Insulation Scandal? Why Good Design and Oversight Matter More Than Ever in Retrofit
The problem is not insulation. It is how it is done.
The external wall insulation scandal now unfolding is one of the most predictable failures of the UK’s retrofit effort. A government-backed scheme designed to lower bills and cut emissions has instead left thousands of homes colder, damper and in some cases uninhabitable.
According to the National Audit Office, audits of external wall insulation installed under ECO4 and the Great British Insulation Scheme found that 92% had at least one major technical non-compliance that could compromise insulation performance. A further 6% had non-compliance that posed a potential health and safety risk.
Moisture has penetrated wall fabric. Mould is spreading. What was meant to protect households has exposed them to greater risk, and eroded public trust in retrofit itself.
Moisture damage from penetrating damp, spotted during a pre-purchase inspection of a recently refurbished property. A result of poor-execution and care.
But insulation is not inherently dangerous. Poor strategy is.
At Studio CMA, insulation is never specified in isolation. It forms part of a whole-house retrofit strategy that considers insulation, ventilation, moisture movement and long-term performance together.
Whether we are improving a period terrace, integrating energy upgrades into an extension, or reworking interiors as part of a wider renovation, we begin with one question:
How will every decision affect comfort, durability and energy performance over time?
This is the difference between a product-led installation and a design-led retrofit.
One story that has stayed with us is that of Awaab Ishak, the two-year-old who died in 2020 from a respiratory condition caused by mould in his family’s Rochdale flat. His father had reported the issue multiple times, but was told to paint over it. A coroner confirmed the mould exposure caused his death.
That case, and the wider failures we are now seeing, underscore the need for careful, design-led retrofit.
That tragedy was not about insulation. But it was about mould, in a poorly maintained and poorly understood home. What we are seeing now is that even well-intended upgrades can lead to the same outcome if they are not designed and delivered with care.
The recent National Audit Office report, along with BBC’s deep-dive reporting, has brought to light what many of us in the industry have known for years: poorly executed retrofit can sometimes leave homes worse off than before.
Homeowners who received external wall insulation upgrades as far back as 2012 are now reporting serious failures, with some unable to use entire rooms because of moisture and mould. One homeowner’s mother, confined to a single downstairs room, told the BBC she can no longer use her bedroom because of the damage. And she is not alone.
How Did the Insulation Scandal Happen?
When speed replaces care, trust suffers
The intention was good: lower energy bills, warmer homes, reduced emissions. But in chasing volume, ticking boxes for grants and incentives, the fundamentals were pushed aside.
The complexity of building fabric, moisture behaviour and ventilation got sidelined.
Instead of taking the time to design for context, some installers followed templates. Instead of checking site conditions, they worked to funding deadlines. Instead of being supported by skilled professionals, some schemes were delivered by teams with limited experience in moisture-aware construction.
As architects working in London’s period housing stock, we see this disconnect all the time.
Older solid-wall homes rely on moisture being able to move safely through the building fabric. When they are rendered, wrapped or sealed without breathable layers and a clear ventilation strategy, the result can look like energy efficiency in the short term. In the long term, it can trap moisture and damage the fabric, finances and health of the people living there.
For homeowners weighing up different wall insulation options, our guide to internal vs external wall insulation for London period homes explains where each approach can help, and where each can create risk in London period homes.
"The tragedy is these installs didn’t just fail to insulate, they actively worsened thermal performance by driving moisture into the wall fabric."
Moisture Does Not Just Cause Mould. It Destroys Performance
Moisture does more than cause mould. It destroys thermal performance.
Here is why.
Dry walls insulate by trapping air, which is a poor conductor of heat. When walls become damp, water replaces that trapped air. Because water conducts heat far more readily than air, thermal performance drops significantly.
The result is higher U-values and faster heat loss. In plain English, the wall loses more heat, not less.
That is the exact opposite of what insulation was meant to achieve.
Building surveyor David Walter, speaking on BBC Radio 4 on 30 October, described the problem plainly:
"The bad design and the bad workmanship of the external wall insulation is causing the rain to actually penetrate into the walls."
Moisture, mould and misunderstanding
This is not just a technical failure. It is a cultural one.
A powerful article from Refurb & Retrofit explains how short-term performance targets and funding deadlines reward surface-level compliance, not real-world outcomes. Homeowners live with the consequences. And in too many cases, they do not have the tools or knowledge to challenge what is being done to their homes.
The poorest outcomes are often found in the most vulnerable communities - where landlords, housing associations or grant-funded schemes take decisions on behalf of residents. But the risk is not confined to social housing. We have seen private homeowners in Camden, Islington and Hackney confused by inconsistent advice, conflicting contractor opinions, or grant schemes that bypass design altogether.
Retrofit is personal. Every house behaves differently depending on its orientation, structure, materials and how people live in it. Solid-walled homes that were never designed to be sealed up have been rendered and wrapped without breathable layers or mechanical ventilation. If you want to understand how different wall types behave before insulating, see our guide to insulating a London home properly.
If you are seeing mould, staining, musty smells or recurring condensation, it is worth reading our guide to avoiding damp and mould in London retrofits before adding more insulation.
Too many schemes were pushed out as a one-size-fits-all offer, often without full survey, design or oversight.
Residents were sold a promise: free insulation, lower bills. In many cases, they got cold, damp homes, higher maintenance costs and long-term health impacts.
