Cavity wall insulation (2023)

Benefits

  • Save energy
  • Cut your heating bill
  • Reduce your carbon footprint

The savings figures on this page are based on the April 2022 energy price cap. They will be reviewed and updated by 1 October 2022 to reflect the October energy price cap, as announced by Ofgem this August.

About a third of all the heat lost in an uninsulated home escapes through the walls. By properly insulating cavity walls, you will save energy and cut costs off your heating bill.

In general, houses built from the 1990s onwards have wall insulation to keep the heat in, but if your house is older than that, it may not have any wall insulation at all.

Houses in the UK mostly have either solid walls or cavity walls:

  • If your house was built after the 1920s, it is likely to have cavity walls. A cavity wall is made up of two walls with a gap in between, known as the cavity; the outer leaf is usually made of brick, and the inner layer of brick or concrete block.
  • Pre-1920 older houses are more likely to have solid walls. A solid wall has no cavity; each wall is a single solid wall, usually made of brick or stone.

Working out your wall type

The first thing you need to find out is what sort of walls you have. If you can see the brickwork on the outside of the house, look at the pattern of the bricks.

Cavity wall

If your home has cavity walls, the bricks will usually have an even pattern with all the bricks laid lengthways.

(Video) Cavity Wall Insulation Problems ~ The Ugly Truth

If the brickwork has been covered, you can also tell by measuring the width of the wall. Examine a window or door on one of your external walls:

  • If a brick wall is more than 260mm thick then it probably has a cavity.
  • A narrower wall is probably solid. Stone walls may be thicker still but are usually solid.

Some houses have a different type of wall structure altogether. If your house is a steel-frame or timber-framed building, or is made from pre-fabricated concrete, then you will need to ask a specialist insulation installer to advise you.

Cavity wall insulation explained

Many cavity walls can be insulated by injecting insulation material into the cavity from the outside. A specialist company will drill holes in the outside walls, inject insulation through the holes and then seal them with cement. The insulation material is usually either mineral wool or polystyrene beads, but polyurethane foam may sometimes be used instead.

To insulate your cavity walls, the installer drills small holes around 22mm in size at intervals of around 1m in the outside wall of your home. The installer then blows insulation into the cavity using special equipment. Once all the insulation is in, the installer fills the holes in the brickwork so you’ll barely notice them.

(Video) Cavity Wall Insulation - How its done

Filling cavity walls is not a job you can do yourself, you will need to employ a registered installer. A professional can do the job in around two hours for an average house with easily accessible walls. It shouldn’t make any mess.

Costs and savings

Typical installation costs of cavity wall insulation vary depending on the size of your home. But whether you live in a large detached house or small flat, you should be able to make back the installation cost in five years or less due to the yearly energy bill savings you will make.

You might be able to reduce these costs by carrying out the work at the same time as other home improvements or by not tackling the whole house at once.

England, Scotland and Wales

Northern Ireland

Is cavity wall insulation right for your home?

If your house was built in the last 20 years or so, the walls are probably already insulated. To find out whether they are, you can do the following:

(Video) Cavity Wall Insulation

  • Ask a registered installer for a borescope inspection. The installer will drill a small hole in your external wall to see if your walls are hollow or filled.
  • Check with your local authority’s building control department.

Your home will be suitable for standard cavity wall insulation if it meets the following criteria:

  • Its external walls are unfilled cavity walls.
  • Your cavity is at least 50mm wide, and is clear of rubble.
  • The masonry or brickwork of your property is in good condition.
  • The walls are not exposed to driving rain.
  • Your house is not at risk of flooding.

You will need an installer to carry out a survey to check that your house is suitable. If so, they will then be able to insulate your walls using mineral wool or polystyrene beads.

If your house has narrow or uneven cavities, is in an exposed site or there is a risk of flooding, then it may be possible to fill the cavity with polyurethane foam. This is more expensive than standard cavity wall insulation but is a particularly effective insulator. You will need a specialist foam insulation installer to survey your home for this, and to carry out the work if suitable.

