The Strategic Imperative of PAS 2035: Advancing Energy Efficiency in the UK’s Existing Housing Stock

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

Abstract

The United Kingdom’s ambitious commitment to achieving net-zero carbon emissions by 2050 places significant emphasis on the decarbonisation of its built environment. The residential sector, representing a substantial proportion of national energy consumption and carbon output, presents a particularly acute challenge, given the age and heterogeneity of the existing housing stock. In response to this critical imperative, PAS 2035, a publicly available specification introduced by the British Standards Institution (BSI), provides a robust and comprehensive framework for retrofitting domestic dwellings. This specification moves beyond piecemeal interventions, advocating for a holistic, risk-managed, and quality-assured methodology designed to deliver durable and effective energy efficiency improvements. This detailed report undertakes an in-depth examination of the contextual drivers, historical evolution, foundational principles, practical implementation strategies, and multifaceted implications of PAS 2035. It critically analyses its pivotal role in transforming the UK’s domestic energy efficiency landscape, addressing long-standing issues of poor workmanship and ensuring the long-term sustainability and performance of retrofit projects, thereby contributing meaningfully to the nation’s overarching climate objectives and energy security.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

1. Introduction

The climate crisis and the imperative of energy security have propelled the United Kingdom to commit legally to achieving net-zero carbon emissions by 2050. This monumental target necessitates transformative action across all sectors of the economy, with the built environment, particularly the residential housing stock, identified as a critical area for intervention. The scale of the challenge is formidable: the Environmental Audit Committee has consistently warned of governmental shortcomings in adequately addressing the decarbonisation of UK housing, underscoring the urgency of the situation (buildingenergyexperts.co.uk).

Statistics paint a stark picture: with over 17 million UK homes currently failing to meet an Energy Performance Certificate (EPC) rating of C or above, the task of achieving the 2050 net-zero target demands an unprecedented pace of retrofitting. Estimates suggest that approximately five homes must be retrofitted every minute, continuously, for the next three decades, to meet this objective (retrofitworks.co.uk). The financial and environmental costs of inaction are substantial, encompassing increased energy bills for households, exacerbation of fuel poverty, compromised indoor air quality, and the continued release of greenhouse gases. Moreover, the inherent inefficiencies of an ageing housing stock contribute significantly to a national carbon footprint that is incompatible with the UK’s climate pledges.

Historically, attempts to improve domestic energy efficiency have faced considerable challenges, often characterised by fragmented approaches, inconsistent quality, and a lack of holistic understanding of building physics. These issues led to suboptimal performance, unintended consequences such as dampness and mould, and a significant erosion of consumer confidence. It was against this backdrop of urgent environmental mandates, pervasive housing inefficiencies, and past retrofit failures that PAS 2035 was conceived and developed. This publicly available specification was designed to establish a comprehensive, integrated framework for retrofitting existing homes, aiming to elevate installation standards, mitigate risks, and ensure that energy efficiency improvements are both effective and sustainable, thereby directly supporting the UK’s net-zero transition (riseretrofit.org.uk). Its introduction marks a paradigm shift, moving the industry towards a professionalised, quality-driven approach essential for the national decarbonisation effort.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

2. Background and Evolution of PAS 2035

The development of PAS 2035 was a direct response to a critical assessment of the UK’s domestic retrofit sector, culminating in the seminal Each Home Counts review. Published in 2017, this independent review, led by Dr. Peter Bonfield, was commissioned following widespread concerns regarding the performance and quality of energy efficiency installations, particularly those carried out under government-backed schemes like the Green Deal. The review meticulously documented a litany of issues, including poor installation standards, insufficient assessment procedures, inadequate technical specifications, and a significant lack of consumer protection. These systemic failures often resulted in unintended consequences, such as increased instances of dampness, mould growth, structural damage, and a considerable ‘performance gap’ between predicted and actual energy savings. Critically, these failures eroded public trust in the benefits of energy efficiency measures and undermined the overall objectives of national decarbonisation programmes (riseretrofit.org.uk).

The Each Home Counts review presented a comprehensive set of recommendations aimed at professionalising the domestic energy retrofit market. Key among these was the call for a new, overarching framework that would mandate a ‘whole-house’ approach, integrate quality assurance at every stage, and establish clear standards for competence across the supply chain. In response, the Department for Business, Energy and Industrial Strategy (BEIS, now the Department for Energy Security and Net Zero) commissioned the British Standards Institution (BSI) to develop a publicly available specification that would embody these recommendations. The BSI, renowned for its expertise in developing standards through collaborative stakeholder engagement, was the ideal body to undertake this task, ensuring a robust, industry-vetted solution.

PAS 2035 was initially published in 2019, marking a significant departure from previous, often piecemeal, approaches to energy efficiency retrofitting. Its introduction represented a foundational shift towards a holistic, risk-managed methodology, where every intervention is considered within the context of the entire dwelling as an interconnected system. Since its initial publication, PAS 2035 has not remained static. The dynamic nature of policy objectives, advancements in building science, emerging technologies, and continuous learning from practical implementation have necessitated periodic revisions. The most notable revision, PAS 2035:2023, reflects an ongoing commitment to refining the standard to align with evolving policy mandates, stricter climate goals, and enhanced consumer protections (vorgroup.co.uk).

These revisions typically address several key areas: clarifying scope and applicability, strengthening requirements for specific measures, incorporating lessons learned from early adoption, improving integration with other standards (e.g., PAS 2030 for installation), and enhancing provisions for data collection and performance monitoring. The iterative process of development and revision underscores the adaptability and responsiveness of PAS 2035 as a living standard, continually evolving to ensure it remains fit-for-purpose in the complex and rapidly developing landscape of domestic energy efficiency retrofitting. This continuous refinement is crucial for maintaining its relevance and effectiveness in driving the quality and performance improvements necessary for the UK’s net-zero ambitions.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

3. Core Principles of PAS 2035

PAS 2035 is underpinned by a set of fundamental principles that collectively form a robust framework for delivering high-quality, sustainable energy efficiency retrofits. These principles move beyond isolated interventions, advocating for a holistic and systematic approach that prioritises long-term performance, occupant well-being, and risk mitigation. Adherence to these core tenets is crucial for avoiding the pitfalls of previous retrofit schemes and ensuring that improvements are effective, durable, and free from unintended consequences (retrofitacademy.org).

