Which SAP version applies to my job?

Published 18 October 2026 — reviewed against the regs as they stand.

Quick answer: the latest version is SAP 10.3, approved on 24 March 2026 for the Future Homes Standard. It applies to new homes notified from 24 March 2027, and to homes notified earlier that haven’t started by 24 March 2028. Everything still under Part L 2021 — most homes being designed or built today — is assessed in SAP 10.2. EPCs on existing homes use a different method, RdSAP 10, and the Home Energy Model has not yet been approved (18 October 2026).

Which version for which job

England unless the row says otherwise. “Notified” means a building notice or initial notice given, or full plans deposited, for the building in question.

The Part L edition checker works out the England rows from your own dates.

Why two versions run at once

Each edition of Part L comes with its own approved version of SAP, and with transitional arrangements that let work already in the system finish under the old rules. SAP 10.3 was approved on 24 March 2026, a year before the edition it belongs to comes into force, and its Notice of Approval carries the same transitional rule as the regulations: a building notified before 24 March 2027 is outside the new approval if work on it starts before 24 March 2028, and for that building “the earlier versions of the methodologies may continue to be used”. Three questions decide it, asked of each building separately:

• When was it notified? A building notice, initial notice or full plans in before 24 March 2027 keeps Part L 2021 open to it.
• When did work on it start? It has to start before 24 March 2028, and “started” has a strict meaning: for most buildings the foundations, any basement and the ground-floor structure must be complete, so digging the trenches is not enough. More in what “commenced” actually means.
• Is it a higher-risk building? Then the test is different: a valid building control approval application (Gateway 2) submitted to the Building Safety Regulator before 24 September 2027, and not rejected. The protection carries through to the later stages of that work.

Protection is per building, not per site. On a phased scheme the plots that start in time stay in SAP 10.2, and any plot that starts after 24 March 2028 needs a new calculation in SAP 10.3 against the 2026 targets. A pass in 10.2 is no evidence of a pass in 10.3. The older transitional provisions that still let some long-running sites build to the 2010 standards are revoked on the same terms: a building relying on them keeps its protection only if work on it starts before 24 March 2028. The Future Homes Standard guide has the full transitional rules.

Expect the overlap to last. Two years after SAP 10 arrived, Elmhurst Energy’s tracking of EPC lodgements found only about 20% of new homes were being built to the latest regulations; the rest were going through under transitional arrangements on SAP 2012 (October 2024). The as-built SAP for a protected building is done when the building is finished, so SAP 10.2 calculations will go on being produced well after March 2027.

What SAP 10.3 changes

SAP 10.3 is SAP 10.2 revised for the Future Homes Standard, not a new method. Its specification (the version dated 12 June 2026) changes the things that move a result:

• Fuel factors. Grid electricity falls from 0.136 to 0.086 kgCO₂e/kWh for carbon but rises from 1.501 to 1.969 for primary energy; mains gas barely moves (0.210 to 0.214, and 1.130 to 1.12). The electricity figure is now one annual value, not the monthly values SAP 10.2 used.
• The notional dwelling that sets the targets: a heat pump at a seasonal COP of 2.5 in place of a gas boiler, air permeability of 4 instead of 5, decentralised mechanical extract, waste water heat recovery on every shower except in single-storey dwellings, and 120 lm/W lighting. The notional fabric U-values do not change.
• Solar PV. The notional dwelling now has the same array as the actual dwelling, capped at 40% of the ground-floor area ÷ 4.5, and on-site generation becomes a requirement in its own right (requirement L3).

The detail, with what the arithmetic does to a heat pump, a gas boiler and a panel heater, is in SAP 10.3: what actually changed. What changed between SAP 2012 and SAP 10 is in the SAP 10 guide, and the targets themselves in DER and TER.

When the Home Energy Model arrives

The Home Energy Model (HEM) is the government’s replacement for SAP: a new calculation engine, run as a single central service, that models a home at half-hourly intervals. The government said it would join SAP 10.3 no earlier than three months after the Future Homes Standard was published; on 8 June 2026 its launch was delayed. The government’s SAP page now says HEM will be introduced for Future Homes Standard compliance alongside SAP 10.3 “in the coming months”. As of 18 October 2026 it has not been approved.

For a job, that means:

• Part L 2021 work is unaffected. It stays in SAP 10.2, whenever HEM arrives.
• Work under the 2026 edition is SAP 10.3 until HEM is approved. Then either can be used for a dual-running period that the government says will last at least 24 months, before HEM replaces SAP. When SAP 10.3 is withdrawn will matter for anything designed in it and finished later; no date has been set.
• EPCs will move too. Reformed domestic EPCs with four headline metrics, produced by HEM, are now due in England and Wales in the second half of 2027.
• Scotland is heading the same way. Its next standard, proposed for autumn 2029, would be calculated in HEM with a Scottish wrapper (the consultation).

The EPC follows the as-built calculation

A new dwelling’s EPC isn’t a separate survey. It is lodged from the as-built SAP, the same model that produces the completion BREL report, so it is full SAP and never RdSAP. RdSAP is the reduced-data method for existing homes; its current version, RdSAP 10, replaced RdSAP 2012 in June 2025.

