Insulate your home properly and stop paying to heat the sky
Loft, walls and floors: how much insulation you really need, which jobs you can do yourself, how to avoid damp and mould, and where to look for grants.
Reviewed, edited and approved by Editor-in-chief Daniel Sköld · Updated 23 October 2026
Contents
Every house has one room nobody heats on purpose: the sky above it. If your loft has a thin, grey layer of something that went in when Duran Duran were in the charts, a good share of what you pay for heating is drifting out through the roof tiles.
Insulation is the least exciting home improvement you can make. Nobody comes round to admire it. It is also one of the few that keeps paying you back, in lower bills, a warmer house and a better energy rating when you come to sell. You just have to do it in a way that doesn’t swap a cold house for a damp one.
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Why insulation pays you back twice
The first payback is the obvious one. Heat moves from warm to cold, and an uninsulated or under-insulated house leaks it through the roof, walls, floors and gaps around doors and windows. The Energy Saving Trust says insulating the loft, attic or roof is one of the simplest ways to cut that heat loss and save money on your bills. Wall insulation, where your house is suitable, is the other big one.
The second payback comes when you sell. Every home sold or let in the UK needs an Energy Performance Certificate, which rates it from A (best) to G (worst) and lasts ten years. Buyers can see it on the listing, and more of them now check it. They know a low rating means high bills, and they know an F or G may need money spent before they can let the place or feel comfortable in it. Insulation is usually among the first recommendations on the certificate, and often one of the cheapest ways to move up a band.
A warm house is also a drier house. Cold walls and ceilings are where condensation settles and black mould follows. Get the insulation and ventilation right and you deal with both.
How much loft insulation do I need?
The figure to remember is 270mm. That is the depth the Energy Saving Trust recommends for standard mineral wool loft insulation. Plenty of older lofts have 100mm or less, laid when the advice was far less ambitious, and some have none at all over the eaves or around the hatch.
Take a tape measure up there. If what you find comes up to the top of the joists and stops, you almost certainly have room for more. The usual method is one layer laid between the joists and a second rolled out across them at right angles, which also covers the joists themselves. Wood conducts heat better than insulation does, so leaving the joists bare is a small leak repeated along the whole loft.
Remember the hatch. A neatly insulated loft with a bare plywood hatch and no draught seal is like wearing a good coat with the zip undone. Insulation boards and draught strip for the hatch cost little at B&Q, Screwfix or Wickes.
Can I insulate my loft myself?
Usually, yes. If the loft is easy to get into, has no damp problems and the roof is sound, topping up the insulation is a solid weekend’s DIY for anyone who can handle a ladder and doesn’t mind the heat. The materials for a typical loft run to hundreds of pounds rather than thousands, and it is one of the rare jobs where doing it yourself is genuinely as good as paying someone.
Do it safely. Wear long sleeves, gloves, goggles and a proper dust mask, because mineral wool itches and irritates. Lay boards across the joists to kneel on, since a foot through the bedroom ceiling will spoil your afternoon and your budget. Take a decent work light.
Before you start, look at what is already up there. Loose, pebble-like granules that are grey, brown or gold may be vermiculite, which in some older homes contains asbestos. If you find it, don’t disturb it, don’t vacuum it and don’t lay anything on top of it. Get it tested by an accredited surveyor first.
Watch for the electrics too. Cables buried under deep insulation can run hotter than they were designed to, and recessed downlights need fire-rated covers or the correct clearance. If you are unsure, ask a registered electrician to take a look. Any new wiring you want while you are up there is a job for them anyway. Leave the area directly under the cold water tank uninsulated so a little warmth reaches it, and insulate the tank and the pipes instead so they don’t freeze.
If you want to store things in the loft, don’t flatten new insulation under chipboard. Squashed insulation loses much of its effect. Raised loft legs or a platform let you board over the full depth.
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Will insulating my house cause damp and mould?
It can if you get it wrong, and this is where the bodges happen.
Insulation and ventilation are a pair. Seal a house up without letting it breathe and you have swapped a cold house for a damp one.
In the loft, the classic mistake is stuffing insulation right into the eaves and blocking the vents that let air flow under the roof. Without that airflow, moisture rising from the house condenses on cold timbers and the underside of the roof. Leave the eaves clear, use proprietary eaves vents or trays if needed, and insulate up to them rather than over them.
Be very wary of spray foam insulation sprayed onto the underside of roof tiles. It is often sold hard, sometimes by cold callers, and it can hide timber rot and trap moisture. It has caused real problems for owners trying to sell or remortgage, because some lenders and surveyors won’t accept it. If somebody offers it on the doorstep, the answer is no.
Wall insulation is a bigger decision than loft insulation, and it is not DIY. Cavity walls, usually found in houses built from the 1920s onwards, can be filled from outside in a day, but not every wall is suitable. Exposed elevations facing driving rain, damaged pointing or rubble-filled cavities can let damp through to the inside. Make sure the installer surveys the house properly and gives you an independent guarantee.
Solid walls, typical of Victorian and Edwardian homes, need internal or external insulation. Both cost serious money, can affect the look of the house and need planning permission or Building Regulations sign-off in some cases. In a conservation area or a listed building, speak to your council before you do anything. Old solid walls handle moisture differently from modern ones, so this is specialist work. Use a TrustMark-registered installer working to the PAS 2035 retrofit standard, and get at least two or three quotes.
Inside the house, keep ventilating once the place is warmer. Extractor fans in the bathroom and kitchen, trickle vents on windows and opening a window after a shower all matter more once you have stopped the draughts.
Are there grants for home insulation?
There often are, but the schemes change regularly and differ across the UK. That is why it pays to check before you spend your own money.
In England, government-backed schemes have funded loft and cavity wall insulation through energy suppliers, usually aimed at lower-income households or homes in lower council tax bands with poor energy ratings. Start with the government’s energy-saving pages on GOV.UK. Wales runs its own scheme, Nest. In Scotland, Home Energy Scotland advises on the grants and interest-free loans on offer. In Northern Ireland, look to NI Energy Advice and the Affordable Warmth scheme run through councils.
A word of warning: genuine schemes rarely arrive as a cold call promising free insulation. Check that the installer is TrustMark-registered or appears on the official scheme’s list before you let anyone up your ladder.
In short
Topping your loft up to the recommended 270mm of mineral wool is the cheapest, easiest insulation win, and you can usually do it yourself in a weekend. Keep the eaves clear for ventilation, steer clear of roof spray foam, and leave anything that looks like vermiculite alone until it has been tested. Wall insulation and any electrical work are for accredited professionals, so check for TrustMark registration, compare quotes and look up the current grants for England, Scotland, Wales or Northern Ireland before you pay.
Alistair Ives writes about the home and the weekend for men 45 and over: DIY, renovation, the garden, the outdoors and the hobbies worth the time. What a job really costs, what you can do yourself, and when it's worth paying someone who knows.
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