The Home Energy Model and its wrappers - Revision history

Editor at 07:40, 10 March 2026

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Editor at 22:49, 9 March 2026

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	= From SAP to HEM, EPC, MEES and FHS =		= From SAP to HEM, EPC, MEES and FHS =

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Editor: moved The Home Energy model and its wrappers to The Home Energy Model and its wrappers

2026-03-09T22:37:15Z

moved The Home Energy model and its wrappers to The Home Energy Model and its wrappers

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Editor at 22:27, 9 March 2026

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	In June 2022 the interim step with the [https://www.gov.uk/government/publications/conservation-of-fuel-and-power-approved-document-l Part L 2021 uplift came into force], this was outlined in January 2021 government response [https://assets.publishing.service.gov.uk/media/60114c6c8fa8f565494239a7/Government_response_to_Future_Homes_Standard_consultation.pdf The Future Homes Standard: 2019 Consultation on changes to Part L (conservation of fuel and power) and Part F (ventilation) of the Building Regulations for new dwellings].		In June 2022 the interim step with the [https://www.gov.uk/government/publications/conservation-of-fuel-and-power-approved-document-l Part L 2021 uplift came into force], this was outlined in January 2021 government response [https://assets.publishing.service.gov.uk/media/60114c6c8fa8f565494239a7/Government_response_to_Future_Homes_Standard_consultation.pdf The Future Homes Standard: 2019 Consultation on changes to Part L (conservation of fuel and power) and Part F (ventilation) of the Building Regulations for new dwellings].
		+
		+	= Related articles on Designing buildings =
		+
		+	* Air permeability testing.
		+	* Air tightness.
		+	* Applying Fabric First principles: Complying with UK energy efficiency requirements FB 80.
		+	* Approved building energy calculation software.
		+	* Approved documents.
		+	* Are Energy Performance Certificates accurate?
		+	* Building energy models.
		+	* Building Regulations.
		+	* Building Research Establishment.
		+	* Changes in SAP 10.
		+	* Co-heating test.
		+	* Conventions for U-value calculations (2006 edition) BR 443.
		+	* Display energy certificate DEC.
		+	* Dynamic Simulation Model.
		+	* Emission rates.
		+	* Energy efficiency of traditional buildings.
		+	* Energy Performance Certificates.
		+	* Energy Performance of Buildings Directive.
		+	* How are EPCs produced?.
		+	* IHBC responds to Energy Company Obligation ECO4 and PAS 2035.
		+	* Minimum energy efficiency standard (MEES).
		+	* National Calculation Method.
		+	* Passivhaus vs SAP.
		+	* Standard Assessment Procedure SAP.
		+	* Simplified Building Energy Model.
		+	* Target fabric energy efficiency rate.
		+	* Thermal dynamic analysis.
		+	* The EPC consultation in the context of changes to the NCM.
		+	* U-value conventions in practice: Worked examples using BR 443.
		+	* The Home Energy Model and Future Homes Standard assessment wrapper.
		+	*

	[[Category:Articles_needing_more_work]]		[[Category:Articles_needing_more_work]]

Editor at 22:23, 9 March 2026

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	In 2021, the government appointed a consortium of experts led by the BRE to carry out a multi-year project to develop a replacement for SAP, which was first published in 1993. SAP was introduced into the Building Regulations to assess the energy performance of dwellings and has been updated periodically in 1998, 2001, 2005, 2009, 2012, and 2022. The accuracy of EPC's has received much criticism over the years see Are Energy Performance Certificates Accurate? HEM was first consulted on in 2019 with further technical detail set out in a 2023 consultation, the government responded in early 2026 with regulations anticipated to come into force by late 2026.		In 2021, the government appointed a consortium of experts led by the BRE to carry out a multi-year project to develop a replacement for SAP, which was first published in 1993. SAP was introduced into the Building Regulations to assess the energy performance of dwellings and has been updated periodically in 1998, 2001, 2005, 2009, 2012, and 2022. The accuracy of EPC's has received much criticism over the years see Are Energy Performance Certificates Accurate? HEM was first consulted on in 2019 with further technical detail set out in a 2023 consultation, the government responded in early 2026 with regulations anticipated to come into force by late 2026.

−	~~Closed [https://www.designingbuildings.co.uk/wiki/Consultation consultation] [https://www.gov.uk/government/consultations/reforms-to-~~the~~-energy-performance-~~of~~-buildings-regime/reforms-to-~~the~~-energy-performance-~~of~~-buildings-regime#what-epcs-measure Reforms~~ to the ~~Energy Performance~~ of ~~Buildings regime Published 4 December 2024]~~. ~~Awaiting response.~~	+	The replacement of SAP and the introduction of HEM is a significant change that will impact a wide variety of areas concerning the estimation, demonstration of compliance, and, to some extent, the assessment of energy use in buildings. Given the importance and timeframe for the development of HEM, the government appointed a consortium led by Etude to quality-assure the work being undertaken. This QA process aims to ensure that issues with the current SAP methodologies are identified and clearly defined, evidence for suggested improvements is thorough, validation processes are robust, the decision-making process is clear, robust, and documented, and project governance is working effectively with the government, key user groups, and technical experts associated with key decisions.
−		+
−	[https://www.designingbuildings.co.uk/wiki/Consultation Consultation] [https://www.designingbuildings.co.uk/wiki/Outcome outcome] [https://www.gov.uk/government/consultations/home-energy-model-replacement-for-the-~~standard-assessment-procedure-sap Home Energy Model: replacement for~~ the ~~Standard Assessment Procedure (SAP)] October 25~~	+
−		+
−	~~Closed [https://www~~.~~designingbuildings.co.uk/wiki/Consultation consultation] [https://www.gov.uk/government/consultations/~~the~~-future-homes-~~and~~-buildings-standards-2023-consultation/~~the-~~future-homes-~~and~~-buildings-standards-2023-consultation The Future Homes~~ and ~~Buildings Standards: 2023 consultation] Updated 4 March 2024~~	+
−		+
−	Closed [https://www.designingbuildings.co.uk/wiki/Consultation consultation] on [https://assets.publishing.service.gov.uk/media/68b852a83f3e5483efdba94e/SRS_MEES_Consultation__FINAL-Publication_version_.pdf Minimum Energy Efficiency Standards in the ~~Social Rented Sector in England] 10th September 2025~~.	+
−		+
−	~~[https://assets.publishing.service.gov.uk/media/6578b3da254aaa0010050bb3/hem-val-01-inter-model-comparison.pdf Inter-Model Comparison: Summary Report Home Energy Model Validation] December 23~~	+
−		+
−	~~[https://www.designingbuildings.co.uk/wiki/The_EPC_consultation_in_the_context_of_changes_to_the_NCM The EPC consultation in the context of changes to the NCM]~~	+
−		+
−	~~What has been published?~~	+

	Open consultation: [https://www.gov.uk/government/consultations/home-energy-model-energy-performance-certificates/home-energy-model-hem-methodology-for-assessing-existing-dwellings-and-producing-new-energy-performance-certificates-metrics-accessible-webpage Home Energy Model (HEM) methodology for assessing existing dwellings and producing new Energy Performance Certificates metrics] (The Home Energy Model: EPC assessment consultation) Published 21 January 2026 Consultation document part of a series of consultations and documents published by the government relating to Energy Performance Certificates (EPC) and the Home Energy Model (HEM). Seeks views on the parts of the new Home Energy Model methodology which are specific to Energy Performance Certificates.		Open consultation: [https://www.gov.uk/government/consultations/home-energy-model-energy-performance-certificates/home-energy-model-hem-methodology-for-assessing-existing-dwellings-and-producing-new-energy-performance-certificates-metrics-accessible-webpage Home Energy Model (HEM) methodology for assessing existing dwellings and producing new Energy Performance Certificates metrics] (The Home Energy Model: EPC assessment consultation) Published 21 January 2026 Consultation document part of a series of consultations and documents published by the government relating to Energy Performance Certificates (EPC) and the Home Energy Model (HEM). Seeks views on the parts of the new Home Energy Model methodology which are specific to Energy Performance Certificates.

