Shallow vs. Deep Retrofits: Breaking Down the Two Paths to Retrofitting

The UK has one of the oldest and least energy-efficient housing stocks in Europe, with 78% of homes built before 1980. This drives higher energy bills and widens the affordability gap, unlike the progress seen across much of Europe.

With 15% of homes in England built before 1900, the age and diversity of the housing stock demand a more strategic and tailored approach to energy upgrades. Unlike renovation, which typically focuses on aesthetics or structural repairs, retrofitting aims to improve energy performance, comfort, and sustainability.

Retrofit measures are crucial for the UK to meet its climate goals, as homes account for 15 – 20% of the country’s national carbon emissions. It offers a defined pathway to reduce energy inefficiency and improve comfort in existing buildings, playing a vital role in both national and global decarbonisation strategies.

Retrofitting as a Modern Construction Imperative

Today, new builds are designed with sustainability in mind from the outset. However, older homes and commercial spaces often fall short due to current energy standards. Poor-quality housing costs the NHS an estimated £1.4 billion each year. This performance gap presents an opportunity – and a necessity – for intervention. Retrofitting enhances warmth and air quality, helping to reduce this burden while supporting better public health.

Retrofit measures can range from light-touch (shallow) upgrades to full-scale (deep) interventions, depending on the building’s condition, the owner’s goals, and available budget.

Shallow retrofits focus on low-cost, low-disruption improvements. Deep retrofits take a whole-building approach that dramatically transforms a building’s energy performance.

The key question is: which is the right fit — shallow or deep? This guide breaks down both approaches to help homeowners make an informed decision based on their property, priorities, and investment horizon.

Shallow Retrofits: Low-Impact, High-Payback Improvements

Definition and Key Characteristics

A shallow retrofit focuses on making targeted, low-disruption improvements to a home’s energy performance. These upgrades are typically straightforward, cost-effective, and can be implemented with minimal impact on daily life.

Ideal for homeowners seeking immediate benefits, shallow retrofits don’t require structural changes and can be a practical starting point toward greater energy efficiency. Many of these measures are accessible, DIY-friendly and quick to complete.

While they may not deliver full Net Zero outcomes, shallow retrofits play a vital role as the first stage in a whole-house retrofit approach, offering meaningful improvements in comfort and energy use.

Common Shallow Retrofit Measures

• Pipe Lagging and Radiator Panels: Reduce heat loss by insulating exposed hot water pipes and placing reflective panels behind radiators to direct warmth back into the room. This simple measure can help reduce heating bills by 5–15%. Particularly effective for older homes with visible pipework.
• Loft Insulation Top-Ups: Adds extra insulation layers of 270 mm depth in attic spaces where existing insulation is thin, compressed, or incomplete to reduce heat loss. Ideal for homes built before 2000 with under 100 mm of current insulation, or where insulation has settled or deteriorated. A straightforward upgrade for DIY enthusiasts or landlords looking to improve EPC ratings.
• Draft Proofing: Seal gaps around doors, windows, floorboards, chimneys, and vents to reduce unwanted airflow. A cost-effective way to cut heating bills by up to 15%, particularly suited to pre-1980s homes. Preserves original architectural features while improving comfort.
• Lighting Upgrades: Replaces inefficient incandescent and CFL bulbs with long-lasting LED alternatives. Reduces lighting costs by up to 85%. It offers flexible lighting design options — from warm to cool tones and dimmable settings.
• Smart Thermostats: Installs programmable, learning-enabled thermostats to optimise heating and cooling schedules. Helps reduce HVAC energy use by 10–20%, with minimal disruption.
• Basic HVAC Maintenance: Addresses the root cause of 60% of HVAC failures — lack of routine servicing. Includes boiler checks, filter replacements, and system tuning to ensure optimal performance. Improves indoor air quality by reducing dust and allergens by up to 40%. Suitable for all homes with heating and cooling systems.

Shallow Retrofit Tip: Combine air sealing with smart heating controls for an easy but effective boost in efficiency.

