Home Insulation UK | Save Energy & Lower Heating Bills

Types of home insulation

Sounds great, you say, but where should I insulate? That depends on your property, where it’s losing heat, and your budget. An insulation plan for a detached house with solid walls, a pitched roof, and a loft used only for storage will be very different from an insulation project for a terraced house with a flat roof and cavity walls.

Almost every side of a home can be insulated, although the ease, cost, and returns of these projects vary widely:

Loft insulation

Insulating the floor or ceiling of a loft in a pitched-roof home

Roof insulation

Insulating the roof of a property with a flat roof, either internally or externally

Cavity wall

Insulation pumped into the gaps in cavity walls, found in most properties built after 1920

Solid wall

Insulation installed either on the inside or outside of solid walls, found in pre-1920 properties

Floor

Insulation installed above or below a ground floor to reduce heat loss into the ground

Doors

Weatherisation measures taken to reduce heat loss from a door, including brush strips or weather bars installed at the bottom of the door, self-adhesive foam or brush strips installed around the edges, letterbox draught excluders with brushes or flaps, and keyhole covers

To help you decide which insulation project to undertake, it's worth getting a heat loss survey, which can zero in on exactly where your home is leaking.

Insulation sites	Suitable for	Amount of heat lost	Cost	DIY?	Energy bill savings	Years to break even	Carbon savings (kg CO2/year)
Loft	Homes with pitched roofs and dry lofts	25%	Cold loft: £300-£1500 Warm loft: £700-£2,000	Yes, especially cold loft insulation	£200-£380/year	1-5 years	500-1000kg
Roof	Homes without lofts, with flat roofs	25%	£400-£600	No	£250-£350	1-3	500-1000kg
Cavity walls	Homes built after 1920	35%	£1,000-£4,000	No	£200-450/year	5-9 years	Up to 1,150kg
Solid walls	Homes built before 1920	35%	£7,500-£13,000	No	£200-£600	21-37 years	Up to 2,100kg
Floor	All homes, especially those with suspended timber floors	10%	£100-500 DIY, £400-£1,000 professional	Yes	£60-110/year	2-10 years	80-300kg
Doors	All homes	15%	£200-£1,000 for a new insulated door, £100 for draught proofing	Yes	Up to £40/year, if all windows and doors draught proofing	Draught proofing: 3-5 years	Draught proofing all windows and doors: 140kg

How does home insulation work?

Loft insulation

Hot air rises so in an uninsulated home, around a quarter of the heat is lost through the roof.^[5] If your loft is accessible and dry, it’s one of the best, and easiest, places to install insulation. You can even do it yourself.

The type of loft insulation most suitable for your property depends on your type of roof (pitched or flat), the accessibility of your loft, and what you use it for.

For pitched roofs, the simplest, cheapest method is called cold loft insulation, where you install insulation over and between wooden joists in the loft’s floor, leaving the space cold. You can buy rolls of insulation at local DIY shops for as little as £5-10 per square metre, although to make it worth your while you should opt for the thicker, more high quality rolls (270mm is recommended), which cost £15-20/m2.

Cold loft insulation is one of the projects most favoured by grant schemes such as the Great British Insulation Scheme.^[6] However, DIY projects are typically excluded from funding.

If you use the loft for living space or to store things you don’t want to get cold, opt for warm loft insulation instead, insulating just under the roof. Although this process is trickier, it can still be done as a weekend project.

Roof insulation

With flat roofs, you’ll need to insulate the roof itself. There are three different types of roof insulation:

Warm deck: insulation placed above the roof’s structural deck (joists, sub deck, etc.) but below the waterproof layer; more expensive but more energy-efficient
Cold deck: insulation laid between the rafters on the inside of the roof; cheaper and easier to install but less energy-efficient
Inverted roof: insulation placed above the waterproofing layer, then covered by gravel or a similar material

Cavity wall

75% of UK properties have cavity walls, consisting of two parallel layers of brick with a gap of 2-10cm between them, designed to prevent damp.^[7] How can you tell which type of walls your home has? The bricks in cavity walls are all laid lengthwise, creating an even pattern.

If you have cavity walls, you're in luck because they're much easier to insulate. A registered installer simply drills small holes into the external wall and injects insulation into the gap: usually fibreglass, mineral wool, polystyrene beads, or polyurethane foam.

The cavity between the walls can be filled with insulation. To install the insulation, installers drill small holes into external wall of your home, inject the insulation into the cavity, then reseal the holes with cement.

