Successful Objection to a Prior Notification for a Larger Home Extension
Overview
In May 2025, we acted on behalf of a neighbour to object to a Prior Notification application (25/0640/PD42) for a 6-metre deep single-storey rear extension at 26 Knebworth Path, Borehamwood.
Unlike full planning applications, Prior Approval (often called Prior Notification) applications are assessed under the General Permitted Development Order (GPDO) rather than the full planning system. These applications move quickly, with strict deadlines, so it is essential that objections are clear, robust, and submitted on time.
Our professional objection focused on the unacceptable loss of light, overshadowing, and overbearing impacts to the adjoining property. The Council agreed, and refused Prior Approval on the exact grounds we identified.
This case highlights why specialist objection support can be decisive in stopping harmful home extensions. Get in touch today for a free initial consultation, and a transparent, fixed-fee quote to provide a full planning objection letter.
The Challenge
The homeowner at No. 26 sought Prior Approval to build a 6m x 3m rear extension, significantly larger than the 3.35m depth normally accepted in Hertsmere’s Planning and Design Guide.
The proposed extension raised key issues:
Overshadowing: The 6m projection would breach the 45-degree rule from the nearest habitable windows at No. 28, blocking light.
Overbearing effect: At 3m in height and directly along the shared boundary, the wall would dominate the neighbour’s garden and patio.
Amenity loss: Both daylight and outlook from the adjoining home would be severely affected, contrary to Policy SADM30 of the Development Management Plan and the NPPF (2024).
Because this was a Prior Notification application, the Council could only refuse if objections were received during the 21-day consultation window and if amenity harm was demonstrated. Timing and precision were therefore critical.
Side elevation showing proposed extension
Our Approach
We acted quickly to prepare and submit a detailed objection, which:
Cited national and local policies requiring protection of residential amenity.
Applied the BRE Guidelines (Daylight & Sunlight, BR209) and the 45-degree test to show unacceptable light loss.
Referenced local design standards that set a 3.35m extension depth threshold, demonstrating how the proposal substantially exceeded accepted limits.
Highlighted the overbearing impact of a continuous 3m-high wall running for 6m directly on the shared boundary.
Requested that the Council visit the site to fully appreciate the impact.
Our objection ensured the Council had clear, evidence-based grounds to refuse.
The Outcome
The Planning Officer agreed entirely with our objection:
The extension breached the 45-degree line, causing unacceptable light loss.
Its bulk and proximity would be overbearing and create an undue sense of enclosure.
The depth exceeded local design guidance by 2.65m, far beyond what is considered acceptable.
As a result, the Council refused Prior Approval, confirming the development would harm the amenity of adjoining occupiers.
Client Testimonial
“I found Owen’s company online after spending a stressful afternoon wondering how to object to my neighbour’s plans for a 6m extension right up to my boundary. Owen’s letter of objection addressed all of my concerns in a precise and professional manner. He also advised me what to put in my own letter of objection. Using Owen reduced the stress involved and it was money very well spent. This time I was successful in my objection but I fear I may be about to go into round 2 — in which case I will have no hesitation in contacting Owen again.”
Why Prior Notification Applications Are Different
Many homeowners assume that because larger rear extensions are allowed under the Permitted Development rules, they cannot be stopped. In reality, that is not the case.
Full planning applications are assessed on a broad range of planning policies (heritage, design, highways, ecology, etc.).
Prior Notification applications for extensions are more limited. The Council can only assess whether the proposal complies with the GPDO and, crucially, whether it harms neighbours’ amenity.
If no objections are received, Prior Approval is often granted by default. If an objection is made, the Council must decide within 42 days.
This makes professional objections even more important. A well-prepared submission can be the difference between refusal and automatic approval.
Conclusion
This case shows that even when an extension is applied for under Permitted Development rights, it can still be refused where it causes residential amenity harm.
Our client was relieved that the objection succeeded, preventing an oppressive and light-blocking extension from being built.
If you receive notice of a Prior Notification application near your home, act quickly. With only 21 days to object, time is critical. Our planning objection experts can assess the proposal, identify strong grounds, and submit a professional objection that carries real weight with the Council.
Protect your light, privacy, and living standards - contact us today for expert support with planning objections.