If you have any damp patches on your internal walls then they should not be insulated until the problem is resolved. Speak to a builder who specialises in damp prevention.

If your home’s external walls are joined to another house, the installer will need to insert a cavity barrier to contain the insulation so your neighbours aren’t affected.

If you live in a flat then you won’t be able to have just your flat insulated – you will usually need to get agreement from everyone to insulate the whole block.

Find an installer

Your installer should be a member of one of these organisations:

Check whether the installer is signed up to a code of professional practice and that the installation is guaranteed for 25 years by CIGA, or through an independent insurance-backed guarantee.

What to do if you are experiencing issues with your cavity wall insulation

If you notice problems with your walls after having cavity wall insulation installed, such as damp and mould, you should first call the company who carried out the installation. They should discuss the problem with you and revisit your property to establish whether the original survey or installation work is contributing to the problem. If it is, they should arrange for remedial work to fix the problem or for removal of the insulation if required.

If the installer is not willing to help or no longer exists then contact CIGA to establish whether you have a 25 year CIGA Guarantee. If you do, they should be able to help resolve the issue under the terms of the guarantee. If you don’t have a CIGA guarantee, check your paperwork from time of installation to see if you have an independent insurance backed guarantee which provides a similar level of cover. CIGA also have a contact form to report bad practice.

The symptoms of damp in a home can be very similar and could be caused by poor or inappropriate insulation, or by other issues such as inadequate home maintenance. Neither your installer nor a guarantee provider will agree to carry out or pay for remedial work if they determine that the problems were not caused by inappropriate insulation, bad workmanship or poor materials. If you believe your installer or guarantee provider is unreasonably refusing to help you, you should follow their complaints procedure.

If you are unable to get help from your installer or a guarantee provider, your final option is to speak to a company that can carry out the necessary work. We recommend that you use a company that is accredited with an appropriate scheme. If you are asking them to remove the insulation, you should use a specialist in cavity wall insulation removal accredited with a cavity wall insulation scheme such as CIGA or BBA.

(Video) Why you shouldn’t have cavity wall insulation installed.

Ventilation

Air needs to flow in and out of your house, so it stays fresh, dry and healthy. A good installer will be sure not to block or seal any intentional ventilation, including:

  • Underfloor grilles or airbricks, which help keep wooden beams and floors dry.
  • Wall vents, which let small amounts of fresh air into rooms.
  • Trickle vents – modern windows often have small vents above them to let fresh air trickle in.

In Northern Ireland, building regulations require adequate ventilation when installing wall insulation. This usually means installing more vents if there are not enough. Check with your local building control office to find out what you need to do for your home.

Further reading

Advice Solid wall insulation Advice Fixing damp and condensation Advice Windows and doors Advice Roof and loft insulation

Related links

(Video) External Wall Insulation ~ The Ugly Truth?

FAQs

Is cavity wall insulation enough? ›

Cavity walls have built-in spaces within the walls where insulation can be injected into. EWI is installed on properties with solid walls with no cavities. Cavity wall insulation is generally considered sufficient insulation and you shouldn't have any need to add a different type of insulation on top.

Is 50mm insulation enough for walls? ›

With 50mm of insulation, you can provide a good level of thermal insulation for most applications. To be sure that 50mm is enough, you should calculate the U-value of the entire structure (not just the board in isolation). It is important to reduce cold spots and thermal bridging to get the best insulation value.

What is the minimum cavity for wall insulation? ›

Your home will be suitable for standard cavity wall insulation if it meets the following criteria: Its external walls are unfilled cavity walls. Your cavity is at least 50mm wide, and is clear of rubble. The masonry or brickwork of your property is in good condition.

Can I add more cavity wall insulation? ›

For homeowners looking to improve the performance of their properties - perhaps to achieve compliance with modern building regulations, or perhaps to go beyond that and meet a retrofit standard such as EnerPhit - replacing or adding more insulation material in an already-treated cavity is not possible.

Will cavity wall insulation stop damp? ›

Cavity walls were designed to prevent the ingress of water however penetrating damp can still occur. A bridge across the cavity can be formed, which allows rainwater to move through to the inner surface of the property.