Solid wall

Homes built before the 1920s may have walls made of one single layer of brick, known as a solid wall. To identify solid walls, look for bricks laid in an alternating pattern, some lengthwise but others turned so you see the smaller side.

Solid walls are trickier and more expensive to insulate. But because they lose more heat, insulating them can make a bigger impact on your energy bills.

There are two methods of insulating solid walls:

Internal solid wall insulation: installed to the interior walls. This is the most common method, especially when planning restrictions and conservation status prevent exterior walls from being modified. The installer may stick rigid insulation boards made to the walls, then cover them with plasterboard. If the wall is uneven or has a problem with damp, they may construct a stud wall against your existing wall and fill it with insulating material such as mineral wool. The latter method will cost you some floorspace. Cheaper but less effective methods include thermal wallpaper and insulating plaster.
External solid wall insulation: adding insulation, usually in the form of insulation boards, to the exterior side of the walls and then covering it with render or cladding. This is the more expensive option and won’t be suitable for every property, but is more energy-efficient.

Floor

While the floor is often overlooked as a site for insulation, around 10% of the heat in our homes is lost through the ground floor.^[8] Floor insulation can reduce this loss and save you around £70 per year on your energy bills, according to the Energy Saving Trust.^[9]

Older homes have suspended timber floors. Insulation, such as mineral wool can be added between the joists that hold up these floorboards. For a quicker fix, you can also fill any gaps in the floorboards with products such as DraughtEx or StopGap, wooden lathes, gunned sealant, or even papier-mâché.

Newer homes have solid concrete floors. The best time to insulate a concrete floor is during its construction or repair when you can add insulation below the slab. For most homes, that’s impractical. A great alternative is to build a floating floor above the concrete floor, with insulation layered between, in the form of rigid insulation boards, insulation matting, or foam or cork underlay.

Doors

Around 15% of the heat in your home is lost through exterior doors.^[10] To prevent this heat loss you can insulate the door itself. If your door is energy inefficient - such as if it’s hollow-core wood, metal, or single-pane glass, or simply ageing - you can get a lot of mileage by replacing it with a newer insulated model, such as a solid-core wood door or a fibreglass or steel door with built-in insulation.

If you don’t have the budget to replace the door, you can attach insulation panels and use plastic insulation film on the glass. If the door isn’t heavily used, you can also install thermal curtains to cover it.

To prevent heat loss from around the door, you can block draughts with:

a draught excluder, or door sweep, at the base
weatherstripping around the frame, with self-adhesive foam or brush strips
letterbox draught excluder
keyhole cover

How much does home insulation cost?

The cost of home insulation ranges widely depending on where you’re insulating, the material you’re using, and the build of your home.

Loft insulation

The cost of loft and roof insulation ranges from £300 to £7,000 depending on the build and size of your home, the insulation method used, and whether you DIY it or turn to a professional.

Loft/Roof insulation type	Cost for a top floor flat	Cost for a terraced house with 2-3 bedrooms	Cost for a semi-detached house with 3-4 bedrooms	Cost for a detached house with 4+ bedrooms
Cold loft insulation	£300-£500	£400-£700	£500 - £800	£700 - £1,500
Warm loft insulation	£700-£1,200	£1,000 - £1,500	£1,500 - £2,500	£2,000 - £4,000
Warm deck roof insulation	£1,000 - £1,800	£1,500 - £3,000	£2,000 - £4,000	£3,000 - £6,000
Cold deck roof insulation	£800-£1500	£1,000 - £2,000	£1,500 - £2,500	£2,000 - £4,000
Inverted roof insulation	£1,500 - £3,000	£2,000 - £4,000	£3,000 - £5,000	£4,000 - £7,000

Wall insulation

Cavity walls are cheaper to insulate than solid walls, with a project costing between £1,100 and £4,300, depending on the size of your home and the material used.^[11]

Terraced homes and flats which share walls with other properties are cheaper to insulate as you have fewer exterior walls to cover.

