If an English planning application for a proposed secondary dwelling is refused, granted with conditions, or left undecided, the applicant may have an appeal route. The route and deadline depend on the planning application class, the date of the application, the decision or non-determination status, and any enforcement action. “ADU” is a general label; it does not determine the legal application class.
Confirm the application class first
The Planning Inspectorate’s procedural guide applies to appeals relating to applications dated on or after 1 April 2026. Its householder rules cover development of an existing dwellinghouse or development within its grounds for a purpose incidental to the dwellinghouse. A self-contained additional home may not fit that definition. Do not assume the householder deadline applies just because the proposal is behind an existing home. Check the application form, validation record, decision notice, and local planning authority’s classification. Applications dated before 1 April 2026 use the earlier procedural guide.
An applicant may be able to appeal when permission is refused, when permission is granted with conditions they object to, or when the local planning authority does not decide by the applicable decision deadline. For non-determination, a standard valid planning application generally has an eight-week decision period; major development and applications requiring an environmental impact assessment have different periods. A longer period can be agreed in writing. Confirm the deadline for the actual application rather than counting from an informal enquiry or incomplete submission.
Check the deadline for the relevant appeal
For applications dated on or after 1 April 2026, the detailed Planning Inspectorate guide gives these examples:
| Circumstance | Stated filing period |
|---|---|
| Refusal of a householder planning application | The Inspectorate must receive the appeal within 12 weeks of the date on the decision notice. |
| Failure to decide a householder application | The Inspectorate must receive the appeal within 6 months after the local authority’s decision period expires. |
| Other planning appeal types | The ordinary period is 6 months from the decision notice or, for non-determination, from expiry of the authority’s decision period. |
The guide lists other appeal classes and exceptions. If an enforcement notice concerns the same or similar development, a shorter 28-day period may apply. The exact notice, application type, and dates control; an appeal received after its filing deadline may not be accepted.
Prepare and submit the appeal
Read the decision notice and record the refusal reasons, conditions, application class, application date, and relevant decision-period dates. Only the person who made the planning application may appeal. If a change to the proposal could address the refusal, the Inspectorate says to consider a new planning application; it describes an appeal as a last resort rather than a bargaining tactic.
Use the current appeal service and submit the appeal form and essential supporting documents before the applicable deadline. The appeal should address the authority’s reasons and the evidence submitted with the original application. New material may be disregarded, and the Inspectorate will validate the appeal and set its procedure and timetable. Send a copy to the local planning authority as required by the procedure.
Read appeal-time figures as past performance
The Planning Inspectorate’s June 2026 statistics report that valid householder appeals decided by written representations had a 12-week median and a 14-week mean across 351 decisions. For section 78 written-representation planning appeals, the median was 17 weeks and the mean was 19 weeks across 758 decisions. These are England-wide results for cases decided in that month, measured from a valid appeal the Inspectorate could progress to its decision. They are not ADU-specific, do not start at the local application, and cannot predict how long a new appeal will take.
An appeal decision is separate from building-regulations approval, other site consents, permit fees, inspections, and construction. Confirm the current procedure and deadline with the Planning Inspectorate or local planning authority before relying on a date. This guide explains the process; it does not determine whether a particular proposal is appealable or whether an appeal is advisable.