Pros of Shallow Retrofits

• Lower Cost: Ideal for budget-conscious homeowners or landlords, with projects starting from £500.
• Quick Implementation: Most measures can be completed within days or weeks, unlike deep retrofits, which may take months.
• Minimal Disruption to Occupants: Upgrades can be carried out without requiring residents to vacate the property.
• Immediate Energy Savings: Simple interventions such as LED lighting can deliver 10–30% reductions in energy bills.
• Easier to Finance and Incentivise: Government and utility-backed rebates are often available for shallow retrofit measures such as insulation and smart thermostats, eliminating the need for complex loans or large upfront investments.
• Flexibility and Scalability: Work can be delivered in phases — starting, for example, with lighting, then progressing to insulation — without committing to a full-scale renovation plan.

Cons and Limitations

• Limited Energy Performance Gains: These upgrades address the “low-hanging fruit” fixes, making it difficult to achieve the deep energy savings, often 50% or more, that older buildings require. Core inefficiencies, such as outdated HVAC systems or poor insulation, remain unresolved.
• Underlying Structural Issues: Without addressing structural challenges such as air leaks, inefficient wiring, or ventilation design, shallow interventions may increase long-term operational costs and delay more comprehensive solutions.
• Potential for “Patchwork” Upgrades: When retrofits are implemented without a whole-building strategy, upgrades can work against each other. For example, improving insulation without enhancing ventilation can result in condensation and indoor air quality issues.
• Lower Long-Term Savings: Although initial costs may be lower, shallow retrofits offer small energy and financial savings of a 10+ year lifecycle compared to holistic retrofit strategies.
• Lack of Future-Readiness: Basic upgrades may require replacement or long-term investment, limiting their ability to support future performance standards or low-carbon technologies.

Estimated Costs

Costs for shallow retrofits range from £500 to £5,000, depending on the home’s size, age, and the specific measures implemented.

Best Fit Scenarios for Shallow Retrofit

Scenario	Suitability
Homes built after 1990	High
Short-term property ownership	High
Historic properties needing consent	Low

Shallow retrofits are well-suited for homeowners, landlords, and businesses seeking to reduce utility costs, meet essential compliance, or lay the foundation for more comprehensive upgrades down the line.

From draught-proofing to smart thermostats, these measures provide a practical and effective entry point into a property’s sustainability journey, showing that significant savings don’t always require major construction.

Deep Retrofits: Whole-Building Transformation

Definition and Key Characteristics

Deep retrofits involve a comprehensive, fabric-first overhaul of a building’s structure and systems. This holistic, whole-building approach transforms energy performance by upgrading multiple components. It improves HVAC systems and appliances in a coordinated and integrated way.

Deep retrofits save 50–80% energy and are often implemented in phases over time. They combine both passive and active measures, including the integration of renewable energy technologies.

By sealing the thermal envelope across walls, roofs, floors, and junctions, this approach goes well beyond quick fixes to deliver Passive House-level performance, reducing heat loss by up to 90%.

Common Deep Retrofit Measures

• Comprehensive Insulation: External and internal wall insulation, roof and underfloor insulation, and airtight membranes all play a critical role in deep retrofit strategies. External wall insulation (EWI) is particularly effective for solid wall constructions, delivering U-values as low as 0.15 W/m²K. Internal wall insulation (IWI), using breathable materials such as wood fibre, is often preferred for heritage or character façades. In more complex buildings, hybrid systems that combine both EWI and IWI can offer the most effective and balanced solution.

Retrofit Tip: Always incorporate airtightness layers during installation to maximise energy efficiency and performance.

