External Wall Insulation Survey: Professional Assessment Guide
What an independent survey of external wall insulation (EWI) checks, what a useful report covers, and what surveys usually cost. If your EWI was fitted under ECO4 or GBIS, start with TrustMark's free audit instead.
What Is an External Wall Insulation Survey?
An EWI survey is a detailed inspection of your external wall insulation to assess its condition, identify defects, work out whether problems are caused by the insulation, and recommend what should be done.
It should be carried out by someone independent of the original installer and of any contractor who could be paid to do the repair. Insulation Crisis Help is an advice and introduction service run by Better Home Hub Ltd; we do not carry out surveys ourselves.
Check the Free Route First
If your external wall insulation was installed under ECO4 or the Great British Insulation Scheme (GBIS), TrustMark offers a free Find & Fix audit. A qualified professional checks the work against technical standards and you get the result. If problems are found, TrustMark arranges for the installer or retrofit coordinator to fix them, and you should not be asked to pay. TrustMark says it may take several months to contact every household, and the audit may not cover purely cosmetic issues.
The scale is why this exists: the National Audit Office found that 98% of homes with external wall insulation under these schemes had major issues needing remediation, based on audits carried out between June and August 2025.
Contact TrustMark on 0333 555 1234 (option 1) or onsitebookings@trustmark.org.uk. Anyone contacting you about the audit should be able to quote the Unique Measure Reference Number from your Ofgem letter. TrustMark advises not letting in anyone who cannot. For internal wall insulation, contact Ofgem's ECO contact centre on 0808 169 4447.
Paperwork to gather before any inspection
- Your Ofgem letter with the Unique Measure Reference Number (ECO4 or GBIS installs)
- The guarantee certificate. If it is missing for an install after 1 January 2020, email TrustMark at info@trustmark.org.uk
- The installer's name. If you do not know who installed ECO work, you can make a subject access request to ECO.SAR@ofgem.gov.uk with two proofs of address
- Dated photos of damp, mould, cracking or staining, and any emails or letters with the installer
Types of Survey
TrustMark Find & Fix audit
An on-site check of external wall insulation installed under ECO4 or GBIS, arranged by TrustMark as part of the government's programme.
- • Only for EWI installed under ECO4 or GBIS
- • It may take several months to be contacted
- • It may not cover cosmetic or appearance issues
Damp survey
An inspection focused on damp, with moisture meter readings, humidity measurements and a condensation risk assessment.
- • Damp or mould inside the house
- • Telling condensation apart from water getting in
- • May not assess how the EWI itself was installed
- • If the firm also sells damp treatments, ask how independent the advice is
Independent EWI inspection
An inspection of the insulation system itself by a building surveyor or specialist, often combined with moisture readings and sometimes thermal imaging or opening up small areas.
- • Privately paid EWI with suspected defects
- • Disagreements with an installer about installation quality
- • Planning what remedial work is needed
- • Moisture readings inside and out
- • Checks of detailing, fixings and junctions
- • A view on the likely cause
- • A written report with photographs
RICS Home Survey Level 3
The most detailed RICS survey of a whole home. It is not an EWI investigation, and may recommend further specialist investigation of the insulation.
- • Buying a house that has EWI
- • An overall view of a property's condition
Survey price ranges from the HomeOwners Alliance (Level 3 prices vary with property value). We found no reliable published price for an independent EWI inspection: the cost depends on the property and scope, so get a fixed written quote first. Last reviewed September 2026.
What Surveyors Check During an EWI Survey
External inspection
Visual assessment
- Render condition and cracking patterns
- Fixing system (mechanical fixings)
- Water ingress points and staining
- Detailing around windows and doors
- Base and ground-level detailing
- Roof and eaves junctions
Technical measurements
- Insulation type and thickness
- Render thickness and specification
- Fixing density and pattern
- External surface moisture readings
- Thermal bridging at junctions
- Compliance with the manufacturer's specification
Internal inspection
Moisture and damp analysis
- Internal wall moisture levels at several points
- Relative humidity in affected rooms
- Condensation risk (dew point) assessment
- Penetrating damp or condensation diagnosis
Damage assessment
- Where mould is growing and how severe it is
- Plaster and decoration damage
- Window reveal and sill problems
- Whether ventilation is adequate
Thermal imaging (if included)
Thermal imaging cameras show temperature differences across wall surfaces, which can point to:
- Cold spots and thermal bridgesAreas where insulation is missing, thin or not working
- Possible damp areasDamp surfaces can show as cooler than dry ones
- Installation defectsGaps between boards and junction failures
- Air leakage pointsDraughts getting through or around the system
The Survey Report: What You Should Receive
1. Summary
The key findings, how serious they are, and the main recommendations.
2. Property description
Property type, construction, the EWI system and when and under which scheme it was installed.
3. Method
What was inspected, the equipment used and any limitations, such as areas that could not be reached.
4. Findings and evidence
Observations, measurements, annotated photographs and any thermal images.
5. Likely cause
The surveyor's opinion on whether the problems come from the EWI installation, linked to the evidence.
