The built environment is undergoing a significant transformation as global commitments to energy efficiency and carbon reduction accelerate. In the United Kingdom, one of the most important drivers behind this transformation is the PAS 2035 framework, which outlines a whole-house approach to energy retrofit. Last revised in 2019, the specification has seen continuous updates—most recently in 2023, (effective from the 1^st of April 2025), to ensure it remains fit for purpose and reflective of best practices.

As the government, local authorities, and industry professionals work diligently to improve housing stock and reduce energy consumption, staying on top of these changes has become more crucial than ever.

This blog post aims to guide you through the latest developments in PAS 2035:2023 and the corresponding Retrofit Design Guidance, providing you with clear strategies to remain compliant and proactive. Whether you’re a retrofit coordinator, designer, contractor, or housing provider, understanding these updates will help you not only mitigate risks but also seize opportunities for innovation and competitive advantage.

In the sections below, we will delve into the most notable changes to the standard, discuss the motivations behind them, and outline actionable steps you can take to keep ahead of the curve. We’ll also touch upon the broader context in which these updates have been introduced—exploring how they align with national objectives, consumer expectations, and the evolving landscape of green financing.

By the end, you’ll have a solid understanding of how PAS 2035:2023 and the accompanying Retrofit Design Guidance can be leveraged to deliver high-quality, future-proof retrofit projects that meet both regulatory requirements and the demands of a changing marketplace.

1. Understanding the Purpose of PAS 2035

Before diving into the 2023 updates, it’s essential to have a clear grasp of why PAS 2035 matters. PAS 2035 is a comprehensive framework that sets out the requirements for a holistic, “whole-house” approach to energy retrofit. It was originally developed to address shortcomings in piecemeal retrofits, where disconnected measures often led to suboptimal outcomes or, worse, unintended consequences such as damp, mould, and ventilation problems. By insisting on a methodical and data-driven process, PAS 2035 ensures that every aspect of a building’s energy performance is taken into account.

A central goal of PAS 2035 is to increase confidence and consistency in retrofit projects across the UK. It does this by defining key roles—such as the Retrofit Assessor, Retrofit Coordinator, Retrofit Designer, and Retrofit Installer—and outlining their responsibilities. This role-based approach encourages accountability, reducing the risks that come from unclear project ownership or inadequate skill sets. The framework also mandates that retrofit solutions are tailored to the specific characteristics of each dwelling, underlining the importance of robust diagnostic assessments and customized design solutions.

PAS 2035 is backed by government and industry stakeholders alike because it addresses multiple national priorities. These include cutting carbon emissions in line with legally binding targets, alleviating fuel poverty, and improving overall building quality. For homeowners and tenants, the specification assures a consistent standard of work, reducing the risk of poor installations and fostering trust in the retrofit process. In the broader context, the rigour and clarity of PAS 2035 also help unlock finance streams—from green bonds to local authority funding—by providing a reliable framework that ensures value for investment.

With PAS 2035:2023 now in effect, staying aligned with the latest requirements can significantly bolster your credibility and project outcomes. In the next sections, we’ll break down the most significant changes introduced in this new version, and examine how they integrate with wider retrofit design principles.

2. Key Changes in PAS 2035:2023

The 2023 iteration of PAS 2035 has introduced a variety of refinements and clarifications, largely shaped by lessons learned since the specification’s initial launch and by evolving policy imperatives. Understanding these key changes is the first step to positioning your work processes for success and compliance.

2.1 Clarifications on Risk Paths

One of the most frequently cited aspects of PAS 2035 is its categorization of dwellings into Risk Paths (Path A, B, or C), which determine the level of scrutiny and oversight required. In PAS 2035:2023, the criteria for deciding a property’s risk path have been updated to reflect a more nuanced understanding of building complexities. Projects involving older properties, those situated in conservation areas, or those with unusual construction types may now fall under a higher risk path by default, ensuring that they receive a level of attention proportionate to the risks.

This shift aims to prevent underestimating the technical challenges associated with certain building types. For retrofit coordinators, this means earlier engagement with specialists such as heritage officers or structural engineers may be necessary to fully comply with the updated protocol.

2.2 Enhanced Detail in the Retrofit Assessment

Assessment has always been a cornerstone of PAS 2035, but the new version elevates the level of detail required. PAS 2035:2023 places greater emphasis on in-depth building condition reports, airtightness testing, and occupant behaviour assessments. The objective is to reduce the possibility of post-installation issues—such as ventilation imbalances or moisture accumulation—by ensuring that these factors are thoroughly evaluated at the outset.

