Improving home energy efficiency - retrofit assessment review: policy report

Annex 1: Independent Review of suitability of existing methodologies to deliver HEETSA

Overview of Existing Methodologies (as identified by participants during the review)

Methodology

A PAS 2035:2023 - Retrofitting Dwellings for improved Energy Efficiency; and PAS 2038:2021 - Retrofitting non-domestic buildings for improved energy efficiency.

B Scottish Building Standards – Technical Handbook

C British Board of Agreement (BBA).

D Royal Institution of Chartered Surveyors (RICS) Residential Retrofit Standard.

E Historic Environment Scotland (HES) guide to retrofit of traditional buildings.

F Passivhaus EnerPHit Standard.

G Association for Environment Conscious Building (AECB) Retrofit Standard.

H BS 40104 Retrofit assessment for domestic dwellings – Code of practice (not published).

I Reduced Standard Assessment Procedure (RdSAP) and Standard Assessment Procedure (SAP).

J Passivhaus Planning Package (PHPP).

K Home Energy Model (HEM).

L Portfolio Energy Assessment Tool (PEAT).

M Energy Performance Certificate (EPC).

N Wärme Und Feuchte Instationär (WUFI).

A

Methodology

PAS 2035:2023 - Retrofitting Dwellings for improved Energy Efficiency; and PAS 2038:2021 - Retrofitting non-domestic buildings for improved energy efficiency.

Description

Standard providing specification and guidance for retrofitting of domestic (PAS2035) and non-domestic (PAS2038) properties for improved energy efficiency, with clear identification of roles and responsibilities through retrofit process.

Purpose

Framework defining best practice, risk management to buildings and occupant’s health.

Suitability to deliver HEETSA

The most ‘all embracing’ technical assessment approach currently in use. Reference to BS 7913: 2013 Guide to the conservation of historic buildings. BS 40104 Retrofit Assessment of Dwellings for Retrofit (not yet published), BS 5250: 2021 Management of moisture in buildings. Clear identification of roles and responsibilities.

Limitations to deliver HEETSA

Needs to be accompanied by suitable energy efficiency and heating system evaluation. There is no prescribed requirement for use of intrusive surveys, air tightness testing, thermal imaging. Where these may be recommended, the decision of suitable assessment method is at the discretion of the assessor. There is no comparison of best suited tools for evaluation of retrofit options and comparative suitability of heating systems.

B

Methodology

Scottish Building Standards – Technical Handbook.

Description

Building Warrant process supported by building standards regulations, technical guidance, and certification.

Purpose

Framework defining best practice, risk management to buildings and occupant’s health.

Suitability to deliver HEETSA

Should Building Warrant be required for majority of retrofit plans, Building Standards could assist in verification of experience of assessors, in a similar manner to Certification of Design and to be compliant with current Section 6 of the Scottish Building Standards covers energy performance, overheating, and ventilation. This would align the approach to retrofit of existing buildings with regulatory context of new build, including alignment with Scottish equivalent to Passivhaus and Heat in Buildings Bill.

Limitations to deliver HEETSA

Retrofit is currently not regulated by Building Standards. There are relevant sections regarding existing buildings and Building Warrant would be required for, for example external wall insulation, but these are isolated instances.

C

Methodology

British Board of Agreement (BBA).

Description

Products, systems, and installers approval.

Purpose

Independent certification against industry standards and regulations including inspection, to ensure safety, quality, and performance.

Suitability to deliver HEETSA

Certification of approved systems and installers, which could assist in streamlining of the verification process. This would assist in moving through retrofit process from assessment into design and delivery.

Limitations to deliver HEETSA

Certification can be used as accountability and risk mitigation measure, to safeguard interest of the occupants. It should be used alongside not instead of dynamic data modelling. BBA certification can also be sued to ensure competence of installers.

D

Methodology

Royal Institution of Chartered Surveyors (RICS) Residential Retrofit Standard.

Description

Professional framework focused on guidance for professionals including conduct, qualifications, and customer journey.

Purpose

To provide framework aligning with code of conduct for chartered building surveyors.

Suitability to deliver HEETSA

Code of practice can be useful in ensuring adherence to HEETSA requirements, with suitable verification of qualification of retrofit assessors. Reference to BS 7913: 2013 Guide to the conservation of historic buildings, BS 40104 Retrofit Assessment of Dwellings for Retrofit (not yet published) & BS 5250: 2021 Management of moisture in buildings.

