External wall insulation damp problems: the warning signs and what to do
In short
On 3 November 2026 the Welsh Government published guidance for householders on problems with external wall insulation (EWI). It lists the signs to look for, including cracked render, bulging walls, staining, water coming in, and damp and mould inside, and sets out the steps to take: gather evidence, find the paperwork, contact the installer, then the guarantee provider. Your local authority may help identify who was involved, and the Financial Services Compensation Scheme may help if the insurer behind a guarantee has stopped trading. The guidance is general information: it does not determine liability for defects or guarantee that remedial works will be carried out.
The guidance is written for Welsh homes, with separate routes for insulation installed under the Arbed scheme, the Nest scheme, and the ECO4 and GBIS schemes. The warning signs it lists are worth checking on any home with external wall insulation.
Can external wall insulation cause damp?
The Welsh Government says external wall insulation can make homes warmer, more comfortable and more energy efficient when it is designed and installed correctly, but that in some cases problems occur. It names four possible causes: poor installation, an unsuitable design, defects in materials, or a lack of ongoing maintenance. Problems can lead to water entering the building, damage to the external finish, and damp and mould.
It also says not all problems are caused by faulty installation. Some develop over time if maintenance is not carried out, and a lack of maintenance may affect any warranty or guarantee.
For insulation fitted under ECO4 and GBIS, the UK Government's guidance says there are quality issues with some solid wall insulation fitted through government schemes, including poor installation or failure to meet building regulations, which can lead to problems like damp or mould.
The warning signs
The guidance lists these signs that there may be a problem with the insulation:
- cracks in the render
- bulging or uneven wall surfaces
- staining or discolouration
- water entering the property
- damp patches on internal walls
- mould growth inside the home
- loose or damaged panels and fittings
For routine checks, it suggests homeowners look periodically for:
- cracks in the render or finish
- damaged sealants around windows and doors
- damage caused by impact
- staining or discolouration
- signs of water penetration
If damage is not repaired promptly, the guidance says, water may enter the system and cause dampness or mould inside the property.
How a damp survey documents it
The guidance asks householders to keep photographs, a note of when the problem first appeared, copies of correspondence, and a record of whether it gets worse in heavy rain. A damp survey adds measured, dated evidence to that record. The guidance does not set out a survey method and does not decide liability, so the survey's job is to record what is there clearly enough for the installer, the guarantee provider or their inspector to assess.
| Record | Why it helps |
|---|---|
| Each elevation, wide and close up | Shows where the cracks, bulging, staining or loose panels are, and how much of the wall is affected. |
| Render cracks | Photograph each one with a scale, and note where it sits in relation to the damp inside. |
| Windows, doors and sills | The guidance lists damaged sealants around windows and doors as a routine check. Record their condition at each opening. |
| The base of the wall | Record where the insulation stops in relation to ground level and the damp-proof course line, and anything against the wall there. |
| Moisture readings inside | Readings at several heights and positions on the affected walls, with the meter and scale used, give a pattern to set against the outside. |
| Thermal images, if you take them | Show surface temperature differences across the wall. Note the conditions at the time. |
| Weather and recent rain | The guidance asks householders to note whether problems get worse in heavy rain. Record the weather on the day, and go back after rain if you can. |
| The occupant's account | When the problem first appeared, whether it has changed, and any correspondence with the installer so far. |
Keep the findings and the opinion apart. A damp patch on an insulated wall can have more than one explanation, so the report should say what the evidence shows, what it does not show, and what further investigation would settle it.
The Welsh Government's steps
The guidance sets out these steps for insulation installed under the Arbed scheme.
| Step | What the guidance says |
|---|---|
| 1. Identify the problem | Look for the warning signs above. |
| 2. Gather evidence | Take photographs, record when the problem first appeared, keep copies of correspondence, and note whether it gets worse during heavy rain. |
| 3. Check your paperwork | Find the Homeowner Agreement, installation certificates, guarantee or warranty documents, and correspondence from the installer or scheme provider. They may show the contractor, the insulation system, any guarantee, and who administers it. Some installations may have an insurance-backed guarantee through organisations such as SWIGA or the IAA. |
| 4. Contact the original installer | The contractor should be given the opportunity to inspect the property and assess whether remedial work is required. |
| 5. Contact the guarantee provider | If the contractor cannot resolve it, or the work may be covered. They may confirm whether cover is in place, explain what is covered, arrange an inspection and advise on the claims process. |
| 6. If the contractor has stopped trading | Contact the organisation responsible for the guarantee or warranty, or the one named on your certificates. They may confirm cover, identify the insurer, replace lost documents and explain how to claim. |
| 7. If you cannot identify the installer or guarantee provider | Your local authority may be able to identify the organisations involved in delivering the scheme and direct you to the right contact. |
| 8. If the insurer has stopped trading | You may be able to seek compensation through the Financial Services Compensation Scheme (FSCS), which protects consumers when authorised financial services firms have failed. |
The guidance also lists where to get further help:
- Solid Wall Insulation Guarantee Agency (SWIGA): may be able to confirm whether a property is covered by a guarantee, explain the extent of the cover and provide information about making a claim.
- Insulation Assurance Authority (IAA): a technical authority and industry body covering insulation, heating and renewable technologies, with a complaints procedure for complaints about the workmanship or service of the IAA or an IAA registered business.
- Citizens Advice consumer service: free and impartial advice on consumer issues and disputes.
- Welsh Government Home Improvement Loans: loans for eligible homeowners who are unable to pay for essential repair and improvement works, managed by local authorities.
