A Comprehensive Analysis of PAS 2035:2023 – Framework for Whole-House Retrofit Projects

2025-12-21 Research Reports 0

Abstract

The PAS 2035:2023 standard stands as a critical framework for holistic, risk-managed whole-house retrofit projects within the United Kingdom. It meticulously guides practitioners through a series of interconnected stages, from initial assessment and sophisticated design to diligent installation and thorough handover, culminating in post-installation evaluation. This comprehensive research report undertakes an in-depth exploration of PAS 2035:2023, meticulously dissecting its underlying principles, sequential stages, and the pivotal roles enacted by key professionals such as the Retrofit Coordinator, Retrofit Assessor, and Retrofit Designer. Furthermore, it scrutinises the stringent compliance requirements, the inherent challenges, and future considerations that shape the efficacy and widespread adoption of this standard. By offering a granular breakdown and augmented detail, this report seeks to furnish professionals, policymakers, and property owners with an exhaustive understanding necessary to effectively navigate the standard, thereby ensuring the delivery of high-quality, performant, durable, and safe retrofit projects that genuinely contribute to national energy efficiency and climate change mitigation targets.

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

1. Introduction

The urgent imperative to drastically enhance the energy efficiency of existing housing stock is globally recognised as a fundamental pillar of climate change mitigation strategies. Buildings, particularly residential properties, are significant contributors to national carbon emissions, and their decarbonisation is crucial for achieving ambitious net-zero targets. In the United Kingdom, where a substantial proportion of housing stock predates modern energy efficiency standards, the challenge is particularly acute. The imperative extends beyond mere energy savings; it encompasses improving occupant health and comfort, reducing fuel poverty, and enhancing the overall resilience of homes to a changing climate.

Historically, retrofit initiatives in the UK have been plagued by a series of systemic failures, often leading to suboptimal performance, unintended consequences such as condensation and mould, and a widespread lack of consumer confidence. These issues underscored a critical need for a standardised, robust, and holistic approach. It was against this backdrop that the PAS 2035 standard was conceived and subsequently evolved. The British Standards Institution (BSI) published PAS 2035:2023 to provide a comprehensive, quality-assured framework specifically designed to guide the retrofitting of dwellings. This standard is not merely a set of guidelines; it represents a paradigm shift towards treating the dwelling as a complex, interconnected system, thereby aiming to prevent historical pitfalls and ensure that improvements are implemented systematically, effectively, and sustainably. It champions a ‘fabric-first’ approach, prioritising improvements to the building’s envelope before addressing heating and energy generation, and mandates a thorough understanding of building physics to avoid creating new problems whilst solving old ones. This report delves into the foundational elements, practical implications, and strategic importance of PAS 2035:2023, equipping stakeholders with the advanced knowledge required for its successful implementation.

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

2. Background and Evolution of PAS 2035

2.1. Origins and Development: The ‘Each Home Counts’ Review

The genesis of PAS 2035 can be directly traced back to the ‘Each Home Counts’ review, an independent inquiry commissioned by the UK government in 2015 and published in December 2016. Chaired by Dr Peter Bonfield, the review was a direct response to widespread concerns regarding the quality and effectiveness of domestic energy efficiency retrofit projects, particularly those delivered under government-backed schemes like the Green Deal. The review highlighted a pervasive ‘performance gap’ where installed measures frequently failed to deliver the anticipated energy savings or comfort improvements. More critically, it uncovered numerous instances of poor workmanship, mis-selling, inadequate consumer protection, and even instances where retrofit measures inadvertently led to issues such as mould, damp, and structural damage due to a lack of understanding of building physics and holistic design principles (gov.uk).

The ‘Each Home Counts’ review made several key recommendations, central among which was the urgent need for a robust quality assurance and consumer protection framework for the domestic retrofit sector. It called for the creation of a ‘golden thread’ of information from initial assessment through to post-completion evaluation, and for clear roles and responsibilities to be defined for all stages of a retrofit project. These recommendations formed the bedrock upon which PAS 2035:2019, ‘Retrofitting dwellings for improved energy efficiency – Specification and guidance’, was developed. The British Standards Institution (BSI) led the development, collaborating extensively with a diverse range of stakeholders. These included government departments such as the Department for Business, Energy & Industrial Strategy (BEIS, now DESNZ), industry trade bodies, certification bodies, consumer groups, housing associations, and technical experts. The initial version, PAS 2035:2019, published in June 2019, established a groundbreaking framework designed to mitigate risks, ensure quality, and promote a holistic, ‘whole-house’ approach to retrofit. It introduced key concepts such as the Retrofit Coordinator role, a defined retrofit process from assessment to evaluation, and a focus on managing potential unintended consequences.

2.2. Transition to PAS 2035:2023: Refinement and Alignment

The landscape of energy efficiency and climate policy is dynamic, continuously evolving in response to new research, technological advancements, and more stringent national targets. Recognising this, and leveraging the invaluable experience gained from the implementation of PAS 2035:2019 over several years, the BSI embarked on an update process. PAS 2035:2023, published in September 2023, represents a significant refinement and enhancement of the original standard, superseding its predecessor. This updated standard incorporates crucial feedback from practitioners, aligns with contemporary national net-zero strategies, and integrates advancements in building science and retrofit best practices.