Limitations to deliver HEETSA

This standard is aimed at ensuring adequate professional conduct of RICS accredited professionals. It is a referential guide aligning practice to relevant British Standards. It is not however an operating framework that can be used as a standalone methodology to deliver aspirations of HEETSA.

E

Methodology

Historic Environment Scotland (HES) guide to retrofit of traditional buildings.

Description

Energy retrofit guide focusing on energy efficiency measures for traditional buildings, including compatibility with existing fabric (based on HES research), compliance with Building Standards and Planning process.

Purpose

Framework defining best practice, risk management to buildings and resulting occupant’s health specific to historic buildings.

Suitability to deliver HEETSA

Holistic guide providing examples of best practice for retrofit measures improving the energy efficiency of traditional buildings, whilst maintaining as much of their historic fabric and creating healthy indoor environments. Emphasis on building condition, maintenance, and compatibility of measures. Can be used as supplementary information informing decisions tested with the use of modelling and simulation tools.

Limitations to deliver HEETSA

This guide can be used as supplementary information for assessment of traditional buildings, alongside standards such as Reference to BS 7913: 2013 Guide to the conservation of historic buildings. It is not an evaluation tool comparing options for energy efficiency and heating improvements.

F

Methodology

Passivhaus EnerPHit Standard.

Description

Retrofit equivalent of Passivhaus Standard, energy reduction focused standard accompanied by certification ensuring quality and as-built performance certified by Approved Certifiers.

Purpose

Performance standard focused on significant improvements to energy efficiency and resulting reductions in heating and cooling demand.

Suitability to deliver HEETSA

Performance and quality standard. Verification of performance is achieved through robust quality checks.

Limitations to deliver HEETSA

Focus on in use building emissions. These are not requirements required for compliance: whole life carbon consideration, user behaviour, building condition & maintenance and post occupancy evaluation. MVHR is a requirement for certification: does not take into account whole building approach recognising suitability of materials and reliant on knowledge & expertise of the assessor/designer.

G

Methodology

Association for Environment Conscious Building (AECB) Retrofit Standard.

Description

Energy reductions focused deep retrofit standard offering step-by-step approaches with Quality Assurance verification by Approved Certifiers.

Purpose

Performance standard offering staged approach to energy efficiency and heating decarbonisation.

Suitability to deliver HEETSA

Performance and quality standard. Verification of performance is achieved through robust quality checks. Variation of Passivhaus standard with lesser operational energy performance. Includes water and indoor air quality/ventilation guidance. Allows for a stepped approach.

Limitations to deliver HEETSA

Focus on operational carbon emissions. These are not requirements resulting in compliance: whole life carbon consideration, user behaviour and building condition.

H

Methodology

BS 40104 Retrofit assessment for domestic dwellings – Code of practice (not published).

Description

Code of practice for retrofit assessment for domestic properties.

Purpose

Standardized, detailed assessment methodology supporting delivery of PAS 2035, ensuring that the building is adequately assessed prior to any retrofit work being designed or carried out.

Suitability to deliver HEETSA

The standard is intended to cover: assessment in building specific context, on-site assessment including building condition, reporting & lodgement, and competencies of assessors.

Limitations to deliver HEETSA

Not suitable as a standalone standard. Suitable methodology and tools enabling comparative analysis of measures is required.

I

Methodology

Reduced Standard Assessment Procedure (RdSAP) and Standard Assessment Procedure (SAP).

Description

Methodology used by Scottish government to estimate energy performance of homes. Conforming to BS EN ISO 13790.

Purpose

Demonstration of compliance of new homes (SAP) and existing homes (RdSAP) with Building Regulations and generation of Energy Performance Certificates (EPCs).

Suitability to deliver HEETSA

RdSAP/SAP can produce energy related analysis (Heat Transfer Co-efficient, Heat Loss Parameter, Specific Heat Loss, Design Heat Loss) that would allow for more in-depth analysis of a dwelling’s performance. Could be supplemented by other tools (e.g. WUFI and condensation risk analysis) to enable risk analysis of proposed improvements.

Limitations to deliver HEETSA

RdSAP does not assess risks with associated improvements.

J

Methodology

Passivhaus Planning Package (PHPP).