• High-Performance Windows and Doors: Triple-glazed, airtight units play a key role in reducing heat loss. Replacing older windows eliminates thermal weak points, which can account for 25–30% of heat loss in uninsulated homes. High-performance glazing also enhances heat pump efficiency by supporting low flow temperatures (35–45°C). This helps prevent condensation by keeping internal surface temperatures above 16°C, minimising the risk of mould and improving indoor comfort.
• Heat Pumps: Replacing gas boilers with air-source or ground-source heat pumps delivers a significant boost in energy efficiency. Operating at 300–400% efficiency (COP 3–4), heat pumps generate 3–4 units of heat for every unit of electricity consumed — far outperforming the 85–95% efficiency of traditional gas boilers. Air-source heat pumps (ASHPs) extract heat from the outdoor air, while ground-source heat pumps (GSHPs) draw heat from the ground through buried pipework. Both technologies provide space heating, cooling, and domestic hot water, positioning them as a key solution in the drive to decarbonise buildings.
• Mechanical Ventilation with Heat Recovery (MVHR): Mechanical Ventilation with Heat Recovery (MVHR) systems maintain healthy indoor air quality while retaining valuable heat. By recovering up to 90% of the heat from extracted air, they significantly reduce overall heating demand. MVHR enhances Indoor Air Quality (IAQ) by continuously delivering fresh, filtered air, supporting compliance with both Part F (ventilation) and Part L (energy efficiency) of building regulations. These systems are particularly well-suited to airtight, well-insulated retrofits, as well as damp homes or properties in polluted or high-noise areas, providing efficient ventilation without compromising warmth.
• Solar PV and Battery Storage: On-site renewable energy generation and storage provide an effective way to reduce dependence on the grid. Combining solar PV panels with battery storage allows for clean electricity generation while storing surplus energy for later use. This approach lowers energy bills, enhances energy independence, and future-proofs homes for electric vehicles and heat pumps. It is especially well-suited to Passive House retrofits, properties with high daytime energy demand, off-grid or low-reliability locations, and projects targeting Net Zero energy performance.
• Smart Home Controls: Integrated systems that monitor and optimise energy use can reduce consumption by 10–30%, delivering annual savings of around £100 by shifting demand to off-peak periods. They enhance heat pump and solar return on investment (ROI) by 15–20% while maintaining indoor comfort within ±0.5°C. These smart controls increase solar self-consumption by 30–50%, cut gas use by 12–18% through zoned heating, and support carbon reductions exceeding 90% in Net Zero retrofit projects.

Deep Retrofit Tip: Prioritise insulation and airtightness first, then size renewable energy systems accordingly for maximum efficiency.

Pros of Deep Retrofits

• Higher Property Value: Buildings with deep retrofits often command higher resale prices and attract eco-conscious buyers or tenants. They also future-proof properties against tightening energy regulations.
• Significant Energy Savings: Deep retrofits can reduce energy consumption by up to 80%, targeting all key inefficiencies — including the building envelope, HVAC, lighting, and renewable energy integration. Some projects even achieve Passive House certification.
• Enhanced Comfort and Indoor Air Quality: These upgrades deliver stable indoor temperatures, reduced noise, improved ventilation, and moisture control. Advanced HVAC systems offer enhanced air filtration and improved humidity management.
• Long-Term Cost Savings: While upfront costs may be higher, lower utility bills over time help offset the investment. Maintenance costs also tend to be lower as newer systems offer greater reliability.
• Grants and Green Financing: Many government programmes provide tax credits, grants, or low-interest loans for deep retrofit projects. Such initiatives may also qualify for green building certifications such as LEED, Passive House, or ENERGY STAR.
• Reduced Carbon Footprint: Deep retrofits play a vital role in reducing greenhouse gas emissions by integrating renewable energy technologies such as solar panels and heat pumps, lowering reliance on fossil fuels and supporting broader climate goals.

Cons and Practical Constraints

• High Upfront Costs: Deep retrofits require significant investment, often 5 to 10 times more than shallow retrofits. Financing options can be complex, including PACE loans and energy mortgages.
• Longer Payback Period: Savings typically take 5 to 20+ years to recoup, which may be less attractive for short-term property owners.
• Major Disruption to Occupants: Construction can cause significant disruption, sometimes requiring temporary relocation. Renovations may last from several months to over a year.
• Complexity and Risk of Over-Engineering: Deep retrofits demand detailed energy audits, modelling, and expert contractors. Poor planning can lead to underperformance or cost overruns.
• Feasibility Issues for Historic Buildings: Some upgrades, such as triple-glazed windows, may conflict with preservation rules and heritage requirements.
• Potential for “Lock-In” with Rapidly Evolving Technology: Cutting-edge systems installed today could become outdated within 10 to 15 years.

Estimated Costs

Deep retrofit projects usually range in cost from £20,000 to over £100,000, depending on the property’s size, complexity, and the materials selected.

Best Fit Scenarios for Deep Retrofit

Indicator	Suitability
Pre-1980s poorly insulated homes	Very High
Long-term ownership (>10 years)	High
Pre-planned renovations	High

The goal of a deep retrofit is to meet Net Zero Carbon standards, ensuring the home minimises energy consumption and generates most of its energy from renewable sources.

These retrofits are usually completed in phases, tailored to the specific type of property. Planning permission and heritage considerations often play a key role, particularly for older buildings.