Property type	Cost of cavity wall insulation
Mid-floor flat	£1,100
Mid-terrace flat	£1,500
Detached bungalow	£2,000
Semi-detached house	£2,700
Detached house	£4,300

Among popular materials for cavity wall insulation, mineral fibre and glass wool are the cheapest, costing £13-18 per m2. Other options are more expensive but have their own positives. For example, wool fibre is the most sustainable option and is also hypoallergenic but costs more, at £25 - £30 per m2. Expanded polystyrene beads are moisture and mould-resistant and recyclable and cost £18 - £22 per m2.^[12]

Solid wall insulation is trickier to install so more expensive. The Energy Saving Trust estimates that for a typical three-bedroom semi-detached home, internal wall insulation would cost around £12,000, while external wall insulation may cost £18,000.^[13]

Floor insulation

Suspended timber floors are the easiest and cheapest to insulate, with insulation installed under the floor between the joists.

Costs vary depending on the insulation material used and the size of the floor.

Insulation material	Cost per m2	Cost for typical 20m2 room
Mineral wool	£5-£10	£100-£200
Rigid foam boards	£10 - £20	£200 - £400
Sheep wool or natural fibre	£15 - £25	£300 - £500

You can expect to pay between £400 and £800 in labour for a typical room, depending on your location and the accessibility of the space under the floors.

If you have a newer home with concrete slab floors, insulation is trickier, requiring you to build a floating floor and insulate underneath it. According to CheckaTrade, you’ll spend about £70 per m2 to insulate with a floating floor, or £1,400 for a standard 20m2 room.^[14]

Door insulation cost

In some cases, you might want to replace an old door with a new insulated model. Costs vary, depending on the type of door and the presence of glass and decorative features.

Solid-core wood door: £200-£1,500
Fibreglass door with built-in insulation: £300-£1,500
Steel door with built-in insulation: £400-£2,000

A cheaper alternative is to simply add insulation to an existing door:

Insulation panels: £10-£30 per door for expanded polystyrene; £30-£80 per door for polyurethane or polyisocyanurate rigid foam panels
Insulation film for glass: £5-£20 for a roll, enough for one door
Thermal curtains: £20-£100 per door, depending on the size of the door and the quality of the thermal curtain

You can also quickly and cheaply weatherise doors to reduce draughts with materials available at all DIY shops:

Door sweep: £5-10 for a basic peel-and-stick door sweep, £10-20 for a screw aluminium door sweep
Weatherstripping around the doorframe: £4-£10 for a roll of self-adhesive foam strips, suitable for one door; £8 - £15 per door for rubber or silicone weatherproofing
Letterbox draught excluder: £5-£15
Keyhole cover: £5-£15

What materials are used in home insulation?

Humans have been insulating their hovels and homes for millennia, first using animal furs and straw. In the 19th century, the Victorians packed their walls with shredded fabric and newspaper, and when that wasn't enough, they used thick curtains and rugs to keep in the heat from their fireplaces and coal-burning stoves.

Fortunately, we’ve moved on from shredding newspaper and now have a plethora of highly effective insulation materials.

Fibreglass, also known as glass wool: First mass-produced in the 1930s, fibreglass is made of fibres of spun glass. It’s what you think of when you imagine insulation, especially the pink or yellow rolls. Fibreglass insulation also comes in batts (pre-cut flat pieces) or in loose-fill form, which can be pumped into a space. It’s affordable, sustainable, fire-resistant, and easy to install, although you'll need to don protective gear as it irritates the skin. The R-value, a measure of the insulation’s resistance to heat transfer, is respectable between 2.2-2.7 per inch.
Mineral wool, also known as rock wool: Mineral wool is made similarly to fibreglass: material is melted, then spun to form wool-like fibres. But instead of glass, the material used is volcanic rock such as basalt or recycled slag from blast furnaces. Mineral wool is more expensive than fibreglass but has a higher R value (3-3.3), is more sustainable and durable, and provides better sound-proofing.
Polystyrene: Polystyrene is a synthetic polymer, usually installed as insulation in rigid boards. It comes in two types: expanded (EPS), made from heating tiny polystyrene beads in a mould until they expand and fuse, and extruded polystyrene (XPS), made from melting the polystyrene beads together, pushing the liquid through a small opening, and letting it expand as it cools. Polystyrene boards are even better insulators than fibreglass and mineral wool and are highly moisture resistant, but are combustible unless treated. They're also less sustainable, particularly XPS, which uses blowing agents that are highly polluting, with high global warming potentials.
Cellulose: Cellulose is recycled wood or paper products treated to be fire resistant. It’s an affordable and sustainability choice and can be installed in hard-to-reach places but can be susceptible to moisture if it’s not installed correctly and can settle over time, reducing its effectiveness.
Polyisocyanurate (PIR): PIR boards have an excellent R-value (5-6/in) and are easy to install, including as a DIY project. They’re durable and moisture and fire-resistant. However, they’re made from petroleum and are difficult to recycle so aren’t environmentally friendly.
Polyurethane spray foam: Polyurethane is usually installed as a foam and is one of the most thermally resistant insulators available. When it’s sprayed into a space, it expands and creates an air-tight, waterproof barrier. It’s particularly good for insulating cavity walls and irregular spaces. However, it can sometimes release harmful gases during installation so must be installed by a professional. It’s also made from petroleum so isn’t sustainable. It’s also one of the more expensive options.

