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What changes the cost of cavity wall insulation?
A cavity wall insulation quote depends on how much wall there is, how easy it is to reach, what the survey finds inside the cavity, and which material is injected. It is notifiable building work, so check the installer will tell building control, and note that this guide does not print a price.
Last reviewed:What is cavity wall insulation?
Some houses have outer walls built as two layers of masonry with a gap between them. Cavity wall insulation fills that gap. An installer drills small holes in a pattern through the outer layer, usually in the mortar joints, injects the insulation, and fills the holes to match.
This guide does not print a price. It explains what changes each quote and what to check before you agree to one. QuoteZila starts in Cheshire, with Crewe, Nantwich and Sandbach first, and anyone in the UK can post the job.
Not every wall has a cavity, and not every cavity is suitable. Solid walls, timber-framed walls and walls with a known damp problem are different jobs. That is why the survey matters.
Building control and the installer
Planning Portal says installing cavity wall insulation is specifically defined as notifiable building work in the Building Regulations, so for buildings not exempted it is necessary to tell a building control body that the work will be carried out [S1]. It says most local authorities do not levy a building control charge for this [S1]. Where the installer is registered with CIGA, one of the cavity insulation schemes, the installer will in most cases deal with this, but building owners should always check that it will be done [S1].
GOV.UK's guide to building work lists cavity and solid wall insulation among notifiable work [S2]. It names Blue Flame, Certass, Certsure, CIGA, NAPIT and STROMA as competent person schemes covering the installation of cavity wall insulation [S2]. If the installer is on a relevant scheme, GOV.UK says you should receive a certificate of compliance within 30 days of completion [S2].
GOV.UK explains building regulations approval. GOV.UK: building regulations approval. QuoteZila is not affiliated with this organisation.
What changes the quote?
| Factor | What to ask | Why it moves the price |
|---|---|---|
| Wall area | The measured area, and which walls are included | More wall means more material and drilling |
| House type | Detached, semi, terraced, bungalow or flat | Shared walls are not insulated, so the exposed area differs |
| Access | Ladders, a tower or scaffolding for upper walls [S7] | High walls and walls over conservatories take longer |
| The survey | How the cavity was checked and what was found | Rubble, existing fill or narrow gaps change the job |
| Material | Beads, mineral wool or another product, and why [S1] | Different products, prices and suitability |
| Old insulation | Whether failed fill must be extracted first | Extraction is a separate, larger job |
| Ventilation | How air bricks and vents will be kept clear | Sleeves or extra work may be needed |
| Making good | How drill holes will be filled and matched | Colour matching on brick or render |
| Paperwork | Who tells building control, and which scheme [S1] [S2] | Missing paperwork causes trouble at sale |
| VAT | Included or extra. Registration applies above £90,000 of taxable turnover [S6] | Changes the total |
What should the survey check?
A proper survey happens before the quote is final. Ask what the surveyor will look at, and ask for the findings in writing.
- Is there a cavity? Brick bond patterns, wall thickness and the age of the house give clues, but a small inspection hole or a borescope shows what is really there.
- Is it clear? Mortar droppings, rubble and old debris at the bottom of a cavity can bridge the gap.
- Is it already filled? Some walls already have partial or full insulation.
- What condition are the walls in? Cracked render, failed pointing or damp patches inside need dealing with first. Our damp proofing page covers that trade. Repointing costs and rendering costs cover the repairs.
- What material suits this wall? Planning Portal says the building regulations require the insulation material to be suitable for the wall construction concerned, and that for some foam materials a formaldehyde risk assessment is needed [S1].
An installer who quotes without looking at the walls cannot know most of this.
Attached houses, extensions and conservatories
Semi-detached and terraced houses share a party wall with the neighbour. The installer should explain how they will stop insulation passing into the neighbour's cavity.
Extensions may have been built at a different time with a different wall. Ask whether they are included and whether they have a cavity.
Walls above conservatories and porches are harder to reach and may need a platform.
Flats usually need the freeholder's or managing agent's agreement, and the job may cover the whole block.
Access and work at height
Drilling and filling the upper part of a two-storey wall means working from a ladder, a tower or scaffolding. HSE says ladders should only be used on firm, level, clean and solid surfaces, where they will not be struck by vehicles or pushed over, where the public cannot walk underneath, and where they have been secured [S7]. Ask the installer what access they will use for each wall, especially above a conservatory or a sloping path. HSE: work at height. QuoteZila is not affiliated with this organisation. HSE has more on work at height.
Government schemes and recommendations
Ofgem says the Great British Insulation Scheme delivered improvements to some of the least energy-efficient homes in Great Britain, and that it began in April 2023 and ended on 31 March 2026 [S3]. It was available to low-income and vulnerable households and to homes with an Energy Performance Certificate rating of D to G in Council Tax bands A to D in England [S3].
That scheme has ended, so treat any caller offering "government-funded" insulation with care and ask which scheme they mean. GOV.UK has a service that gives recommendations for home improvements if you own a property in England or Wales [S4]. Your energy supplier and your council can tell you about any current support.
What about removing old cavity insulation?
If existing cavity insulation has become wet or has failed, the fix may be to extract it before anything else is done. Extraction is a separate job with its own equipment and its own quote. Ask the installer to explain why they think extraction is needed and what evidence they have, and get a second opinion before you agree. If damp is the reason, find and fix the cause, such as defective pointing, render or gutters, at the same time.
What should you check after the work?
Walk round the house with the installer before they leave. Look at every drill hole and check it has been filled to match the mortar or render. Check that air bricks and vents are clear and working. Look inside at walls that had damp patches before.
