Home insulation: the boring upgrade that saves the most money

Where your heat actually goes

In a typical uninsulated UK home, you're paying to heat the outside. Literally. Here's roughly where the heat escapes:

That's why insulation should come before everything else. There's no point installing an expensive new heating system if half the heat leaks out through the walls and roof. Insulate first, upgrade heating second. This is the order that saves you the most money.

The right order (cheapest wins first)

Not all insulation is equal. Some is cheap and easy, some is expensive and disruptive. Here's the practical order — start at the top, work down as budget allows:

The first three items on this list often cost under £2,000 combined and can cut your heating bills by 25–40%. Windows are the last thing to do, not the first — even though they're what most people think of.

Loft insulation

The easiest and cheapest insulation you can do. Heat rises, and if your loft isn't insulated (or the insulation is thin and old), about a quarter of your heating goes straight through the ceiling.

Check what you've got: go into the loft with a torch. If you can see the joists (the horizontal timbers) above the insulation, you probably need more. Current standard is 270mm — most older homes have 100mm or less.

Many households qualify for free loft insulation through the Great British Insulation Scheme (GBIS) or ECO4. Even if you don't qualify, it's still the best-value upgrade you can do.

Cavity wall insulation

Most houses built between the 1920s and 1990s have “cavity walls” — two layers of brick with a gap (cavity) between them. That gap can be filled with insulating material.

How to tell if you have cavities: Look at the outside brickwork. If all the bricks are the same length (stretcher bond — the standard pattern you see everywhere), you probably have cavity walls. If you see some bricks laid end-on (shorter, square ends poking out), you likely have solid walls.

Your EPC report will tell you your wall type. You can also check by measuring wall thickness at a window or door — cavity walls are typically 260mm+, solid walls around 220mm.

Solid wall insulation (the expensive one)

Older homes (generally pre-1920s) have solid walls — no cavity to fill. These lose the most heat but are the most expensive to insulate. You have two options:

This is where grants make the biggest difference. Qualifying households can get solid wall insulation fully funded through the Warm Homes Plan or ECO4. Without a grant, the payback is long — with a grant, it's immediate.

Floor insulation

Suspended timber floors (the kind that bounce slightly when you walk on them) can be insulated from underneath if there's crawl space, or by lifting floorboards. Solid concrete floors are harder — you'd insulate on top, raising the floor level.

Draught-proofing

Twenty per cent of heat loss comes from draughts — gaps around windows, doors, letterboxes, floorboards, loft hatches, and pipework. This is the cheapest fix and you can do a lot of it yourself.

Start with the obvious ones: sit near your windows and doors on a cold day and feel for cold air. Letterbox covers, chimney balloons (if you don't use the fireplace), and self-adhesive draught strips around windows are all cheap and easy.

Double and triple glazing (do this last)

Windows only account for about 10% of heat loss, yet they're one of the most expensive upgrades. New double glazing for a whole house costs £3,000–£7,000. Triple glazing costs more again.

If your windows are single-glazed, yes, upgrading helps. But if you already have double glazing (even old double glazing), your money is almost always better spent on loft, wall, or draught-proofing first.

A cheaper option: secondary glazing (a second pane fitted inside your existing frame) costs £100–£400 per window and captures most of the benefit. Particularly good for listed buildings where you can't change the original windows.

What your EPC tells you about insulation

Your Energy Performance Certificate (EPC) rates individual elements of your home — walls, roof, floor, windows — from Very Good to Very Poor. These are called the “fabric ratings.”

If your EPC says your walls are “Poor” and your roof is “Average,” that tells you exactly where to focus. The EPC recommendations section also lists the specific upgrades that would improve your rating, with estimated savings.

Enter your postcode below and we'll pull up your property's EPC data, including these fabric ratings.

How to tell what insulation you already have

Grants that cover insulation

Insulation is one of the upgrades most likely to be fully funded by government schemes. Three main routes:

These schemes overlap — you may qualify for more than one. An installer or your local authority can help you navigate which applies. The key thing: check before you pay, because many people qualify for free insulation without realising it.

Common mistakes

Where to start

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