Improving home energy efficiency - retrofit assessment review: policy report

Objective 1: Overview of existing methodologies

What are the limitations of existing retrofit assessment methodologies for meeting HEETSA’s objectives?

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Technical

Fabric Energy Efficiency and Ventilation

• Roof
• Walls
• Floors
• Glazing
• Doors
• Ventilation

Individual home heating system

• Does existing heating adequately heat the home?
• If no, repair or upgrade existing heating?
• Or install new heating?
• Is heating system needed at all?

Heat Network (HN)

Communal Heating (CH)

District Heating / Combined Heat and Power

• Is the dwelling connected already to a HN, CH or DH/CHP scheme?
• Does an existing HN, CH or DH/CHP exist that the dwelling can be connected to?
• If no, is the locality heat demand sufficient to sustain a HN, CH or DH/CHP scheme?

Suitability

To be identified:

Improvement measures needed

Standards to be met

Risks

Design specification

Costs

Skills to deliver

Assessment

Reduce energy demand

Reduce CO2(e) emissions

Reduce fuel costs

Reduce fuel poverty

Health and wellbeing (indoor air, noise, daylight, accessibility, comfort)

Aesthetics

Limitations of currently used methodologies

While combination of existing methodologies can provide a foundation for assessing clean heating and energy efficiency measures, the success is often reliant on the experience and expertise of the professionals involved. The process too often relies on predicted data, lacks context specific assessments, sufficient site investigations, produces inconsistent and non-comparable results, and is often dictated by financial constraints and funding mechanisms that do not align with best practice and long-term benefits for the occupants. A more thorough, transparent, and standardized approach is needed to ensure high-quality retrofits that improve energy efficiency, protect building integrity, and enhance occupant well-being supporting their long-term needs.

Methodologies, including frameworks, guides, certification and software currently used have been listed in Annex 1, including comparative analysis of purpose, characteristics and suitability to meet HEETSA’s goals.

Among all identified methodologies, PAS 2035 and PAS 2038 with complementing standards such as BS 40104 have been considered most holistic in attempting to provide a comprehensive technical assessment. However, these standards are not only voluntary, but also frequently revised, which prevents the industry from fully adopting them. This may make it difficult for the industry to learn from past mistakes and implement improvements over time. Additionally, majority of British Standards require paid access, which can hinder widespread adoption and best practice.

Assumption based assessment

The criticism of current approaches was that assessment methodologies rely on models like RdSAP (Reduced Standard Assessment Procedure) and Passivhaus Planning Package (PHPP)^[2], which include assumptions that may not always reflect real-world conditions, underutilising future climate predictions. These assumptions can contribute to misleading results. For instance, Energy Performance Certificate (EPC) ratings do not always capture the true efficiency of a retrofit. Measures like installing photovoltaic (PV) panels or air-source heat pumps (ASHPs) may improve an EPC score but fail to address fundamental building issues such as poor insulation or moisture risks. This can be particularly problematic for vulnerable populations who may end up living in homes that remain inefficient and difficult to heat, aggravating health inequalities.

The Scottish Government accepts that EPCs are limited (and driven by a specific logic) in relation to the ways that improvement measures are specified, and hence why HEETSA is being discussed in the first place.

Building condition, maintenance and building surveys

Additionally, assessments fail to account for key building conditions, such as existing moisture risks or the state of cavity wall insulation. Current methods often assume that these features are in good condition rather than verifying them through detailed inspections, such as thermal imaging or intrusive surveys. More advanced methods, like hygrothermal assessments using WUFI software^[3], exist but are rarely used due to additional complexity, cost, and time required. This lack of detailed investigation can lead to retrofits that are ineffective or even damaging to buildings, and potentially having negative impacts on occupants’ health.

Misalignment of funding and retrofit goals

Current funding mechanisms often encourage quick installations where many programs do not provide financial support for addressing pre-existing structural or moisture issues, leading to ineffective retrofits and unintended consequences affecting public health. Some projects have focused on quick, low-cost solutions rather than high-quality, durable improvements. For example, some Energy Company Obligation (ECO) schemes have been managed by energy companies that prioritize profit over quality, leading to poorly executed installations. Social landlords face additional challenges in balancing the cost of retrofits with educating tenants on energy efficiency.

Currently, use of different methodologies can produce varying results, leading to inconsistent recommendations for homeowners and businesses. Decisions can also be driven by funding programs, underestimating the importance of detailed assessments, which without clear comparative analysis and robust operating framework may be considered costly and time-consuming.

Expertise of assessors and value of independent advice

It is therefore imperative that the assessment is carried out by independent and competent assessors to ensure retrofit recommendations are genuinely in the best interest of the building and its occupants.

Adequate assessments help prevent costly mistakes and ensure homeowners can make informed decisions that align with their long-term needs, including reducing fuel poverty, lowering carbon emissions, and improving their health.