−	The Home Energy Model consultation (2023) and government response (2025). [https://www.gov.uk/government/consultations/home-energy-model-replacement-for-the-standard-assessment-procedure-sap Home Energy Model: replacement for the Standard Assessment Procedure (SAP)] Explains the overhaul to the SAP methodology and sought views on the approach taken by its replacement, the Home Energy Model. The government response ~~details~~ key decisions made on HEM coremethodology following review of consultee feedback.	+	Closed consultation: The Home Energy Model consultation (2023) and government response (2025). [https://www.gov.uk/government/consultations/home-energy-model-replacement-for-the-standard-assessment-procedure-sap Home Energy Model: replacement for the Standard Assessment Procedure (SAP)] Explains the overhaul to the SAP methodology and sought views on the approach taken by its replacement, the Home Energy Model. The government response detailed key decisions made on HEM coremethodology following review of consultee feedback. Proposed changes in the Future Homes Standard, to ensure [https://www.gov.uk/government/news/rooftop-solar-for-new-builds-to-save-people-money new homes to have mandatory solar were announced in June 2025.]

−	The [https://www.gov.uk/government/consultations/reforms-to-the-energy-performance-of-buildings-regime/reforms-to-the-energy-performance-of-buildings-regime#what-epcs-measure Reforms to the Energy Performance of Buildings regime] consultation (2024) ~~consultations/reforms-to-the-energy-performance-of-buildings-regime [and~~ partial response (2025)]. This consultation sought views on reforms to EPCs, including principles for new metrics to be used in generating EPC ratings. In particular, the Technical Annex to Chapter 2 of the consultation sets out the issues arising within metric design, which the present proposals aim to address. The EPB consultation will be of interest to those who want to understand the proposed changes to EPCs, which drive the ~~metricdesign~~ proposals for HEM:EPC.	+	The [https://www.gov.uk/government/consultations/reforms-to-the-energy-performance-of-buildings-regime/reforms-to-the-energy-performance-of-buildings-regime#what-epcs-measure Reforms to the Energy Performance of Buildings regime] consultation outcome (2024) partial response 2025. This consultation sought views on reforms to EPCs, including principles for new metrics to be used in generating EPC ratings. In particular, the Technical Annex to Chapter 2 of the consultation sets out the issues arising within metric design, which the present proposals aim to address. The EPB consultation will be of interest to those who want to understand the proposed changes to EPCs, which drive the metric design proposals for HEM:EPC.

	[https://www.gov.uk/government/consultations/home-energy-model-future-homes-standard-assessment Home Energy Model: Future Homes Standard assessment consultation] (2023) and [https://www.gov.uk/government/publications/home-energy-model-future-homes-standard-assessment-technical-documentation Home Energy Model: Future Homes Standard assessment accompanying technical documentation] The government previously consulted on a wrapper for HEM to support assessments determining compliance with Building Regulations Part L (the Future Homes Standard). This consultation is accompanied by several technical documents which go into further detail on the assumptions and validationexercises that have been carried out. Although the EPC wrapper may differ in some respects and contain updates to some assumptions, these documents remain the best way to understand how the EPC assessment will approach inputstandardisation, where this is common to both new and existing dwellings. These technical documents will be of interest to those who want to understand the justifications and evidence base behind the standardisation assumptions used in the model (relating to energy demand, weather, fuels etc).		[https://www.gov.uk/government/consultations/home-energy-model-future-homes-standard-assessment Home Energy Model: Future Homes Standard assessment consultation] (2023) and [https://www.gov.uk/government/publications/home-energy-model-future-homes-standard-assessment-technical-documentation Home Energy Model: Future Homes Standard assessment accompanying technical documentation] The government previously consulted on a wrapper for HEM to support assessments determining compliance with Building Regulations Part L (the Future Homes Standard). This consultation is accompanied by several technical documents which go into further detail on the assumptions and validationexercises that have been carried out. Although the EPC wrapper may differ in some respects and contain updates to some assumptions, these documents remain the best way to understand how the EPC assessment will approach inputstandardisation, where this is common to both new and existing dwellings. These technical documents will be of interest to those who want to understand the justifications and evidence base behind the standardisation assumptions used in the model (relating to energy demand, weather, fuels etc).
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	[https://dev.azure.com/Sustenic/Home%20Energy%20Model%20Reference/_git/Home%20Energy%20Model The Home Energy Model reference code]. Full Python source code for the Home Energy Model and the Home Energy Model: EPC assessment has been published in a series of Git repositories. The government has not published a userinterface for HEM:EPC to accompany this consultation. The reference code will be of interest to those who want to understand how the model has been implemented in code, and those wishing to fully clarify their understanding of the new methodology. It will also be of interest to any potential contributors to the Home Energy Model.		[https://dev.azure.com/Sustenic/Home%20Energy%20Model%20Reference/_git/Home%20Energy%20Model The Home Energy Model reference code]. Full Python source code for the Home Energy Model and the Home Energy Model: EPC assessment has been published in a series of Git repositories. The government has not published a userinterface for HEM:EPC to accompany this consultation. The reference code will be of interest to those who want to understand how the model has been implemented in code, and those wishing to fully clarify their understanding of the new methodology. It will also be of interest to any potential contributors to the Home Energy Model.

−	* First completed FHS consultation October 2019	+	In June 2022 the interim step with the [https://www.gov.uk/government/publications/conservation-of-fuel-and-power-approved-document-l Part L 2021 uplift came into force], this was outlined in January 2021 government response [https://assets.publishing.service.gov.uk/media/60114c6c8fa8f565494239a7/Government_response_to_Future_Homes_Standard_consultation.pdf The Future Homes Standard: 2019 Consultation on changes to Part L (conservation of fuel and power) and Part F (ventilation) of the Building Regulations for new dwellings].
−	* Government response to first consultation January 2021	+
−	* The interim step with the Part L 2021 uplift ~~June 2022~~ came into force	+
−	* The second FHS consultation was ~~compoeted~~ in ~~December 2023~~	+
−	* The HEM consultation response ~~was published in October 2025~~	+
−	* The ~~mandatory requirement for solar was announced in June 2025~~	+
−	* The Government response to ~~2023 FHS consultation is expected in Quarter 1 2026~~	+
−	* The Final regulations are then to be laid before Parliament during 2026	+
−	* FHS is expected to come into force later in 2026	+
−	* The transitional period for the implementation is expected to be 12 months ending in 2027	+
−		+
−	~~The replacement~~ of ~~SAP~~ and ~~the introduction of HEM is a significant change that will impact a wide variety of areas concerning the estimation, demonstration of compliance,~~ and~~, to some extent, the assessment~~ of ~~energy use in buildings. Given~~ the ~~importance and timeframe~~ for the development of HEM, the government appointed a consortium led by Etude to quality-assure the work being undertaken. This QA process aims to ensure that issues with the current SAP methodologies are identified and clearly defined, evidence for suggested improvements is thorough, validation processes are robust, the decision-making process is clear, robust, and documented, and project governance is working effectively with the government, key user groups, and technical experts associated with key decisions.	+

	[[Category:Articles_needing_more_work]]		[[Category:Articles_needing_more_work]]

Editor at 22:10, 9 March 2026

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	The Future Homes Standard (FHS) is the forthcoming update to Part L (Conservation of Fuel and Power) of the Building Regulations for England, representing the most significant change to new-build standards in over a decade. The standard requires new homes to produce 75–80% less carbon emissions than homes built to the 2013 baseline, a substantial step beyond the 2021 Part L uplift which only required a 31% reduction and compliance will be demonstrated using the Home Energy Model (HEM) or SAP 10.3 during a transitional period.		The Future Homes Standard (FHS) is the forthcoming update to Part L (Conservation of Fuel and Power) of the Building Regulations for England, representing the most significant change to new-build standards in over a decade. The standard requires new homes to produce 75–80% less carbon emissions than homes built to the 2013 baseline, a substantial step beyond the 2021 Part L uplift which only required a 31% reduction and compliance will be demonstrated using the Home Energy Model (HEM) or SAP 10.3 during a transitional period.
		+
		+	It is expected that the final regulations will be laid before Parliament during 2026, and FHS is expected to come into force later in 2026 with transitional period for the implementation is expected to be 12 months ending in 2027.