Can cavity wall insulation make your house colder? ›

Insulating a cavity wall helps to provide a thermal barrier which slows the flow of heat out of a room considerably. By slowing down the rate at which heat escapes from the home, less heating is needed to keep the house at the required temperature.

Can I have a 25mm cavity? ›

IDEAL FOR BRICK

SureCav25 will prevent any water ingress due to wind-driven rain, even in the most severe weather zones. This means that just a 25mm clear cavity can be used instead of the usual 50mm or even75mm in some cases. SureCav25 is BBA approved and accepted by LABC and NHBC!

Can I have a 50mm cavity? ›

Cavities are typically 65mm wide, but range from about 50mm to more than 85mm. The majority of existing cavity walls up to 12 metres in height are suitable for cavity fill.

How effective is 50mm insulation? ›

With 50mm of insulation you should expect to see a reduction in your heating bills by around 30%, but with 100mm that percentage will shoot to over 50%. Your heating system won't have to work as hard, and as a result won't use as much gas – so more cash in your pocket!

How thick should insulation be in walls? ›

In the walls: Typically, there is not an abundance of space inside your walls, so packing in the insulation isn't a bad idea. To get an R-value of 13 to 16, you will need four to five inches of insulation. However, if you use a more effective type of insulation, you may be able to get away with less.

What is the minimum cavity wall thickness? ›

Wall thickness

You'll need to find a doorway or a window you can open, so you can measure the thickness between the inside and the outside of the wall. A typical cavity wall will be around 250mm (10 inches) whereas a solid brick wall will be around 220mm (8½ inches).

How do you tell if your house is well insulated UK? ›

How to tell if your house is well insulated or not
  1. Sign #1 Drafts and cold areas. ...
  2. Sign #2 Fluctuating temperatures. ...
  3. Sign #3 Some rooms are colder than others. ...
  4. Sign #5 Snow and ice melt away from your roof quickly. ...
  5. Sign #6 Pigeons…? ...
  6. Sign #7 Rising energy bills. ...
  7. Sign #8 Ice forming in your home. ...
  8. Sign#9 Damp from the outside.
20 Dec 2019

Can you fill cavity wall with expanding foam? ›

Can You Use Expanding Foam Insulation as Cavity Wall Insulation? Yes, you can use expanding foam insulation as cavity wall insulation. Expanding foam is often found in the form of spray foam insulation as it is the easiest method to apply the reactive, two-component mixture that expands once blown.

What is the alternative to cavity wall insulation? ›

It may seem a bit off topic, but loft insulation is, in fact, a great alternative for cavity wall insulation. People are made to believe that wall insulation is the only way to reduce heat loss which is false.

Why are people having cavity wall insulation removed? ›

There are a few reasons why you may need to remove cavity wall insulation. For example, you could be having internal damp issues, or problems with vermin. The insulation may have been installed incorrectly, or is experiencing degradation.

Can too much insulation cause mold? ›

Mold in the Middle

It is possible to over-insulate your house so much that it can't breathe. The whole point of home insulation is to tightly seal your home's interior. But if it becomes too tightly sealed with too many layers of insulation, moisture can get trapped inside those layers. That's when mold starts to grow.

How can you tell if your house is well insulated? ›

To help you determine if your home is under insulated, our team has put together this list of nine tell-tale signs to watch out for.
  • Inconsistent Household Temperatures. ...
  • Energy Bills Are High. ...
  • Your Walls and Ceilings Are Cold to The Touch. ...
  • Issues with Pests. ...
  • Water Leaks. ...
  • Pipes Freeze on a Regular Basis. ...
  • Ice Dams. ...
  • Drafts.
22 Sept 2018

How long does wall cavity insulation last? ›

Unless damage occurs to it, all blown-in types of cavity wall insulation should last for up to a century. For other insulation methods used during the construction process, the numbers should be similar, lasting up to a hundred years.

