For most homes the order is loft first, then unfilled cavity walls, then draught-proofing and floors, with solid wall insulation last because it costs the most and needs the most care. That order follows cost and simplicity: loft insulation is the cheapest and easiest job, cavity wall insulation comes next, and solid wall insulation can cost twenty times as much as a loft.
The figures below are the Energy Saving Trust's typical costs for Great Britain. They are national averages, not a price for your home, and a survey should always come before any work.
Why does the loft usually come first?
The Energy Saving Trust says an uninsulated home loses around a quarter of its heat through the roof, and that loft insulation, fitted properly, lasts around 40 years. It is also the cheapest of the main jobs:
- About £750 to insulate a loft to 270mm from nothing.
- About £600 to top up from around 120mm to 270mm, which the Trust estimates saves about £17 a year in Great Britain.
The Trust says current building regulations recommend at least 270mm of mineral wool. If your loft is easy to reach, free of damp and not a flat roof, it says you may be able to do it yourself. If you want to store things up there, the insulation should not be squashed under boards; the usual answer is to raise the floor and lay boards over the top, leaving a small gap for ventilation. Better Lofts explains how loft boarding works with insulation underneath.
Two checks come first. If the loft is damp, the Trust says to get the cause fixed before insulating, because a colder loft makes condensation more likely. And make sure vents, grilles and airbricks stay clear. For the options beyond mineral wool rolls, such as rigid board between rafters, see Better Lofts' guide to loft insulation types or our own loft insulation page.
When should cavity wall insulation be next?
The Energy Saving Trust says about a third of the heat lost from an uninsulated home goes through the walls. If your home was built after the 1920s it probably has cavity walls, and homes built from the 1990s onwards usually already have wall insulation.
For a typical home in Great Britain the Trust puts cavity wall insulation at around £2,200 and says the energy savings will likely pay that back in five years or less. An installer can usually do an average home with easy-to-reach walls in about two hours.
It is not right for every wall. The Trust lists the cases where it may not be suitable: homes exposed to extreme weather or flooding, homes in poor condition, homes at risk of overheating, and cavities narrower than 50mm. It also says brickwork, pointing, roofs, gutters and downpipes should be repaired before any wall insulation goes in, or damp can be trapped. Cavity Wall Advice covers what goes wrong when a cavity fill does not suit the wall, which is worth reading before you book a survey. Ask for a 25-year guarantee from the Cavity Insulation Guarantee Agency (CIGA) or an independent insurance-backed one. More on our cavity wall insulation page.
What about draught-proofing and floors?
These are smaller jobs that can be done at any point. The Energy Saving Trust's figures for Great Britain:
- Draught-proofing windows and doors professionally costs around £250 for a whole house, and draught-proofing windows, floors and doors could save around £55 a year.
- Suspended timber floor insulation costs between about £1,400 and £2,500 depending on the house, and saves about £55 a year for an average house (up to £85 for a detached one).
The Trust adds that if you replace 50% or more of a floor, you must insulate it to building regulation standards. See our floor insulation page.
Why is solid wall insulation usually last?
Homes built before about 1920 are more likely to have solid walls, which need insulating from outside or inside. For a typical three-bedroom semi-detached house, the Energy Saving Trust puts external wall insulation at around £15,000 and internal wall insulation at around £12,000.
Cost is only part of it. The Trust says moisture has to be thought about carefully with solid walls, because insulation can trap it or reduce ventilation through the wall, and that any existing damp must be dealt with first. It also reports that 98% of homes fitted with external wall insulation under ECO4 and the Great British Insulation Scheme have problems that need fixing. That is a reason to take your time, get more than one survey and check the installer's registration, not a reason to rule it out.
Is there help with the cost?
Schemes change often. As of 2 October 2026, GOV.UK says:
- Warm Homes: Local Grant (England) can fund wall, loft and underfloor insulation through your council for privately owned homes rated EPC D to G, where household income is usually £36,000 or less, or you get certain benefits or live in an eligible postcode. Check on GOV.UK.
- ECO4 runs until 31 December 2026; the government confirmed the extension in January 2026. The Great British Insulation Scheme ended on 31 March 2026.
- VAT: installing insulation in a home is zero-rated in Great Britain until 31 March 2027, then 5%.
In Scotland, the Energy Saving Trust points people to Home Energy Scotland; in Wales, to Nest. We are not a government body and cannot tell you whether you qualify.
So what order suits your home?
- Fix leaks, damp and damaged brickwork or gutters first.
- Loft: top up to at least 270mm, keeping ventilation clear.
- Cavity walls, if they are unfilled and a survey says they are suitable.
- Draught-proofing and floor insulation, whenever convenient.
- Solid wall insulation, with a careful survey and a plan for moisture.
Sources, checked 2 October 2026: Energy Saving Trust guides to roof and loft insulation, cavity wall insulation, solid wall insulation, floor insulation and draught-proofing; GOV.UK on the ECO4 extension, the Great British Insulation Scheme and VAT on energy-saving materials.
Get free quotes from local insulation specialists: tell us about your home and we will pass it to Better Home Hub, which looks for up to 3 specialists who cover your area. It is free and you choose whether to go ahead.