	= What are assessment wrappers? =		= What are assessment wrappers? =

Editor at 22:08, 9 March 2026

2026-03-09T22:08:21Z

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	What has been published?		What has been published?

−	Open consultation: [https://www.gov.uk/government/consultations/home-energy-model-energy-performance-certificates/home-energy-model-hem-methodology-for-assessing-existing-dwellings-and-producing-new-energy-performance-certificates-metrics-accessible-webpage Home Energy Model (HEM) methodology for assessing existing dwellings and producing new Energy Performance Certificates metrics] (The Home ~~[https://www.designingbuildings.co.uk/wiki/~~Energy ~~Energy]~~ Model: ~~[https://www.designingbuildings.co.uk/wiki/~~EPC ~~EPC] [https://www.designingbuildings.co.uk/wiki/Assessment~~ assessment~~] [https://www.designingbuildings.co.uk/wiki/Consultation~~ consultation]) Published 21 January 2026 ~~[https://www.designingbuildings.co.uk/wiki/~~Consultation ~~Consultation] [https://www.designingbuildings.co.uk/wiki/Document~~ document~~] [https://www.designingbuildings.co.uk/wiki/Part~~ part] of a series of ~~[https://www.designingbuildings.co.uk/wiki/Consultation~~ consultations] and ~~[https://www.designingbuildings.co.uk/wiki/Document~~ documents] published by the ~~[https://www.designingbuildings.co.uk/wiki/Government~~ government] relating to ~~[https://www.designingbuildings.co.uk/wiki/Energy_performance_certificate~~ Energy Performance Certificates] (~~[https://www.designingbuildings.co.uk/wiki/~~EPC ~~EPC]~~) and the ~~[https://www.designingbuildings.co.uk/wiki/Home_Energy_Model~~ Home Energy Model] (HEM). Seeks ~~[https://www.designingbuildings.co.uk/wiki/View~~ views] on the ~~[https://www.designingbuildings.co.uk/wiki/Part~~ parts] of the new ~~[https://www.designingbuildings.co.uk/wiki/Home_Energy_Model~~ Home Energy Model] methodology which are specific to ~~[https://www.designingbuildings.co.uk/wiki/Energy_performance_certificate~~ Energy Performance Certificates].	+	Open consultation: [https://www.gov.uk/government/consultations/home-energy-model-energy-performance-certificates/home-energy-model-hem-methodology-for-assessing-existing-dwellings-and-producing-new-energy-performance-certificates-metrics-accessible-webpage Home Energy Model (HEM) methodology for assessing existing dwellings and producing new Energy Performance Certificates metrics] (The Home Energy Model: EPC assessment consultation) Published 21 January 2026 Consultation document part of a series of consultations and documents published by the government relating to Energy Performance Certificates (EPC) and the Home Energy Model (HEM). Seeks views on the parts of the new Home Energy Model methodology which are specific to Energy Performance Certificates.

−	The ~~[https://www.designingbuildings.co.uk/wiki/Home_Energy_Model~~ Home Energy Model~~] [https://www.designingbuildings.co.uk/wiki/Consultation~~ consultation] (2023) and ~~[https://www.designingbuildings.co.uk/wiki/Government~~ government] response (2025). [https://www.gov.uk/government/consultations/home-energy-model-replacement-for-the-standard-assessment-procedure-sap Home Energy Model: replacement for the Standard Assessment Procedure (SAP)] Explains the overhaul to the ~~[https://www.designingbuildings.co.uk/wiki/~~SAP ~~SAP]~~ methodology and sought ~~[https://www.designingbuildings.co.uk/wiki/View~~ views] on the approach taken by its replacement, the ~~[https://www.designingbuildings.co.uk/wiki/Home_Energy_Model~~ Home Energy Model]. The ~~[https://www.designingbuildings.co.uk/wiki/Government~~ government] response ~~[https://www.designingbuildings.co.uk/wiki/Details~~ details] key decisions made on HEM ~~[https://www.designingbuildings.co.uk/wiki/Core core]methodology~~ following ~~[https://www.designingbuildings.co.uk/wiki/Review~~ review] of consultee ~~[https://www.designingbuildings.co.uk/wiki/Feedback~~ feedback]..	+	The Home Energy Model consultation (2023) and government response (2025). [https://www.gov.uk/government/consultations/home-energy-model-replacement-for-the-standard-assessment-procedure-sap Home Energy Model: replacement for the Standard Assessment Procedure (SAP)] Explains the overhaul to the SAP methodology and sought views on the approach taken by its replacement, the Home Energy Model. The government response details key decisions made on HEM coremethodology following review of consultee feedback.

−	The [https://www.gov.uk/government/consultations/reforms-to-the-energy-performance-of-buildings-regime/reforms-to-the-energy-performance-of-buildings-regime#what-epcs-measure Reforms to the Energy Performance of Buildings regime] ~~[https://www.designingbuildings.co.uk/wiki/Consultation~~ consultation] (2024) ~~[https://www.designingbuildings.co.uk/wiki/Consultation~~ consultations~~][http://www.gov.uk/government/~~ /reforms-to-the-energy-performance-of-~~][https://www.designingbuildings.co.uk/wiki/Building~~ buildings]-regime [and partial response (2025)]. This ~~[https://www.designingbuildings.co.uk/wiki/Consultation~~ consultation] sought ~~[https://www.designingbuildings.co.uk/wiki/View~~ views] on reforms to ~~[https://www.designingbuildings.co.uk/wiki/EPC~~ EPCs], including principles for new ~~[https://www.designingbuildings.co.uk/wiki/Metric~~ metrics] to be used in generating ~~[https://www.designingbuildings.co.uk/wiki/~~EPC ~~EPC]~~ ratings. In particular, the Technical Annex to Chapter 2 of the ~~[https://www.designingbuildings.co.uk/wiki/Consultation~~ consultation] sets out the ~~[https://www.designingbuildings.co.uk/wiki/Issue~~ issues] arising within ~~[https://www.designingbuildings.co.uk/wiki/Metric~~ metric~~] [https://www.designingbuildings.co.uk/wiki/Design~~ design], which the present ~~[https://www.designingbuildings.co.uk/wiki/Proposals~~ proposals] aim to ~~[https://www.designingbuildings.co.uk/wiki/Address~~ address]. The EPB ~~[https://www.designingbuildings.co.uk/wiki/Consultation~~ consultation] will be of ~~[https://www.designingbuildings.co.uk/wiki/Interest~~ interest] to those who want to understand the proposed changes to ~~[https://www.designingbuildings.co.uk/wiki/EPC~~ EPCs], which drive the ~~[https://www.designingbuildings.co.uk/wiki/Metric metric][https://www.designingbuildings.co.uk/wiki/Design_proposals design~~ proposals] for HEM:~~[https://www.designingbuildings.co.uk/wiki/~~EPC ~~EPC]~~.	+	The [https://www.gov.uk/government/consultations/reforms-to-the-energy-performance-of-buildings-regime/reforms-to-the-energy-performance-of-buildings-regime#what-epcs-measure Reforms to the Energy Performance of Buildings regime] consultation (2024) consultations/reforms-to-the-energy-performance-of-buildings-regime [and partial response (2025)]. This consultation sought views on reforms to EPCs, including principles for new metrics to be used in generating EPC ratings. In particular, the Technical Annex to Chapter 2 of the consultation sets out the issues arising within metric design, which the present proposals aim to address. The EPB consultation will be of interest to those who want to understand the proposed changes to EPCs, which drive the metricdesign proposals for HEM:EPC.

