Insulation is usually the cheapest way to cut your heating bill, and it also makes any new heating system work better. This guide covers the main types, what they typically cost, what they save, and where to look for help.
Loft insulation
A big share of a house’s heat can escape through the roof, so topping up loft insulation is almost always the best place to start. A professional job usually costs from a few hundred pounds up to around £1,000, depending on the size of the loft. Typical savings are around £150 to £350 a year when you add up to 270mm to a loft with little or no insulation, so payback is often within a few years.
Cavity wall insulation
Homes built from roughly the 1920s onward often have a gap between two layers of brick. Filling it costs around £500 to £3,000 depending on the size and type of the house, and typical savings are about £100 to £400 a year. Not every home is suitable. Properties exposed to driving rain, or those with damp problems, need a proper survey first, because the wrong insulation in the wrong wall can cause problems.
Solid walls
Older homes, often built before the 1920s, usually have solid walls. Insulating them is the biggest job: internal insulation commonly costs about £7,000 to £12,000, and external insulation about £11,000 to £18,000 for a typical semi-detached house. Savings are larger, roughly £400 to £700 a year, but so is the payback period, so this is often done as part of a wider renovation rather than on its own.
Draught-proofing and floors
Having a whole house draught-proofed professionally can cost around £200 and saves a modest amount every year. It’s cheap and quick, though you need to make sure kitchens, bathrooms and other rooms still have enough ventilation. Floor insulation helps in older homes with suspended timber floors but is usually a smaller saving.
Why the numbers differ
You’ll see different figures on different sites. The Energy Saving Trust’s numbers are for a typical gas-heated semi-detached home, and other sources quote their own ranges. Your own savings depend on the size and age of your house, how much insulation it already has, what you pay for fuel, and how you use the heating. Treat any figure as a guide and ask for itemised quotes.
Help with costs
ECO4 has funded insulation for some lower-income households, but it’s winding down, as we explain in our ECO4 and Warm Homes Plan guide. The Warm Homes: Local Grant is delivered through councils in England for eligible low-income households. Scotland and Wales run their own schemes, so check your nation’s energy advice service. Energy-saving materials are currently installed at 0% VAT, but check the current rules before you commit.
A sensible order
Start with the cheap, quick wins: draught-proofing and a deeper layer of loft insulation. Then fill the cavity walls if your home is suitable. Floors, windows and solid walls come next, ideally as part of a bigger project. Only then choose your heating, because better insulation can allow a smaller, cheaper system, which matters if you’re planning a heat pump. Our Boiler Upgrade Scheme guide covers that side.
Choosing an installer
Use installers registered with an approved guarantee scheme and ask for the guarantee in writing. Get at least two or three quotes, and have each one say exactly what’s included, how they’ll deal with ventilation and what happens if there’s a problem later. For cavity walls in particular, a decent firm will survey the property first and refuse to fill walls that aren’t suitable.
Mistakes to avoid
Don’t insulate over damp: find and fix the cause first. Don’t block loft ventilation at the eaves, and remember that insulating over a cold water tank without protecting it can let it freeze. Be wary of cavity wall filling in exposed locations without a survey, and of any firm that quotes without looking at the property. Keep ventilation in mind too, since a better-sealed home needs the extractor fans and trickle vents to do their job.
Two quick questions
How do I know if I have cavity walls? A surveyor or installer can check, often by looking at the brick pattern and measuring the wall thickness.
Can insulation cause damp? Poor installation or an unsuitable property can, which is why surveys and guarantees matter.
To compare insulation with other upgrades, try our UK calculator.