insulation”. Genuine schemes never charge a fee to apply, and you can always check eligibility through official channels first.
Choosing an installer
Ask for at least three quotes and check that each installer is a member of a recognised trade or certification body, such as TrustMark, and offers an independent insurance-backed guarantee. A good quote names the product and thickness, describes any preparation work, and explains how ventilation will be maintained.
Costs and savings based on Energy Saving Trust estimates for a typical gas-heated home.
Independent guide – not linked to any insulation installer or manufacturer.