−	[https://www.gov.uk/government/consultations/home-energy-model-future-homes-standard-assessment Home Energy Model: Future Homes Standard assessment consultation] (2023) and [https://www.gov.uk/government/publications/home-energy-model-future-homes-standard-assessment-technical-documentation Home Energy Model: Future Homes Standard assessment accompanying technical documentation] The ~~[https://www.designingbuildings.co.uk/wiki/Government~~ government] previously consulted on a wrapper for HEM to support ~~[https://www.designingbuildings.co.uk/wiki/Assessment~~ assessments] determining ~~[https://www.designingbuildings.co.uk/wiki/Compliance~~ compliance] with ~~[https://www.designingbuildings.co.uk/wiki/Building_regulations~~ Building Regulations~~] [https://www.designingbuildings.co.uk/wiki/Part_l~~ Part L] (the ~~[https://www.designingbuildings.co.uk/wiki/Future_Homes_Standard~~ Future Homes Standard]). This ~~[https://www.designingbuildings.co.uk/wiki/Consultation~~ consultation] is accompanied by several technical ~~[https://www.designingbuildings.co.uk/wiki/Document~~ documents] which go into further ~~[https://www.designingbuildings.co.uk/wiki/Details~~ detail] on the ~~[https://www.designingbuildings.co.uk/wiki/Assumption~~ assumptions] and ~~[https://www.designingbuildings.co.uk/wiki/Validation validation]exercises~~ that have been carried out. Although the ~~[https://www.designingbuildings.co.uk/wiki/EPC~~ EPC] wrapper may differ in some respects and contain updates to some ~~[https://www.designingbuildings.co.uk/wiki/Assumption~~ assumptions], these ~~[https://www.designingbuildings.co.uk/wiki/Document~~ documents] remain the best way to understand how the ~~[https://www.designingbuildings.co.uk/wiki/~~EPC ~~EPC] [https://www.designingbuildings.co.uk/wiki/Assessment~~ assessment] will approach ~~[https://www.designingbuildings.co.uk/wiki/Input input][https://www.designingbuildings.co.uk/wiki/Standardisation standardisation]~~, where this is ~~[https://www.designingbuildings.co.uk/wiki/Common~~ common] to both new and existing ~~[https://www.designingbuildings.co.uk/wiki/Dwelling~~ dwellings]. These technical ~~[https://www.designingbuildings.co.uk/wiki/Document~~ documents] will be of ~~[https://www.designingbuildings.co.uk/wiki/Interest~~ interest] to those who want to understand the justifications and evidence base behind the ~~[https://www.designingbuildings.co.uk/wiki/Standardisation~~ standardisation~~] [https://www.designingbuildings.co.uk/wiki/Assumption~~ assumptions] used in the ~~[https://www.designingbuildings.co.uk/wiki/Model~~ model] (relating to ~~[https://www.designingbuildings.co.uk/wiki/Energy_demand~~ energy demand], ~~[https://www.designingbuildings.co.uk/wiki/Weather~~ weather], ~~[https://www.designingbuildings.co.uk/wiki/Fuel~~ fuels] etc).	+	[https://www.gov.uk/government/consultations/home-energy-model-future-homes-standard-assessment Home Energy Model: Future Homes Standard assessment consultation] (2023) and [https://www.gov.uk/government/publications/home-energy-model-future-homes-standard-assessment-technical-documentation Home Energy Model: Future Homes Standard assessment accompanying technical documentation] The government previously consulted on a wrapper for HEM to support assessments determining compliance with Building Regulations Part L (the Future Homes Standard). This consultation is accompanied by several technical documents which go into further detail on the assumptions and validationexercises that have been carried out. Although the EPC wrapper may differ in some respects and contain updates to some assumptions, these documents remain the best way to understand how the EPC assessment will approach inputstandardisation, where this is common to both new and existing dwellings. These technical documents will be of interest to those who want to understand the justifications and evidence base behind the standardisation assumptions used in the model (relating to energy demand, weather, fuels etc).

−	[https://dev.azure.com/Sustenic/Home%20Energy%20Model%20Reference/_git/Home%20Energy%20Model The Home Energy Model reference code]. Full Python source ~~[https://www.designingbuildings.co.uk/wiki/Codes~~ code] for the ~~[https://www.designingbuildings.co.uk/wiki/Home_Energy_Model~~ Home Energy Model] and the ~~[https://www.designingbuildings.co.uk/wiki/Home_Energy_Model~~ Home Energy Model]: ~~[https://www.designingbuildings.co.uk/wiki/~~EPC ~~EPC] [https://www.designingbuildings.co.uk/wiki/Assessment~~ assessment] has been published in a series of Git repositories. The ~~[https://www.designingbuildings.co.uk/wiki/Government~~ government] has not published a ~~[https://www.designingbuildings.co.uk/wiki/Users user][https://www.designingbuildings.co.uk/wiki/Interface interface]~~ for HEM:~~[https://www.designingbuildings.co.uk/wiki/~~EPC ~~EPC]~~ to accompany this ~~[https://www.designingbuildings.co.uk/wiki/Consultation~~ consultation]. The reference ~~[https://www.designingbuildings.co.uk/wiki/Codes~~ code] will be of ~~[https://www.designingbuildings.co.uk/wiki/Interest~~ interest] to those who want to understand how the ~~[https://www.designingbuildings.co.uk/wiki/Model~~ model] has been implemented in ~~[https://www.designingbuildings.co.uk/wiki/Codes~~ code], and those wishing to fully clarify their understanding of the new methodology. It will also be of ~~[https://www.designingbuildings.co.uk/wiki/Interest~~ interest] to any potential contributors to the ~~[https://www.designingbuildings.co.uk/wiki/Home_Energy_Model~~ Home Energy Model].	+	[https://dev.azure.com/Sustenic/Home%20Energy%20Model%20Reference/_git/Home%20Energy%20Model The Home Energy Model reference code]. Full Python source code for the Home Energy Model and the Home Energy Model: EPC assessment has been published in a series of Git repositories. The government has not published a userinterface for HEM:EPC to accompany this consultation. The reference code will be of interest to those who want to understand how the model has been implemented in code, and those wishing to fully clarify their understanding of the new methodology. It will also be of interest to any potential contributors to the Home Energy Model.

	* First completed FHS consultation October 2019		* First completed FHS consultation October 2019

Editor at 22:05, 9 March 2026

2026-03-09T22:05:02Z

← Older revision		Revision as of 22:05, 9 March 2026
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	= From SAP to HEM, EPC, MEES and FHS =		= From SAP to HEM, EPC, MEES and FHS =

−	The Home Energy Model, or HEM, is to be introduced in the UK to replace the Standard Assessment Procedure (SAP), which is currently used to demonstrate that new homes comply with Part L of the Building Regulations and to produce EPC's. The reduced version of SAP (RdSAP) is the current methodology for calculating EPCs for existing buildings.	+	[https://www.gov.uk/government/consultations/home-energy-model-replacement-for-the-standard-assessment-procedure-sap/the-home-energy-model-making-the-standard-assessment-procedure-fit-for-a-net-zero-accessible-webpage The Home Energy Model, or HEM], is to be introduced in the UK to replace the Standard Assessment Procedure (SAP), which is currently used to demonstrate that new homes comply with Part L of the Building Regulations and to produce EPC's. The reduced version of SAP (RdSAP) is the current methodology for calculating EPCs for existing buildings.

	Under the Minimum Energy Efficiency Standards (MEES) since April 1, 2020, all private rented properties (both domestic and commercial) must have an EPC rating of at least 'E', with plans for this to be raised the minimum standard to 'C' by 2030, with interim targets potentially starting in 2028. Currently the methodology to calculate EPCs uses RdSAP, however this will change over the coming years towards an option to use either HEM or RdSAP, and eventally just HEM.		Under the Minimum Energy Efficiency Standards (MEES) since April 1, 2020, all private rented properties (both domestic and commercial) must have an EPC rating of at least 'E', with plans for this to be raised the minimum standard to 'C' by 2030, with interim targets potentially starting in 2028. Currently the methodology to calculate EPCs uses RdSAP, however this will change over the coming years towards an option to use either HEM or RdSAP, and eventally just HEM.
Line 17:		Line 17:
	The current government consultation The Home Energy Model: Energy Performance Certificates. HEM methodology for assessing existing dwellings and producing new EPC metrics looks at aspects of these changes. The consultation looks at a ‘modular’ approach, where the assessor enters as much data as they have access to in each dwelling. The modular structure of the HEM core engine permits this approach, where data for a given module can be provided in multiple ways without interfering with the rest of the calculation. In this new approach, the “all-or-nothing” of RdSAP would be replaced by a flexible series of input simplifications. These aspects are being covered by what are termed as wrappers.		The current government consultation The Home Energy Model: Energy Performance Certificates. HEM methodology for assessing existing dwellings and producing new EPC metrics looks at aspects of these changes. The consultation looks at a ‘modular’ approach, where the assessor enters as much data as they have access to in each dwelling. The modular structure of the HEM core engine permits this approach, where data for a given module can be provided in multiple ways without interfering with the rest of the calculation. In this new approach, the “all-or-nothing” of RdSAP would be replaced by a flexible series of input simplifications. These aspects are being covered by what are termed as wrappers.

