Insulation: what pays back first (loft, walls, floor)

KiloWise editorial team · Last updated 5 November 2026 · Category: Insulation & Draughts

Insulation is the biggest energy-saving spend most homes ever make, which is why the order you do it in matters. Done in the wrong order, you can spend thousands on a job that pays back slowly while a cheaper job that pays back quickly sits undone. This guide ranks the three main types — loft, walls, and floor — by payback, explains why that order is usually loft first, and shows you how to run your own quote through the payback checker so the ranking is based on your house, not a national average.

It does not promise a saving figure for any type of insulation. Savings depend on the size of your home, what insulation is already there, how warm you keep it, and the price you pay for energy. A figure quoted for a different house is not your figure. Instead, every worked example in this guide uses clearly labelled example numbers, and tells you to replace them with your own quote and your own estimated saving before you spend anything.

One distinction to keep clear from the start: insulation is not draught-proofing. Draught-proofing stops air moving through gaps — around doors, windows, and the loft hatch. Insulation slows heat moving through solid material — through the roof, the walls, and the floor. They are different jobs, and draught-proofing should usually come first because it is cheaper and faster. If you have not sealed the gaps yet, start with our guide to the cheapest draught-proofing fixes, then come back here.

Why the order is usually loft first

Warm air rises. That is the whole reason loft insulation usually pays back first, and it comes down to three things: area, access, and heat flow. The roof is the largest single surface through which a house loses heat, because it is the whole footprint of the house in one flat layer. It is also the easiest to reach — in most homes you can walk into the loft and lay insulation between and across the joists without opening up a wall or lifting a floor. And because warm air rises, the loft is where the warmest air in the house meets the coldest surface, so the temperature difference driving heat loss is at its greatest there.

That combination — biggest area, easiest access, warmest air — is why loft insulation is normally the first job in the ranking. It is also the cheapest of the three per square metre, because the material is simple and the labour is straightforward. None of that makes it right for every house. If your loft is already insulated to a good depth, adding more will pay back slowly, because the first layer of insulation does most of the work and each extra layer adds less. If your loft has been converted into a room, the job is different — insulating a converted loft means insulating the sloping roof itself, which is more work and more cost. The ranking below is a starting order, not a rule: run your own numbers before you commit.

Loft insulation

Loft insulation is a layer of material — usually mineral wool, but other materials are available — laid between the joists of the loft floor and often across them in a second layer, so that the ceiling of the rooms below is insulated from the cold loft above. It works by trapping still air, and still air is a poor conductor of heat. The job is usually done in a day for a typical house, and it needs no planning permission.

Before you buy, check what is already there. Lift a corner of the existing insulation and measure its depth, and look for gaps, compressed patches, and places where it has been pushed aside to make room for storage or downlights. Compressed insulation insulates less, because it traps less air. Downlights that get hot need a guard so insulation does not sit directly on them — ask an electrician if you are unsure. Do not block the ventilation at the eaves, the gaps under the roof edge that let air move through the loft and keep the roof timbers dry.

Wall insulation

Wall insulation comes in two very different forms, and which one your home needs depends on how it was built. Cavity wall insulation fills the gap between the two skins of a cavity wall — the standard construction for most homes built from the 1930s onwards. It is injected through small holes drilled in the outside wall, takes a few hours, and the holes are filled afterwards. It is the cheaper of the two wall jobs, and it is the one that usually ranks second in the payback order, after the loft. One caution applies to all wall insulation: never insulate a damp wall — fix the damp first, because insulation can trap moisture in the wall, and get the cause checked by a qualified surveyor if you have damp patches or peeling plaster.

Solid wall insulation is for homes with solid walls — most homes built before the 1930s, and some later ones. There is no cavity to fill, so the insulation goes on the inside face of the wall or the outside face. Internal insulation takes up room space and means redecorating; external insulation changes the look of the house and can need planning permission. Both cost far more than cavity fill, and the payback is correspondingly longer. That does not make solid wall insulation a bad job — a solid-walled home can lose a great deal of heat through its walls — but it does mean it belongs later in the order, after the loft and after any cavity work, and it is the job where checking for a grant first matters most. See our guide to what to check before you spend on grants and rebates before you get a quote for solid wall insulation.

Floor insulation

Floor insulation usually ranks last, not because floors do not lose heat, but because the job is harder and the area is smaller in effect than the roof. A suspended timber floor — boards over a void, common in older homes — can be insulated from below if there is access to the void, or from above by lifting the boards. A solid concrete floor can be insulated from above, but that raises the floor level, which means adjusting doors and skirting boards. Both versions are more disruptive than loft or cavity work, and the payback is usually longer.

That said, floor insulation has a benefit the other two do not: comfort. A cold floor is something you feel every time you walk barefoot, and insulating it removes the draught that rises through gaps between floorboards — which is also a draught-proofing job, and the cheaper draught fixes in our draught-proofing guide are worth doing first. If you are already lifting floorboards for another reason, adding insulation while they are up is the cheapest time to do it. If you are not, it can wait until the loft and walls are done.

How to use your own quote in the payback checker

The insulation payback checker does one simple calculation — the one in the worked example — but it does it with your numbers instead of ours. You need three things before you open it. First, your quote: the full installed cost, including materials, labour, and VAT, in writing from the installer. Second, your estimated annual saving: ask the installer to put it in writing, with the energy rate they used, and check that rate against your bill. Third, your energy rate from your bill — the unit rate in pence or cents per kilowatt-hour — because a saving in kilowatt-hours is only worth money at the rate you pay.

Simple payback has limits, and you should know them before you trust it. It ignores the fact that energy prices change, so a job that pays back in 8 years at today's rate pays back faster if rates rise. It ignores the value of comfort — a warmer house is worth something even before the bill falls. And it says nothing about the life of the insulation, which can last decades. None of that makes the calculation useless: it is the right tool for ranking jobs against each other, which is what this guide is for. Use it to decide the order, not to decide whether a warm house is worth having.

Grants change payback — check before spending

A grant or rebate that covers part of the cost shortens the payback by the same proportion. In the worked example, a grant covering half the cost halved the payback from 8 years to 4. That is a large enough difference to change the ranking: a solid wall job that looks too slow at full price can become the best job available once a grant is counted. The mistake is to get the quote, agree the work, and then discover a scheme you could have used. Check first, spend second.

Schemes change often, they have eligibility rules, and many have expiry dates — so this site does not list individual schemes or amounts. Instead, our guide to energy grants and rebates: what to check before you spend teaches you how to find the official scheme pages for your country, what eligibility means, and how to work a grant into the payback calculation. Read it before you sign anything.

What to do next

Start with the walk-around in the whole-home energy audit: it will tell you whether your loft is bare, your walls are cold to the touch, or your floors are the draught source. Then seal the draughts — the cheap fixes first — and get quotes for the insulation job that ranks first for your home. Run each quote through the payback checker with your own rate from your bill, check for grants before you sign, and do the jobs in payback order. A house done in the right order is warmer sooner, for less money, than a house done in the order the salesperson suggested.

Related: run your own numbers in the insulation payback checker, then read the cheapest draught-proofing fixes and the whole-home energy audit to plan your next step.

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