Insulation material	Cost per m2	R value per inch	Fire resistance	Sustainability	Suitable for
Fibreglass	£10/m2	2.2-2.7	High	Moderate, 20-30% recycled material	Loft insulation, cavity and solid wall, floor insulation
Mineral wool	£18/m2	3-3.3	High	Moderate, 70% recycled material	Loft insulation, cavity and solid wall insulation, floor insulation
Polystyrene	EPS: £10/m2 XPS: £21/m2	EPS: 3.6 - 4.0 XPS: 4.5 - 5.0	Combustible unless treated	Poor. EPS: available with some recycled content XPS: requires blowing agents with high global warming potential	Walls,roofs
Cellulose	£11/m2	3.2 - 3.7	Moderate	High, up to 85% recycled material, biodegradable and non-toxic	Walls, lofts, floors
PIR	£12/m2	5-6	High	Low, made from petroleum	Solid walls, roofs, floors
Polyurethane spray foam	£21/m2	5.5-6.5	Combustible unless treated	Low, made from petroleum, can release harmful gases during installation	Cavity walls, irregular spaces

Why should you invest in home insulation?

For many homes, insulation is a no-brainer, with many advantages and few drawbacks.

The best reasons to invest in home insulation include:

Lower energy bills

Insulation can knock hundreds off your annual heating bills and pay for itself in just a few years. For example, the Energy Saving Trust estimates that loft insulation can reduce the energy bills of a detached house by £380 per year, compared to an installation cost of £1,100.
Smaller carbon footprint

A 2023 survey from the Met Office found that 59% of Britons are concerned about their carbon footprint and make deliberate low-carbon choices. Insulation can reduce your household’s use of natural gas for heating, leading to huge carbon savings. For instance, installing loft insulation in a detached house could save 1,000kg of CO2 per year, the equivalent to the carbon emissions of a flight from Paris and New York.
Protection from energy market fluctuations

Energy prices are vulnerable to geopolitical friction, as we experienced in 2021-22 when Russia’s invasion of Ukraine sent British energy bills soaring. If you’re using less energy to heat your home, you’ll be somewhat shielded from shock energy bills.
More comfort at home

A well-insulated home feels warmer in the winter and cooler in the summer.
Better resale value

New insulation can add between 5% and 10% to your home’s value, depending on the property’s current EPC rating.
Acoustic insulation

Most thermal insulation materials offer some acoustic insulation as well, which can dampen noises from neighbours and roads.
Reduce damp

Properly installed insulation can reduce condensation and damp in homes.
Longer lifespan for your boiler

In a well-insulated home a boiler doesn’t have to work as hard to maintain temperature so will last longer and require fewer repairs.
Protection of the building

Insulation can protect the structure of your home from extreme temperatures and damp.

Are there any grants available for home insulation?

The £1 billion Great British Insulation Scheme (GBIS) is providing grants for insulation for 300,000 energy-inefficient homes. GBIS is part of the Energy Company Obligation (ECO), which requires large and mid-sized energy supplies to fund efficiency upgrades for their most vulnerable customers.

GBIS is open to two groups of households. The first group, the low-income group, can qualify for fully-funded upgrades, including insulation. Households in this group live in properties with EPC ratings of D or below and have someone who qualifies for certain means-tested benefits, are in social housing and vulnerable to the cold (e.g. elderly or ill), or have gross incomes below £31,000.

The general group includes homeowners in properties in council tax band A – D in England, or A – E in Scotland and Wales, with EPC ratings of D or worse. This group can qualify for one type of insulation, such as cavity wall or loft insulation but not both. This group may also be asked to contribute a small amount toward the cost.