−	The Home Energy Model: Future Homes Standard assessment is a methodology designed to assess compliance with the 2025 Future Homes Standard (“FHS”). The Home Energy Model and FHS assessment wrapper together make up the Home Energy Model: FHS assessment~~; both are still under development~~ and ~~will be implemented alongside~~ the ~~FHS~~ in ~~2025~~.	+	The Home Energy Model: Future Homes Standard assessment is a methodology designed to assess compliance with the 2025 Future Homes Standard (“FHS”). The Home Energy Model and FHS assessment wrapper together make up the Home Energy Model: FHS assessment. see [https://www.gov.uk/government/consultations/home-energy-model-replacement-for-the-standard-assessment-procedure-sap/an-evaluation-of-the-home-energy-model-and-future-homes-standard-assessment-wrapper-accessible-webpage An evaluation of the Home Energy Model and Future Homes Standard assessment wrapper]. The HEM:EPC wrapper is effectively the same approoach for the production of EPCs on which views are being sought in the consultation [https://assets.publishing.service.gov.uk/media/69720b6821a2f53a6a4fd474/home-energy-model-energy-performance-certificates-methodology.pdf The Home Energy Model:Energy Performance Certificates. HEM methodology for assessing existing dwellings and producing new EPC Metrics.]

	= Key elements of FHS =		= Key elements of FHS =

−	~~Heating, Energy and Renewables~~ The FHS carbon targets ~~are~~ deliberately ~~set~~ at a level that fossil fuel heating systems cannot meet, meaning that in practice air source or ground source heat pumps will become the primary heating technology for new homes, with heat networks using low-carbon sources also acceptable. Hybrid boilers, hydrogen-ready boilers, and gas boilers will not comply, though existing homes remain unaffected. Alongside this, solar PV panels will become a functional requirement under Building Regulations, with developers required to achieve 40% solar coverage of a building's floor area where feasible, helping new homes generate and self-consume renewable electricity and reducing energy bills by an expected 40–50% compared to conventionally built properties.	+	The FHS sets carbon targets deliberately at a level that fossil fuel heating systems cannot meet, meaning that in practice air source or ground source heat pumps will become the primary heating technology for new homes, with heat networks using low-carbon sources also acceptable. Hybrid boilers, hydrogen-ready boilers, and gas boilers will not comply, though existing homes remain unaffected. Alongside this, solar PV panels will become a functional requirement under Building Regulations, with developers required to achieve 40% solar coverage of a building's floor area where feasible, helping new homes generate and self-consume renewable electricity and reducing energy bills by an expected 40–50% compared to conventionally built properties.

−	~~Fabric Performance, Ventilation and Overheating The~~ FHS introduces significantly improved fabric performance targets through a whole-building approach, with the notional dwelling specification requiring external walls at 0.18 W/m²K, roofs at 0.11 W/m²K, and windows at 1.2 W/m²K — all considerably better than current 2021 standards. The airtightness target of 3 m³/(h·m²) at 50 Pa is particularly demanding, less than half the current regulatory maximum, and will typically require mechanical ventilation with heat recovery (MVHR) to maintain indoor air quality. Given that highly insulated, airtight homes can be prone to summer overheating, the FHS works in conjunction with Part O of the Building Regulations, with HEM's half-hourly simulation well suited to modelling overheating risk and tracking internal temperatures throughout the year.	+	FHS also introduces significantly improved fabric performance targets through a whole-building approach, with the notional dwelling specification requiring external walls at 0.18 W/m²K, roofs at 0.11 W/m²K, and windows at 1.2 W/m²K, all considerably better than current 2021 standards. The airtightness target of 3 m³/(h·m²) at 50 Pa is particularly demanding, less than half the current regulatory maximum, and will typically require mechanical ventilation with heat recovery (MVHR) to maintain indoor air quality. Given that highly insulated, airtight homes can be prone to summer overheating, the FHS works in conjunction with Part O of the Building Regulations, with HEM's half-hourly simulation well suited to modelling overheating risk and tracking internal temperatures throughout the year.

