Property guides

Home insulation guide: cavity walls, floors, roof and loft spaces

Take a look at some of the most effective ways to reduce heat loss in your home and find out how different types of insulation could reduce your energy bills.

Good insulation prevents heat from escaping from your home, or from entering, and can help to reduce energy bills. And it will keep your home at a more constant temperature, so you can use your heating – or cooling system – efficiently.

Around a third of all heat lost in a poorly insulated home escapes through the walls, while up to 25% can be lost through the roof. And between 10-15% of a home’s heat can also be lost through poorly insulated floors.

So, if your home feels unbearably hot in summer, and too cold in winter, no matter how high you put the heating on, what are the steps you can take?

Energy experts have to use thermal imaging cameras to assess the insulation in the spaces of your home that you can’t access. But you can start by checking if your home has an Energy Performance Certificate (EPC). It will tell you if your property has cavity walls, or solid walls, and what type of insulation is thought to be fitted in loft spaces, and underneath floors. The insulation in each space will also a rating, which ranges from very good to very poor.

Find out how to check if your home has an Energy Performance Certificate.

How does insulation impact a home’s energy rating?

If an energy assessor identifies sources of draughts, or places where heat can escape, this can lower your home’s energy-efficiency rating. Details about the standard of window glazing, and wall, floor, roof and loft insulation (if it’s installed), will also be recorded.

But it’s difficult for an assessor to access floor and wall spaces, so they’ll often need to make an assumption about the standard and type of material used, based on the type of property and when it was built. So, if you’re improving your home’s insulation, or buying a new home, it’s a good idea to keep any records of the type of insulation that has been fitted so you can produce these when your EPC is next updated.

How else can I check how well my home is insulated?

You can start by finding the places where heat may be escaping from your home. Look for anywhere that you have an unwanted draught or flow of air. That includes windows and doors, brickwork, keyholes, loft hatches and pipework. Other signs of draughts include rooms that are noticeably colder than others when they’re all heated equally, and interior walls that feel colder to the touch than other rooms.

And during the winter months, you can also check if the frost or snow on your roof melts before your neighbour’s does. That would indicate you’re losing heat through your roof.

What are the some of the cheapest ways to insulate my home?

1. Draught-proofing
Potential annual saving: £60

Draught-proofing is a good place to start, as there are things you can do yourself. Block unwanted gaps around windows, doors, chimneys and floors that let the cold air in and warm air out (but first make sure they’re not being used for ventilation). Add doorstep or draught excluders on the inside of external doors, put window film on windows to stop heat from escaping through the glass, and use sealant or filler around windows that don’t open.

2. Insulating hot water tanks, pipes and radiators
Potential annual saving: £70

Put a hot water cylinder jacket that’s at least 80mm thick around your hot water tank to keep water hot for longer while reducing the amount of heat the cylinder loses.

You can also buy foam tubing to cover any exposed pipes between your hot water cylinder and boiler to reduce heat loss.

Radiator reflector panels can be fitted behind your radiators fitted behind external walls, to reflect the heat back into the room, rather than letting it escape.

Wall, floor and loft insulation

When looking into more expensive options for installing insulation, such as in roof and loft spaces, walls and floors, it’s good to know what will make the biggest difference to heating savings and how long it will last.

Roof and loft insulation
Potential annual saving: £260-£475

Loft spaces are the easiest and most affordable areas to insulate, compared to walls and floors. When done effectively, loft insulation produces the most noticeable results that can last for around 40 years.

Even if you already have insulation up there, over time, any boxes piled up and stored on top of it can make it less thermally efficient.

According to the Energy Saving Trust, installing mineral wool insulation at a thickness of 270mm in a semi-detached, gas-heated house (with no roof or loft insulation) could save you £285 a year. And upgrading the thickness of existing insulation to 270mm will also reduce energy costs.