6. Recommendations
Remedial options in order of priority, and what should happen first.
7. Appendices
The surveyor's qualifications, standards referred to and a full photo record.
Defects Surveyors Look For
The National Audit Office found that 92% of homes with external wall insulation under ECO4 and GBIS had major issues affecting the insulation's performance, often creating a risk of water getting in and mould, and 6% had health and safety risks needing immediate correction, such as inadequate ventilation.
Serious issues
- •Missing or inadequate mesh reinforcement in the base coat
- •Missing or inadequate mechanical fixings
- •No base track or ground-level protection
- •Wrong board thickness or specification
- •Poor detailing at window reveals
Other issues
- •Render thinner than the manufacturer's specification
- •Too little mesh overlap at joints
- •Poorly treated joints between boards
- •Incompatible system components mixed together
- •Too little curing time between coats
Design and suitability issues
- Unsuitable wallFor example deteriorated or already damp masonry that was not assessed or repaired first
- Existing damp ignoredMoisture problems trapped behind the insulation
- Inadequate ventilationNo ventilation improvements despite a more airtight house and higher condensation risk
- Wrong system for the exposureA system or detailing not suited to how exposed the wall is to wind-driven rain
Survey Costs
| Type | Typical cost | Source |
|---|---|---|
| Find & Fix audit (ECO4/GBIS external wall insulation) | Free | TrustMark |
| Damp survey | £150 to £300 | HomeOwners Alliance, August 2026 |
| RICS Home Survey Level 3 | £630 to £1,500, depending on property value | |
| Independent EWI inspection, with or without thermal imaging | No reliable published figure. It depends on the property and scope, so get a fixed written quote. | None found |
Last reviewed September 2026.
Choosing the Right Surveyor
Questions to ask before booking
- 1.Have you inspected external wall insulation before, including ECO4 or GBIS installations?
- 2.Are you independent of the installer and of any company that could do the repair?
- 3.What testing will you use (moisture meters, thermal imaging, opening up small areas)?
- 4.How long will the inspection take, and when will I get the report?
- 5.Is the price fixed, and does it include all testing and the written report?
- 6.Will the report give a view on the likely cause and the remedial work needed?
- 7.What professional indemnity insurance do you hold?
What Happens After the Survey?
Read the report carefully and note how serious the problems are, what the surveyor thinks caused them and what they recommend. Ask the surveyor to explain anything unclear before you act on it.
Minor issues
If problems are minor and repairable:
- • Send the report to the installer
- • Ask for the repair in writing
- • Ask what guarantee covers the repair
Significant defects
If the installer will not put it right:
- • Complain in writing
- • Contact your guarantee provider
- • Use TrustMark's complaints process if the business is registered
Safety risk or major failure
If there is a safety risk or widespread failure:
- • Tell the installer and guarantee provider straight away
- • ECO4/GBIS: contact TrustMark (EWI) or Ofgem (IWI)
- • Get independent advice, e.g. Citizens Advice on 0808 223 1133
How a Survey Report Can Be Used
- Complaints to the installer: setting out what is wrong and what needs fixing
- Guarantee providers: evidence of defects in materials or workmanship
- TrustMark complaints: supporting information for the Scheme Provider or the Dispute Resolution Ombudsman
- Remediation planning: a clear scope for contractors to quote against
- Selling your home: your conveyancer and buyers may ask about the insulation and any work done
- Legal advice: any independent adviser you consult will want to see it
If no free route covers you
If your EWI was not fitted under ECO4 or GBIS, we can introduce you to a surveyor or specialist through Better Home Hub. Sending an enquiry is free. The specialist may pay Better Home Hub a fee, and any survey is agreed and paid for between you and them, so check their qualifications, insurance and independence yourself.
Frequently Asked Questions
Is the TrustMark audit really free?
Yes. The government has said the audits are at no cost to the consumer. It applies to external wall insulation installed under ECO4 or GBIS. Nobody should charge you to arrange it.
How long does an EWI survey take, and do I need to be there?
It depends on the size of the house and the testing involved, so ask for the time on site and the report turnaround in writing. Someone usually needs to give access inside for moisture readings and to explain the history of the problem.
Can the installer dispute a survey report?
Yes. A clear report from an independent, qualified surveyor sets out the facts, but it does not guarantee an outcome. If the installer will not act, go to your guarantee provider or use TrustMark's complaints process if the business is registered.
Should I get more than one survey?
Usually one thorough independent inspection is enough. Consider a second opinion if the first report seems incomplete or does not explain the cause of the problem.
Sources
- TrustMark: free Find & Fix audit offer
- TrustMark: complaints process
- Written ministerial statement HCWS953 (13 October 2025)
- National Audit Office: Energy efficiency installations under the Energy Company Obligation (HC 1334, 14 October 2025)
- Ofgem: ECO complaints process
- HomeOwners Alliance: How much does a house survey cost?
- RICS: Find a Surveyor
- Property Care Association
- Citizens Advice: consumer helpline
Last reviewed September 2026.