Does cavity wall insulation need ventilation? ›

If you are eligible for funding for cavity wall insulation and have it installed after the 1st of July 2021, you may be required to have additional ventilation installed at the same time. Effective ventilation helps keep your home energy-efficient, safe, and healthy as it helps to control the air flow.

What is the minimum cavity wall thickness UK? ›

(d) cavity walls

All cavities should be at least 50mm nominal clear width.

Do 1930s houses have cavity wall insulation? ›

Does your house have cavity walls? Most houses built after 1930 have cavity walls. It is very rare for houses build before 1920 to have cavity walls, while most houses built after 1985 will have been constructed with cavity wall insulation built in. Most older houses will have solid walls.

What is the most efficient cavity wall insulation? ›

Foam insulation, typically made of polyurethane, has been hailed as the best thermal cavity wall insulation.

Can you put Celotex in a cavity? ›

Celotex CW4000 is an easy to install polyisocyanurate (PIR) insulation board with excellent thermal performance, featuring a low emissivity foil facing. Available in thicknesses from 40mm to 100mm, it can be considered for use in partial fill cavity wall applications.

What is the R value of 50mm Celotex? ›

• 50mm Kooltherm – R Value = 2.75

o So use 70mm Celotex PIR – R Value = 3.15 (Higher so better!)

How wide is the gap in a cavity wall? ›

Very simply, instead of having a 9 inch thick brick wall between the inside and outside of the house, a cavity wall has two layers of brick, with a gap in between. The gap can be anything from 20 to 100mm wide and therefore means that cavity walls tend to be much wider than a solid brick wall.

Can you double up insulation? ›

Doubling the thickness of insulation will double the insulation's R-value, cutting heat loss in half. Each time the insulation layer is doubled in thickness, this rule applies.

Is 50mm insulation enough for roof? ›

You can use two sheets of 50mm but it is not enough to comply with current regulations. You will not achieve the correct "U Value" which is the thermal resistance. In a nutshell your roof could end up with condensation (interstitial). Ideally if using Celotex you need a minimum of 120mm.

Can I double up kingspan? ›

Any foam or foil-backed foam product, such as Celotex or Kingspan, can have the measured thickness doubled due to the better thermal resistance of the material used.

Is R60 too much insulation? ›

Recommended R-Value Varies by State

You need exactly as much as the area you live in determines. Here, where temps get pretty hot for much of the year, attics should have from R30 to R60 (average is R38). Those living up north want anything from R49 to R60. This helps insulate against the extreme cold weather.

What is a good R-value for walls? ›

Depending on where you live and the part of your home you're insulating (walls, crawlspace, attic, etc.), you'll need a different R-Value. Typical recommendations for exterior walls are R-13 to R-23, while R-30, R-38 and R-49 are common for ceilings and attic spaces.

Do you need building regs for cavity wall insulation? ›

As well having to meet building regulations, the installation of cavity wall insulation is defined as 'notifiable building work', which means that it may be necessary to submit a building notice to a local authority advising that cavity wall insulation is to be installed.

What are the changes to the building regulations in 2022? ›

From 15 June 2022, all new homes must produce 30% less carbon dioxide emissions than current standards. The Building Regulations also include new standards to reduce energy use and carbon emissions during home improvements.

What are the three required elements for a cavity wall? ›

There are three essential requirements for cavity wall construction: the cavity wall must have a gutter at its base to collect leakage water and drains to direct water out of it; the two parts of the wall must be anchored together with metal ties that are corrosion resistant and adequately strong; the wall must have a ...

When did cavity wall insulation become compulsory in the UK? ›

Cavity wall insulation was first introduced during the 1970s, becoming compulsory in the 1990s for all new UK buildings. Any London property built after 1983 should already have cavity wall insulation fitted, but in older homes it may not be present.

Why are my internal walls so cold? ›

Simply put, cold walls are caused by poor insulation. If your home is poorly insulated, it means that heat from inside the home is easily escaping to the outside. Warm air moves from inside the rooms, passing through the walls to be lost outside. Without insulation, there's no barrier to keep the heat in.

