VIEWPOINT
FABRIC FIRST IS THE ESSENTIAL FIRST STEP IN DECARBONISING
Joe Ragdale, technical director at Wetherby Wall Systems Ltd
THE UK’S AMBITION to hit Net Zero relies heavily on decarbonising its housing stock, a task made uniquely challenging by having one of the oldest housing stocks in Europe. While the Government’s focus on the rollout of low-carbon heating, particularly heat pumps, is crucial, this “technology first” approach is fundamentally flawed if it bypasses the necessary precursor: the ‘Fabric First’ principle. According to the Parliament’s Environmental Audit Committee, 80% of the homes we will occupy in 2050 have already been built. These existing dwellings, many of which are poorly insulated, risk turning a promising climate policy into a nationwide efficiency crisis. We must fix the building before fitting the technology. A house is a system, and ignoring its fundamental thermal performance leads directly to inefficient, oversized, and costly heat pump installations. In an uninsulated home, a significant portion of energy is simply lost to the environment. The Energy Saving Trust estimates that a house with uninsulated solid walls can lose up to a third of its heat through the walls alone.
While switching from a gas boiler to a heat pump in a highly inefficient home can still provide energy demand savings, the potential is vastly compromised without fabric upgrades. Research models show that while an uninsulated solid-walled house with a heat pump may save 60-70% on energy, adding a high level of solid wall insulation can see that saving soar to a staggering 90% reduction in annual heating energy demand In economic terms, this means every £1 spent on high-quality External or Internal Wall Insulation (EWI/IWI) offers a better long- term return than an oversized,
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inefficient heat pump struggling to maintain comfort in a draughty shell. This issue is amplified by the sheer volume of properties affected.
The UK has approximately 7.7 million homes with solid walls, representing around 90% of the total solid wall stock that currently lacks insulation. They are among the least energy-efficient in Europe.
The high-quality retrofit of the UK’s solid wall stock is non- negotiable for Net Zero. Without certified EWI or IWI, we are essentially asking homeowners to fit expensive, high-tech systems into thermal sieves. This leads to high electricity bills, and a widespread failure to achieve the low flow temperatures required for heat pumps to run efficiently.
Comfort Cost and Grid Resilience
A poorly insulated home compromises the efficiency and comfort of a heat pump. Heat pumps are designed to operate optimally at lower flow temperatures over longer periods. If a dwelling has high heat loss, the system must work harder and hotter, driving up running costs and increasing the risk of resident discomfort.
“The Energy Saving Trust estimates that a house with uninsulated solid walls can lose up to a third of its heat through the walls alone.”
Furthermore, a nation of uninsulated homes places an unnecessary peak-demand burden on the electricity grid. During a cold snap, millions of inefficient heat pumps fighting high heat loss will place a far greater and more instantaneous demand on the national grid than a network of systems operating in well-insulated, thermally stable homes. A ‘Fabric First’ approach is a national resilience strategy. To ensure high-quality, durable,
and effective domestic retrofit, a strategic sequence of work must be enforced. This is the core function of the PAS 2035 standard.
PAS 2035 mandates a ‘Whole House’ assessment, forcing designers to consider the building fabric (insulation, ventilation, airtightness) before specifying energy generation technology. The Retrofit Coordinator is the vital professional responsible for overseeing this process. They: • Perform an initial Risk Assessment. • Develop a Medium-Term Improvement Plan outlining the correct sequence of works, prioritising fabric measures. • Ensure that all retrofit measures, including EWI/IWI, are correctly integrated and comply with safety and quality standards (Source: TrustMark / Retrofit Academy).
This rigorous process is the only way to avoid ‘unintended consequences’ like damp, mould, or system failure, issues that have plagued previous, uncoordinated government retrofit schemes. Local Authorities and Housing Providers must adopt this standard to deliver certified, high- quality, net-zero retrofits that stand the test of time. BMJ
www.buildersmerchantsjournal.net December 2025
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