	= Background =		= Background =

	In 2021, the government appointed a consortium of experts led by the BRE to carry out a multi-year project to develop a replacement for SAP, which was first published in 1993. SAP was introduced into the Building Regulations to assess the energy performance of dwellings and has been updated periodically in 1998, 2001, 2005, 2009, 2012, and 2022. The accuracy of EPC's has received much criticism over the years see Are Energy Performance Certificates Accurate? HEM was first consulted on in 2019 with further technical detail set out in a 2023 consultation, the government responded in early 2026 with regulations anticipated to come into force by late 2026.		In 2021, the government appointed a consortium of experts led by the BRE to carry out a multi-year project to develop a replacement for SAP, which was first published in 1993. SAP was introduced into the Building Regulations to assess the energy performance of dwellings and has been updated periodically in 1998, 2001, 2005, 2009, 2012, and 2022. The accuracy of EPC's has received much criticism over the years see Are Energy Performance Certificates Accurate? HEM was first consulted on in 2019 with further technical detail set out in a 2023 consultation, the government responded in early 2026 with regulations anticipated to come into force by late 2026.
		+
		+	Closed [https://www.designingbuildings.co.uk/wiki/Consultation consultation] [https://www.gov.uk/government/consultations/reforms-to-the-energy-performance-of-buildings-regime/reforms-to-the-energy-performance-of-buildings-regime#what-epcs-measure Reforms to the Energy Performance of Buildings regime Published 4 December 2024]. Awaiting response.
		+
		+	[https://www.designingbuildings.co.uk/wiki/Consultation Consultation] [https://www.designingbuildings.co.uk/wiki/Outcome outcome] [https://www.gov.uk/government/consultations/home-energy-model-replacement-for-the-standard-assessment-procedure-sap Home Energy Model: replacement for the Standard Assessment Procedure (SAP)] October 25
		+
		+	Closed [https://www.designingbuildings.co.uk/wiki/Consultation consultation] [https://www.gov.uk/government/consultations/the-future-homes-and-buildings-standards-2023-consultation/the-future-homes-and-buildings-standards-2023-consultation The Future Homes and Buildings Standards: 2023 consultation] Updated 4 March 2024
		+
		+	Closed [https://www.designingbuildings.co.uk/wiki/Consultation consultation] on [https://assets.publishing.service.gov.uk/media/68b852a83f3e5483efdba94e/SRS_MEES_Consultation__FINAL-Publication_version_.pdf Minimum Energy Efficiency Standards in the Social Rented Sector in England] 10th September 2025.
		+
		+	[https://assets.publishing.service.gov.uk/media/6578b3da254aaa0010050bb3/hem-val-01-inter-model-comparison.pdf Inter-Model Comparison: Summary Report Home Energy Model Validation] December 23
		+
		+	[https://www.designingbuildings.co.uk/wiki/The_EPC_consultation_in_the_context_of_changes_to_the_NCM The EPC consultation in the context of changes to the NCM]
		+
		+	What has been published?
		+
		+	Open consultation: [https://www.gov.uk/government/consultations/home-energy-model-energy-performance-certificates/home-energy-model-hem-methodology-for-assessing-existing-dwellings-and-producing-new-energy-performance-certificates-metrics-accessible-webpage Home Energy Model (HEM) methodology for assessing existing dwellings and producing new Energy Performance Certificates metrics] (The Home [https://www.designingbuildings.co.uk/wiki/Energy Energy] Model: [https://www.designingbuildings.co.uk/wiki/EPC EPC] [https://www.designingbuildings.co.uk/wiki/Assessment assessment] [https://www.designingbuildings.co.uk/wiki/Consultation consultation]) Published 21 January 2026 [https://www.designingbuildings.co.uk/wiki/Consultation Consultation] [https://www.designingbuildings.co.uk/wiki/Document document] [https://www.designingbuildings.co.uk/wiki/Part part] of a series of [https://www.designingbuildings.co.uk/wiki/Consultation consultations] and [https://www.designingbuildings.co.uk/wiki/Document documents] published by the [https://www.designingbuildings.co.uk/wiki/Government government] relating to [https://www.designingbuildings.co.uk/wiki/Energy_performance_certificate Energy Performance Certificates] ([https://www.designingbuildings.co.uk/wiki/EPC EPC]) and the [https://www.designingbuildings.co.uk/wiki/Home_Energy_Model Home Energy Model] (HEM). Seeks [https://www.designingbuildings.co.uk/wiki/View views] on the [https://www.designingbuildings.co.uk/wiki/Part parts] of the new [https://www.designingbuildings.co.uk/wiki/Home_Energy_Model Home Energy Model] methodology which are specific to [https://www.designingbuildings.co.uk/wiki/Energy_performance_certificate Energy Performance Certificates].
		+
		+	The [https://www.designingbuildings.co.uk/wiki/Home_Energy_Model Home Energy Model] [https://www.designingbuildings.co.uk/wiki/Consultation consultation] (2023) and [https://www.designingbuildings.co.uk/wiki/Government government] response (2025). [https://www.gov.uk/government/consultations/home-energy-model-replacement-for-the-standard-assessment-procedure-sap Home Energy Model: replacement for the Standard Assessment Procedure (SAP)] Explains the overhaul to the [https://www.designingbuildings.co.uk/wiki/SAP SAP] methodology and sought [https://www.designingbuildings.co.uk/wiki/View views] on the approach taken by its replacement, the [https://www.designingbuildings.co.uk/wiki/Home_Energy_Model Home Energy Model]. The [https://www.designingbuildings.co.uk/wiki/Government government] response [https://www.designingbuildings.co.uk/wiki/Details details] key decisions made on HEM [https://www.designingbuildings.co.uk/wiki/Core core]methodology following [https://www.designingbuildings.co.uk/wiki/Review review] of consultee [https://www.designingbuildings.co.uk/wiki/Feedback feedback]..
		+
		+	The [https://www.gov.uk/government/consultations/reforms-to-the-energy-performance-of-buildings-regime/reforms-to-the-energy-performance-of-buildings-regime#what-epcs-measure Reforms to the Energy Performance of Buildings regime] [https://www.designingbuildings.co.uk/wiki/Consultation consultation] (2024) [https://www.designingbuildings.co.uk/wiki/Consultation consultations][http://www.gov.uk/government/ /reforms-to-the-energy-performance-of-][https://www.designingbuildings.co.uk/wiki/Building buildings]-regime [and partial response (2025)]. This [https://www.designingbuildings.co.uk/wiki/Consultation consultation] sought [https://www.designingbuildings.co.uk/wiki/View views] on reforms to [https://www.designingbuildings.co.uk/wiki/EPC EPCs], including principles for new [https://www.designingbuildings.co.uk/wiki/Metric metrics] to be used in generating [https://www.designingbuildings.co.uk/wiki/EPC EPC] ratings. In particular, the Technical Annex to Chapter 2 of the [https://www.designingbuildings.co.uk/wiki/Consultation consultation] sets out the [https://www.designingbuildings.co.uk/wiki/Issue issues] arising within [https://www.designingbuildings.co.uk/wiki/Metric metric] [https://www.designingbuildings.co.uk/wiki/Design design], which the present [https://www.designingbuildings.co.uk/wiki/Proposals proposals] aim to [https://www.designingbuildings.co.uk/wiki/Address address]. The EPB [https://www.designingbuildings.co.uk/wiki/Consultation consultation] will be of [https://www.designingbuildings.co.uk/wiki/Interest interest] to those who want to understand the proposed changes to [https://www.designingbuildings.co.uk/wiki/EPC EPCs], which drive the [https://www.designingbuildings.co.uk/wiki/Metric metric][https://www.designingbuildings.co.uk/wiki/Design_proposals design proposals] for HEM:[https://www.designingbuildings.co.uk/wiki/EPC EPC].
		+
		+	[https://www.gov.uk/government/consultations/home-energy-model-future-homes-standard-assessment Home Energy Model: Future Homes Standard assessment consultation] (2023) and [https://www.gov.uk/government/publications/home-energy-model-future-homes-standard-assessment-technical-documentation Home Energy Model: Future Homes Standard assessment accompanying technical documentation] The [https://www.designingbuildings.co.uk/wiki/Government government] previously consulted on a wrapper for HEM to support [https://www.designingbuildings.co.uk/wiki/Assessment assessments] determining [https://www.designingbuildings.co.uk/wiki/Compliance compliance] with [https://www.designingbuildings.co.uk/wiki/Building_regulations Building Regulations] [https://www.designingbuildings.co.uk/wiki/Part_l Part L] (the [https://www.designingbuildings.co.uk/wiki/Future_Homes_Standard Future Homes Standard]). This [https://www.designingbuildings.co.uk/wiki/Consultation consultation] is accompanied by several technical [https://www.designingbuildings.co.uk/wiki/Document documents] which go into further [https://www.designingbuildings.co.uk/wiki/Details detail] on the [https://www.designingbuildings.co.uk/wiki/Assumption assumptions] and [https://www.designingbuildings.co.uk/wiki/Validation validation]exercises that have been carried out. Although the [https://www.designingbuildings.co.uk/wiki/EPC EPC] wrapper may differ in some respects and contain updates to some [https://www.designingbuildings.co.uk/wiki/Assumption assumptions], these [https://www.designingbuildings.co.uk/wiki/Document documents] remain the best way to understand how the [https://www.designingbuildings.co.uk/wiki/EPC EPC] [https://www.designingbuildings.co.uk/wiki/Assessment assessment] will approach [https://www.designingbuildings.co.uk/wiki/Input input][https://www.designingbuildings.co.uk/wiki/Standardisation standardisation], where this is [https://www.designingbuildings.co.uk/wiki/Common common] to both new and existing [https://www.designingbuildings.co.uk/wiki/Dwelling dwellings]. These technical [https://www.designingbuildings.co.uk/wiki/Document documents] will be of [https://www.designingbuildings.co.uk/wiki/Interest interest] to those who want to understand the justifications and evidence base behind the [https://www.designingbuildings.co.uk/wiki/Standardisation standardisation] [https://www.designingbuildings.co.uk/wiki/Assumption assumptions] used in the [https://www.designingbuildings.co.uk/wiki/Model model] (relating to [https://www.designingbuildings.co.uk/wiki/Energy_demand energy demand], [https://www.designingbuildings.co.uk/wiki/Weather weather], [https://www.designingbuildings.co.uk/wiki/Fuel fuels] etc).
		+
		+	[https://dev.azure.com/Sustenic/Home%20Energy%20Model%20Reference/_git/Home%20Energy%20Model The Home Energy Model reference code]. Full Python source [https://www.designingbuildings.co.uk/wiki/Codes code] for the [https://www.designingbuildings.co.uk/wiki/Home_Energy_Model Home Energy Model] and the [https://www.designingbuildings.co.uk/wiki/Home_Energy_Model Home Energy Model]: [https://www.designingbuildings.co.uk/wiki/EPC EPC] [https://www.designingbuildings.co.uk/wiki/Assessment assessment] has been published in a series of Git repositories. The [https://www.designingbuildings.co.uk/wiki/Government government] has not published a [https://www.designingbuildings.co.uk/wiki/Users user][https://www.designingbuildings.co.uk/wiki/Interface interface] for HEM:[https://www.designingbuildings.co.uk/wiki/EPC EPC] to accompany this [https://www.designingbuildings.co.uk/wiki/Consultation consultation]. The reference [https://www.designingbuildings.co.uk/wiki/Codes code] will be of [https://www.designingbuildings.co.uk/wiki/Interest interest] to those who want to understand how the [https://www.designingbuildings.co.uk/wiki/Model model] has been implemented in [https://www.designingbuildings.co.uk/wiki/Codes code], and those wishing to fully clarify their understanding of the new methodology. It will also be of [https://www.designingbuildings.co.uk/wiki/Interest interest] to any potential contributors to the [https://www.designingbuildings.co.uk/wiki/Home_Energy_Model Home Energy Model].