Key drivers for the update included a need for greater clarity in certain areas, particularly concerning traditional and historically significant buildings, enhanced emphasis on moisture management and ventilation strategies, and a stronger focus on avoiding the performance gap. The updated standard also sought to refine the responsibilities of various retrofit roles and improve the overall user experience for professionals. Notable changes in PAS 2035:2023 include, but are not limited to:

  • Clarification of Risk Pathways: More precise definitions and guidance for categorising projects into risk pathways (A, B, C) based on complexity and potential impact, which in turn dictate the level of design and coordination required.
  • Enhanced Ventilation Requirements: Greater emphasis on robust ventilation strategies to mitigate indoor air quality issues and condensation risks, often requiring explicit mechanical ventilation design for certain fabric improvements.
  • Moisture Management: Strengthened guidance on assessing and managing moisture risks, including a deeper dive into hygroscopic materials and interstitial condensation analysis.
  • Traditional Buildings: Specific considerations and guidance for retrofitting older and historically significant properties, recognising their unique characteristics and performance needs, often requiring a ‘fabric-first, do no harm’ approach.
  • Performance Evaluation: Greater clarity on the requirements for post-installation evaluation and monitoring, aiming to closer match predicted and actual performance.
  • Competency Requirements: Refinements to the competency requirements for all roles, ensuring that professionals possess the necessary skills and knowledge for the updated standard.
  • Updated Terminology: Adjustments to terminology for improved clarity and consistency across the sector.

The transition period for adopting PAS 2035:2023 concluded on 30th March 2025 (proficiency.services). After this date, compliance with the new standard became mandatory for all domestic retrofit projects requiring PAS 2035 certification, particularly those funded through government schemes such as the Energy Company Obligation (ECO) and the Social Housing Decarbonisation Fund (SHDF). This mandatory adoption underscores the UK government’s commitment to ensuring that all future domestic retrofits are delivered to the highest possible standards, thereby protecting consumers, maximising energy savings, and accelerating progress towards net-zero targets.

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

3. Structure and Stages of PAS 2035:2023

PAS 2035:2023 meticulously outlines a structured, iterative, and systematic approach to domestic retrofit projects. This framework is designed to ensure a holistic understanding of the dwelling, mitigate risks, and deliver optimal, long-lasting performance. The standard breaks down the retrofit process into five sequential, yet often overlapping, key stages:

3.1. Retrofit Assessment: The Foundation of Understanding

The initial phase of any PAS 2035 compliant project is the Retrofit Assessment, which involves a comprehensive and multi-faceted evaluation of the dwelling. This stage is critical for establishing an accurate baseline of the property’s existing condition, energy performance, and the unique characteristics that will influence any retrofit interventions. The assessment is conducted by a qualified Retrofit Assessor and typically comprises several distinct components:

  • RdSAP/EPC Assessment: A fundamental element, providing an initial energy performance indicator and identifying potential areas for improvement. While RdSAP (Reduced data Standard Assessment Procedure) provides a standardised methodology for calculating energy efficiency, PAS 2035 goes significantly beyond its scope to ensure a deeper understanding of the building.
  • Occupancy Assessment (OCC): This involves gathering detailed information about the occupants’ energy usage patterns, comfort requirements, health conditions, and any vulnerabilities (e.g., fuel poverty risk). Understanding occupant behaviour is crucial for designing solutions that are both effective and user-friendly, and to prevent any adverse impacts on their wellbeing.
  • Condition Report: A thorough inspection of the building’s fabric, structure, and services to identify existing defects, areas of deterioration, and potential problems that could be exacerbated by retrofit measures. This includes assessing the condition of walls, roofs, floors, windows, doors, existing insulation, and heating systems. Particular attention is paid to identifying issues like damp, mould, structural cracks, and asbestos, which must be addressed before or during the retrofit.
  • Ventilation Assessment: A critical component, evaluating the dwelling’s current ventilation strategy, air tightness, and identifying any existing issues like poor indoor air quality or condensation. This assessment informs the design of a suitable ventilation strategy for the post-retrofit dwelling, ensuring adequate fresh air provision and moisture removal without excessive heat loss.
  • Moisture Risk Assessment: A detailed analysis of potential moisture risks, both present and future. This goes beyond simple damp checks to consider factors like interstitial condensation, surface condensation, driving rain, and groundwater ingress. For traditional solid wall buildings, understanding moisture movement through breathable materials is paramount.
  • Traditional Building Assessment (for pre-1919 properties): For older and heritage buildings, specific assessment protocols are followed, acknowledging their unique construction methods, materials, and potential for harm from inappropriate modern interventions. This often involves a more in-depth understanding of lime mortars, breathable plasters, and timber structures.

The Retrofit Assessor compiles these findings into a comprehensive report, providing an objective and detailed picture of the dwelling, which then serves as the indispensable input for the subsequent design phase. The overarching aim is to treat the building as an integrated system, recognising that altering one element can have ripple effects on others.

3.2. Retrofit Design: Crafting the Holistic Solution

Based meticulously on the comprehensive findings from the Retrofit Assessment, the Retrofit Design phase involves the creation of a bespoke, detailed plan for the proposed energy efficiency measures. This stage is undertaken by a qualified Retrofit Designer, often working closely with the Retrofit Coordinator. The core principle here is the ‘whole-house’ approach, ensuring that all proposed measures are compatible with each other, with the building’s characteristics, and crucially, with the occupants’ needs and lifestyle. The design process adheres to a hierarchy of measures, typically prioritising a ‘fabric-first’ approach:

  1. Fabric Improvements: Enhancing the thermal envelope through measures like loft insulation, external or internal wall insulation, floor insulation, and high-performance windows and doors. The design specifies U-values (thermal transmittance), psi-values (thermal bridging), and addresses potential cold spots.
  2. Air Tightness: Measures to reduce uncontrolled air leakage, complementing the fabric improvements and enhancing the effectiveness of ventilation systems.
  3. Ventilation: Designing a robust and effective ventilation strategy (natural, mechanical extract, or mechanical ventilation with heat recovery – MVHR) to ensure optimal indoor air quality and manage moisture, preventing condensation and mould, particularly in more airtight homes.
  4. Heating and Hot Water Systems: Upgrading or replacing inefficient boilers with modern, high-efficiency alternatives, or transitioning to low-carbon heating systems like heat pumps.
  5. Renewable Energy Generation: Integrating renewable technologies such as solar photovoltaic (PV) panels or solar thermal systems.