3.1. Whole-House Retrofit and Holistic Approach

The concept of ‘Whole-House Retrofit’ lies at the heart of PAS 2035. This principle dictates that a dwelling should be considered as a single, interconnected system rather than a collection of independent components. Historically, energy efficiency measures were often installed in isolation – a boiler upgrade here, some loft insulation there – without fully appreciating the complex interplay between different building elements. Such piecemeal approaches frequently led to unintended and detrimental consequences. For instance, increasing airtightness without considering adequate ventilation could exacerbate indoor air quality issues, promote condensation, and foster mould growth. Similarly, installing external wall insulation without addressing the thermal performance of windows or floors could shift thermal bridging problems to other areas of the building envelope.

PAS 2035 mandates that all potential interactions between various building elements and energy efficiency measures (EEMs) must be rigorously assessed. This involves understanding the building’s thermal envelope, its ventilation strategy, heating systems, and the behaviour of its occupants. A holistic approach ensures that interventions are coordinated and complementary, optimising overall building performance, maintaining structural integrity, and safeguarding occupant health and comfort. It considers not just energy savings but also factors like moisture management, indoor air quality, fire safety, and acoustic performance, treating the home as a complex physiological entity.

3.2. Fabric First

The ‘Fabric First’ principle establishes a hierarchy for energy efficiency interventions. It prioritises reducing the demand for heat before introducing new or more efficient heating systems. The rationale is elegantly simple: a building that is inherently inefficient, losing heat rapidly through its walls, roof, floor, and windows, will always require more energy to heat, irrespective of the efficiency of the heating system. Attempting to compensate for poor fabric performance with oversized or highly efficient mechanical systems is not only costly but also fundamentally inefficient and less sustainable in the long run.

This principle advocates for first addressing the building’s thermal envelope by enhancing insulation levels (walls, roofs, floors), improving window performance (double or triple glazing), and minimising uncontrolled air leakage (draught proofing, sealing). By substantially reducing heat loss, the demand for heating is significantly lowered, which in turn allows for smaller, more appropriately sized, and therefore more efficient, heating systems. This approach often reduces the operational costs of the building, improves thermal comfort, and enhances resilience to external temperature fluctuations. It is a logical and economically sound strategy that maximises the return on investment in energy efficiency measures.

3.3. Build Tight, Ventilate Right

This principle directly addresses one of the most common pitfalls of poorly executed energy retrofits: the creation of ‘sick building syndrome’ conditions due to a lack of proper ventilation in increasingly airtight homes. While reducing uncontrolled air leakage (building ‘tight’) is crucial for minimising heat loss and improving energy efficiency, it must be balanced with adequate, controlled ventilation (‘ventilate right’). Without sufficient fresh air exchange, internal moisture generated by daily activities (cooking, showering, breathing) can accumulate, leading to condensation, mould growth, and degradation of indoor air quality. Pollutants from cleaning products, furnishings, and human respiration can also build up, potentially impacting occupant health.

PAS 2035 therefore mandates a meticulous approach to ventilation strategy. As dwellings are made more airtight through measures like insulation and draught-proofing, the reliance on incidental ventilation (air leaking through gaps and cracks) diminishes. This necessitates the introduction of controlled ventilation systems, which can range from upgraded passive vents to sophisticated mechanical ventilation with heat recovery (MVHR) systems. MVHR systems, for example, not only remove stale, moist air but also recover heat from it, transferring it to incoming fresh air, thus maintaining good air quality without significant heat loss. The ‘Build Tight, Ventilate Right’ principle is vital for ensuring that energy efficiency gains do not come at the expense of building integrity or occupant health and comfort.

3.4. Quality Assurance and Risk Management

Central to PAS 2035 is an unwavering commitment to ‘Quality Assurance and Risk Management’. Recognising the long history of substandard installations and failed retrofit projects, the standard introduces a rigorous framework designed to minimise defects, maximise long-term performance, and protect consumers. This principle permeates every stage of the retrofit process, from initial assessment through to post-completion monitoring.

Risk management involves a systematic identification, assessment, and mitigation of potential hazards associated with retrofit interventions. These risks can be diverse, encompassing issues such as moisture ingress, interstitial condensation, structural stability, fire safety, overheating, and adverse impacts on listed buildings or conservation areas. PAS 2035 introduces the concept of ‘Risk Paths’ (A, B, C) which categorise projects based on their complexity and the potential risks involved, thereby dictating the level of assessment, design, and oversight required. For example, a simple, single measure like loft insulation in a straightforward property might follow Risk Path A, requiring less intensive oversight than a complex whole-house retrofit on a multi-property block or a historic building, which would typically fall under Risk Path C.

Quality assurance is enforced through the requirement for accredited professionals at each stage, adherence to specified methodologies, meticulous documentation, and independent validation. It includes robust contractual arrangements, clear specifications for materials and workmanship, and processes for handling unforeseen issues. This comprehensive approach to quality and risk ensures that retrofit projects are not only energy-efficient but also safe, durable, and deliver their intended benefits without creating new problems. It aims to restore and build consumer trust, which is fundamental to achieving widespread adoption of retrofit measures across the UK.

3.5. Occupant Engagement and User Guides

While not explicitly listed as a primary principle in the initial brief, effective ‘Occupant Engagement’ is an implicit and crucial component of the holistic approach within PAS 2035. The performance of a retrofitted home is not solely determined by the quality of its insulation or heating system; occupant behaviour plays a significant role in actual energy consumption and comfort levels. For instance, understanding how to properly operate a new ventilation system, utilise thermostatic controls effectively, or manage humidity levels can significantly impact the success of a retrofit. Lack of occupant understanding can lead to suboptimal performance, discomfort, or even the creation of new issues, such as moisture problems if ventilation systems are switched off.

