In short
- In an uninsulated home, around a third of the heat is lost through the walls, according to the Energy Saving Trust.
- Draught-proofing and loft insulation are usually the simplest and cheapest places to start.
- Cavity wall insulation costs around £2,200 in Great Britain and typically pays for itself within five years, while solid wall insulation is a much bigger job, at around £12,000 to £15,000.
- Deal with any damp first, and make sure insulation never blocks the ventilation your home needs.
Why insulation is worth thinking about
Insulation keeps the heat you pay for inside your home for longer. That can make rooms more comfortable, reduce the energy you need to heat them and, over time, lower your bills. It also matters if you're thinking about a heat pump, because a home that loses less heat needs a smaller heat pump and costs less to run.
A sensible order to work in
Every home is different, but this order suits many properties, starting with the cheapest and simplest jobs.
1. Draught-proofing
Sealing gaps around doors, windows, loft hatches and floorboards is inexpensive and can make a noticeable difference to comfort. The one thing to avoid is blocking deliberate ventilation, such as air bricks, trickle vents in windows and extractor fans.
2. Loft insulation
Building regulations recommend at least 270mm of mineral wool insulation in a loft. The Energy Saving Trust estimates these typical costs in Great Britain:
| Job | Typical cost |
|---|---|
| Insulating to 270mm from nothing | £750 |
| Topping up from 120mm to 270mm | £600 |
Source: Energy Saving Trust. Costs in Northern Ireland are higher.
The biggest gains come from insulating a loft that has little or none. Topping up a loft that already has a reasonable depth saves much less, so check what's there before you spend. Properly installed loft insulation should last around 40 years.
If you want to use your loft for storage, boards need to sit above the insulation without squashing it, because compressed insulation works less well. If there's any damp in the loft, get advice before insulating.
3. Cavity wall insulation
Homes built after the 1920s are likely to have cavity walls, made of two layers of masonry with a gap between them. Filling that gap is one of the more cost-effective upgrades. The Energy Saving Trust puts the typical cost in Great Britain at around £2,200 and says it will likely pay for itself within five years.
Not every cavity wall is suitable. Installers should check that the cavity is at least 50mm wide and clear of rubble, that the walls aren't exposed to driving rain, and that the brickwork is in good condition. The work should come with a 25-year guarantee from the Cavity Insulation Guarantee Agency (CIGA), or an equivalent insurance-backed guarantee.
4. Floors
If you have suspended timber floors on the ground floor, insulating between the joists and sealing gaps at the skirting boards can reduce draughts and cold underfoot. It's often easiest to do when floors are already up for other work.
5. Solid wall insulation
Older homes, typically those built before the 1920s, often have solid walls. These can be insulated from the outside or the inside, but it's a substantial project. The Energy Saving Trust gives these typical costs for a three-bedroom semi-detached house in Great Britain:
| Type | Typical cost | Trade-offs |
|---|---|---|
| External wall insulation | Around £15,000 | Little disruption inside and no loss of floor space, but it changes how the outside looks and may need planning permission. |
| Internal wall insulation | Around £12,000 | Usually cheaper and doesn't change the outside, but it slightly reduces room sizes and rooms can't be used during the work. |
Source: Energy Saving Trust. Costs can fall if the work is combined with other jobs that need scaffolding, such as roof repairs.
Get your home ready for winter
Tell us about your property and we'll connect you with relevant insulation installers.
Before you start: damp and ventilation
Insulation done badly can trap moisture and cause damp. Fix any existing damp, leaking gutters or damaged brickwork before insulating. For solid walls in particular, materials that let moisture escape are often recommended. A good installer will check for these problems first and won't block the ventilation your home relies on.
Help with costs
- England, Wales and Scotland. The Great British Insulation Scheme closed on 31 March 2026. ECO4, which funds upgrades for eligible households through energy suppliers, ends on 31 December 2026, and no successor scheme will be run through suppliers. Installers may stop taking new applications before then, so apply soon if you think you're eligible.
- The Warm Homes Plan. The government plans to bring support for low-income households into a single scheme from 2027/28, including cost-effective insulation. Check GOV.UK for the latest details.
- Scotland. The Home Energy Scotland Grant and Loan offers owner-occupiers grants of up to £1,500 for loft, cavity or underfloor insulation and up to £7,500 for solid wall insulation, alongside optional loans. Grants cover up to 75% of the cost, and some rural and island homes can get more.
- Your local council. Some councils run their own schemes, so it's worth checking their website.
Questions to ask an installer
- Which measures would make the biggest difference to my home, and in what order?
- Have you checked for damp, and is any repair work needed first?
- How will you make sure ventilation isn't blocked?
- What guarantee comes with the work, and who provides it?
- Is my home eligible for any funding, and will you help with the application?
This guide is general information, not financial or professional advice. Prices, grants and rules change, so check the sources below before you make a decision. EnergyAdvise is a matching service and doesn’t install products itself.
Sources
- Roof and loft insulation, Energy Saving Trust
- Cavity wall insulation, Energy Saving Trust
- Solid wall insulation, Energy Saving Trust
- Extending the ECO4 end date: government response, GOV.UK
- Warm Homes Plan, GOV.UK
- Home Energy Scotland Grant and Loan, Home Energy Scotland