The output of this stage is a detailed Retrofit Design document, which must include:

  • Technical Specifications: Precise details for each measure, including materials, thicknesses, U-values, and specific installation instructions.
  • Construction Details: Drawings and specifications detailing how different measures integrate, especially at interfaces (e.g., wall-floor junctions, around windows) to avoid thermal bridging.
  • Ventilation Strategy: A clear design for the proposed ventilation system, including calculations and system schematics.
  • Condensation Risk Analysis: Calculations to confirm that the proposed measures will not lead to interstitial or surface condensation, using tools like WUFI where necessary.
  • Overheating Risk Assessment: Particularly important for modern, highly insulated and airtight homes, to ensure thermal comfort in warmer months.
  • Projected Performance: An updated energy performance calculation (e.g., post-retrofit EPC rating, predicted energy savings).

The Retrofit Designer must consider the project’s risk pathway (determined by the Retrofit Coordinator) which dictates the level of detail and complexity required in the design. For higher risk pathways (B and C), more sophisticated design calculations and potentially bespoke engineering solutions are necessary. The design must also explicitly address how any potential unintended consequences identified during the assessment phase will be mitigated.

3.3. Retrofit Coordination: The Project Orchestrator

Effective Retrofit Coordination is arguably the most crucial element for the successful execution of any PAS 2035 project. The Retrofit Coordinator acts as the central point of contact and overall project manager, overseeing the entire retrofit journey from inception to completion. Their primary responsibility is to ensure compliance with PAS 2035:2023, manage risks, and facilitate seamless communication among all stakeholders: the homeowner, Assessor, Designer, and Installer. This role is pivotal in safeguarding quality, ensuring the project adheres to the Retrofit Plan, and ultimately delivering the intended outcomes.

The Retrofit Coordinator’s extensive responsibilities include:

  • Developing the Retrofit Plan: Creating a comprehensive plan based on the assessment and design, detailing the scope of works, timelines, roles and responsibilities, risk management strategy, and budget.
  • Risk Management: Identifying, assessing, and mitigating technical, financial, and social risks throughout the project. This includes determining the appropriate ‘risk pathway’ (A, B, or C) for the project, which dictates the level of design and quality assurance required.
  • Stakeholder Liaison: Acting as the communication hub, ensuring clear and timely information flow between the homeowner, designers, and installers, and resolving any conflicts or issues that arise.
  • Quality Assurance Oversight: Verifying that the Retrofit Assessor and Designer are competent and that their outputs (assessment report, design) are robust and compliant. They also ensure that installers are appropriately qualified (PAS 2030 certified) and adhere strictly to the design specifications.
  • Managing Variations: Approving any necessary changes to the design or plan during installation, ensuring these changes are documented and do not compromise the project’s integrity.
  • Documentation and the ‘Golden Thread’: Ensuring that all project documentation – from initial assessment reports to handover information – is meticulously recorded and maintained, forming the ‘golden thread’ of information required by the standard.
  • Client Communication: Regularly updating the homeowner on progress, addressing concerns, and ensuring their understanding of the process and the implications of the retrofit measures.

Without competent Retrofit Coordination, the holistic approach championed by PAS 2035 would be significantly undermined, increasing the likelihood of poor outcomes and project failures. The Coordinator acts as the ultimate guardian of the project’s integrity and quality.

3.4. Retrofit Installation: Precision and Competence

The installation phase is where the carefully crafted Retrofit Design is brought to life. This stage focuses on the practical application of the specified retrofit measures, adhering rigorously to the design specifications, quality standards, and industry best practices. Crucially, all installers involved in PAS 2035 compliant projects must be certified to PAS 2030 (Specification for the installation of energy efficiency measures in existing dwellings and insulation in residential park homes), or an equivalent certification scheme recognised by TrustMark. This ensures that installers possess the necessary competence, quality management systems, and consumer protection measures.

Key aspects of the installation phase include:

  • Adherence to Design: Installers must work precisely to the Retrofit Design document, ensuring that materials, techniques, and specifications match those outlined. Any proposed deviations must be approved by the Retrofit Coordinator and Retrofit Designer.
  • Quality Workmanship: The standard demands high-quality workmanship, ensuring that measures are installed correctly to achieve their intended performance and durability.
  • Site Supervision: The Retrofit Coordinator, or a competent site supervisor under their direction, may conduct site visits to monitor progress, address technical queries, and verify compliance with the design and PAS 2030 requirements. This includes taking photographic evidence of key stages of installation.
  • Commissioning: For complex systems like heat pumps or MVHR, thorough commissioning is required to ensure they are operating optimally and as per design specifications.
  • Health and Safety: All work must be conducted in strict adherence to health and safety regulations, protecting both installers and occupants.
  • Waste Management: Environmentally responsible disposal of waste materials generated during the retrofit.

Upon completion of installation, the Retrofit Coordinator obtains sign-off from the installers, confirming that all works have been completed in accordance with the design and the requirements of PAS 2030/PAS 2035.

3.5. Handover and Post-Installation Evaluation: Ensuring Long-Term Success

The final stages of a PAS 2035 project are critical for realising the long-term benefits and ensuring occupant satisfaction. After successful installation, the project transitions to the handover and post-installation evaluation phase.