Average costs of installing loft insulation and average savings

Type of propertyAverage costAverage annual saving
Detached house£1,200£475
Semi-detached house£930£285
Mid-terrace house£880£260
Detached bungalow£1,200£470
Source: Energy Saving Trust

Estimates are based on insulating a gas-heated home. Installation costs will vary. Figures for England, Scotland and Wales are based on fuel prices as of July 2023.

Underfloor insulation
Potential annual saving: £75 to £195

Floor insulation prevents heat loss in winter and can also help to keep your home cool during the summer months. It creates a barrier that protects your home from the air flow beneath your property. It can also help reduce your heating bills.

Newly-built homes tend to have solid concrete floors, while older homes are most likely to have suspended timber floors and insulation can be added underneath.

The Energy Saving Trust estimates that a typical suspended floor installation costs between £1,600 and £2,900, depending on the size of the space and how it’s accessed. There’s a higher cost for insulating solid floors.

Cavity wall insulation
Potential annual saving: £145 to £520

If your home was built after 1920, it’s likely to have cavity walls. This type of insulation is injected into the cavity between the inner and outer walls of a home and sealed with cement, to help to keep heat inside.

Installation costs vary, depending on the size of your home, but the Energy Saving Trust estimates that you should be able to make it back in energy bill savings within five years.

Average costs of cavity wall insulation and average savings

Type of propertyTypical installation costAverage annual saving
Detached house£4,600£520
Semi-detached house£2,700£300
Mid-terrace house£1,500£180
Detached bungalow£2,100£225
Mid-floor flat£1,000£145
Source: Energy Saving Trust.

Estimates are based on a gas-heated home. The average install cost is unsubsidised. Figures for England, Scotland and Wales are based on fuel prices as of July 2023.

If you’re looking to install cavity wall insulation, the first step is to arrange a survey from a qualified installer to check that your home is suitable. TrustMark can help you to find a trusted installer that is thoroughly vetted and continually monitored to ensure they meet required standards.

Solid wall insulation

An estimated 45% of the heat could be escaping from your home if you have solid walls. But insulating solid walls is considerably more expensive than insulating cavity walls. There’s no gap between the inner and outer walls, so they can’t be filled with cavity wall insulation.

Solid walls can be insulated from the inside or the outside, and doing this will provide bigger savings on your heating bills. But it can be a disruptive process. The easiest, and most cost-saving time to insulate solid walls is to plan the work for when you’re carrying out other home improvements, such as kitchen or bathroom renovations, or external extensions.

The Energy Saving Trust estimates that solid wall insulation for a typical three-bedroom, semi-detached house can be around £12,000 for external wall insulation, or £8,500 for internal wall insulation. Energy bill savings range from £195 a year if you live in a mid-floor flat up to £710 if you live in a detached house.

What insulation grants are there?

The government’s Help to Heat scheme includes a Boiler Upgrade scheme which provides grants to property owners to install low carbon heating systems such as heat pumps. It also provides funding to local authorities to help them upgrade energy-inefficient homes of low-income households in England.

It comes with the Energy Company Obligation (ECO) which requires energy suppliers to help certain households to fit energy-saving measures.

The Great British Insulation Scheme (formerly known as ECO+) is a new government scheme that is set to launch in the summer of 2023 and run until March 2026. It aims to help around 300,000 households by obligating energy suppliers to help people to reduce their heating bills through partial or full subsidised grants for the installation of things like loft and cavity wall insulation. Low-income households as well as those people living in the least energy-efficient homes (with an EPC rating of D or below) will have access to the scheme.

Who qualifies for these grants?

Which grants you might be eligible for will depend on your household income, where you live and who your energy supplier is. Further details and contact information here.

Can I get my home insulated for free?

If you or anyone in your home receives certain benefits, you could be eligible for full funding on insulation. The benefits include Universal Credit, Working tax Credit, Severe disablement allowance, Income support and Child Tax Credit. See the full list and how to apply here.

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