The government’s EPC notice of approval of 24 March 2026 moved new homes in England from SAP 10.2 to SAP 10.3, with the same transitional rule as the Building Regulations notice: for a building notified before 24 March 2027 and started before 24 March 2028, “the earlier versions of the methodologies may continue to be used”. So a protected Part L 2021 plot’s EPC is lodged from its SAP 10.2 as-built calculation, as SAP 2012 plots were last time (which is what the Elmhurst figures above measure), and a plot that loses its protection is calculated, and lodged, in SAP 10.3. If a predicted EPC band is already in your sales particulars, check it again for any plot that moves.

Wales, Scotland and Northern Ireland

Wales has its own Part L. Today that is Approved Document L 2022, in force since 23 November 2022, with SAP 10.2 approved for it from the same date. The Welsh Government’s 2026 amending regulations bring the next changes into force on 4 March 2027: a new energy use intensity rating in place of the energy efficiency rating, and on-site renewable electricity for new dwellings. The Welsh Approved Document L 2026, published on 7 April 2026, says the calculation must use SAP 10.3. Work notified before 4 March 2027 stays under the 2022 edition if work on that building starts within 12 months, before 4 March 2028; as in England, it goes building by building. The English dates do not apply in Wales.

Scotland has no Part L. The equivalent is Section 6 of the Building Standards Technical Handbook; its 2023 standards apply to building warrant applications made from 1 February 2023 and are assessed in SAP 10.2. The next revision, the “Passivhaus equivalent” standard, is proposed for autumn 2029 and would be calculated in HEM with a Scottish wrapper.

Northern Ireland uses Technical Booklets F1 and F2, last revised on 30 June 2022, which kept SAP 2009 for dwellings (and SBEM version 4 for other buildings). The Department of Finance consulted on a review of the energy standards in 2023, but draft regulations and Technical Booklets have yet to go out to consultation, and there is no date.

What to ask your assessor

Give your assessor three dates for each building — when the notice or plans went in, when work will start and when it should finish — and say whether any building is higher-risk. Then ask:

• Which edition, and which SAP version, does each building fall under? On a phased site the answer can differ from plot to plot.
• What happens if a start slips past 24 March 2028? That plot needs a new SAP 10.3 calculation against the 2026 targets, and possibly a different specification. Better to know before the slab than after it.
• If a plot moves to SAP 10.3, does its predicted EPC band still hold? The EPC is lodged in the same version as the as-built calculation.
• For a scheme notified from 24 March 2027: is HEM approved yet, and will you run HEM or SAP 10.3?
• For a conversion or an extension: which route, and which version? Conversions and over-glazed extensions follow different rules from a new build.
• In Wales: the 2022 or the 2026 Welsh edition?

Some inputs are the same whichever version runs. Wall, roof and floor build-ups can be checked against the limiting U-values in U-Monkey, and calculated junction Ψ-values from ΨMonkey replace the defaults in SAP 10.2, SAP 10.3 and HEM alike, often the cheapest way to close a gap in any of them. The compliance timeline shows where each calculation falls on the programme, and the Part L guide covers the tests the SAP has to pass.

Sources

• MHCLG, Notice of approval of the methodologies of calculation of the energy performance of new buildings in England (24 March 2026) — SAP 10.3, and the transitional rule.
• MHCLG, The Future Homes and Buildings Standards: Building Circular 01/2026 — commencement dates, higher-risk buildings, the older transitional provisions (SI 2026/335, regulation 10).
• MHCLG, The Future Homes and Buildings Standards: consultation response (March 2026) — the Home Energy Model no earlier than three months after, and at least 24 months of dual running.
• MHCLG, Methodologies for expressing the energy performance of buildings in England and Wales: notice of approval (24 March 2026) — EPCs for new dwellings.
• GOV.UK, Standard Assessment Procedure (updated 8 June 2026) — SAP 10.3 as the sole approved methodology, and the Home Energy Model delay.
• MHCLG, Approved Document L: conservation of fuel and power — the 2021 edition, in force 15 June 2022.
• BRE, SAP 10 — SAP 10.2 in England, Wales and Scotland — and the SAP 10.3 specification, version 12-06-2026.
• Welsh Government, Notice of approval of updated calculation methodologies in Wales (WGC 007/2022) (23 November 2022).
• Welsh Government, The Building etc. (Amendment) (Wales) Regulations 2026 (WGC 003/2026) (6 March 2026; SI 2026/60), and Approved Document L 2026, volume 1 (7 April 2026), paragraph 1.3.
• Scottish Government, Building regulations: Passivhaus equivalent — Stage 2 consultation (24 July 2026).
• Elmhurst Energy, Section 6 Scottish building regulations now live (1 February 2023); Northern Ireland government announce new Part F standards (2022); Tracking the transition to SAP 10 (3 October 2024); MHCLG release the Future Homes Standard (24 March 2026).
• MHCLG, Methodologies for expressing the energy performance of buildings in England and Wales: notice of approval (15 June 2025) — RdSAP 10 for existing dwellings.
• Department of Finance (Northern Ireland), Review of energy efficiency requirements and related areas of the Building Regulations (consultation, 2023).