Head-to-Head: Shallow vs. Deep Retrofits

When planning energy upgrades, it’s essential to understand the key differences between shallow and deep retrofits. Here’s a side-by-side comparison.

Feature	Shallow Retrofit	Deep Retrofit
Scope	Targeted upgrades	Whole-house transformation
Cost Range	£500–£5,000	£20,000–£100,000+
Energy Savings	10–30%	60–90%
Disruption Level	Minimal	Significant
Payback period	2–6 years	10–20 years
Ideal For	Budget-conscious homeowners	Long-term planners and green home enthusiasts
Duration	Days to a few weeks	Months or phased over years (due to planning, design, construction)
Planning Complexity	Low	High (may require PAS 2035 design)
Carbon Reduction	Low to Moderate	High (Net Zero alignment possible)
Overall Impact	Addresses specific energy leaks	Comprehensive, make a home energy efficient

Core Measures Comparison

Each retrofit approach includes different upgrades. Here’s a breakdown of the core measures in shallow versus deep retrofits.

Measure Category	Shallow Retrofit Examples	Deep Retrofit Examples
Insulation	Loft top-up (to 300mm), sealing cracks	Internal/external wall insulation, floor and roof insulation
Ventilation	Basic extractor fans, trickle vents	MVHR (Mechanical Ventilation with Heat Recovery)
Heating Systems	Improved controls, pipe lagging	Heat pumps (ASHP or GSHP), electric boiler upgrade
Windows/Doors	Draught proofing, secondary glazing	Triple glazing, Passive House-certified doors
Air Tightness	Sealing gaps, basic air-tightness measures	Airtight membranes
Renewables	Usually not included	Solar PV systems (2-5kWp arrays)

Retrofit by House Type

According to house archetypes and their corresponding retrofit pathways, here’s how shallow versus deep retrofits apply:

House Type	Age Range	Shallow Retrofit Feasibility	Deep Retrofit Considerations
Victorian terrace/cottage, Large historical townhouse	Pre-1914	Ideal for low-cost: loft insulation, secondary glazing, and Draught proofing	Internal wall insulation is needed due to heritage facades
Post-war semi-detached	1945–1960	Moderate effort; poor insulation baseline	External wall insulation, ASHP, MVHR, and Solar PV are highly beneficial
Semis and modern	1960s–1980s	Loft & cavity insulation	Full airtightness plan, upgraded heating & glazing
Modern mass-built homes	1980–2015	Already partially insulated	Deep retrofit may have diminishing returns

Older homes often require the use of breathable materials and need heritage consent when applying insulation or external finishes, to ensure compatibility with the building’s fabric and to preserve its charm.

Which Retrofit is Right? Matching Strategy to Goals

Deciding between a shallow or deep retrofit depends on a range of personal and structural factors:

• Budget: If upfront capital is limited, a shallow retrofit offers immediate, cost-effective improvements. For those with a larger budget or access to financing, deep retrofits provide greater long-term value.
• Goals: Set targeted goals, either seeking short-term savings or aiming for long-term sustainability and energy independence.
• Home Condition: Older homes with poor insulation and outdated systems tend to benefit more from a deep retrofit approach.
• Duration of Stay: Deep retrofits are more suitable if homeowners are planning to remain in their home for 10 years or more, allowing time to realise the full return on investment.
• Tolerance for Disruption: Consider accommodation plans, such as temporarily vacating the property during the retrofit process.
• Property Type: Assess whether homes and buildings are structurally suitable for more invasive upgrades.

Example Scenarios:

• Scenario A: A young family in a 1995 semi-detached home — a shallow retrofit is likely the most practical and cost-effective solution.
• Scenario B: A couple living in a 1930s detached property with plans to stay long-term — a deep retrofit offers the greatest long-term benefits.

Retrofit Tip: Even when undertaking individual upgrades, take a whole-house perspective. This ensures future compatibility and avoids unnecessary rework down the line.

Incentives, Grants & Financing for Retrofits

Homeowners can access a range of funding options to help reduce the cost of retrofit projects, from direct grants to long-term financing tailored to energy efficiency improvements.