  • Handover: The Retrofit Coordinator formally hands over the completed project to the occupants. This is a vital step for ensuring the homeowner understands the new measures and how to operate and maintain them correctly. The handover includes:

    • User Manuals: Comprehensive documentation for all new systems (e.g., heat pumps, MVHR), explaining their operation, maintenance schedule, and troubleshooting.
    • Performance Expectations: Explaining the anticipated energy savings and comfort improvements.
    • Maintenance Advice: Guidance on general building maintenance relevant to the new retrofit measures.
    • Warranty Information: Details of warranties for installed products and workmanship guarantees.
    • Emergency Contacts: Information for who to contact in case of issues.
      The goal is to empower occupants to effectively use and benefit from their retrofitted home, thereby reducing the likelihood of a ‘performance gap’ due to occupant behaviour.

  • Post-Installation Evaluation: This stage assesses the actual performance of the retrofit measures against the intended objectives. It typically involves:

    • Visual Inspection: An initial inspection by the Retrofit Coordinator to confirm the quality of the finished work and adherence to the design.
    • Updated EPC: A post-retrofit Energy Performance Certificate (EPC) is usually obtained to reflect the improved energy rating.
    • Performance Monitoring (for higher risk pathways): For certain projects (e.g., higher risk pathways, specific funding schemes), ongoing monitoring of energy consumption, indoor air quality, and temperature may be required over a period (e.g., 12 months). This provides invaluable data on actual performance and helps to identify any ‘performance gap’ between predicted and actual outcomes. This feedback loop is crucial for continuous improvement of retrofit practices.
    • Occupant Feedback: Gathering feedback from residents on their comfort levels, energy use, and overall satisfaction with the retrofit. This qualitative data complements quantitative performance data.

The meticulous documentation maintained throughout the project, often referred to as the ‘Retrofit Golden Thread,’ ensures full traceability and accountability from initial assessment to final evaluation. This comprehensive record is invaluable for any future works, dispute resolution, or long-term building management.

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

4. Roles and Responsibilities in PAS 2035:2023

The success of any PAS 2035 compliant retrofit project hinges on the clear definition and diligent execution of responsibilities by a team of qualified professionals. The standard mandates specific roles, each with distinct competencies and contributions, working collaboratively under the overarching guidance of the Retrofit Coordinator. These roles are critical in upholding the ‘golden thread’ of information and ensuring the holistic, risk-managed approach is consistently applied.

4.1. Retrofit Coordinator: The Project Steward

The Retrofit Coordinator (RC) is arguably the most critical role within the PAS 2035 framework, acting as the central nexus for all project activities. They are the overarching project manager, risk manager, and quality assurance guardian, responsible for ensuring that all stages of the retrofit process are conducted in strict compliance with the standard and that the entire project aligns with the Retrofit Plan. The RC’s role begins at the very outset of the project and continues through to post-installation evaluation and handover.

Core Responsibilities:

  • Developing the Retrofit Plan: Based on the Retrofit Assessment and Retrofit Design, the RC compiles a comprehensive Retrofit Plan that outlines the scope of work, timelines, budget, risk mitigation strategies, and the roles and responsibilities of all parties involved. This plan is the guiding document for the entire project.
  • Risk Management: The RC is responsible for identifying, assessing, and managing technical, financial, and social risks associated with the retrofit. This includes determining the appropriate ‘risk pathway’ (A, B, or C) for the project, which dictates the level of design detail, installer qualifications, and post-installation monitoring required. They must anticipate potential unintended consequences and ensure they are addressed in the design and installation phases.
  • Stakeholder Liaison and Communication: Serving as the primary point of contact, the RC facilitates clear and consistent communication between the homeowner, Retrofit Assessor, Retrofit Designer, and Retrofit Installer. They are responsible for conveying technical information in an understandable manner, mediating disagreements, and ensuring all parties are aligned.
  • Quality Assurance Oversight: The RC verifies the competence and suitability of the Assessor, Designer, and Installers. They review and approve all key project documents, including the assessment reports, design specifications, and installation plans, ensuring they meet the requirements of PAS 2035 and PAS 2030.
  • Monitoring and Supervision: During the installation phase, the RC monitors progress, conducts site visits (or oversees a competent site supervisor), addresses technical queries from installers, and ensures that the work is progressing according to the design and quality standards.
  • Compliance and Documentation: Maintaining the ‘Retrofit Golden Thread’ of information is a key responsibility. The RC ensures that all project documentation—from initial reports to commissioning certificates and handover packs—is meticulously recorded, stored, and readily accessible, providing a comprehensive audit trail.
  • Handover and Post-Installation: The RC oversees the formal handover to the homeowner, ensuring they receive all necessary information and training. They also coordinate any required post-installation evaluation or monitoring.

Required Competencies: A Retrofit Coordinator typically holds a Level 5 Diploma in Retrofit Coordination and Risk Management, demonstrating a deep understanding of building physics, retrofit technologies, risk assessment, project management, and the PAS 2035 standard itself. They must possess strong organisational, communication, and problem-solving skills, coupled with an impartial and objective approach.

4.2. Retrofit Assessor: The Diagnostician

The Retrofit Assessor (RA) is responsible for conducting the initial, comprehensive evaluation of the dwelling. Their role is to provide an objective and detailed diagnostic report that forms the essential foundation for the subsequent design and planning stages. The quality and accuracy of the assessment directly impact the effectiveness of the entire retrofit project.