PAS 2035 therefore emphasises the importance of clear communication with homeowners throughout the process, from initial assessment to post-installation. This includes providing detailed ‘User Guides’ that explain the newly installed measures, how they function, and how occupants can best interact with them to maximise energy savings and maintain a healthy indoor environment. The handover process is crucial, ensuring that residents are fully informed and empowered to get the most out of their retrofitted homes. This principle acknowledges that a technically sound retrofit can only achieve its full potential if the occupants are active and informed participants in its operation and maintenance, thus fostering a sense of ownership and responsibility for the efficiency and comfort of their living space.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

4. Key Roles in the Retrofit Process

PAS 2035 establishes a clear organisational structure for retrofit projects, defining distinct roles and responsibilities to ensure accountability, competence, and coordination across the entire delivery chain. This professionalisation of the retrofit industry is a direct response to past failures associated with fragmented responsibilities and inadequate skill sets. Each role within the PAS 2035 framework is designed to contribute specific expertise and oversight, collectively safeguarding the quality, safety, and effectiveness of retrofit interventions (retrofitacademy.org).

4.1. Retrofit Assessor

The Retrofit Assessor is the initial point of technical engagement with a property and a pivotal role in establishing the baseline understanding of the dwelling. Their primary responsibility is to conduct a thorough and comprehensive assessment of the existing building, gathering critical data that will inform all subsequent design and installation decisions. This assessment goes significantly beyond a standard Energy Performance Certificate (EPC) assessment. Key aspects of the Retrofit Assessor’s role include:

• EPC Data Collection: Gathering information required for an RdSAP (Reduced data Standard Assessment Procedure) or SAP (Standard Assessment Procedure) calculation to generate an EPC. This includes dimensions, construction type, existing insulation levels, heating system details, and window specifications.
• Occupancy Assessment: Understanding the specific needs, behaviours, and aspirations of the occupants. This involves discussions about current energy use, comfort levels, health concerns, and potential sensitivities to proposed changes. It’s crucial for tailoring retrofit measures to individual household requirements.
• Condition Survey: A detailed visual inspection of the property to identify existing defects, structural issues, moisture problems (dampness, mould), ventilation inadequacies, and any other factors that could affect the feasibility or performance of retrofit measures. This proactive identification of issues is critical for risk management.
• Ventilation Assessment: Evaluating the current ventilation strategy of the dwelling, including both natural and mechanical means, and identifying potential areas of concern if airtightness is increased.
• Photo Evidence & Data Capture: Documenting the property’s condition through comprehensive photographic evidence and detailed data entry into approved software. This forms the basis for the Retrofit Coordinator’s initial appraisal and subsequent design work.

The Retrofit Assessor must possess a deep understanding of building physics, construction methods, and the potential impacts of energy efficiency measures. Their work directly feeds into the development of the ‘Individual Dwelling Retrofit Plan’ and the identification of the appropriate ‘Risk Path’ for the project.

4.2. Retrofit Coordinator

The Retrofit Coordinator (RC) is arguably the most critical role within the PAS 2035 framework, acting as the overarching project manager and quality guardian for the entire retrofit journey. The RC is responsible for overseeing the project from inception to completion and post-installation monitoring, ensuring compliance with PAS 2035 requirements at every stage. Their responsibilities are extensive and multifaceted:

• Client Liaison: Serving as the primary point of contact for the homeowner, explaining the process, managing expectations, and ensuring their needs are met.
• Initial Appraisal & Risk Path Determination: Reviewing the Retrofit Assessor’s reports, conducting a preliminary appraisal, and determining the appropriate Risk Path (A, B, or C) for the project, which dictates the level of scrutiny required.
• Option Appraisal & Medium-Term Plan: Working with the Retrofit Designer, evaluating various retrofit options based on technical feasibility, cost-effectiveness, and client priorities. Developing a ‘Medium-Term Retrofit Plan’ for the dwelling, outlining a phased approach to energy efficiency improvements over a period of up to 25 years.
• Design Management: Commissioning and managing the Retrofit Designer, ensuring that designs are appropriate, compliant, and integrated into the overall plan. Reviewing and approving the ‘Design Pack’.
• Installer Selection & Supervision: Managing the procurement process for installers, ensuring they are competent and accredited (to PAS 2030, where applicable). Overseeing the installation phase, conducting site visits, and verifying adherence to the design specifications and quality standards.
• Handover & Commissioning: Ensuring all systems are correctly commissioned, and the homeowner receives a comprehensive ‘Resident Retrofit Guide’ and appropriate training on new systems.
• Post-Completion Monitoring: Arranging for post-installation monitoring and evaluation to assess the actual performance of the retrofit measures and address any issues.
• Compliance & Documentation: Maintaining meticulous records throughout the project, ensuring full compliance with PAS 2035 and all relevant regulations, and ultimately signing off on the project’s adherence to the standard.

The Retrofit Coordinator requires exceptional project management skills, a deep understanding of building science, excellent communication abilities, and a comprehensive knowledge of PAS 2035 and associated standards. They are the ultimate arbiter of quality and compliance.

4.3. Retrofit Designer

The Retrofit Designer is responsible for translating the assessment data and the Retrofit Coordinator’s strategic plan into a detailed, technically sound design for the energy efficiency measures. This role is crucial for ensuring that interventions are effective, integrated, and avoid unintended consequences. Key tasks include:

• Developing the Design Pack: Producing detailed drawings, specifications, calculations, and risk assessments for each proposed measure. This includes U-value calculations, condensation risk analysis (e.g., using WUFI software), ventilation calculations, and thermal bridging details.
• Material and System Specification: Selecting appropriate materials and systems that are compatible with the existing building fabric and meet performance targets. This involves considering durability, environmental impact, and cost-effectiveness.
• Integration of Measures: Ensuring that different energy efficiency measures work synergistically within the whole-house context, avoiding conflicts or detrimental interactions.
• Compliance with Regulations: Ensuring that the design adheres to all relevant Building Regulations, planning permissions (especially for listed buildings or conservation areas), and other statutory requirements.
• Risk Mitigation in Design: Proactively designing out risks identified during the assessment phase, such as managing moisture, preventing overheating, and ensuring fire safety.
• Collaboration: Working closely with the Retrofit Coordinator to refine the design based on client feedback, budget constraints, and site-specific challenges.