Key UK Schemes:

• Boiler Upgrade Scheme (BUS): Offers up to £7,500 towards heat pump installation.
• ECO4 (Energy Company Obligation): Supports low-income households with insulation and heating upgrades.
• Green Mortgages: Provide preferential rates for energy-efficient homes.
• Local Authority Grants: Region-specific programmes with varying eligibility criteria.
• Great British Insulation Scheme (GBIS): Focuses on fabric-first improvements for shallow retrofits.

For deep retrofit funding and certified installers, visit the Gov.uk energy grants portal, explore local council programmes, and search for accredited professionals through the TrustMark directory.

Funding solutions also include green mortgage products from major lenders such as Barclays and Nationwide, as well as retrofit loans and targeted grants provided by energy suppliers and local authorities.

Finding the Qualified Retrofit Professionals

Selecting the right professionals for shallow or deep retrofits demands rigorous scrutiny of credentials and alignment with industry benchmarks. Due to the technical complexity and regulatory requirements of energy efficiency projects, prioritising practitioners with PAS 2035 accreditation is essential. This certification is mandatory for government-funded work and ensures compliance with UK retrofit standards.

Equally important is TrustMark certification, a government-backed scheme that confirms thorough vetting and reliability. For specialists installing renewable technologies such as solar PV and heat pumps, MCS accreditation is vital to ensure compliance with performance and safety standards.

Quantum Training equips future retrofit professionals with the practical skills and accredited knowledge needed to support the UK’s shift to low-carbon housing.

Our Green Skills Training Solutions focus on hands-on expertise, covering Air Source Heat Pumps, Ground Source Heat Pumps, Solar Thermal, and Electrical Ecosystem. Designed for installers and technicians, all courses are delivered in custom-built Training Bays and aligned with real-world simulations.

Within fully custom-built Retrofit Training Bays, professionals can learn energy-efficient insulation, airtightness, ventilation, and solar panel mounting.

Beyond Efficiency: Long-term Benefits of Retrofitting

While energy savings are a key driver, both shallow and deep retrofits offer broader long-term benefits. These include:

• Carbon Emissions: Reduced carbon footprint contributes to national Net Zero goals.
• Durability and Maintenance: Modern materials and systems reduce wear and tear.
• Health improvements: Reduced damp, mould, and allergens.
• Thermal comfort and air quality: Stable indoor temperatures and cleaner air.
• Soundproofing: Insulation reduces outside noise.
• Property value: An Improved EPC rating increases market appeal.
• Compliance: Future-ready for stricter regulations.

Unique Scenarios and Special Cases

Retrofitting requires tailored strategies that optimise energy efficiency while maintaining structural integrity and ensuring long-term performance. Two key scenarios illustrate this need:

1.  Older or Historic Homes

Retrofitting heritage properties demands careful material choices. Breathable insulation, such as wood fibre or hemp lime, improves thermal performance without damaging the building fabric.

External wall insulation can enhance efficiency and preserve interior features; however, planning approval is often required. Collaboration with conservation experts is essential to ensure both compliance and effectiveness.

2.  Renewables Integration

Deep retrofits involve integrating renewable energy technologies: solar PV, heat pumps, EV chargers, and battery storage. When combined with improvements in insulation and airtightness, these systems create efficient, low-carbon buildings that lower energy consumption and decrease utility costs.

Success depends on a holistic approach, ensuring that thermal upgrades and renewables work together to deliver a future-proof, high-value property.

Case Study: Quantum’s Sustainable Regency Project – A Deep Retrofit Model

The Sustainable Regency Project by Quantum showcases a high-performance deep retrofit of a Grade II listed Regency manor, successfully balancing modern energy efficiency with heritage preservation.

Approach: Quantum delivered a full retrofit, integrating advanced climate systems, smart zoning, and renewables within the building’s historic fabric.

Key Technologies:

• Daikin Air Source Heat Pumps: Replaced gas systems, delivering low-carbon heating for both underfloor and air-based systems.
• Invisible Air Comfort System: Compact mini-ducts enabled unobtrusive air distribution. Humidity was reduced by 30%, lowered energy demand and enhanced overall comfort. Room-by-room temperature control optimised efficiency across the large, compartmentalised layout. 

All systems were concealed in ceiling voids and partition walls to preserve the original structures.

Outcome: Obtained substantial energy savings. Heritage integrity was maintained with discreet 25mm slot diffusers instead of radiators or bulky air units.

The project shows how a deep retrofit can be successfully applied to listed buildings, delivering lasting efficiency without compromising historic charm.