In tandem, the specification stresses the importance of robust documentation. This includes clear photographic evidence, detailed measurements, and records of discussions with homeowners and tenants. By providing unambiguous data, retrofit coordinators and designers can craft more accurate retrofit plans, ultimately improving the long-term performance of installed measures.

2.3 New Guidance on Retrofit Coordination and Designer Qualifications

Given the central role of the Retrofit Coordinator, PAS 2035:2023 further refines expectations around their involvement. Coordinators are now advised to take on a more proactive project management function—monitoring progress not just during installation, but also post-completion. This includes validating the energy savings achieved, assessing occupant feedback, and ensuring that any follow-up issues are resolved promptly.

Historically, Retrofit Coordinators could also take on the role of Retrofit Designer. However, in line with the changes to the standard, effective from 1 April 2025, outlined in PAS2035:2023 Retrofit Design Guidance – Rev 00, the Retrofit Designer must now hold specific qualifications. The standard now stipulates that the Retrofit Designer must be one of the following:

• A chartered architectural technologist (MCIAT or FCIAT) registered by the Chartered Institute of Architectural Technologists (CIAT);
• An architect registered by the Architects Registration Board (ARB);
• A professional member of the Chartered Institute of Building (MCIOB or FCIOB); or
• A chartered building surveyor (MRICS or FRICS).

This marks a significant change in the delineation of roles, ensuring that the design aspect of retrofit work is carried out by professionals with advanced, recognised qualifications. By requiring specialist credentials, the updated standard aims to enhance design quality, reduce errors, and bring more robust professional accountability into retrofit projects.

2.4 Material and Design Innovations

Another key change is the recognition of evolving materials and technologies within the retrofit space. As new insulation materials, ventilation systems, and smart energy solutions enter the market, PAS 2035:2023 acknowledges the need for up-to-date design guidance. While the specification itself does not prescribe specific products, it does mandate thorough testing, certifications, and compatibility assessments for any chosen materials and technologies.

For example, the standard increasingly highlights the importance of hybrid solutions that blend fabric measures (like insulation and airtightness) with mechanical systems (like heat pumps and mechanical ventilation). The updated guidance encourages a balanced approach that avoids oversizing or undersizing systems and ensures that new technologies can integrate seamlessly with existing building components.

2.5 Emphasis on Whole Life Performance

Although whole-house thinking has always been the ethos of PAS 2035, the 2023 version places more explicit emphasis on whole life performance. This means looking beyond immediate energy savings to consider the embodied carbon of materials, the maintenance requirements, and the overall lifecycle costs of retrofit measures. If you’re involved in funding or large-scale retrofit programmes, this expanded focus can be especially relevant, as many investment decisions are now being made with an eye towards long-term sustainability and carbon accounting.

2.6 Occupant Engagement and Education

Finally, occupant engagement has been elevated to a core principle in PAS 2035:2023. The standard insists on better communication with residents—through user-friendly documentation, demonstration of new technologies, and ongoing support. Since occupant behaviour greatly influences a dwelling’s energy performance, an informed and engaged resident is more likely to realize the full benefits of retrofitted measures. Furthermore, higher occupant satisfaction can reduce complaints and call-backs, making for a more efficient project lifecycle overall.

3. Strategies for Staying Ahead of PAS 2035:2023 Changes

With the key changes mapped out, how can industry professionals ensure they aren’t just playing catch-up, but instead using PAS 2035:2023 as a springboard for ongoing excellence? Below are several strategies to help you stay ahead.

3.1 Continuous Professional Development

CPD (Continuous Professional Development) is indispensable for anyone playing a leadership role in retrofit. Whether you’re a coordinator, designer, or installer, keep updating your skill set through accredited training schemes that focus on PAS 2035, building physics, and new technologies. Industry bodies and professional associations often run relevant workshops and seminars that delve into the practical aspects of the standard. By actively participating in these, you’ll not only stay abreast of technical developments but also network with peers who may share valuable insights.

3.2 Leverage Digital Tools

The increased requirements for documentation and data in PAS 2035:2023 can be made more manageable through digital solutions. Using a Building Information Modeling (BIM) platform, for instance, can streamline the collection, storage, and analysis of data throughout the retrofit lifecycle. Likewise, cloud-based project management tools and mobile inspection apps can simplify on-site data capture, ensuring that your records are both comprehensive and easily accessible when needed for audits or compliance checks.