The Retrofit Designer must possess advanced knowledge of building physics, architectural design, material science, and relevant software tools. Their role is to ensure that the technical solutions are robust, buildable, and deliver the intended performance.

4.4. Retrofit Installer

The Retrofit Installer is responsible for the physical execution of the energy efficiency measures on-site, strictly adhering to the Retrofit Designer’s specifications and the Retrofit Coordinator’s oversight. This role requires highly skilled and certified tradespeople who can implement complex interventions with precision and quality. Their responsibilities include:

• Adherence to Design: Installing measures exactly as specified in the Retrofit Design Pack, including correct material application, detailing, and sequencing.
• Quality Workmanship: Ensuring that all work is carried out to the highest standards of quality, craftsmanship, and safety.
• Compliance with PAS 2030: Retrofit Installers must be certified to PAS 2030, the companion standard to PAS 2035, which sets out the requirements for the installation of energy efficiency measures in existing buildings. This ensures competence and quality control in the installation process.
• On-site Risk Management: Identifying and reporting any unforeseen site conditions or issues that may impact the design or installation, and working with the Retrofit Coordinator to resolve them.
• Documentation: Providing evidence of completed work, including photographic records and signing off on installation checklists.
• Health and Safety: Adhering to all health and safety regulations on site, protecting both workers and occupants.

The Installer’s competence and diligence are paramount, as even the best design can be undermined by poor execution. PAS 2035 and PAS 2030 together ensure a rigorous approach to installation quality.

4.5. Other Potential Roles and the Importance of Accreditation

While the four roles above are central, larger or more complex projects might involve other specialists, such as structural engineers, heritage consultants, or M&E (Mechanical & Electrical) specialists. Regardless of the specific role, a fundamental requirement within the PAS 2035 framework is the accreditation of all professionals involved. This typically involves demonstrating competence through recognised qualifications, continuous professional development (CPD), and certification by reputable schemes. This emphasis on accredited professionals across the supply chain is a cornerstone of PAS 2035, ensuring that every stage of a retrofit project is managed by individuals with verified expertise, thereby enhancing overall project quality, mitigating risks, and fostering consumer trust.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

5. Implementation Strategies: The Retrofit Journey under PAS 2035

Implementing PAS 2035 involves a highly structured and iterative process, designed to ensure that every retrofit project is meticulously planned, executed, and evaluated. This ‘retrofit journey’ moves systematically through distinct stages, each with specific requirements for assessment, design, installation, and verification. The process is overseen by the Retrofit Coordinator, ensuring seamless coordination and compliance from initial client engagement to post-completion monitoring (retrofitacademy.org).

5.1. Initial Engagement and Client Briefing

The retrofit journey commences with the initial engagement between the homeowner (or client) and the Retrofit Coordinator or an accredited Retrofit Advisor. This crucial phase involves understanding the client’s motivations for undertaking a retrofit – whether it’s reducing energy bills, improving comfort, addressing damp issues, or contributing to environmental goals. A comprehensive client brief is developed, outlining their budget, timeline, specific requirements, and any known concerns about the property. This early dialogue establishes clear expectations and ensures the retrofit strategy is aligned with the occupants’ needs and aspirations.

5.2. Comprehensive Assessment

Following the initial briefing, a thorough and multi-faceted assessment of the dwelling is undertaken by a qualified Retrofit Assessor. This stage is far more detailed than a standard EPC survey and forms the bedrock upon which the entire retrofit strategy is built. It comprises:

• Energy Assessment (RdSAP/SAP): A detailed evaluation of the property’s current energy performance, including U-values (thermal transmittance) of the building fabric (walls, roof, floor, windows), current heating and hot water systems, and ventilation provision. This provides the baseline energy performance data.
• Occupancy Assessment: A critical evaluation of how the building is currently used, including patterns of heating, ventilation, and hot water consumption. This also captures occupant feedback on existing comfort levels, any perceived problems (e.g., draughts, cold spots, condensation), and their expectations for improvement. Understanding occupant behaviour is vital for realistic performance predictions and for avoiding the ‘performance gap’.
• Condition Survey: A comprehensive visual inspection and investigation of the building’s physical condition. This identifies existing defects, structural integrity issues, evidence of dampness (rising, penetrating, or condensation), mould growth, asbestos presence, and any other factors that could influence or be affected by retrofit measures. Particular attention is paid to the interfaces between proposed measures and existing fabric.
• Ventilation Assessment: A specific focus on the current ventilation strategy, identifying passive and active ventilation routes, assessing their effectiveness, and anticipating changes needed once the building becomes more airtight. This is crucial for maintaining indoor air quality and preventing moisture-related problems.
• Contextual Assessment: Understanding the property’s location, exposure to weather, potential for overheating, and any planning constraints (e.g., listed building status, conservation area designations) that might affect material choices or external alterations.

Based on these assessments, the Retrofit Coordinator determines the appropriate Risk Path (A, B, or C) for the project, which dictates the level of design rigor and oversight required. Risk Path A covers simple, low-risk measures; Risk Path B involves more complex single measures or combinations; and Risk Path C applies to whole-house retrofits or projects on complex/historic buildings, demanding the most comprehensive approach.