Core Responsibilities:

  • Multi-faceted Property Evaluation: Conducting all aspects of the Retrofit Assessment as detailed in Section 3.1, including:
    • RdSAP/EPC Assessment: Calculating the dwelling’s current energy performance.
    • Occupancy Assessment: Interviewing occupants to understand their energy use and comfort needs.
    • Condition Survey: Identifying existing defects, structural issues, and potential hazards.
    • Ventilation Assessment: Evaluating current ventilation provisions and identifying indoor air quality or condensation issues.
    • Moisture Risk Assessment: Diagnosing moisture sources, pathways, and potential risks.
    • Traditional Building Assessment: For older properties, assessing unique construction characteristics and materials.
  • Data Collection and Reporting: Accurately collecting detailed data on the building’s fabric, services, and environment, and compiling a comprehensive Retrofit Assessment Report that clearly articulates findings, identified risks, and recommendations for further investigation.
  • Impartiality: Operating with strict impartiality, providing factual information and avoiding any undue influence on the design or installation choices.

Required Competencies: A Retrofit Assessor typically holds a recognised qualification such as the Level 3 Award in Domestic Energy Assessment (for RdSAP), and a specific Retrofit Assessor qualification (e.g., Level 3 Diploma in Retrofit Assessment) which includes specific training in condition reporting, ventilation, moisture risk, and traditional building assessment. They must possess a keen eye for detail, strong analytical skills, and a thorough understanding of building pathology and physics.

4.3. Retrofit Designer: The Solution Architect

The Retrofit Designer (RD) is responsible for translating the findings of the Retrofit Assessment into a detailed, technical design that specifies the appropriate energy efficiency measures. Their expertise lies in building physics, construction methods, and the integration of various technologies to create a holistic, high-performing solution that addresses the identified needs and risks.

Core Responsibilities:

  • Developing the Retrofit Design: Creating a comprehensive design document that specifies all proposed retrofit measures, their technical specifications, materials, and installation methods. This includes detailed drawings, U-value calculations, condensation risk analysis, and a robust ventilation strategy.
  • Integrating Measures: Ensuring that all individual measures are compatible with each other and with the existing building fabric, avoiding unintended consequences such as thermal bridging, condensation, or overheating.
  • Risk Mitigation in Design: Incorporating design solutions that actively mitigate the risks identified in the Retrofit Assessment and the Retrofit Plan. This involves selecting appropriate materials and systems for the specific building type and context, especially for traditional and heritage buildings.
  • Performance Prediction: Using appropriate modelling tools to predict the energy performance improvements and carbon savings resulting from the proposed design.
  • Collaboration with RC: Working closely with the Retrofit Coordinator to ensure the design aligns with the Retrofit Plan, addresses all identified risks, and is feasible for installation.
  • Compliance with Regulations: Ensuring the design adheres to all relevant building regulations, planning consents (where applicable), and the specific requirements of PAS 2035.

Required Competencies: A Retrofit Designer often comes from an architectural, building services engineering, or surveying background, augmented with specialist retrofit design qualifications (e.g., Level 5 Diploma in Retrofit Design). They must have advanced knowledge of building physics, thermal modelling, ventilation design, and a deep understanding of various retrofit technologies and their interfaces. Their creativity is balanced with technical precision and an acute awareness of practical buildability.

Other Key Roles (Implicit or Explicit in PAS 2035):

  • Retrofit Installer: While not a ‘PAS 2035 role’ in the same vein as the above, the installer is critical. They must be certified to PAS 2030 (or equivalent TrustMark scheme) and possess the specific competence to install the proposed measures according to the Retrofit Design. They are responsible for quality workmanship on site and adhering to health and safety protocols.
  • The Client/Homeowner: An often-overlooked but vital stakeholder. Active engagement from the homeowner in providing accurate information during assessment, understanding the Retrofit Plan, making informed decisions, and providing feedback throughout the process is essential for achieving successful outcomes and occupant satisfaction.

The robust delineation of these roles and their interdependencies underpins the integrity and effectiveness of the PAS 2035 framework, fostering accountability and promoting a systematic approach to quality assurance in domestic retrofit.

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

5. Compliance Requirements and Quality Assurance

Adherence to PAS 2035:2023 is not merely a formality; it is a fundamental prerequisite for ensuring the quality, effectiveness, and safety of domestic retrofit projects. The standard establishes a stringent framework of compliance requirements and quality assurance mechanisms designed to mitigate risks, prevent failures, and deliver measurable improvements in energy performance and occupant comfort. These mechanisms are crucial for rebuilding consumer confidence in the retrofit sector.

5.1. The ‘Retrofit Golden Thread’ of Documentation and Record-Keeping

A cornerstone of PAS 2035 is the concept of the ‘Retrofit Golden Thread’ – a comprehensive, continuous, and auditable record of information that documents every stage of the retrofit process. This thread ensures transparency, accountability, and traceability, making it possible to review decisions, track progress, and learn from outcomes. The Retrofit Coordinator is primarily responsible for maintaining this detailed information trail.

Key Documentation Requirements:

  • Retrofit Advice Report: Issued at the project’s outset, outlining initial recommendations and the benefits of a holistic retrofit.
  • Retrofit Assessment Reports: All detailed reports from the Retrofit Assessor (RdSAP, Occupancy, Condition, Ventilation, Moisture, Traditional Building Assessment).
  • Retrofit Design Document: The comprehensive technical specifications, drawings, calculations (U-values, condensation risk), and ventilation strategy from the Retrofit Designer.
  • Retrofit Plan: The overarching project management document created by the Retrofit Coordinator, detailing scope, risks, timelines, and responsibilities.
  • Installer Certification: Evidence of PAS 2030 or equivalent certification for all installing contractors.
  • Installation Records: Photographic evidence of key installation stages, details of materials used, and sign-off sheets from installers.
  • Commissioning Reports: For complex systems (e.g., heat pumps, MVHR), documentation confirming correct installation and operation.
  • Handover Pack: All user manuals, maintenance guides, warranties, and emergency contact information provided to the homeowner.
  • Post-Installation Evaluation Report: Results of visual inspections, updated EPCs, and any performance monitoring data.
  • Compliance Declarations: Statements from the Retrofit Coordinator at various project milestones confirming compliance with PAS 2035.

