Securing planning permission for a residential project in London is a major step-and often the result of careful design development, detailed submission documents and extended dialogue with the local council. But once permission is granted, how long does it actually last?
Whether you’re considering a new build, extension, loft conversion or basement, understanding the validity period-and what happens if you wait too long to start-can help you avoid costly delays and unnecessary reapplications.
The Standard Validity Period: Three Years
In most cases, full planning permission for residential development in London is valid for three years from the date the decision notice is issued. This is set out under Section 91 of the Town and Country Planning Act 1990.
That means you must commence development within three years, or the permission will expire-and you may need to go through the application process again, potentially under updated policies or altered planning contexts.
What Counts as “Commencement”?
This is where many homeowners become unsure. Starting development doesn’t necessarily mean completing major construction-but it must go beyond preparatory steps.
To be considered a legal commencement, work must usually include:
- Demolition of existing structures (if relevant)
- Excavation for foundations or footings
- Laying of underground drainage
- Any permanent construction above or below ground
- Material operation as defined by planning law
Simply clearing the site, putting up fencing, or ordering materials won’t suffice.
It’s strongly advised that commencement be formally documented, with photographs, dated contractor records, and where possible, written confirmation from your architect or planning consultant.
What if Your Permission Expires?
If three years pass and no valid commencement has taken place, the permission lapses. You’ll then need to submit a new application-even if the design and site haven’t changed.
This can be problematic if local planning policies have tightened, or if previously supported elements (such as glazing ratios, height, or massing) are no longer in favour. In some boroughs, even minor shifts in policy can make re-approval harder to secure.
To avoid this, we often advise clients to review their planning status at the two-year mark and make a clear plan for starting works-even if phasing is required.
Outline vs Full Permission
It’s worth noting that outline planning permissions (used mostly for larger or speculative developments) have different rules. They usually require the submission of “reserved matters” within three years, with an extended period for commencement following final approval.
However, for most residential homeowners, full planning permission is the format used-and the three-year window applies.
Can You Apply to Extend Planning Permission?
There is no formal route to “extend” a planning permission once it has been granted. Previously, temporary COVID-era extensions were permitted, but these have since ended.
If you’re approaching the deadline with no realistic start date, the best course of action is often to resubmit the application with the same design-ideally before the original permission expires. This is usually straightforward if there have been no policy changes or site constraints.
Your architect can guide you on timing, documentation, and potential risks.
Planning vs Building Control
It’s also important to note that planning permission and Building Regulations approval are separate. Even if you’ve started on site within your three-year planning window, you must still secure Building Control approval before or during construction to ensure technical compliance.
This includes structural design, insulation, drainage, fire safety and more. Both permissions are required for lawful and insurable development.
Keeping Permissions Alive with Strategic Planning
For many London homeowners, timelines shift: life changes, financing evolves, or construction resources become stretched. But planning permissions are fixed-and failing to act within the window can mean starting over.
That’s why it’s important to monitor decision dates, document legal commencement correctly, and seek advice before key deadlines approach. Many architects offering architectural services in London can support homeowners in navigating this process-ensuring permissions remain valid and projects progress with confidence.