3.3 Engage Specialists Early

With risk path determinations becoming more stringent and potential heritage or structural issues taking centre stage, involving specialists at the outset is now crucial. Heritage consultants, structural engineers, and damp specialists can offer guidance that shapes the retrofit design process in fundamental ways. By front-loading these assessments, you can avoid costly redesigns and installation delays later in the project. Early engagement also provides more accurate cost estimates, reducing the likelihood of budget overruns.

3.4 Form Strong Supply Chain Partnerships

Staying ahead in the world of PAS 2035 is not solely about technical expertise—it’s also about having reliable partners who share your commitment to quality. Seek out suppliers with proven track records in delivering materials or systems that meet the enhanced requirements. Select installation teams who are well-versed in the standard’s mandates, and maintain open channels of communication with them. By cultivating a robust network, you can streamline procurement, reduce miscommunication, and improve overall project execution.

3.5 Plan for Post-Occupancy Evaluation

Given the emphasis on post-completion monitoring, consider integrating post-occupancy evaluation (POE) into your project plan from the start. POE involves gathering feedback on both energy performance data (e.g., actual vs. predicted energy use) and occupant comfort (e.g., indoor temperatures, perceived air quality). This feedback loop will not only help you verify compliance with PAS 2035:2023 but also glean valuable lessons that can be applied to future projects. In many cases, POE data can be a selling point for future clients, demonstrating your commitment to transparency and real-world outcomes.

4. Embracing Retrofit Design Guidance

Alongside the updates to PAS 2035, there’s an emerging body of Retrofit Design Guidance that complements and extends the specification’s principles. This guidance is often produced by professional bodies or research institutions and offers deeper dives into areas such as thermal bridging, moisture risk, ventilation strategies, and occupant health.

4.1 The Rationale Behind Retrofit Design Guidance

Retrofit projects can be especially challenging because they deal with existing structures that often come with unique defects or limitations. New-build guidelines don’t always directly translate to retrofit scenarios, where the fabric of a building can be decades—or even centuries—old. Retrofit Design Guidance bridges this gap by offering specialized advice on diagnosing issues, specifying appropriate materials, and sequencing works effectively. This is especially critical in older and historic properties, where traditional construction methods may require more sympathetic approaches.

4.2 Core Elements of Effective Retrofit Design

Effective Retrofit Design Guidance usually emphasizes the following:

1. Holistic Assessment: Recognizing that any intervention can have cascading effects on other parts of the building—such as how improving airtightness might necessitate additional ventilation measures.

2. Material Compatibility: Choosing materials and systems that work harmoniously with existing construction, reducing the risk of trapped moisture or unexpected thermal bridging.

3. Risk Modelling: Employing tools like the Warm: Low Energy Building Practice or BS 5250 for moisture risk analysis can help avert issues like condensation and mould growth.

4. Performance Validation: Incorporating methods like Thermographic Imaging or Heat Flux Measurements to confirm the efficacy of installed measures.

5. Occupant-Centric Design: Ensuring that design solutions consider the occupant’s lifestyle, health needs, and comfort preferences.

4.3 Aligning Retrofit Design Guidance with PAS 2035:2023

While Retrofit Design Guidance stands as a body of knowledge in its own right, it should be viewed as an extension of PAS 2035 rather than a replacement. In fact, PAS 2035:2023 actively encourages designers to consult such guidance as part of the risk assessment and solutions design stages. For example, if the standard mandates more rigorous moisture assessments, the guidance might provide practical instructions and calculation models to fulfil that requirement. Thus, a synergy between PAS 2035 and design best practices can lead to higher-quality outcomes.

4.4 The Importance of Documentation

In embracing Retrofit Design Guidance, you’ll also find a strong emphasis on thorough documentation—an area where PAS 2035:2023 has introduced more stringent requirements. Documentation goes beyond ticking a compliance box; it’s a valuable resource for your team, clients, and future stakeholders. Comprehensive design reports, installation manuals, and post-works evaluation data help maintain the integrity of a project over its lifespan, particularly when new owners or tenants take over.

5. Practical Steps to Implement Changes

Understanding the “why” and “what” of PAS 2035:2023 and Retrofit Design Guidance is only half the journey. Below are concrete steps you can take to integrate these changes into your daily operations.

5.1 Conduct a Gap Analysis

Start by conducting a gap analysis against your current processes and the new PAS 2035 requirements. Identify areas where you might be falling short, such as documentation standards, risk assessment protocols, or occupant engagement strategies. By pinpointing these gaps, you can develop a targeted plan to address them—whether through training, additional hires, or technology investments.