This meticulous record-keeping is vital for demonstrating compliance, addressing any disputes, providing valuable data for future projects, and ensuring the long-term performance and maintainability of the retrofitted dwelling. It ensures that critical information is not lost as a project progresses through different hands.

5.2. Independent Verification, Certification, and Accreditation

To ensure robustness and credibility, PAS 2035 relies heavily on independent verification and a system of certification and accreditation. This system provides an external layer of scrutiny and assurance regarding the competence of professionals and the quality of work.

  • TrustMark: For projects accessing government funding, compliance with PAS 2035 and PAS 2030 is typically mandated through TrustMark, the only government-endorsed quality scheme for domestic retrofits. TrustMark operates a framework of approved Scheme Providers who license and audit individual businesses and professionals. This provides a robust consumer protection mechanism, including a complaints handling process and access to redress.
  • PAS 2030 Certification: All companies undertaking the installation of energy efficiency measures under a PAS 2035 project must be certified to PAS 2030. This standard sets out rigorous requirements for the installation process, including quality management systems, operative competence, equipment, and customer care. PAS 2030 certification is awarded by independent certification bodies accredited by the United Kingdom Accreditation Service (UKAS).
  • Individual Competency Certification: Retrofit Coordinators, Assessors, and Designers must hold recognised, accredited qualifications for their respective roles. These qualifications are typically awarded by bodies approved by Ofqual and demonstrate that individuals have met specific competency standards.
  • Surveillance and Auditing: Scheme Providers and certification bodies conduct regular surveillance audits of businesses and individuals operating under PAS 2030 and PAS 2035. This includes reviewing project documentation, conducting on-site inspections, and assessing the ongoing competence of professionals. This continuous oversight helps to maintain high standards and identify any deviations from the specified requirements.

This multi-layered approach to independent verification and accreditation instils confidence among homeowners and funding bodies that retrofit projects are being delivered to a consistently high standard.

5.3. Risk Management: Pathways and Mitigation Strategies

At the heart of PAS 2035 is a robust, proactive approach to risk management, designed to minimise the likelihood of unintended consequences. The standard classifies projects into three ‘risk pathways’ (A, B, and C), determined by the Retrofit Coordinator, based on the complexity of the dwelling, the extent of the proposed works, and the potential impact of failure.

  • Risk Pathway A (Lowest Risk): Generally applies to simpler measures on straightforward properties (e.g., loft insulation in a modern home). Requires a basic level of assessment, design, and coordination.
  • Risk Pathway B (Medium Risk): Encompasses more complex measures or properties, such as internal wall insulation, floor insulation, or major heating system upgrades. Requires more detailed assessment, design (including condensation risk analysis), and more intensive coordination and oversight.
  • Risk Pathway C (Highest Risk): Reserved for the most complex projects, including external wall insulation (EWI) on solid wall properties, comprehensive whole-house retrofits, or interventions in traditional/heritage buildings. This pathway mandates the most rigorous assessment, bespoke design (often involving building services engineers), advanced condensation and overheating risk analysis, and continuous, intensive Retrofit Coordinator involvement, potentially including post-installation performance monitoring.

The Retrofit Coordinator’s role is crucial in identifying potential risks (technical, social, financial, health & safety) and ensuring that appropriate mitigation strategies are integrated into the Retrofit Plan and Design. This proactive approach aims to ‘design out’ problems before they arise, preventing issues like mould, damp, structural damage, or inadequate ventilation that have historically plagued retrofit projects.

5.4. Continuous Professional Development and Competence

The building and energy efficiency sectors are constantly evolving, with new technologies, materials, and best practices emerging regularly. PAS 2035 mandates that all professionals involved in retrofit projects – Coordinators, Assessors, Designers, and Installers – engage in continuous professional development (CPD). This commitment to lifelong learning ensures that practitioners remain abreast of the latest standards, scientific understanding, and technological innovations. Regular refresher training, attendance at industry seminars, and staying informed about updates to the standard are essential for maintaining competence and delivering high-quality, compliant projects. This ongoing investment in skills is vital for building a highly capable and reputable retrofit workforce capable of tackling the UK’s decarbonisation challenge.

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

6. Practical Guidance for Homeowners

For homeowners embarking on a retrofit journey, understanding PAS 2035:2023 is not merely academic; it is a vital step towards ensuring the success, quality, and long-term benefits of their home improvement project. Engaging with the process knowledgeably can protect their investment and maximise the positive outcomes.

6.1. Selecting Qualified Professionals and Leveraging TrustMark

The single most important decision a homeowner will make is the selection of their retrofit team. PAS 2035 explicitly demands a high level of competence and professional conduct, and homeowners should prioritise engagement with qualified and accredited entities.