"It’s like wearing a soaked jacket. You feel colder - not warmer. And if that jacket isn’t breathable, you just sweat into it and feel worse. That is exactly what has happened to many of these homes."
Why ventilation matters as much as insulation
Insulation changes how a building retains heat - but it also changes how it breathes. Blocking drafts is one thing. Blocking draughts is one thing. Reducing air movement without a clear ventilation strategy is quite another.
One of the biggest myths in retrofit is that insulation alone will make a home warmer. The reality is more nuanced. If you trap moisture in the process, you increase humidity, raise the risk of condensation inside walls and create the conditions for mould.
Many of the government schemes failed to deal with this properly. We have reviewed retrofit assessments that recommend cavity wall insulation or external wall insulation with little or no explanation of air changes, vapour movement or background ventilation.
We have also seen builders block air bricks, foam gaps or seal traditional walls with waterproof coatings that are not suited to older solid-wall homes.
Without a planned route for fresh air, improvements can easily backfire. You risk sealing in problems rather than solving them.
We explain the wider principles in our guide to airtightness and ventilation for old London houses, including why reducing draughts is not the same as sealing a home without a plan.
Where a home is being made significantly more airtight, or where natural ventilation is not enough, mechanical ventilation may need to be considered. Our guide to mechanical ventilation and indoor air quality in London homes explains when natural ventilation may be sufficient and when a mechanical system such as MVHR may be appropriate.
Myth: Insulation makes a home warmer.
Reality: Insulation plus ventilation and moisture control makes a home warmer, healthier and more efficient.
Mould growth in a recently built home. Caused by poor ventilation and inadequate understanding of moisture risk.
The Real Fix? Proper Design, Proper Delivery
At Studio CMA, we work on Victorian and Edwardian homes every day. We understand their quirks. We have seen first-hand what works and what does not.
We do not believe in isolated upgrades. We believe in strategy.
That is the difference between a quick fix and a properly planned retrofit.
That means:
Starting with a diagnostic home visit
Using energy modelling and moisture analysis tools where needed
Testing assumptions with ventilation checks, thermal imaging, PHPP or SAP, depending on the project
Designing breathable build-ups with clear detailing at junctions, sills, parapets and party walls
Considering sequencing, future phases and practicalities
Working with contractors who understand what they are building
If you are planning an insulation retrofit in London, especially for a period property, it is worth taking time to get the design right up front. Not just for comfort and energy savings, but to avoid the kind of issues now emerging in homes across the UK.
Natural fibre insulations can support moisture buffering and healthier indoor air when used as part of the right wall build-up.
Natural materials are not a magic fix, but in the right build-up they can help older walls manage moisture more safely. We explain this further in our guide to natural materials for retrofitting London period homes.
What can homeowners do?
If you had external wall insulation installed through a government scheme, especially after 2012, you may be affected.
Start by:
Checking your installer and scheme documentation
Looking for signs of damp, staining, mould or unusual heat loss
Asking for a moisture survey or thermal imaging assessment
Keeping a record of photos, dates, correspondence and visible changes
If you are planning a retrofit, ask these questions before work begins.
Planning an Insulation Retrofit in London? Ask These Questions First:
Who is doing the design, and how will they assess moisture and ventilation?
What materials are being used, and are they breathable, compatible and repairable?
What is the ventilation strategy?
Who is supervising the installation?
How will performance be tested or monitored after installation?
What guarantees are offered?
What happens if something goes wrong?
You can also download our free guide, or speak to us for a Retrofit Strategy tailored to your home.
Where we go from here
This scandal should not put anyone off retrofitting their home. But it should shift the focus from products to process.
Done right, retrofit delivers quieter, warmer, healthier homes with much lower energy use. We have seen it. We have measured it. But it only works when you treat the building, and the people living in it, with care.
On-site installation of breathable insulating render made with cork and lime.
Breathable external wall insulation system completed on a 1930s solid-wall home.
The Warm Homes Plan has now been published. The plan itself acknowledges the problem: homeowners need stronger protection, clearer accountability and simpler routes to redress when energy-efficiency work goes wrong.
But policy alone will not fix poor retrofit. The real test will be whether delivery avoids the same mistake: treating retrofit as a numbers exercise rather than a design, workmanship and accountability challenge.
There is nothing wrong with ambition. But ambition without attention is how we got here.
Retrofit must be careful, detailed and human. Not a numbers game.
In the meantime, we will keep doing what we have always done: slow, careful, detail-led retrofit design that respects both the building and the people inside it.
Concerned About Your Retrofit Plans?
Insulation should make your home warmer and healthier. When it is poorly designed or poorly supervised, it can do the opposite.
The lesson from the insulation scandal is simple: retrofit only works when insulation, ventilation and fabric behaviour are considered together.
Our Retrofit Strategy Service sets out a clear, whole-house plan. We assess moisture risk, ventilation requirements, sequencing and long-term performance before work begins, so that upgrades improve comfort without creating unintended problems.
An Architect’s Home Visit and Appraisal is an on-site feasibility review. We assess your building, budget range and constraints, and identify where risks may sit before further upgrades are planned.
If you are unsure where to begin, the best starting point is a free 45-minute Project Consultation. We can help you decide whether a Home Visit and Appraisal or a Retrofit Strategy is the right next step for your home.
Greg and Daniela from Studio CMA bring both architectural rigour and lived experience as architects, property investors and owners to their retrofit work.