Should outside walls feel cold? ›

Interior walls should be warm and dry to the touch, whereas your exterior walls should be cold to the touch (dryness will depend on the weather).

How much warmer does insulation make your house? ›

The EPA's research says that homeowners who have quality insulation in their homes can expect to see an average of 15 percent savings on their heating and cooling costs, and about a 25 percent reduction in total air infiltration.

Does cavity wall insulation make a big difference? ›

General Cavity Insulation Advantages:

It reduces the amount of heat that escapes through the walls of your home. It can reduce draughts in your home. It can reduce sound transmission through your walls. It's relatively cheap to install.

How long does wall cavity insulation last? ›

Unless damage occurs to it, all blown-in types of cavity wall insulation should last for up to a century. For other insulation methods used during the construction process, the numbers should be similar, lasting up to a hundred years.

How much difference does wall insulation make? ›

The EPA's research says that homeowners who have quality insulation in their homes can expect to see an average of 15 percent savings on their heating and cooling costs, and about a 25 percent reduction in total air infiltration. That adds up over time, saving you hundreds of dollars per year.

How much heat do cavity walls lose? ›

Why get cavity wall insulation? A home can lose as much as 35% of its heat through uninsulated external walls. By investing in cavity wall insulation, you can significantly reduce the heat loss from your home.

What is the most efficient cavity wall insulation? ›

Foam insulation, typically made of polyurethane, has been hailed as the best thermal cavity wall insulation.

Can old cavity wall insulation be removed? ›

It is possible to remove a range of cavity wall insulation types, including mineral fibre, expanded polystyrene beads, and polyurethane foam. You can also get older urea-formaldehyde foam removed. This is a job that will require professional equipment.

Can you fill cavity wall with expanding foam? ›

Can You Use Expanding Foam Insulation as Cavity Wall Insulation? Yes, you can use expanding foam insulation as cavity wall insulation. Expanding foam is often found in the form of spray foam insulation as it is the easiest method to apply the reactive, two-component mixture that expands once blown.

How do you tell if your house is well insulated UK? ›

How to tell if your house is well insulated or not
  1. Sign #1 Drafts and cold areas. ...
  2. Sign #2 Fluctuating temperatures. ...
  3. Sign #3 Some rooms are colder than others. ...
  4. Sign #5 Snow and ice melt away from your roof quickly. ...
  5. Sign #6 Pigeons…? ...
  6. Sign #7 Rising energy bills. ...
  7. Sign #8 Ice forming in your home. ...
  8. Sign#9 Damp from the outside.
20 Dec 2019

Does extra insulation really help? ›

Unless your home was specially constructed for energy efficiency, you can probably reduce your energy bills by adding more insulation. Many older homes have less insulation than homes built today, but even adding insulation to a newer home can pay for itself within a few years.

How much warmer is an insulated house? ›

Floors of a home generally conduct heat, losing precious heat to the cool ground below. An under insulated home in winter can lose up to 35% of your expensive internal warmth through the ceilings, another 25% through the walls and up to 20% through the floor and windows. That's a lot of expensive hot air to lose.

Should you insulate walls or ceiling first? ›

No Attic Space

For low-slope roofs or houses with roof truss construction, it's standard to insulate the ceiling before insulating the walls. Insulation batts, faced on one side with paper, are available in widths that fit between standard 16- and 24-inch joists. Batt thickness determines R-value.

Do 1980s houses have cavity wall insulation? ›

These days, all cavity walls need to be insulated. Cavity wall insulation was first introduced during the 1970s, becoming compulsory in the 1990s for all new UK buildings. Any London property built after 1983 should already have cavity wall insulation fitted, but in older homes it may not be present.

Do 1950s houses have cavity walls? ›

Most houses in mid 50s built in 250mm cavity construction with brickwork in both leaves or with brick outer leaf and block inner one. By the 1960s, blockwork almost universal in inner leaf. Wall ties mostly galvanised steel, twist or wire type.

What year did cavity wall insulation become compulsory? ›

The introduction of insulation into the cavity became standard in the 1970s and compulsory in the 1990s.

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