  • Verify TrustMark Registration: Always ensure that any company or individual you engage for assessment, design, or installation is registered with TrustMark, the government-endorsed quality scheme. TrustMark registration signifies that the business has been vetted against strict quality, financial, and customer service criteria. It also provides consumers with a robust complaints handling and dispute resolution process, offering an invaluable layer of protection (trustmark.org.uk).
  • Check Individual Qualifications: Go beyond company registration and verify the specific qualifications of the Retrofit Coordinator, Assessor, and Designer. Request to see their Level 5 Diploma (for RC and RD) or Level 3 Diploma (for RA) certificates, and check their accreditation with relevant industry bodies.
  • Understand Roles: Familiarise yourself with the distinct roles (Retrofit Coordinator, Assessor, Designer, Installer) and their responsibilities as outlined in Section 4. This understanding will help you communicate effectively and know who to contact at each stage of the project.
  • Seek Referrals: Ask for references from previous clients and, if possible, visit completed projects to assess the quality of work and client satisfaction.

Engaging a TrustMark-registered Retrofit Coordinator first is often the best starting point, as they will then guide you through the process of selecting other qualified professionals required for your project.

6.2. Understanding the Investment, Benefits, and Funding Options

Retrofit projects, particularly those adhering to PAS 2035, represent a significant investment, but they also yield substantial long-term benefits that extend far beyond simple energy cost savings.

  • Long-Term Financial Savings: While initial costs can be considerable, quality retrofits lead to significant reductions in energy consumption, translating into lower utility bills over the lifetime of the property. The ‘performance gap’ (where predicted savings are not realised) is actively mitigated by PAS 2035’s rigorous approach.
  • Enhanced Comfort and Health: A well-insulated, airtight, and properly ventilated home is warmer in winter, cooler in summer, and free from issues like draughts, damp, and mould. This directly improves occupant comfort, reduces the incidence of respiratory illnesses, and creates a healthier living environment.
  • Reduced Carbon Footprint: Contributing to climate change mitigation by significantly reducing the dwelling’s operational carbon emissions, aligning with personal and national environmental goals.
  • Increased Property Value: Energy-efficient homes are increasingly attractive to buyers, often commanding higher market values and future-proofing the property against potential regulatory changes or fluctuating energy prices.
  • Resilience: Improving the building’s resilience to future climate changes, such as extreme heatwaves or colder winters.
  • Funding and Grants: Research available government grants and local authority schemes (e.g., ECO4, Social Housing Decarbonisation Fund, local council initiatives). Your Retrofit Coordinator can often advise on eligibility and application processes for these schemes, many of which mandate PAS 2035 compliance.

Approach a retrofit as a long-term investment in your home’s future, considering both the financial returns and the intangible benefits to comfort, health, and environmental responsibility.

6.3. Active Participation and Communication Throughout the Process

While professionals manage the technical aspects, the homeowner’s active involvement and clear communication are crucial for a successful outcome.

  • Provide Accurate Information: During the Retrofit Assessment, provide your Assessor with as much detail as possible about your home’s history, any previous works, current energy usage, and your family’s lifestyle and comfort preferences. Your input is vital for an accurate assessment and a tailored design.
  • Understand the Retrofit Plan: Review the Retrofit Plan prepared by the Retrofit Coordinator carefully. Ask questions until you fully understand the proposed measures, the anticipated costs, the timeline, and the expected outcomes. Ensure your priorities are reflected in the plan.
  • Maintain Open Communication: Establish a clear line of communication with your Retrofit Coordinator. Report any concerns, questions, or observations promptly throughout the assessment, design, and installation phases. Do not hesitate to seek clarification on technical aspects or changes.
  • Site Access and Cooperation: Provide necessary access to your home for assessments, installations, and inspections. Cooperation with the team will help ensure the project progresses smoothly and on schedule.
  • Understand Handover Information: Pay close attention during the handover session. Ask questions about how to operate and maintain new systems, such as heat pumps or MVHR units. Proper use and maintenance are critical for achieving the intended performance and longevity of the retrofit measures.
  • Provide Feedback: Be prepared to offer feedback during and after the project. Your experience can provide valuable insights for continuous improvement of retrofit practices.

By engaging actively and maintaining open dialogue, homeowners become integral partners in the retrofit process, helping to ensure that the project not only complies with PAS 2035 but also perfectly meets their specific needs and aspirations for a warmer, healthier, and more energy-efficient home.

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

7. Challenges and Future Considerations

While PAS 2035:2023 provides a robust and essential framework for high-quality retrofit, its widespread implementation and the broader ambition of decarbonising the UK’s housing stock face several significant challenges and require ongoing strategic considerations.

7.1. Skills Gap and Workforce Development

Perhaps the most pressing challenge is the substantial skills gap across the entire retrofit supply chain. The sheer scale of the UK’s retrofit challenge – millions of homes requiring significant energy efficiency upgrades by 2050 – demands a massive expansion of a skilled workforce. There is a critical shortage of:

  • Qualified Retrofit Coordinators: The central role requires extensive training and experience, and the current number falls far short of demand.
  • Competent Retrofit Assessors and Designers: Professionals with deep understanding of building physics, moisture management, and traditional construction are scarce.
  • PAS 2030 Certified Installers: A significant number of tradespeople (insulators, plumbers, electricians, builders) need to be upskilled and certified to the PAS 2030 standard to ensure quality installation of new technologies and materials.

Addressing this requires a concerted national effort, including government funding for training programmes, vocational colleges offering specialised retrofit courses, apprenticeships, and industry initiatives to attract and retain talent. Without a substantial increase in skilled professionals, the pace and quality of retrofit deployment will be severely constrained.

7.2. Public Awareness and Uptake

Despite the clear benefits, public awareness of the importance of high-quality retrofit and the advantages of a PAS 2035 compliant approach remains relatively low. Many homeowners are still focused on single measures (e.g., ‘just a new boiler’) rather than a holistic, whole-house strategy. Challenges include:

  • Complexity and Cost Perception: The comprehensive nature of PAS 2035 can appear complex and costly to homeowners, particularly compared to historical, piecemeal approaches.
  • Trust and Misinformation: Past failures have eroded consumer trust, and there is a need to clearly differentiate PAS 2035 projects from previous ‘cowboy’ installations.
  • Information Overload: Homeowners face a deluge of information and choices, making it difficult to discern reliable advice and quality providers.

