The green potential of existing homes has never been more important. While the government’s Green Homes Grant scheme has ended, the imperative to retrofit existing properties remains critical—around 80% of the homes that will exist in 2050 are already built today. This means retrofitting existing properties is not optional; it’s essential to meeting the UK’s Net Zero 2050 target. Recording Heat Loss at the House with or without facade

The challenge is clear: upgrading existing homes to meet carbon-zero standards requires coordinated improvements across multiple building systems. The good news? Modern retrofits deliver exceptional results, often surpassing the environmental benefits of new construction while significantly reducing operational carbon emissions.

Understanding zero-carbon vs. carbon-neutral homes

Zero-carbon homes produce as much energy as they consume through a combination of energy efficiency measures and renewable energy generation. The building’s operational energy demand is met entirely by on-site or imported renewable sources.

Carbon-neutral homes offset the energy they consume through renewable energy credits or production elsewhere. While valuable, this approach relies on continuous offsetting or energy generation to maintain carbon-neutral status.

Low-carbon homes reduce energy consumption significantly through efficiency improvements such as insulation, high-performance windows, airtightness, and upgraded heating systems, even without on-site renewable generation. This “fabric first” approach forms the foundation of any successful retrofit strategy.

It’s also important to consider embodied carbon. The carbon emissions involved in constructing a new-build home—from material sourcing and processing to construction—often outweigh any achieved zero-carbon operational status for many years. By comparison, zero- or low-carbon retrofits generate far lower embodied carbon while delivering similar operational performance, making them the fastest and most sustainable route to meeting climate targets.

The four pillars of zero-carbon retrofits

Retrofitting for zero-carbon performance requires improvements across four interconnected areas. Each represents a worthwhile project in its own right, but when combined in a coordinated way, the building’s performance is truly optimised.

Building fabric improvements – Insulation, high-performance windows and doors, and airtightness measures reduce heat loss through the roof, walls, floors and openings.
Heating system decarbonisation – Replacing fossil fuel boilers with electric heat pumps, air source systems, or low-carbon district heating eliminates operational carbon from space heating.
Renewable energy generation – Solar PV, solar thermal and other on-site renewables offset remaining electrical consumption.
Ventilation & air quality management – Mechanical ventilation with heat recovery (MVHR) maintains healthy indoor air quality in airtight buildings while minimising heat loss.

Key principle: a fabric-first approach means prioritising the building envelope (insulation, windows, doors and airtightness) before investing in renewables. By reducing heating demand first, heat pumps can be smaller, more affordable and more efficient. This sequencing improves return on investment and ensures long-term performance.

Where heat loss happens: understanding your building’s weak points

According to the Energy Saving Trust, heat loss in a typical UK home is distributed approximately as follows:

Roof/loft: 25% of heat loss
Walls: 35% of heat loss
Windows & doors: 10% of heat loss
Floors: 15% of heat loss
Ventilation & air leakage: 15% of heat loss

While windows and doors account for a smaller proportion of total heat loss than walls or roofs, they are often among the easiest building elements to upgrade. Replacing outdated glazing with modern, high-performance sealed units can deliver immediate comfort improvements, reduce draughts and condensation, and cut operational carbon.

Insulation and airtightness

Insulating your home is one of the most important steps towards achieving a zero- or low-carbon home. Effective insulation reduces the amount of heat required to keep a property comfortable, which in turn lowers running costs and carbon emissions.

Loft insulation is relatively inexpensive and easy to install. Experts recommend loft insulation thickness of at least 250–300mm (around 10–12 inches) to optimise heat retention and align with modern efficiency expectations.

Cavity wall insulation is suitable for most properties built between 1930 and 2000. These walls can typically be insulated by injecting insulation material into the cavity, significantly improving thermal performance via a straightforward process. For older, solid-wall properties (usually pre-1930), internal or external wall insulation—such as insulated cladding systems—will be required. Although more complex and costly, these solutions can deliver equivalent performance benefits when correctly designed and installed.

Airtightness is equally important. Uncontrolled air leakage can account for around 10–15% of total heat loss. Professional airtightness testing (blower door testing) can identify and quantify unwanted air leakage before and after retrofit work, ensuring that design targets are achieved and that ventilation strategies (such as MVHR) perform as intended.

