The 2026 editions of Approved Document L, conservation of fuel and power, and Approved Document F, ventilation, were published on 24 March 2026 and come into force on 24 March 2027. Between those two dates the current editions apply, and an application made under them is protected by transitional provisions.
The three dates
| Date | What happens |
|---|---|
| 24 March 2026 | The 2026 editions are published. Nothing changes for applications yet. |
| 24 March 2027 | The 2026 editions come into force for ordinary domestic work. Applications made from this date are assessed against them. |
| 24 March 2028 | The end of the transitional period. Work with an application made before 24 March 2027 must have commenced by this date to remain under the current standards. |
What "transitional" means for a job
An application made before 24 March 2027 is assessed against the current editions, and the work stays under those standards provided it commences before 24 March 2028. A job that is designed this year, submitted this year and started next year is under the current editions throughout. A job that is submitted this year but does not start until the spring of 2028 loses that protection, and the design has to meet the new editions.
For a practice, the practical point is that the date of the application matters, and so does the date work starts. A specification issued now should say which editions it is written to and should carry the transitional provision, so that the reader of the document, in 2027, knows what it was written against.
A note, not an instruction. The right thing on the last page of a specification is a short paragraph under a plain heading: that the specification is written to the Approved Documents in force at the date of issue, that the 2026 editions come into force on 24 March 2027, and that work with an application made before that date remains under the current standards provided it commences before 24 March 2028.
The wrong thing is an internal quality-control instruction left on the issued document. "Verify before issue" tells building control that the document in their hands was not.
What a library has to do about it
The 2026 editions are a rewrite of the Part L and Part F guidance, not an amendment. A clause library written to the current editions will need a full pass against the new ones during 2027: every U-value target, every ventilation rate, every reference to a table or a section. That is why a specification library is maintained on a subscription and not sold once. A one-off purchase commits the buyer to a document that stops being current on a known date.
Until the new editions have been read in full, no figure from them should be stated in a specification. A number inferred from a summary, a press release or a filename is a number invented, and a specification that goes to building control must never carry one.