Keep the paperwork together: the survey, the quote, the invoice, the scheme registration and the certificate of compliance. GOV.UK says a scheme installer should provide that certificate within 30 days of completion [S2]. It also warns that if work is not notified or done by a scheme installer, the local authority will have no record it complies, which can matter when you sell [S2].
If a damp patch appears inside later, write to the installer straight away with photos and dates.
How do you compare quotes?
Ask each installer for the same things: the measured wall area, which walls are included, the survey findings, the material, the access method, how holes will be made good, who tells building control, and which competent person scheme they belong to.
Citizens Advice suggests trying to get written quotes from at least 3 different traders, and says some traders charge for quotes, so ask about this first [S8]. It says a quote is a fixed price and an estimate is just a rough guess [S8]. Do not agree to pay everything up front. If a deposit cannot be avoided, push it down as much as possible, do not agree to more than 25%, and always get a receipt [S8].
Be cautious with doorstep sellers and cold calls that press for a decision that day. You might be able to cancel within 14 days, but Citizens Advice says that if you asked for the work to start within those 14 days, you might have to pay for some or all of it [S8].
Loft insulation costs covers the other insulation job people often compare with this one.
Jobs you might post
These are examples, not taken from real job posts.
- "Semi-detached house, I think the walls have a cavity but I am not sure if it is already filled. Please survey and quote, including who tells building control."
- "Bungalow with a damp patch on one wall after cavity insulation was put in years ago. Please inspect and advise before quoting any extraction."
- "End terrace with a conservatory on the side wall. Please quote for cavity wall insulation and say how you will reach the wall above the conservatory roof."
Posting an insulation job
Photos of each outside wall, any damp patches inside and the air bricks help an installer quote. Your job goes to up to five matched local businesses [QZ2]. QuoteZila is free for customers and local businesses [QZ1].
Honest status: QuoteZila is new. We're starting in Cheshire, beginning with Crewe, Nantwich and Sandbach, and growing area by area. Anyone in the UK can still post a job or register a business. How fast you get quotes depends on how many local businesses have joined near you. Businesses can register and receive jobs straight away. We don't check insurance, qualifications or registrations, so please check these yourself before you hire.
Posting a job is not open yet
Questions about cavity wall insulation costs
How much does cavity wall insulation cost?
This guide does not print a figure. A small mid-terrace with two exposed walls and a detached house with four are very different amounts of wall, and access, the survey findings and the material all change the total. Ask each installer for the wall area they have measured and what the price includes.
Does cavity wall insulation need building regulations approval?
Yes. Planning Portal says installing cavity wall insulation is specifically defined as notifiable building work, so a building control body must be told it will be carried out. It says that where the installer is registered with CIGA, the installer will in most cases deal with this, but building owners should always check it is done.
Do I need planning permission?
Planning Portal says planning permission is not normally required for fitting insulation where there is no change in external appearance, but that you should consult your local planning authority if the building is listed or in a conservation area.
Is there still a government scheme for free cavity wall insulation?
Ofgem says the Great British Insulation Scheme began in April 2023 and ended on 31 March 2026. GOV.UK has a service that gives recommendations for home improvements if you own a property in England or Wales. Check with your energy supplier and your council for any support available now.
Can any insulation go in any wall?
No. Planning Portal says the building regulations require the insulation material used to be suitable for the wall construction concerned, and that some foam materials need an assessment of the risk of formaldehyde gas. A survey of your walls should come before the quote.
Does VAT change the price?
It can. A business must register for VAT if its taxable turnover for the last 12 months goes over £90,000. Ask whether the quote includes VAT, and whether any relief applies to your job.
Does QuoteZila check insulation installers?
No. We don't check insurance, qualifications or registrations, so please check these yourself before you hire. You can report a quote or a business from your job page.
This page is general information, not professional or legal advice. QuoteZila does not check Gas Safe, WaterSafe, NFRC, NICEIC or other registrations against the register on your behalf: look them up yourself.
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Sources
- QZ1: QuoteZila product fact. QuoteZila home and FAQ copy.
- QZ2: QuoteZila product fact. QuoteZila FAQ How does getting quotes work.
- S1: Insulation: Building Regulations cavity wall, Planning Portal. Accessed 2026-10-30. https://www.planningportal.co.uk/permission/common-projects/insulation/building-regulations-cavity-wall
- S2: Building work, replacements and repairs to your home, GOV.UK. Accessed 2026-10-30. https://www.gov.uk/government/publications/building-work-replacements-and-repairs-to-your-home/building-work-replacements-and-repairs-to-your-home
- S3: Great British Insulation Scheme, Ofgem. Accessed 2026-10-30. https://www.ofgem.gov.uk/environmental-and-social-schemes/great-british-insulation-scheme
- S4: Find ways to save energy in your home, GOV.UK. Accessed 2026-10-30. https://www.gov.uk/improve-energy-efficiency
- S5: Insulation: planning permission, Planning Portal. Accessed 2026-10-30. https://www.planningportal.co.uk/permission/common-projects/insulation/planning-permission
- S6: Register for VAT, GOV.UK. Accessed 2026-10-30. https://www.gov.uk/register-for-vat
- S7: Where ladders should be used, Health and Safety Executive. Accessed 2026-10-30. https://www.hse.gov.uk/work-at-height/ladders/where-ladders-should-be-used.htm
- S8: Before you get building work done, Citizens Advice. Accessed 2026-10-30. https://www.citizensadvice.org.uk/consumer/getting-home-improvements-done/before-you-get-building-work-done/