If you find that your Retrofit Coordinator is not able to act as your Retrofit Designer, you can connect with companies such as Assured Safety to undertake Retrofit Design-Only Services on your behalf.

5.2 Update Your Internal Procedures

With the gap analysis complete, the next step is to revise your internal procedures. This could mean updating template documents, reformatting your project checklist to include new data fields, or reworking your standard operating procedures to reflect revised risk path criteria. Ensure that everyone in your organisation—from project managers to site supervisors—knows these changes and understands why they are necessary. Clear internal communication is crucial for consistency and compliance.

5.3 Pilot a Test Project

If possible, select a low-risk or smaller-scale property to pilot the updated processes. This approach lets you test-run the revised protocols under real-world conditions without the risk of compromising a major project. Gather feedback from the entire team and from occupants or clients, if applicable. Use lessons learned to refine your processes before rolling them out at scale.

5.4 Create Robust Feedback Loops

The updated PAS 2035 emphasizes continuous learning, so embed feedback loops into your workflow. This could be monthly check-ins with on-site teams, digital dashboards that track compliance metrics, or post-completion surveys for occupants. The aim is to identify issues early, rectify them promptly, and capture insights that can inform best practices for future projects.

5.5 Document Everything

Finally, make documentation a priority at every step. From retrofit assessments and design specifications to installation records and post-occupancy evaluations, your goal should be to maintain an accessible, detailed, and transparent project record. Not only will this help you demonstrate compliance if audited, but it also arms you with data to refine your own processes and advocate for your successes in grant or funding applications.

6. Future Outlook: Evolving Standards and Technologies
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While PAS 2035:2023 marks a significant leap forward, the standard is not static. As the industry gains experience with the new requirements, further updates are inevitable—particularly as new technologies, materials, and policy goals come to the fore. For instance, the UK government’s ongoing drive towards net zero by 2050 could catalyse even more stringent regulations around embodied carbon, onsite renewable generation, and occupant health metrics.

Staying ahead therefore requires not just compliance with the current iteration but an adaptive mindset that anticipates future trends. Keep a lookout for developments such as:

* Integration of Smart Technologies: As IoT (Internet of Things) devices become more sophisticated, they may be used to collect real-time performance data and automate building controls, thereby enhancing occupant comfort and energy efficiency.

* Expanded Energy Tariffs: Time-of-use tariffs and dynamic pricing structures could affect the cost-effectiveness of certain retrofit measures, emphasising the importance of flexible, future-proof solutions.

* Urban-Scale Retrofit Programs: Larger local authorities and housing associations may roll out portfolio-wide retrofit schemes, potentially leading to more standardized approaches and partnerships.

* International Standards Alignment: With growing international cooperation on climate goals, elements of European or global standards (e.g., ISO frameworks) might inform future revisions of PAS 2035.

By keeping an ear to the ground and engaging in dialogues with standards bodies, industry groups, and academic researchers, you’ll be well-equipped to navigate these evolutions.

7. Summary

PAS 2035:2023 and the associated Retrofit Design Guidance represent both a challenge and an opportunity for professionals in the retrofit sector. On one hand, the revised standards introduce more stringent requirements, demanding greater attention to detail, robust documentation, and proactive risk management. On the other, they also pave the way for higher-quality, more sustainable retrofit projects that can significantly enhance a building’s energy performance and occupant wellbeing.

Staying ahead of these changes requires a multifaceted approach. It starts with a deep understanding of the updates, how they shape roles, responsibilities, and technical processes and extends to practical strategies such as continuous training, the integration of digital tools, and early specialist involvement.

Just as importantly, aligning with current Retrofit Design Guidance helps ensure that your approach is grounded in best practices, from material selection to occupant engagement.

In a rapidly evolving sector, adhering to, and ideally exceeding PAS 2035:2023 can set you apart as a trusted, forward-thinking professional or organisation. With mounting pressure to decarbonise the built environment, clients and authorities will increasingly look for teams that can demonstrate both compliance and innovation. By committing to ongoing learning, robust processes, and proactive planning, you’ll not only meet the current standard but help shape the future of sustainable housing in the UK and beyond.

At Assured Safety, we specialise in Retrofit Design Services, with a focus on risk management and mitigation. Whether you’re a Retrofit Coordinator or Installer managing a small residential project or working on a large commercial development, our team of experts can help you develop a Retrofit Design that keeps your project compliant.

Contact Us today to see how we can assist with your upcoming Retrofit Projects and ensure ongoing quality and compliance with delivery.