5.3. Option Appraisal and Design Development

With the comprehensive assessment complete, the Retrofit Coordinator, in collaboration with a Retrofit Designer, embarks on the option appraisal and design development phase. This stage is iterative and highly collaborative:

• Medium-Term Retrofit Plan: For most projects (especially those in Risk Paths B and C), a ‘Medium-Term Retrofit Plan’ is developed. This strategic document outlines a phased approach to energy efficiency improvements over a period of up to 25 years. It considers the dwelling’s current condition, the client’s budget, lifestyle, and the overarching goal of achieving deep retrofit over time. This plan ensures that individual measures are not just standalone interventions but contribute to a coherent long-term strategy.
• Technical Design Pack: The Retrofit Designer then develops a detailed ‘Retrofit Design Pack’ for the immediate planned measures. This includes:
  • Detailed Drawings: Showing proposed interventions, sections, and critical junctions.
  • Specifications: Explicit requirements for materials, products, and workmanship, including U-values, R-values, and air permeability targets.
  • Calculations: Such as condensation risk analysis (e.g., using BS 5250 and software like WUFI), heat loss calculations, and ventilation rates.
  • Risk Assessment: A specific design-stage risk assessment for each measure, identifying potential unintended consequences and proposing mitigation strategies.
  • Integration Details: How new measures will integrate with existing fabric and other systems.
• Client Review: The proposed plan and design are presented to the client for review, discussion, and approval. Any modifications are incorporated, ensuring transparency and client buy-in.

5.4. Specification and Tendering

Once the design is approved, detailed specifications are finalised for all materials, products, and installation processes. The Retrofit Coordinator then manages the tendering process, inviting bids from accredited Retrofit Installers (who must be certified to PAS 2030, the companion standard to PAS 2035). The selection process considers not only cost but also the installer’s competence, experience, quality management systems, and references.

5.5. Installation and Project Management

The installation phase is managed closely by the Retrofit Coordinator. This involves:

• Site Supervision: Regular site visits to monitor progress, ensure compliance with the design pack and PAS 2030 requirements, and address any unforeseen issues or variations.
• Quality Checks: Performing interim quality checks during the installation of specific measures (e.g., before insulation layers are covered). Photographic evidence is typically required at key stages.
• Communication: Facilitating clear communication between the client, installers, and any other specialists involved, ensuring minimal disruption and timely resolution of queries.
• Health and Safety: Ensuring all work is carried out in accordance with relevant health and safety regulations.

5.6. Handover and Commissioning

Upon completion of the installation, a critical handover process takes place:

• Commissioning: All new systems (e.g., heating, ventilation, renewable technologies) are thoroughly commissioned to ensure they are operating correctly and efficiently according to design specifications.
• Resident Retrofit Guide: The client receives a comprehensive ‘Resident Retrofit Guide’ (or ‘Home User Guide’). This document explains the installed measures, their operation, maintenance requirements, and how the occupant can best interact with them to maximise energy savings and maintain comfort and indoor air quality. This includes instructions for new heating controls, ventilation systems, and advice on managing condensation.
• Training: The Retrofit Coordinator provides practical training and demonstrations to the client on how to use new systems and manage their home effectively post-retrofit.

5.7. Monitoring and Evaluation

PAS 2035 mandates a degree of post-completion monitoring and evaluation to assess the actual performance of the retrofit measures. This may involve:

• Performance Monitoring: Collecting energy consumption data (e.g., through smart meters) to compare actual performance against predicted savings.
• Occupancy Feedback: Gathering feedback from residents on comfort levels, indoor air quality, and the functionality of new systems.
• Post-Installation Inspection: In some cases, a follow-up inspection to check for any defects or unintended consequences.

This feedback loop is invaluable for refining future retrofit strategies, identifying common issues, and continuously improving the overall effectiveness of the PAS 2035 framework. The entire process is meticulously documented, culminating in a final report from the Retrofit Coordinator confirming adherence to the standard, thus ensuring a fully traceable and quality-assured retrofit journey.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

6. Implications and Impact

The widespread adoption of PAS 2035 has profound implications across the UK’s energy efficiency landscape, extending beyond merely improving individual dwelling performance. It represents a paradigm shift towards professionalisation, quality assurance, and a systemic approach to addressing the national retrofit challenge. Its impact is felt across various stakeholders, from homeowners and industry professionals to policymakers and the broader environment (retrofitacademy.org).

6.1. Enhanced Quality Assurance and Risk Mitigation

One of the most significant impacts of PAS 2035 is the dramatic improvement in quality assurance. By mandating a rigorous, stage-gated process with clearly defined roles and responsibilities, the standard significantly reduces the risk of poorly executed retrofit projects. This directly tackles the historical issues that plagued previous schemes, such as the Green Deal, where inconsistent standards led to widespread problems. The requirement for accredited professionals, detailed assessments, comprehensive design packs, and supervised installations means that measures are more likely to be installed correctly and function as intended. This includes:

• Reduction of Unintended Consequences: The ‘whole-house’ approach and the emphasis on risk management actively work to prevent common issues like interstitial condensation, mould growth, and overheating, which were often side effects of piecemeal, uncoordinated interventions. This directly contributes to healthier and more comfortable living environments.
• Minimisation of the ‘Performance Gap’: By ensuring that design calculations are robust and installations adhere to specifications, PAS 2035 helps bridge the ‘performance gap’ – the discrepancy between predicted energy savings and actual in-use performance. This delivers more reliable energy bill reductions for homeowners and more accurate contributions to national carbon targets.
• Increased Durability and Longevity: Higher quality installations and careful consideration of building physics mean that retrofit measures are more durable and have a longer effective lifespan, reducing the need for costly remedial work and ensuring a better return on investment over time.

6.2. Consumer Protection and Confidence

PAS 2035 offers a robust framework for consumer protection, which is vital for building trust and encouraging wider adoption of energy efficiency measures. Homeowners engaging with a PAS 2035 compliant scheme benefit from:

• Clear and Transparent Process: The structured retrofit journey, from initial assessment to handover, ensures homeowners understand what to expect at each stage, reducing uncertainty and confusion.
• Qualified Professionals: The requirement for accredited Retrofit Assessors, Coordinators, Designers, and Installers provides assurance that projects are managed and executed by competent individuals, mitigating the risk of cowboy builders or substandard work.
• Risk Management: Homeowners are protected from the negative impacts of poorly thought-out retrofits, as risks related to moisture, ventilation, and structural integrity are systematically identified and mitigated during the design and installation phases.
• Formal Documentation and Guarantees: The detailed documentation, including the ‘Resident Retrofit Guide’ and associated guarantees/warranties for products and workmanship, provides a clear recourse in case of issues and empowers homeowners to manage their retrofitted homes effectively.
• Redress Mechanisms: As PAS 2035 is often linked to government funding schemes and industry certification bodies, it typically comes with access to established redress mechanisms for resolving disputes, further safeguarding consumer interests.