Effective public engagement campaigns, clear communication of the long-term benefits (comfort, health, property value, energy bill savings), and simplified access to accredited professionals are crucial to driving demand and encouraging widespread uptake of quality retrofits.

7.3. Integration with Policy and Funding Mechanisms

The efficacy of PAS 2035 is intrinsically linked to government policy and funding mechanisms. Many large-scale retrofit programmes, such as the Energy Company Obligation (ECO) and the Social Housing Decarbonisation Fund (SHDF), mandate PAS 2035 compliance, thereby driving its adoption. However, continued challenges include:

  • Long-Term Policy Certainty: The retrofit sector requires long-term, consistent policy signals and funding commitments to allow businesses to invest in skills, equipment, and innovation.
  • Funding Accessibility: Ensuring that funding schemes are accessible and attractive to a wide range of homeowners, including those in different income brackets and with diverse property types.
  • Alignment with Planning Regulations: Harmonising PAS 2035 requirements with local planning regulations, especially for traditional and heritage buildings, to streamline the process.
  • Performance-Based Funding: Moving towards funding mechanisms that reward actual energy performance improvements, rather than just installation of measures, could further incentivise quality and adherence to PAS 2035’s outcomes-focused approach.

7.4. Cost Implications vs. Long-Term Value

Implementing the rigorous requirements of PAS 2035, including comprehensive assessments, detailed design, and qualified coordination, inevitably adds to the upfront cost of a retrofit project compared to less regulated approaches. This can be a barrier for some homeowners and housing providers.

  • Perceived vs. Actual Cost: While the initial outlay may be higher, the ‘value’ delivered by a PAS 2035 project is significantly greater due to reduced risks, guaranteed quality, and maximised long-term performance. The cost of rectifying a failed retrofit far outweighs the cost of doing it right the first time.
  • Financing Solutions: The development of innovative financing solutions (e.g., green mortgages, loan schemes linked to energy performance) is crucial to make comprehensive retrofits more affordable and accessible, allowing homeowners to spread the cost over time and benefit from lower energy bills.

Advocating for the long-term economic and social benefits of a quality-assured approach is vital to overcome the focus on short-term costs.

7.5. Addressing Traditional and Hard-to-Treat Homes

The UK’s housing stock includes a vast number of traditional, pre-1919 solid wall buildings and other ‘hard-to-treat’ properties (e.g., high-rise flats, non-standard construction). These properties present unique technical challenges for retrofit:

  • Building Physics Complexity: Traditional buildings require a nuanced understanding of their breathable fabric, moisture dynamics, and heritage value. Inappropriate modern materials can cause irreparable damage.
  • Technical Solutions: Hard-to-treat homes often require bespoke, intricate solutions that are more complex and costly than standard interventions.
  • Risk Pathway C: Many interventions in these properties will fall under Risk Pathway C, mandating the highest level of assessment, design, and coordination.

PAS 2035 provides a robust framework to address these complexities by requiring specialist assessment and design expertise for such buildings. However, ensuring a sufficient pool of professionals with this specialised knowledge and experience remains a critical ongoing consideration.

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

8. Conclusion

PAS 2035:2023 represents a profound and necessary advancement in the standardisation and quality assurance of domestic retrofit practices within the United Kingdom. Born from the critical insights of the ‘Each Home Counts’ review, the standard systematically addresses historical failures and lays a robust foundation for a future where energy efficiency improvements are delivered with integrity, efficacy, and occupant well-being at their core. By mandating a holistic, risk-managed approach from the initial, multi-faceted assessment through sophisticated design, meticulous installation, and comprehensive handover, PAS 2035:2023 ensures that dwellings are treated as complex, interconnected systems, thereby mitigating unintended consequences and optimising long-term performance.

The clearly delineated roles of the Retrofit Coordinator, Assessor, and Designer are pivotal to this framework, each professional contributing their specialised expertise under the overarching guidance of the Coordinator to maintain the critical ‘Retrofit Golden Thread’ of information. This rigorous documentation, coupled with independent verification through schemes like TrustMark and PAS 2030, establishes a powerful multi-layered quality assurance system. For homeowners, engaging with this standard means investing in a demonstrably higher quality outcome: a home that is not only more energy-efficient but also healthier, more comfortable, and resilient, while simultaneously contributing to national carbon reduction targets.

However, the ambitious goals enshrined within PAS 2035 are not without significant challenges. The urgent need for a massive upskilling and expansion of the retrofit workforce, increasing public awareness and confidence, securing long-term policy and funding certainty, and innovating finance mechanisms remain critical areas for focused effort. Addressing the unique complexities of traditional and hard-to-treat homes further underscores the ongoing demand for specialist expertise and adaptive solutions.

In summation, PAS 2035:2023 is more than a technical specification; it is a strategic blueprint for transforming the UK’s existing housing stock into a more sustainable and high-performing asset. Its successful and widespread implementation hinges on sustained collaboration between government, industry, academia, and homeowners, underpinned by continuous education, innovation, and an unwavering commitment to quality. By embracing the principles and requirements of PAS 2035:2023, professionals and stakeholders are not merely complying with a standard; they are actively shaping comfortable, sustainable, and energy-efficient living environments that are indispensable to achieving national net-zero ambitions and enhancing the quality of life for millions.

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

References

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