Thermally efficient windows and doors

Modern double and triple-glazed sealed units can have a dramatic impact on a property’s thermal performance. When you replace old, poorly performing glazing with modern high-performance alternatives, you can:

Reduce heat loss through advanced glass and frame technology
Improve acoustic insulation as a valuable secondary benefit
Lower energy usage and operational carbon emissions
Reduce condensation and damp by maintaining warmer internal glass surface temperatures

What makes modern sealed units efficient?

Today’s high-performance windows typically combine three key technologies:

Low-emissivity (Low-E) glass – A microscopic metallic oxide coating reflects radiant heat back into the building in winter and helps limit solar gain in summer. This can improve insulation performance by 30–50% compared to standard glass.
Inert gas fill – An inert gas such as Argon between the glass panes is denser than air, slowing heat transfer by conduction and convection and improving the unit’s overall thermal resistance.
Multi-chambered frames – Modern uPVC, timber and aluminium frames are designed with multiple internal chambers. These pockets of air provide additional insulation, while thermal breaks in aluminium systems prevent heat bridging through the frame.

The critical component: spacer bars

Often overlooked, the spacer bar—the component that separates the panes of glass around the edge of the sealed unit—is crucial to overall window thermal performance.

Traditional aluminium spacer bars conduct heat extremely well, creating a thermal bridge at the edge of the glass. This causes the edge of the window to become much colder than the centre, increasing the risk of condensation, creating cold spots and raising overall heat loss.

Edgetech warm edge spacers are manufactured from low-conductivity materials specifically engineered to minimise this thermal bridging effect. The benefits include:

Up to 94% reduction in edge heat loss compared with aluminium spacer bars
Typical 0.4–0.6 point improvement in overall window U-value
Up to 70% reduction in condensation risk through warmer edge temperatures
Reduced likelihood of mould growth around the window perimeter
Consistent thermal performance across the entire sealed unit lifespan

To maximise the performance of replacement glazing, Edgetech has developed a comprehensive range of warm edge spacer products that are built into window designs during manufacture. Fitted between the glass panes of a sealed unit, these low-conductivity spacer bars significantly reduce heat loss, help prevent condensation, and lower exterior noise penetration.

Building Regulations Part L: meeting compliance standards

For homeowners planning retrofit projects, Building Regulations Part L sets mandatory energy efficiency standards for replacement windows and doors in England and Wales.

Part L 2023 update: replacement windows in existing homes must now achieve a U-value of 1.4 W/m²K or better (or a minimum Window Energy Rating of B). New-build homes are subject to even tighter requirements, with typical window U-values needing to achieve 1.2 W/m²K or better. Meeting or exceeding these standards is essential not only for compliance but also for futureproofing property value.

How high-performance sealed units help: modern double-glazed units that incorporate warm edge spacers can typically achieve U-values around 1.2 W/m²K or better. Triple-glazed units using warm edge technology can reach as low as 0.8 W/m²K or below, providing a generous compliance margin alongside superior comfort and energy performance.

Financial and environmental returns

When comprehensive improvements are made across all four retrofit pillars—fabric, heating systems, renewables and ventilation—homeowners can benefit from substantial energy, carbon and cost savings. Although there may be a significant upfront investment, the medium- and long-term benefits are compelling.

Energy bill savings: whole-house retrofits typically reduce heating energy consumption by 60–80%, which can equate to £1,200–£2,000 per year in reduced energy costs, depending on property size and tariffs.
Property value uplift: energy-efficient homes often command a 3–5% premium on property value, reflecting increased desirability and lower running costs.
Payback timeline: many retrofit measures achieve a positive return on investment within 5–7 years, with many components (such as high-quality windows and warm edge spacers) delivering performance benefits for 25 years or more.
Futureproofing: higher efficiency standards help protect households against rising energy prices and position properties to meet future tightening of Building Regulations and environmental legislation.

Taking the next step

Retrofitting existing properties to zero-carbon or low-carbon standards is achievable, economically justified and environmentally essential. Success depends on a holistic, fabric-first approach: improving insulation, upgrading to high-performance windows and doors, and enhancing airtightness before investing in low-carbon heating systems and renewable technologies.

High-performance sealed units incorporating Edgetech warm edge spacers provide the thermal performance required to meet modern Building Regulations, eliminate many condensation issues and ensure consistent long-term energy savings. As a result, warm edge technology has become a specified standard in deep-retrofit projects and high-performance window systems across the UK.

If you’re interested in finding out more about how Edgetech products can help you get one step closer to creating a zero- or low-carbon home, get in touch today. For more information about any of Edgetech’s energy saving products, contact us online.