Risks, Challenges, and How to Avoid Them

Retrofitting delivers clear benefits — from lower energy bills to greater comfort — but it also comes with challenges. Knowing these pitfalls and how to address them helps homeowners avoid costly delays and frustrations.

1.  Poor Workmanship

• Problem: Poorly installed insulation, incorrectly sized heating systems, or inadequate airtightness can undermine energy savings.
• Solution: Choose accredited professionals, request workmanship guarantees, and check client references to ensure quality.

2.  Moisture and Mould

• Problem: Incorrect retrofits can trap moisture, leading to dampness, mould growth, and potential structural damage, especially in older properties.
• Solution: Incorporate a robust ventilation strategy, such as Mechanical Ventilation with Heat Recovery (MVHR) or passive ventilation, to ensure proper moisture management.

3.  Budget Overruns

• Problem: Hidden issues, such as damp walls or outdated wiring, can cause unexpected cost increases.
• Solution: Include a contingency of 10–20% in your budget to cover unforeseen expenses.

4.  Incomplete Retrofit Sequencing

• Problem: Installing insulation before addressing draughts or fitting a heat pump without proper insulation can reduce efficiency and waste investment.
• Solution: Follow a whole-building approach, ideally overseen by a retrofit coordinator, to ensure upgrades happen in the right order.

Why Deep Retrofit is the Future

Deep retrofit sets the benchmark for energy efficiency and comfort, but it’s not always the immediate choice for every homeowner. A phased approach is recommended — beginning with cost-effective measures while planning and budgeting for more extensive upgrades later.

It’s important to recognise that the final 10–20% of energy savings needed to achieve full Net Zero can be costly and challenging. This is especially true in urban settings with shading, roof orientation issues, or listed building restrictions.

Retrofit Tip: Even starting with shallow upgrades, plan with deep retrofit goals in mind to avoid costly rework and maximise long-term value.

Conclusion: Start Smart, Plan Deep

Choosing between shallow and deep retrofits depends on budget, goals, building type, and long-term plans. Both offer value but address different needs and timelines.

Shallow retrofits deliver low-disruption improvements with quick energy savings, usually targeting symptoms rather than root causes. Deep retrofits involve whole-house upgrades that enhance comfort and facilitate the integration of renewable heating systems. Though requiring greater investment and planning, they future-proof homes and support Net Zero goals.

A phased approach is recommended: begin with shallow measures while preparing for deeper upgrades. The best strategy depends on the property’s age, structure, and conservation status.

FAQs

What’s the cheapest way to retrofit a home?

The most cost-effective way to start retrofitting is by focusing on low-cost, high-impact measures. Usually costing between £500 and £5,000 and completed within days, they are ideal for limited budgets, quick improvements, or rental properties. Many of these measures are DIY-friendly or supported by local grants.

Are deep retrofits worth the money?

Deep retrofits are a worthwhile investment, especially for long-term homeowners, those focused on reducing their carbon footprint, or those facing rising energy costs. They can reduce space heating demand by up to 90–95% in older homes and, when paired with renewable technologies, enable Net Zero Carbon performance.

How to do a deep retrofit in phases?

Absolutely — a phased deep retrofit is often the most practical and cost-effective approach. For example, start with:

• Phase 1: Loft insulation, cavity wall insulation, draught-proofing.
• Phase 2: Window replacements, floor insulation, airtightness detailing.
• Phase 3: Heat pump installation, MVHR, solar PV system.

This staged approach spreads costs, minimises disruption, and lets homeowners stay in their homes throughout the process.

How long does a deep retrofit take?

On average:

• A full, one-time deep retrofit can take 3 to 9 months of on-site work.
• Phased deep retrofits may stretch over 1 to 2 years or longer.

When to choose a shallow retrofit?

Consider a shallow retrofit if:

• Budget is under £10,000.
• Renting or living in a temporary home.
• Want quick, DIY-friendly improvements.
• Aiming to reduce energy bills in the short term without a long-term commitment.

When is a deep retrofit the better choice?

Choose a deep retrofit if:

• Plan to live in the property long-term.
• Eligible for government grants or incentives (like the Boiler Upgrade Scheme).
• The home is poorly insulated and relies on fossil fuel heating systems.
• If already undertaking major renovations or extensions.