Insulation installed under Nest
For insulation installed under the Nest scheme, the guidance points to the Nest customer service and complaints policy. That policy says a complaint must be made within 6 months of the event, or of finding out you have reason to complain, and no later than 12 months after the event. The Nest team acknowledges complaints within 2 working days and, if a complaint is not resolved within 5 working days, gets back in touch to say what it is doing. If you are not satisfied with the outcome, you can take it to the Customer Service Manager. The Welsh guidance adds that Nest installations come with information on how to maintain the insulation.
Insulation installed under ECO4 or GBIS
For insulation installed under the Energy Company Obligation (ECO4) or the Great British Insulation Scheme (GBIS), the Welsh guidance points to the UK Government's guidance, What to do if you have poor quality wall insulation, published by the Department for Energy Security and Net Zero (DESNZ) and Ofgem. It says:
- all properties that had external wall insulation installed under these schemes will be offered a home check, with the work quality checked by qualified professionals;
- you may be contacted by Ofgem, TrustMark or a certification body, and all of them will use the Unique Measure Reference in your letter;
- if the work is found to be faulty, your installer will be asked to fix it, and you should not be asked to pay;
- if you have had a home check since January 2025, no further action is required;
- for a separate complaint, follow the TrustMark complaints process, which covers installers that are no longer operating.
Questions go to Ofgem, using the contact details on that page.
How widespread the ECO4 and GBIS problems are
In October 2024 TrustMark told DESNZ that an abnormally high rate of non-compliance had been detected in solid wall insulation installed under ECO4 and GBIS. In April 2025 Ofgem commissioned random audits on behalf of DESNZ, carried out by chartered surveyors against PAS 2035. The audit results, published on 13 October 2025, found:
- 92% of the external wall insulation audited had at least one major technical non-compliance, which will undermine the performance of the system and may over time result in a risk to the health of the occupants;
- a further 6% had a Category 1 non-compliance, a risk to the health and safety of occupants;
- 378 properties with external wall insulation were audited, from a population of 24,600 installations.
Because of those rates, the report says, every recipient of external wall insulation under ECO4 and GBIS is now being offered an audit.
Outside Wales
The warning signs are not specific to Wales, and nor is the UK Government's ECO4 and GBIS guidance above. Welsh social landlords also have their own timescales for investigating hazards such as damp and mould: see damp and hazard rules in Wales.
Where DampApp Pro fits
DampApp Pro keeps the inspection in one dated report, from the outside of the wall to the readings inside:
- Outside, elevation by elevation: record cracked render, staining or a bridged damp-proof course with photos of each. Area checklists cover the walls, each elevation, windows and doors and the damp-proof course, with a severity for every defect and a Schedule of Defects in the report.
- Readings up the wall (Pro): a grid of meter readings by height and position for each wall, shaded dry, at risk or wet against your own meter's scale. The app shades the readings but never names a cause.
- Dated photos: take photos on site or add them from the gallery, including thermal images from a separate camera. The report can show each photo's capture time from its EXIF data.
- Weather (Pro): the temperature, humidity, wind and conditions at the address on the day, with a rain radar for the last two hours.
- Follow-up visits: go back after heavy rain with last visit's readings under each box. Pro adds before-and-after photos.
- The wall build-up: condensation and U-value analysis models the insulated wall layer by layer, with a Glaser assessment in the report.
The PDF is built on your device before you leave. See the damp and mould survey app for everything else it records.
Are you the housing association, not the surveyor?
DampApp Pro is for the surveyor doing the inspection. If you're the housing association or council running Awaab's Law across a whole stock, with statutory clocks, work orders and links to NEC, Civica, MRI or Aareon, our sister platform HousingSurvey Pro is built for that.
See HousingSurvey Pro for housing associations & councils →Frequently asked questions
Can external wall insulation cause damp?▾
It can when something goes wrong. The Welsh Government's guidance says problems with external wall insulation may be caused by poor installation, an unsuitable design, defects in materials or a lack of ongoing maintenance, and can lead to water entering the building, damage to the external finish, and damp and mould. It also says insulation that is designed and installed correctly can make a home warmer and more energy efficient, and that not every problem is caused by faulty installation.
What are the signs of a problem with external wall insulation?▾
The guidance lists cracks in the render, bulging or uneven wall surfaces, staining or discolouration, water entering the property, damp patches on internal walls, mould growth inside the home, and loose or damaged panels and fittings.
Who do I contact first in Wales?▾
For insulation installed under the Arbed scheme, the guidance says to contact the contractor who did the work and give them the opportunity to inspect. If they cannot resolve it, contact the organisation that issued the guarantee, such as SWIGA or the IAA. If you cannot identify the installer or the guarantee provider, your local authority may be able to help. If the insurer behind a guarantee has stopped trading, you may be able to seek compensation through the Financial Services Compensation Scheme.
What if my insulation was installed under ECO4 or GBIS?▾
The UK Government's guidance says every property that had external wall insulation installed under ECO4 or GBIS will be offered a home check. If the work is found to be faulty, the installer will be asked to fix it, and you should not be asked to pay. If you have had a home check since January 2025, no further action is required. Ofgem answers questions, and asks for your Unique Measure Reference if you have one.
Does the Welsh Government guidance decide who is liable?▾
No. It says it is general information for householders, that it does not determine liability for defects or guarantee that remedial works will be carried out, and that any warranty, guarantee or compensation depends on the circumstances of each installation.
Does DampApp Pro decide what caused the damp?▾
No. DampApp Pro records the readings, photos and observations and produces the report. The surveyor is responsible for the findings, and the app does not decide liability or the outcome of a claim.