GBIS favours cheaper projects such as cavity wall and loft insulation but in some cases, you may qualify for full or partial funding for other, more expensive measures:

Solid wall insulation - internal or external
Flat roof insulation
Pitched roof insulation
Underfloor insulation
Solid floor insulation

Scottish households may qualify for free or subsidised home energy efficiency upgrades, including insulation, through the Warmer Homes Scotland scheme. The scheme is open to residents in homes with energy ratings of 64 or below (some D properties, all E, F, and G properties) who also meet other eligibility criteria, such as being pregnant or having children under 16 while receiving passport benefits.

Welsh households could qualify for fully-funded energy efficiency upgrades, including insulation, through the Warm Homes Nest scheme. Eligible households are low-income or receive certain benefits and live in properties with EPC ratings of 54 (E), or 68 (D) or less if a member of the household has certain chronic illnesses.

FAQs

Can I install home insulation myself?

Yes, some types of home insulation are easy to install yourself. For example, installing mineral wool or fibreglass cold loft insulation is a great DIY project and doing it on your own could save you hundreds of pounds. You can also likely install rigid foam board insulation to walls and doors without professional help.

However, some types of insulation are best left to the experts. For instance, you shouldn’t undertake cavity wall or flat roof insulation yourself and some materials such as polyurethane spray foam must be installed by a professional.

Can I get free home insulation?

Yes, you may be able to get free home insulation through the government or your energy supplier. Schemes currently accepting applications include the Great British Insulation Scheme (GBIS), the Scottish government’s Warmer Homes Scotland or the Welsh government’s Warm Homes Nest scheme. Eligibility depends on the current EPC rating of your property and your income, benefits, and vulnerability of members of your household.

Can I improve my existing home insulation?

Most homes built after the 1990s have some form of insulation. However, it may be inadequate or have lost effectiveness through age or due to poor installation.

A heat loss survey can identify where your property is losing heat, including places that may already be insulated, but insufficiently.

For example, the current recommendation is that loft insulation should be 270mm thick. Prior to 2003, however, the recommended depth was 200mm and before 1995, it was just 100mm. So if your loft insulation was installed more than 20 years ago, it’s likely too thin and should be topped up.

Your existing installation may also have been installed incorrectly, making it less effectively and vulnerable to damp and pests which can erode its thermal resistance. Some materials also have shorter lifespans. For instance, fibreglass insulation typically needs to be replaced after 15 to 20 years.

Will insulation add value to my home?

Yes, a well-insulated home is attractive to buyers, who are willing to pay more for a property with warm rooms and lower energy bills.

However, the uplift depends on the type of insulation you install and the energy efficiency of your property before. Research by the government in 2013 found that boosting your property’s energy performance certificate (EPC) rating from G to A or B could increase the value by an average of 14%. However, such a dramatic increase in EPC rating would likely require more than one area of new insulation. More modest increases, from G to D, could boost values by 8%.

What is the best insulation material?

The best insulation material depends on your project, budget, and priorities.

Going purely off r value - a measure of a material’s thermal resistance - the best insulation material is polyurethane spray foam. However, it’s not environmentally friendly and can only be installed by professionals.

In general, the best materials for loft insulation are fibreglass, mineral wool, and PIR boards, all of which can be installed as DIY projects. Cellulose, PIR boards, and polyurethane spray foam are best for roof insulation, which should usually be undertaken by a professional.

For cavity walls, polystyrene beads, mineral wool, and polyurethane spray foam are best, while for solid walls, consider rigid foam boards, such as PIR, and expanded and extruded polystyrene. For floor insulation, mineral wool and PIR boards are best.

Resources:

Author

Lauren Smith

Lauren Smith is a seasoned content writer with over a decade of experience creating clear and engaging articles for a wide range of audiences. Throughout her career, she has produced thousands of guides, features, and explainers across a diverse range of sectors. She is particularly interested in sustainability, renewable energy, and the transition to a low-carbon future, focusing her writing on helping readers understand the technologies, policies, and innovations that are driving the UK’s clean-energy shift.

Activity History - Last updated: 26 November 2025, Published date: 16 November 2025

Reviewer

Mike Rowe

Energy Expert

Mike is a recognised leader in the UK energy sector with over two decades of experience, having run one of the country's most trusted Ofgem-accredited energy comparison platforms before selling in 2019. Today, he advises EnergyComparison.co.uk and works with businesses on the transition to net zero.

Activity History - Expert Reviewed on 17 November 2025 and last checked on 26 November 2025