This enhanced protection and transparency are critical for overcoming historical consumer apprehension and fostering a positive perception of domestic retrofit as a reliable and beneficial investment.

6.3. Alignment with Policy Goals and Environmental Benefits

PAS 2035 is intricately woven into the UK’s broader climate and energy policy landscape, directly supporting several key governmental objectives:

• Net-Zero Target (2050): By driving significant improvements in the energy efficiency of existing housing stock, PAS 2035 is a cornerstone strategy for reducing residential carbon emissions, which are a major contributor to the UK’s overall footprint. The scale of retrofitting required to meet the 2050 net-zero target necessitates a standardised, quality-driven approach that PAS 2035 provides.
• Fuel Poverty Reduction: More energy-efficient homes require less energy to heat, directly leading to lower energy bills. This is particularly impactful for households in fuel poverty, providing warmer homes and significant cost savings, thereby contributing to the government’s ambitions to eradicate fuel poverty.
• Green Economy and Job Creation: The rigorous requirements of PAS 2035 stimulate demand for a skilled workforce across the retrofit supply chain – assessors, coordinators, designers, and installers. This fosters the creation of ‘green jobs’, supports training and upskilling initiatives, and contributes to the growth of a professionalised, sustainable construction sector in the UK.
• Energy Security: Reducing reliance on imported fossil fuels through decreased domestic energy consumption enhances the UK’s energy security and resilience against volatile global energy markets.
• Environmental Impact: Beyond carbon emissions, improved energy efficiency reduces the demand for energy generation, potentially lessening the environmental impact associated with resource extraction, power plant operations, and transmission losses.

6.4. Industry Professionalisation and Upskilling

PAS 2035 has been a powerful catalyst for industry professionalisation and upskilling. By setting clear competence requirements for each role, it has driven a significant demand for accredited training and certification across the sector. This has led to:

• Development of New Qualifications: The emergence of specialised qualifications for Retrofit Assessors, Coordinators, and Designers, delivered by organisations like The Retrofit Academy.
• Elevated Standards: A general raising of standards across the retrofit supply chain, encouraging companies to invest in training their workforce and implementing robust quality management systems.
• Clear Career Pathways: The defined roles within PAS 2035 offer clear career progression opportunities for individuals entering or advancing within the energy efficiency sector.
• Increased Collaboration: The integrated nature of the standard encourages greater collaboration between different trades and professions, fostering a more cohesive and efficient industry.

In essence, PAS 2035 is transforming what was once a fragmented and often inconsistent market into a structured, professionalised industry, equipped to deliver the scale and quality of retrofit required for the UK’s energy and climate ambitions.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

7. Challenges and Considerations

Despite its robust framework and significant potential, the widespread implementation of PAS 2035 is not without its challenges. These complexities arise from the inherent nature of transforming an ageing, diverse housing stock, the economic landscape, and the human element of behavioural change. Addressing these considerations is crucial for the long-term success and scalability of the standard (retrofitspecialist.co.uk).

7.1. Skills Gap and Workforce Development

One of the most pressing challenges is the substantial skills gap across the entire retrofit supply chain. The sheer scale of retrofitting required to meet the 2050 net-zero target – retrofitting millions of homes – demands a workforce far larger and more skilled than currently exists. This includes a shortage of qualified:

• Retrofit Assessors: Capable of conducting detailed, holistic assessments.
• Retrofit Coordinators: With the complex project management and technical oversight skills required.
• Retrofit Designers: Possessing deep building physics knowledge to create robust, integrated designs.
• Accredited Installers: Tradespeople (e.g., plasterers, electricians, plumbers, roofers, insulation installers) who are trained in the specific techniques required for energy efficiency measures, understand how to work with different building types, and adhere to the stringent quality requirements of PAS 2030 (the installation standard).

Addressing this requires a concerted national effort to invest in comprehensive training programmes, apprenticeships, and upskilling initiatives. Educational institutions, industry bodies (like The Retrofit Academy), and government funding are all vital to rapidly expand the pool of competent professionals. Furthermore, attracting a diverse workforce and promoting retrofit as a desirable career path are essential.

7.2. Cost Implications and Funding Mechanisms

The financial burden of comprehensive retrofitting remains a significant barrier for many homeowners. While the long-term benefits in terms of energy savings and increased property value are clear, the upfront capital cost can be substantial, particularly for whole-house, deep retrofits. This issue is compounded by:

• High Upfront Costs: Detailed assessments, design work, and the installation of multiple, high-quality measures are inherently more expensive than single, superficial interventions.
• Lack of Accessible Finance: While various government schemes (e.g., ECO – Energy Company Obligation, local authority grants) exist, their scope and funding levels can be inconsistent and often insufficient to cover the full cost of deep retrofit for all households. Green finance products (e.g., low-interest loans, green mortgages) are emerging but are not yet widely adopted or sufficiently attractive to a broad market segment.
• Perceived Complexity of Funding: Navigating the array of available grants and funding streams can be confusing and time-consuming for homeowners, creating a deterrent.

Innovative and long-term funding models, including grant schemes, property-linked finance, and fiscal incentives, are needed to make retrofitting more accessible and affordable for a wider demographic, particularly those in fuel poverty or with limited disposable income.

