RdSAP 10 Conventions v12.2 Updates for Domestic Energy Assessors
Updated 3 November 2026: the final section of this article has been corrected following a line by line comparison of v12.1 and v12.2. An earlier version wrongly said that several conventions had simply been given a new date, with no change to their wording.
RdSAP Conventions v12.2 became applicable from 6 August 2026, with the amendments themselves dated 13 July 2026. It is a bigger update than the version number suggests: sixteen conventions amended, four brand new conventions added, and Appendix 4 deleted outright. If you assess room in roof conversions, annexes, conservatories, heat networks, electric combi boilers, or dwellings with two mechanical ventilation systems, several of these will show up on your next job. Here is what has actually changed, convention by convention, rather than what has simply been re-dated.
Room in roof: Appendix 4 is gone, and three new rules take its place
Convention 2.06 has three genuine additions. First, where a gable wall is only partly connected to another part of the dwelling because of stepped arrangements, there is now a clear threshold: disregard the connection and treat the gable as exposed if less than 25% of the total area is connected, and record it as connected if more than 25% is connected.
Second, where the stud wall of a roof room has no observed insulation but the adjoining rafters or slopes are insulated in a way that continues to the eaves, like a warm roof, you can now record the stud wall as insulated to the same level and thickness as the rafter or slope insulation. This only applies where visual or physical evidence confirms the insulation actually extends to, or abuts, the stud and eaves junction without a significant gap.
Third, and this is the one to know about: Appendix 4, the standalone table of Room in Roof U-values, has been deleted. In its place, 2.06 now says the U-value of a roof room’s common or gable wall may be inferred directly from Table 18, column ‘Room-in-Roof’, in the RdSAP 10 specification itself. If you have been flicking to Appendix 4 out of habit, that reference no longer exists; the same figures now live in the main specification document.
The dormer window 20% floor area rule has not changed and is easy to assume has moved along with everything else. It has not: the guidance is identical to v12.1.
Conservatories get their own convention for the first time
Previously, the 50% wall glazing and 75% roof glazing definition of a conservatory only existed as an aside inside convention 2.17 (Sun room). It has now been promoted to its own convention, 2.28, with considerably more detail.
The useful addition is what to do when a conservatory’s roof no longer meets that glazing threshold, typically after a solid roof replacement or a false ceiling. In that situation it must now be recorded as an extension rather than a conservatory, and 2.28 sets out exactly how to enter the insulation: use visual or documentary evidence where available; if the roof pitch is less than 10 degrees, enter as flat with insulation unknown; if it is more than 10 degrees with no access, enter as pitched, no access, insulation none; and if it is more than 10 degrees with loft access, follow convention 3.04 instead.
Convention 2.17 has been amended in turn to simply cross-refer to 2.28 rather than repeating the definition inline.
Self-contained annexes: the bar has been made explicit
Convention 1.04a, covering when an attached building unit needs its own EPC, now spells out what ‘self-contained’ actually requires: fixed cooking and bathing facilities, specifically a fixed oven, a sink, and either two or four fixed hot rings (two is sufficient for a one bedroom dwelling, four for anything larger), plus its own access from outside or via a communal corridor. An internal connecting door to the main building does not, on its own, disqualify it from being treated as self-contained.
Bungalow definition tightened
Convention 1.02b previously defined a bungalow as a dwelling with all habitable accommodation ‘on one floor only’. It now reads ‘at the ground floor only’. Worth double-checking any borderline cases you have on file: a single-storey dwelling that happens to sit above another unit, with no accommodation at ground level, could arguably have qualified under the old wording but should not under the new one.
Heat as a Service arrives as its own category
Community heating (4.05a) has always followed a simple rule: if the heat generator is in the dwelling, it is that dwelling’s own system; if it is not, treat it as community heating. Heat as a Service does not follow that rule, and now has its own convention, 4.05b. A Heat-as-a-Service arrangement is treated as community heating regardless of whether the generator sits inside or outside the dwelling, provided the service provider owns and/or operates it. Specific documentary evidence is required to confirm a Heat-as-a-Service installation is actually present. Record it as community heat pump where the service is electric, or community boiler in other cases.