Description

Spreadsheet based simplified building energy simulation software with monthly results of energy demand for designing and evaluating scenarios in achieving energy efficiency in buildings, including calculation of energy demand, overheating, performance. Conforming to BS EN ISO 13790 Energy performance of buildings - Calculation of energy use for space heating and cooling.

Purpose

Tool for designing and evaluating scenarios in achieving energy efficiency in buildings, including calculation of energy demand, overheating, performance.

Suitability to deliver HEETSA

PHPP can produce analysis of energy demand including variables affecting heat loss, energy use and internal comfort. Can be used as an energy modelling tool for any project.

Limitations to deliver HEETSA

Pass/fail assessment with no recommendations. Time consuming and focused on solutions such as MVHR. Requirement for Passivhaus projects including EnerPHit. Conform to the same BS EN as RdSAP and SAP.

K

Methodology

Home Energy Model (HEM).

Description

Simplified building energy modelling software based on Environmental Systems Performance – Research (ESP-r) results, giving results of building retrofit measures based on dynamic results.

Purpose

Building energy modelling software enabling comparison of retrofit options.

Suitability to deliver HEETSA

Simplified modelling program allowing for assessment of retrofit options. Suitable for evaluation of multiple building options and easy comparison of options for energy efficiency measures.

Limitations to deliver HEETSA

Building parameters are based on building archetypes and some level of predicted data. Although the model could be useful for evaluation of methods, it needs to be supplemented by accurate, site specific data.

L

Methodology

Portfolio Energy Assessment Tool (PEAT).

Description

Modelling tool for comparative analysis. Relies on accuracy of Energy Saving Trust (EST) Home Analytics data. Uses SAP score as a comparative baseline.

Purpose

PEAT models individual properties, portfolios, and specific areas or neighbourhoods, including options of cost, maintenance and replacement cycles, carbon reductions, space heating demand and enable comparison of several retrofit options.

Suitability to deliver HEETSA

Ability to compare options of energy efficiency improvements aligned to funding streams.

Limitations to deliver HEETSA

Home Analytics data has uncertainty because it is modelled, though it is based on a robust and well-tested methodology. The tool does not capture the full range of factors required for holistic retrofit assessments of individual buildings and is mainly used by the social housing sector. PEAT and Home Analytics includes data derived from Energy Performance Certificates; these data are subject to the quality assurance requirements as per the national operational framework for EPC Approved Organisations.

M

Methodology

Energy Performance Certificate (EPC).

Description

Rating system used by the Scottish Government produced using RdSAP (for existing dwellings) and SAP (for new built homes).

Purpose

Report indicating energy efficiency and climate impact of the property, including recommendations report of possible, generic improvement measures.

Suitability to deliver HEETSA

EPC could assist in providing improvement options as opposed to recommendations, recognising requirement for detailed, data-based assessments undertaken by suitably qualified, independent assessors.

Limitations to deliver HEETSA

Produced by energy assessors using assumption-based data. The EPC includes recommendations on how to improve energy efficiency that are generic and not property specific.

N

Methodology

Wärme Und Feuchte Instationär (WUFI).

Description

Software family for hygrothermal simulation and assessment of building envelope with consideration to climate predictions, and location specific weather data.

Purpose

Moisture and heat transfer analysis through multilayer components (such as walls) allowing for risk analysis of moisture build ups in building envelope.

Suitability to deliver HEETSA

Enabling risk analysis of retrofit options in improving energy efficiency of buildings with consideration of dynamic, location and climate specific data and ability to evaluate long term hygrothermal performance simulations and incorporate climate predictions. Particularly relevant for assessment of measures in traditional buildings.

Limitations to deliver HEETSA

This is a supplementary tool enabling evaluation of risks associated with proposed energy efficiency improvements to the building envelope. Cannot be sued as standalone assessment tool for comprehensive retrofit assessment.

Other tools may be required for adequate retrofit design, such as and not limited to thermal bridging coefficient tool and whole life carbon assessment tool. Note: This table does not consider models for designing or assessing communal / district heating systems. Some of these models (e.g. SAP) go some way to identifying potential, and bespoke ‘EPC+’ assessments that involve engaging with householders are useful for underpinning feasibility studies (e.g., by gauging local interest and acceptability). However, designing these systems requires full technical assessments. Such assessments benefit significantly from using real demand and supply data, and may be subject to commercial confidentiality restriction.