7.3. Regulatory Compliance and Integration with Existing Legislation

Navigating the complex landscape of regulatory compliance poses another challenge. While PAS 2035 provides a clear framework for energy efficiency, it must interact seamlessly with other established regulations and standards:

• Building Regulations: Ensuring PAS 2035 designs and installations comply with Part L (Conservation of Fuel and Power), Part F (Ventilation), Part B (Fire Safety), and other relevant sections of the Building Regulations. This requires careful coordination, especially for structural alterations or changes to ventilation systems.
• Planning Permission: For external wall insulation, window replacements, or alterations to historic buildings (listed buildings or those in conservation areas), planning permission is often required. The specific requirements can vary significantly between local authorities and can add considerable time and complexity to a project.
• Conservation and Heritage: Retrofitting historic or traditionally constructed buildings (often pre-1919) presents unique challenges. Measures must be carefully chosen to avoid damaging the building fabric, compromising its aesthetic value, or impacting its moisture-managing properties. PAS 2035 provides pathways for this but requires highly specialised expertise from assessors and designers.
• Party Wall Act: Interventions that affect party walls (e.g., external wall insulation) may require compliance with the Party Wall Act, adding further legal and logistical steps.

Harmonising PAS 2035 with these diverse regulatory requirements demands a high level of expertise from practitioners and clear guidance from regulatory bodies to streamline the process.

7.4. Homeowner Engagement and Behavioural Change

Even with a technically sound retrofit, the ultimate success depends on homeowner engagement and behavioural change. Challenges here include:

• Overcoming Apathy and Misinformation: Many homeowners may not fully understand the benefits of retrofit or may be wary due to past negative experiences or concerns about disruption.
• Understanding New Systems: The need for clear, actionable ‘Resident Retrofit Guides’ and training to ensure occupants understand how to operate new heating, ventilation, and control systems effectively.
• Managing Expectations: Communicating realistic energy savings, potential disruption during installation, and the long-term benefits is crucial to client satisfaction.
• Post-Occupancy Behaviour: The ‘performance gap’ can sometimes be influenced by how occupants interact with their home post-retrofit. Ensuring sustained engagement and correct usage is vital.

Effective communication, transparent processes, and ongoing support are essential to empower homeowners and ensure they derive the maximum benefit from their retrofitted homes.

7.5. Variability of Housing Stock and Material Compatibility

The UK’s housing stock is incredibly diverse, ranging from Victorian terraces to post-war estates and modern constructions, utilising a multitude of different building materials and construction techniques. Applying a standardised framework like PAS 2035 to such variability is complex:

• Material Compatibility: Different insulation types, renders, and ventilation solutions perform differently on various substrates (e.g., solid brick, cavity wall, timber frame). Choosing the wrong material can lead to moisture entrapment, degradation, or structural issues.
• Construction Detailing: Achieving airtightness and thermal bridging reduction requires highly specific detailing that varies significantly depending on the original construction. Generic solutions are often inadequate.
• Unforeseen Site Conditions: The older the building, the greater the likelihood of encountering unexpected conditions (e.g., hidden defects, asbestos, variations from original plans) during the assessment or installation phase, which can lead to costly delays and design modifications.

This necessitates a high level of diagnostic skill from Assessors and Designers, and adaptability from Installers, ensuring that solutions are tailored to the specific characteristics of each individual dwelling.

Addressing these challenges comprehensively requires ongoing policy support, significant investment in skills development, innovative funding solutions, and continuous engagement with both industry and homeowners to ensure PAS 2035 can fulfil its transformative potential for the UK’s housing stock.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

8. Future Outlook and Recommendations

The journey towards a fully decarbonised housing stock by 2050 is a long-term endeavour, and PAS 2035 represents a critical, yet evolving, component of this national strategy. The future outlook for PAS 2035 involves continuous refinement, deeper integration with emerging technologies, and a concerted effort to overcome existing challenges. To truly embed its principles and achieve its ambitious goals, several strategic recommendations can be put forth.

8.1. Ongoing Evolution and Adaptation of PAS 2035

PAS 2035, like any effective standard, must remain dynamic and responsive to change. Future revisions will likely focus on:

• Integration with Advanced Technologies: Incorporating guidelines for the seamless integration of smart home technologies, advanced building management systems, and new renewable energy solutions (e.g., novel heat pump designs, integrated solar PV and storage) within the whole-house retrofit plan. This ensures the standard remains at the forefront of technological innovation.
• Enhanced Data Utilisation: Further developing requirements for comprehensive data collection and analysis, particularly post-retrofit performance monitoring. This will allow for robust evidence-based adjustments to the standard, refining predictions, and reducing the ‘performance gap’. The potential of digital twins for buildings could offer unprecedented insights into building performance.
• Climate Resilience: Expanding the scope to explicitly address climate change adaptation measures, such as mitigating overheating risks in summer months, managing extreme weather events (e.g., flood resilience), and ensuring retrofits contribute to the long-term resilience of dwellings in a changing climate.
• Standardisation of Measurement and Verification: Strengthening protocols for consistent measurement and verification of energy savings and other performance metrics to ensure accountability and validate the effectiveness of interventions.

8.2. Policy and Regulatory Framework Strengthening

For PAS 2035 to achieve its full impact, it requires robust and consistent governmental support, coupled with clear regulatory signals:

• Long-Term Funding Commitment: The cyclical nature of retrofit funding schemes has historically hindered sustained industry growth. A commitment to long-term, stable funding mechanisms – possibly for a decade or more – would provide certainty for businesses to invest in skills, training, and capacity, thereby scaling up the retrofit supply chain.
• Mandatory Adoption: Exploring pathways for wider, and eventually mandatory, adoption of PAS 2035 for all domestic retrofit projects, not just those receiving public funding. This could be phased in conjunction with tightening EPC regulations or at points of property sale.
• Streamlined Planning and Building Regulations: Reviewing and simplifying the interface between PAS 2035 and existing planning and building regulations, particularly for complex and heritage buildings. Providing clearer national guidance and potentially fast-track approval processes for PAS 2035-compliant projects could reduce administrative burdens.
• Fiscal Incentives: Introducing more attractive fiscal incentives for homeowners, such as Stamp Duty rebates for energy-efficient homes, low-interest green mortgages, or council tax reductions for homes achieving higher EPC ratings post-retrofit. This would stimulate private investment in retrofit.