Two mechanical ventilation systems now have a pecking order
New convention 7.03e covers dwellings with two mechanical ventilation systems. If both systems are identical, select that system type and input it with half the number of wet rooms. If they differ, input whichever one can be found in the PCDB. If both are in the PCDB, or both are default systems, work through this order of precedence: mechanical ventilation with heat recovery, then mechanical ventilation, then mechanical extract ventilation, then PIV from outside, then PIV from the loft.
Electric combi boilers get a proper entry method
New convention 4.22 confirms that space heating from an electric combi boiler should be recorded manually as a standard boiler, direct acting, fuel type electricity. Water heating from the same unit is handled separately under convention 6.08.
Two smaller clarifications worth knowing
Convention 9.02, on documentary evidence for insulation upgrades, has been tightened. Where an upgrade is evidenced but the exact thickness is not, the wording now explicitly directs you to use the ‘unknown insulation thickness’ category rather than the more ambiguous ‘lowest selectable thickness better than as-built’ phrasing it replaced.
Convention 10.01, air tightness, gains one new line that matters if you rely on air pressure test certificates: if material changes have been made to the property since the original test, the certificate becomes invalid for RdSAP entry. Our recent piece on the RdSAP 10 changes covers why that evidence matters so much for new builds moving from design stage SAP onto RdSAP.
Other amended conventions: what has really changed
The 13 July 2026 amendment date appears on more conventions than the sections above cover. An earlier version of this article wrongly said that eight of them had not really changed. Comparing the wording of v12.1 and v12.2 shows that seven of those eight contain real changes:
- 2.13, alternative walls: where a construction type that needs to be included (more than 10% of the area) is of very poor thermal quality, such as single leaf or uninsulated timber panel below windows, treat it as a curtain wall.
- 2.16, secondary glazing: unusual single glazing improvements, such as plastic glazing units over single glass or panes of glass separated by large distances, are now treated as secondary glazing.
- 4.09, two main systems: if a high heat retention storage heater is identified but is not in the PCDB, enter it as a fan assisted storage heater.
- 4.20, storage heater in a non habitable room: the rule now applies where the sole source of heat, rather than the primary source of heat, is the storage heater.
- 9.01, open chimneys: the wording has been expanded. A fully sealed chimney with no air bricks does not need to be counted. A decommissioned chimney with air bricks and a ventilation area under 30,000mm2 is treated as blocked and modelled at 20 m3/hr, while one at 30,000mm2 or more is treated as open, and an open chimney is modelled at 80 m3/hr.
- 9.05, photovoltaics: where an individual battery has a storage capacity greater than 5kWh, enter it as two separate batteries: the first at 5kWh, with the excess entered as a second battery.
- 9.08, waste water heat recovery: extra data items are now required: the total number of baths in the property, the number of baths connected to the system, and the type and number of non electric showers. Where a shower is connected to waste water heat recovery, Instantaneous or Storage should be selected.
Convention 4.01a is listed as amended in the official version history and carries the 13 July 2026 date, but we could not find any difference in its wording from v12.1, so there is nothing new to action there. Convention 4.05a is listed as amended only because the old convention 4.05 has been split into 4.05a and 4.05b, and its definition reads the same as before.
Convention 4.03 has a small wording change, extending it explicitly to hot water sources and referencing ‘Direct Hot Water Type’, but it does not change how you would already be handling an inaccessible or incomplete system.
Where to read the full document
This is a summary, not a replacement for the source. The full text for RdSAP Conventions v12.2, including every convention referenced above, is published by BRE as part of the RdSAP 10 documentation. If you want a refresher on the v12.1 conventions that came before this update, we covered those in our earlier v12.1 guide.
If you would like to talk through how any of these changes affect your day to day assessments, or you are considering mentoring or CPD support, get in touch.