	* First completed FHS consultation October 2019		* First completed FHS consultation October 2019

Editor at 21:51, 9 March 2026

2026-03-09T21:51:54Z

← Older revision		Revision as of 21:51, 9 March 2026
Line 1:		Line 1:
−	From SAP to HEM	+	= From SAP to HEM, EPC, MEES and FHS =

−	The Home Energy Model, or HEM, is to be introduced in the UK to replace the Standard Assessment Procedure (SAP), which is currently used to demonstrate that new homes comply with Part L of the Building Regulations and to produce EPC's. The ~~Future Homes Standard~~ (~~FHS~~) is the ~~forthcoming update to Part L (Conservation of Fuel and Power) of the Building Regulations~~ for ~~England, representing the most significant change to new-build standards in over a decade~~.	+	The Home Energy Model, or HEM, is to be introduced in the UK to replace the Standard Assessment Procedure (SAP), which is currently used to demonstrate that new homes comply with Part L of the Building Regulations and to produce EPC's. The reduced version of SAP (RdSAP) is the current methodology for calculating EPCs for existing buildings.

−	The standard requires new homes to produce 75–80% less carbon emissions than homes built to the 2013 baseline, a substantial step beyond the 2021 Part L uplift which only required a 31% reduction and compliance will be demonstrated using the Home Energy Model (HEM) or SAP 10.3 during a transitional period.	+	Under the Minimum Energy Efficiency Standards (MEES) since April 1, 2020, all private rented properties (both domestic and commercial) must have an EPC rating of at least 'E', with plans for this to be raised the minimum standard to 'C' by 2030, with interim targets potentially starting in 2028. Currently the methodology to calculate EPCs uses RdSAP, however this will change over the coming years towards an option to use either HEM or RdSAP, and eventally just HEM.
		+
		+	The introduction of HEM gives an opportunity to introduce flexibility around the inputs assessors make within EPC assessments, depending on the data and tools available to them. To balance flexibilty against the need to have a consistent and efficient assessment process in the interests of clarity for consumers, and time and cost effectiveness for assessors a consultation was launched.
		+
		+	The Future Homes Standard (FHS) is the forthcoming update to Part L (Conservation of Fuel and Power) of the Building Regulations for England, representing the most significant change to new-build standards in over a decade. The standard requires new homes to produce 75–80% less carbon emissions than homes built to the 2013 baseline, a substantial step beyond the 2021 Part L uplift which only required a 31% reduction and compliance will be demonstrated using the Home Energy Model (HEM) or SAP 10.3 during a transitional period.
		+
		+	= What are assessment wrappers? =

	Where SAP was effectively the calculated or estimated potential energy consumption on a monthly basis, the HEM has the potential to calculate or estimate this on a half-hourly basis. As such, in order to model the energy buildings might use at this level, more detailed data points or inputs are likely to be required, making the model potentially more complex to use.		Where SAP was effectively the calculated or estimated potential energy consumption on a monthly basis, the HEM has the potential to calculate or estimate this on a half-hourly basis. As such, in order to model the energy buildings might use at this level, more detailed data points or inputs are likely to be required, making the model potentially more complex to use.

−	~~What are~~ assessment ~~wrappers?~~	+	To manage the broad range of data points or inputs which the new HEM will be capable to interpreting, it is likely that the model will have the possibility to use a number of assumptions rather than inputting individual data for each project. These assumptions may range in relation to the purpose of the assessment, the occupancy patterns, localised weather patterns, links to other building standards, white goods, air tightness, ventilation, and so on. They may also expand with time. The model is intended to be flexible enough to account for and allow for adjustments based on specific buildings while being simple enough to be workable.

−	~~To manage the broad range of data points or inputs which the new~~ HEM ~~will be capable to interpreing~~, ~~it is likely that~~ the ~~model will~~ have ~~the possibility~~ to ~~use a number~~ of ~~assumptions rather than inputting individual~~ data for ~~each project. These assumptions may range~~ in ~~relation to~~ the ~~purpose~~ of the ~~assessment~~, the ~~occupancy patterns, localised weather patterns, links to other building standards, white goods, air tightness, ventilation, and so on~~. ~~They may also expand with time~~. The ~~model~~ is ~~intended to be flexible enough~~ to ~~account for~~ and ~~allow for adjustments based on specific buildings while being simple enough to~~ be ~~workable~~.	+	The current government consultation The Home Energy Model: Energy Performance Certificates. HEM methodology for assessing existing dwellings and producing new EPC metrics looks at aspects of these changes. The consultation looks at a ‘modular’ approach, where the assessor enters as much data as they have access to in each dwelling. The modular structure of the HEM core engine permits this approach, where data for a given module can be provided in multiple ways without interfering with the rest of the calculation. In this new approach, the “all-or-nothing” of RdSAP would be replaced by a flexible series of input simplifications. These aspects are being covered by what are termed as wrappers.
		+
		+	The Home Energy Model: Future Homes Standard assessment is a methodology designed to assess compliance with the 2025 Future Homes Standard (“FHS”). The Home Energy Model and FHS assessment wrapper together make up the Home Energy Model: FHS assessment; both are still under development and will be implemented alongside the FHS in 2025.
		+
		+	= Key elements of FHS =

	Heating, Energy and Renewables The FHS carbon targets are deliberately set at a level that fossil fuel heating systems cannot meet, meaning that in practice air source or ground source heat pumps will become the primary heating technology for new homes, with heat networks using low-carbon sources also acceptable. Hybrid boilers, hydrogen-ready boilers, and gas boilers will not comply, though existing homes remain unaffected. Alongside this, solar PV panels will become a functional requirement under Building Regulations, with developers required to achieve 40% solar coverage of a building's floor area where feasible, helping new homes generate and self-consume renewable electricity and reducing energy bills by an expected 40–50% compared to conventionally built properties.		Heating, Energy and Renewables The FHS carbon targets are deliberately set at a level that fossil fuel heating systems cannot meet, meaning that in practice air source or ground source heat pumps will become the primary heating technology for new homes, with heat networks using low-carbon sources also acceptable. Hybrid boilers, hydrogen-ready boilers, and gas boilers will not comply, though existing homes remain unaffected. Alongside this, solar PV panels will become a functional requirement under Building Regulations, with developers required to achieve 40% solar coverage of a building's floor area where feasible, helping new homes generate and self-consume renewable electricity and reducing energy bills by an expected 40–50% compared to conventionally built properties.
Line 15:		Line 25:
	Fabric Performance, Ventilation and Overheating The FHS introduces significantly improved fabric performance targets through a whole-building approach, with the notional dwelling specification requiring external walls at 0.18 W/m²K, roofs at 0.11 W/m²K, and windows at 1.2 W/m²K — all considerably better than current 2021 standards. The airtightness target of 3 m³/(h·m²) at 50 Pa is particularly demanding, less than half the current regulatory maximum, and will typically require mechanical ventilation with heat recovery (MVHR) to maintain indoor air quality. Given that highly insulated, airtight homes can be prone to summer overheating, the FHS works in conjunction with Part O of the Building Regulations, with HEM's half-hourly simulation well suited to modelling overheating risk and tracking internal temperatures throughout the year.		Fabric Performance, Ventilation and Overheating The FHS introduces significantly improved fabric performance targets through a whole-building approach, with the notional dwelling specification requiring external walls at 0.18 W/m²K, roofs at 0.11 W/m²K, and windows at 1.2 W/m²K — all considerably better than current 2021 standards. The airtightness target of 3 m³/(h·m²) at 50 Pa is particularly demanding, less than half the current regulatory maximum, and will typically require mechanical ventilation with heat recovery (MVHR) to maintain indoor air quality. Given that highly insulated, airtight homes can be prone to summer overheating, the FHS works in conjunction with Part O of the Building Regulations, with HEM's half-hourly simulation well suited to modelling overheating risk and tracking internal temperatures throughout the year.

