The transition from Part L 2021 to the Future Buildings Standard follows a structured 12-month arrangement set out in Building Circular 01/2026. Projects that have already been submitted to building control before the enforcement date may continue under the current regulations, provided work commences within the transition period.
Enforcement dates
The FBS has two enforcement dates (Building Circular 01/2026):
- March 2027 – all non-domestic buildings except higher-risk buildings
- September 2027 – higher-risk buildings (HRBs)
Who is affected?
The transitional provisions apply to projects where a building control application (full plans) or initial notice has been submitted before the relevant enforcement date. This includes:
- Non-HRB projects submitted to a local authority or approved inspector before March 2027
- HRB projects submitted to the Building Safety Regulator before September 2027
Projects that have not been submitted before the enforcement date must comply with the FBS, regardless of when design work started.
What counts as “commenced work”?
To benefit from transitional provisions (for non-HRB projects), work must have commenced within 12 months of the enforcement date. For new buildings, “commenced” means the sub-structure — foundations, basement structure, and ground floor structure — must be completed, not merely that work has started on site. Transitional protection applies per individual building, not site-wide (Building Circular 01/2026).
The 12-month transition period
The transition period runs for 12 months from each enforcement date:
- Non-HRB transition: March 2027 to March 2028 – work must commence (sub-structure completed) within 12 months
- HRB transition: HRBs have application-validity-based protection with no 12-month commencement deadline. Projects with valid applications submitted to the Building Safety Regulator before September 2027 retain transitional protection for as long as the application remains valid (Building Circular 01/2026, Section 2.2)
For non-HRB projects, if a project was submitted before the enforcement date but work has not commenced within the 12-month window, the transitional provisions no longer apply. The project must then comply with the FBS. This means the building control application or initial notice effectively lapses for energy compliance purposes.
Practical implications for live projects
Projects already on site
If your project is already under construction with an active building control application under Part L 2021, you can complete the project under those standards. The transitional provisions protect projects that are genuinely underway.
Projects in design
If your project is still in design and you plan to submit before the enforcement date, consider whether construction will realistically start within 12 months. If not, it may be more pragmatic to design to FBS standards from the outset, avoiding the risk of needing to redesign later.
Projects not yet submitted
Any project submitted after the enforcement date must comply with the FBS. There is no option to use the previous standards. Review the notional building specification and solar PV requirements early in the design process.
Work to existing buildings
The transitional arrangements primarily concern new buildings. Work to existing non-domestic buildings (extensions, renovations, change of use) follows separate rules based on the type and scale of work. In general, the applicable standard is determined by when the building control application is made, with the FBS applying to submissions after the enforcement date.
Frequently Asked Questions
How long is the FBS transition period?
For non-HRB buildings, the transition period is 12 months from the enforcement date (March 2027 to March 2028). For higher-risk buildings, transitional protection is application-validity-based with no fixed commencement deadline; protection continues for as long as the application submitted before September 2027 remains valid.
What counts as 'commenced work' under the FBS transition?
For new buildings, commenced work means the sub-structure (foundations, basement structure, and ground floor structure) must be completed – not merely that work has started on site. Preparatory steps like ordering materials or obtaining planning permission do not count. Protection applies per individual building, not site-wide.
What if my project was submitted before the enforcement date?
If your project was submitted to building control before the enforcement date and work commences within 12 months, you can complete under Part L 2021. If work does not commence within 12 months, the project must comply with the FBS.