8.3. Workforce Development and Professionalisation Acceleration

The skills gap remains a critical bottleneck. Addressing this requires a multi-pronged approach:

• Scalable Training Infrastructure: Significantly increasing government and industry investment in training centres, colleges, and apprenticeship programmes specifically tailored to retrofit roles. This includes funding for both new entrants and the reskilling of existing trades.
• Standardised Competence Frameworks: Continuing to develop and promote robust, industry-recognised competence frameworks and qualifications for all retrofit roles, ensuring consistency in skill levels across the country.
• Industry Collaboration: Fostering greater collaboration between professional bodies, trade associations, and educational institutions to develop curricula that meet industry needs and to promote retrofit careers.
• Public Awareness Campaigns: Launching national campaigns to raise awareness of career opportunities in the green economy and promote the value and professionalism of retrofit work.

8.4. Enhanced Homeowner Engagement and Support

Successful retrofitting depends not only on technical excellence but also on informed and engaged homeowners:

• Clear Information Hubs: Developing easily accessible, government-backed information hubs that provide impartial advice, guide homeowners through the retrofit process, explain funding options, and offer tools for assessing potential benefits.
• Simplified Client Journeys: Simplifying the initial client engagement process, potentially through trusted local authority schemes or accredited national providers who can manage the entire PAS 2035 journey on behalf of the homeowner.
• Post-Retrofit Support: Extending support beyond handover, possibly through follow-up visits, community support groups, or digital platforms, to ensure occupants are comfortable with and correctly using their new systems and to address any emergent issues.

8.5. Research, Development, and Innovation

Continued investment in research and development is vital to push the boundaries of retrofit technology and methodology:

• Building Pathology and Materials Science: Further research into the long-term performance of retrofit materials, particularly for different building types and climates, and developing innovative solutions for hard-to-treat homes.
• Performance Monitoring and Feedback: Investing in advanced monitoring technologies and data analytics to gather robust evidence on actual retrofit performance, providing critical feedback for continuous improvement of the standard and design practices.
• Offsite and Modular Retrofit: Exploring and scaling up offsite manufacturing and modular solutions for retrofit components (e.g., insulated panels, integrated service pods) to accelerate installation times, reduce disruption, and enhance quality control.

By proactively addressing these areas, the UK can ensure that PAS 2035 remains a powerful driver of change, facilitating the transformation of the existing housing stock into energy-efficient, healthy, and sustainable homes that are fit for the future and demonstrably contribute to the nation’s climate obligations.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

9. Conclusion

PAS 2035 represents a transformative leap forward in the United Kingdom’s strategy for enhancing the energy efficiency of its existing housing stock and, by extension, achieving its legally binding net-zero carbon emissions target by 2050. Born out of the critical findings of the Each Home Counts review, the standard was specifically designed to rectify the systemic failures of previous retrofit schemes, which were characterised by fragmented approaches, inconsistent quality, and a significant erosion of consumer confidence.

At its core, PAS 2035 champions a holistic, risk-managed methodology, demanding that every dwelling be treated as an interconnected system. Its foundational principles – ‘Whole-House Retrofit’, ‘Fabric First’, ‘Build Tight, Ventilate Right’, and rigorous ‘Quality Assurance and Risk Management’ – collectively ensure that energy efficiency improvements are not only technically sound but also durable, safe, and free from unintended consequences such as dampness, mould, or compromised indoor air quality. The defined roles of the Retrofit Assessor, Coordinator, Designer, and Installer professionalise the industry, embedding accountability and competence at every stage of the retrofit journey, from initial detailed assessment to post-completion monitoring.

The widespread adoption of PAS 2035 has profound and far-reaching implications. It significantly enhances quality assurance and mitigates risks, thereby building crucial consumer protection and trust, which are vital for widespread public engagement. Crucially, it provides a robust framework that aligns directly with the UK’s ambitious policy goals, including the net-zero target, the alleviation of fuel poverty, and the stimulation of a green economy through the creation of skilled employment opportunities. It signifies a decisive move towards an evidence-based, quality-driven approach that is essential for addressing the monumental challenge of decarbonising over 17 million homes.

While the standard offers a powerful solution, its full potential is contingent upon overcoming several significant challenges. The pressing need to address the pervasive skills gap, establish consistent and equitable funding mechanisms, streamline regulatory compliance, and ensure sustained homeowner engagement demands ongoing commitment and innovation. The future outlook for PAS 2035 necessitates continuous evolution, embracing new technologies, strengthening policy support, and fostering a collaborative ecosystem of industry, government, and academia.

In essence, PAS 2035 is more than just a technical specification; it is a strategic imperative. It underpins the nation’s ability to deliver sustainable, high-quality retrofit outcomes that not only improve the comfort and reduce the energy bills of millions of homeowners but also contribute meaningfully and demonstrably to the United Kingdom’s overarching climate objectives and long-term energy security. Its continued refinement and comprehensive implementation are non-negotiable for the successful realisation of a decarbonised future.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

References

• Building Energy Experts. (n.d.). PAS 2035: What is PAS 2035? Retrieved from https://buildingenergyexperts.co.uk/resources/what-is-pas-2035/
• Retrofit Specialist. (n.d.). What is PAS? Retrieved from https://retrofitspecialist.co.uk/what-is-pas2035/
• Retrofitworks. (2025, June 22). Understanding PAS 2035/2030:2023 – The Foundation of Quality Retrofit in the UK. Retrieved from https://retrofitworks.co.uk/understanding-pas/
• Rise Retrofit. (n.d.). PAS 2035. Retrieved from https://riseretrofit.org.uk/resources/toolkits/pas-2035
• The Retrofit Academy. (n.d.). PAS 2035 Guide. Retrieved from https://retrofitacademy.org/pas-2035-guide/
• UK Energy Assessors. (n.d.). PAS 2035. Retrieved from https://www.uk-energy-assessors.co.uk/services/pas-2035
• Value Optimised Retrofit. (2025, March 31). PAS 2035:2023 – What the New Retrofit Standard Means for You. Retrieved from https://www.vorgroup.co.uk/pas-20352023-what-the-new-retrofit-standard-means-for-you/