What is required to meet HEETSA’s objectives

Standardised and Comprehensive Retrofit Process

There is a strong need for a standardised approach that allows for general, comparative assessments but can also accommodate the complexities of historic and traditional buildings. This process should include:

• Detailed occupancy assessments in person-centred approach
• Condition reports that evaluate moisture risks, ventilation, and structural integrity
• Intrusive surveys and thorough investigations to improve accuracy
• Bespoke desk-based assessment supported by knowledge and expertise of the assessor providing critical evaluation of model-generated recommendations

Archetype-based solutions can be useful for area-wide schemes and high-level planning. However, it is required to recognise these recommendations will be generic, not accounting for unique features of individual homes, and the way they are used by the occupants. Robust framework must therefore allow for:

• Bespoke solutions that consider local geography, wind exposure, rainfall data, and other environmental factors
• Flexibility to account for individual building characteristics
• Consideration of human behaviour factors

Person-Centred Approach and Customer Engagement

A customer-focused approach can empower occupiers to understand and manage their buildings effectively, as well as recognise suitability of approach relative to individual circumstances. Encouraging knowledge-sharing and occupant involvement in decision-making fosters better engagement and informed choices about retrofit measures, and the importance of maintenance as the first step of a retrofit journey.

Retrofit measures must consider both building performance and how occupants interact with their homes. This means including occupancy assessments alongside building performance evaluations to ensure solutions are sustainable. Assessors should also help homeowners understand the long-term carbon and financial costs of different measures, including staged approaches, guiding them toward choices that avoid quick fixes causing costly consequences of building failures. Consumers must also be better informed about the trade-offs between basic, low-cost assessments and more thorough, expert-led evaluations that prevent costly mistakes that can have detrimental outcomes to building performance, property values, and occupant health.

A strong consensus emerged that site visits should be a mandatory part of the assessment process. Expert assessors can identify building defects and poorly installed systems that may not be apparent through remote or desk-based assessments. Direct conversations between occupants and assessors enhance understanding, ensuring that measures are adequate for the building in its context and align with the needs of the occupants recognizing their individual circumstances.

Additionally, quality assurance of installed products and systems can be supported by follow-up engagement with occupants post-installation, and by mandatory Post Occupancy Evaluation (POE).

Improving the Customer Journey

It was recognised that to improve outcomes and ensure customer protection, the role of the retrofit assessor should be supported by dedicated training and qualifications. Currently, Retrofit Assessors^[4] often have limited expertise to evaluate critical building physics and condition related variables. Insufficient skills may then lead to inadequate assessments and recommendations. This is a particularly important issue in rural and remote areas, where the lack of adequately trained retrofit assessors is most evident. Their role should be regulated to ensure unbiased recommendations tailored to each property’s needs rather than commercial interests, and to safeguard consumers by ensuring assessors are sufficiently skilled to produce high quality retrofit plans.

To enable a successful customer journey, investment is required in building local capacity. Many small, local firms often possess the necessary skills for retrofitting but avoid government schemes due to upfront costs of accreditation and past negative experiences. Support mechanisms, such as council-provided affordable premises and financial support for upskilling and the delivery of retrofit assessments, could help these firms grow and community-based pilot projects, backed by seed funding, could foster local expertise and expand networks through hands-on learning.

While this study did not determine which groups should receive subsidies, financial support is essential for certain demographics and building types. A more streamlined, accessible system is needed to ensure homeowners receive clear and accurate guidance.

Recognised issues affecting customer trust in effective delivery of retrofit are a lack of experienced assessors, a lack of quality control, and insufficient validation processes. Additionally, assessors may not be trained in evaluating different heating and hot water systems tailored to occupant needs. The Scottish Government should thus invest in upskilling programs to ensure assessors are well-qualified, including having sufficient knowledge of evaluating heat and hot water systems, and an understanding of communal / district heating systems. This must include continuous learning requirements to ensure relevant knowledge is maintained and developed. Training within adequate and recognised delivery models must be accessible, reliable and available across Scotland. We also recommend further stakeholder consultation to clarify the role of assessors in the HEETSA model.

Summary

Current methodologies often produce generic recommendations, lacking solutions tailored to individual buildings and without sufficiently recognising critical factors like building condition, moisture risks, and long-term effectiveness. Additionally, limited assessor expertise and inconsistencies in assessment outcomes dependant on use of particular methodologies highlight the need for standardized, detailed processes incorporating site visits, consideration of climate and location specific data, and independent assessments. Assessment of clean heating and energy efficiency strategy delivered under HEETSA should thus include:

• Centrally defined operating framework based on real data, recognising building condition and human behaviour.
• Funding aligned to value of quality and long term effectiveness of measures.
• Methods of safeguarding of customer journey supported by competent workforce (assessors and installers).

Clearly defined roles, means of demonstrating competency and compliance supported by stronger collaboration between professionals and clearer funding mechanisms are essential to delivering high-quality retrofits that align with national carbon reduction and energy efficiency goals. Risk management and adequacy of approaches could be supported by development of decision-making matrix/tool to assess suitability of current approaches adequate to the needs of the customer, similar to the Sustainable Traditional Buildings Alliance (STBA) Responsible Retrofit Guidance Wheel^[5].

There are a range of existing methodologies which attempt to go beyond the EPC, many of which could be a foundation for a HEETSA, but none of them go far enough to meet all of its needs. For example, some surveyors will offer an ‘EPC+’ approach that can take into account factors such as occupancy, but these are not codified approaches and (as far as we’re aware) not advertised. Rather, they are negotiated as part of (for example) community projects. Neither are they required by any existing regulations. However, even these are insufficient to meet the needs of designing communal and district heating systems, which ideally require very accurate energy demand data, therefore the Scottish Government must regulate this space - both for methodologies and for assessor skills.