−	Background	+	= Background =

	In 2021, the government appointed a consortium of experts led by the BRE to carry out a multi-year project to develop a replacement for SAP, which was first published in 1993. SAP was introduced into the Building Regulations to assess the energy performance of dwellings and has been updated periodically in 1998, 2001, 2005, 2009, 2012, and 2022. The accuracy of EPC's has received much criticism over the years see Are Energy Performance Certificates Accurate? HEM was first consulted on in 2019 with further technical detail set out in a 2023 consultation, the government responded in early 2026 with regulations anticipated to come into force by late 2026.		In 2021, the government appointed a consortium of experts led by the BRE to carry out a multi-year project to develop a replacement for SAP, which was first published in 1993. SAP was introduced into the Building Regulations to assess the energy performance of dwellings and has been updated periodically in 1998, 2001, 2005, 2009, 2012, and 2022. The accuracy of EPC's has received much criticism over the years see Are Energy Performance Certificates Accurate? HEM was first consulted on in 2019 with further technical detail set out in a 2023 consultation, the government responded in early 2026 with regulations anticipated to come into force by late 2026.
Line 31:		Line 41:

	The replacement of SAP and the introduction of HEM is a significant change that will impact a wide variety of areas concerning the estimation, demonstration of compliance, and, to some extent, the assessment of energy use in buildings. Given the importance and timeframe for the development of HEM, the government appointed a consortium led by Etude to quality-assure the work being undertaken. This QA process aims to ensure that issues with the current SAP methodologies are identified and clearly defined, evidence for suggested improvements is thorough, validation processes are robust, the decision-making process is clear, robust, and documented, and project governance is working effectively with the government, key user groups, and technical experts associated with key decisions.		The replacement of SAP and the introduction of HEM is a significant change that will impact a wide variety of areas concerning the estimation, demonstration of compliance, and, to some extent, the assessment of energy use in buildings. Given the importance and timeframe for the development of HEM, the government appointed a consortium led by Etude to quality-assure the work being undertaken. This QA process aims to ensure that issues with the current SAP methodologies are identified and clearly defined, evidence for suggested improvements is thorough, validation processes are robust, the decision-making process is clear, robust, and documented, and project governance is working effectively with the government, key user groups, and technical experts associated with key decisions.
−
−	~~How does HEM relate to the Future Homes Standard?~~
−
−	The Home Energy Model: Future Homes Standard assessment is a methodology designed to assess compliance with the 2025 Future Homes Standard (“FHS”). The Home Energy Model and FHS assessment wrapper together make up the Home Energy Model: FHS assessment; both are still under development and will be implemented alongside the FHS in 2025. All elements of the topic are under development and, as such, are also at the consultation stage, enabling the industry to participate in their development process.
−
−	~~The consultation will close at 11:59pm on 6 March 2024, for further information about HEM, the Future Homes Standard and the consultation visit the government web page here.~~

	[[Category:Articles_needing_more_work]]		[[Category:Articles_needing_more_work]]

Editor at 21:15, 9 March 2026

2026-03-09T21:15:10Z

← Older revision		Revision as of 21:15, 9 March 2026
Line 1:		Line 1:
		+	From SAP to HEM

		+	The Home Energy Model, or HEM, is to be introduced in the UK to replace the Standard Assessment Procedure (SAP), which is currently used to demonstrate that new homes comply with Part L of the Building Regulations and to produce EPC's. The Future Homes Standard (FHS) is the forthcoming update to Part L (Conservation of Fuel and Power) of the Building Regulations for England, representing the most significant change to new-build standards in over a decade.
		+
		+	The standard requires new homes to produce 75–80% less carbon emissions than homes built to the 2013 baseline, a substantial step beyond the 2021 Part L uplift which only required a 31% reduction and compliance will be demonstrated using the Home Energy Model (HEM) or SAP 10.3 during a transitional period.
		+
		+	Where SAP was effectively the calculated or estimated potential energy consumption on a monthly basis, the HEM has the potential to calculate or estimate this on a half-hourly basis. As such, in order to model the energy buildings might use at this level, more detailed data points or inputs are likely to be required, making the model potentially more complex to use.
		+
		+	What are assessment wrappers?
		+
		+	To manage the broad range of data points or inputs which the new HEM will be capable to interpreing, it is likely that the model will have the possibility to use a number of assumptions rather than inputting individual data for each project. These assumptions may range in relation to the purpose of the assessment, the occupancy patterns, localised weather patterns, links to other building standards, white goods, air tightness, ventilation, and so on. They may also expand with time. The model is intended to be flexible enough to account for and allow for adjustments based on specific buildings while being simple enough to be workable.
		+
		+	Heating, Energy and Renewables The FHS carbon targets are deliberately set at a level that fossil fuel heating systems cannot meet, meaning that in practice air source or ground source heat pumps will become the primary heating technology for new homes, with heat networks using low-carbon sources also acceptable. Hybrid boilers, hydrogen-ready boilers, and gas boilers will not comply, though existing homes remain unaffected. Alongside this, solar PV panels will become a functional requirement under Building Regulations, with developers required to achieve 40% solar coverage of a building's floor area where feasible, helping new homes generate and self-consume renewable electricity and reducing energy bills by an expected 40–50% compared to conventionally built properties.
		+
		+	Fabric Performance, Ventilation and Overheating The FHS introduces significantly improved fabric performance targets through a whole-building approach, with the notional dwelling specification requiring external walls at 0.18 W/m²K, roofs at 0.11 W/m²K, and windows at 1.2 W/m²K — all considerably better than current 2021 standards. The airtightness target of 3 m³/(h·m²) at 50 Pa is particularly demanding, less than half the current regulatory maximum, and will typically require mechanical ventilation with heat recovery (MVHR) to maintain indoor air quality. Given that highly insulated, airtight homes can be prone to summer overheating, the FHS works in conjunction with Part O of the Building Regulations, with HEM's half-hourly simulation well suited to modelling overheating risk and tracking internal temperatures throughout the year.
		+
		+	Background
		+
		+	In 2021, the government appointed a consortium of experts led by the BRE to carry out a multi-year project to develop a replacement for SAP, which was first published in 1993. SAP was introduced into the Building Regulations to assess the energy performance of dwellings and has been updated periodically in 1998, 2001, 2005, 2009, 2012, and 2022. The accuracy of EPC's has received much criticism over the years see Are Energy Performance Certificates Accurate? HEM was first consulted on in 2019 with further technical detail set out in a 2023 consultation, the government responded in early 2026 with regulations anticipated to come into force by late 2026.
		+
		+	* First completed FHS consultation October 2019
		+	* Government response to first consultation January 2021
		+	* The interim step with the Part L 2021 uplift June 2022 came into force
		+	* The second FHS consultation was compoeted in December 2023
		+	* The HEM consultation response was published in October 2025
		+	* The mandatory requirement for solar was announced in June 2025
		+	* The Government response to 2023 FHS consultation is expected in Quarter 1 2026
		+	* The Final regulations are then to be laid before Parliament during 2026
		+	* FHS is expected to come into force later in 2026
		+	* The transitional period for the implementation is expected to be 12 months ending in 2027
		+
		+	The replacement of SAP and the introduction of HEM is a significant change that will impact a wide variety of areas concerning the estimation, demonstration of compliance, and, to some extent, the assessment of energy use in buildings. Given the importance and timeframe for the development of HEM, the government appointed a consortium led by Etude to quality-assure the work being undertaken. This QA process aims to ensure that issues with the current SAP methodologies are identified and clearly defined, evidence for suggested improvements is thorough, validation processes are robust, the decision-making process is clear, robust, and documented, and project governance is working effectively with the government, key user groups, and technical experts associated with key decisions.
		+
		+	How does HEM relate to the Future Homes Standard?
		+
		+	The Home Energy Model: Future Homes Standard assessment is a methodology designed to assess compliance with the 2025 Future Homes Standard (“FHS”). The Home Energy Model and FHS assessment wrapper together make up the Home Energy Model: FHS assessment; both are still under development and will be implemented alongside the FHS in 2025. All elements of the topic are under development and, as such, are also at the consultation stage, enabling the industry to participate in their development process.
		+
		+	The consultation will close at 11:59pm on 6 March 2024, for further information about HEM, the Future Homes Standard and the consultation visit the government web page here.

	[[Category:Articles_needing_more_work]]		[[Category:Articles_needing_more_work]]