Using Fallback Positions for Extensions and Conversions
Introduction
In the UK planning system, householder proposals such as extensions and conversions often fall within strict policy boundaries relating to size, scale, and impact. However, one effective way to justify a proposal that exceeds or deviates from policy expectations is to rely on a fallback position—a form of development that could be carried out lawfully if permission were refused.
In householder applications, these fallback positions are often established through:
• Certificates of Lawful Development (under sections 191 or 192 of the Town and Country Planning Act 1990), and
• Prior Approval mechanisms, such as the larger home extension scheme under Class A of the General Permitted Development Order (GPDO).
This blog examines how fallback positions can be used to strengthen planning applications for home extensions and conversions, how to lawfully establish them, and the strategic considerations involved.
What is a Fallback Position?
A fallback position is a development that could be carried out without further planning permission, and which an applicant may genuinely pursue if their preferred scheme is refused. In the context of extensions and conversions, these are typically:
• Works allowed under permitted development rights (e.g. side/rear extensions, loft dormers, garage conversions);
• Lawful existing developments confirmed through a Certificate of Lawfulness (LDC); or
• Larger home extensions approved via the prior approval process.
Used correctly, a fallback position can help demonstrate that the proposed development is no more harmful (or less harmful) than something that could be built anyway.
Key Legal Context
Fallback arguments are supported in case law, notably the Mansell v Tonbridge and Malling BC [2017] judgment, which reaffirmed that a fallback must:
1. Have a real prospect of being implemented;
2. Be lawful or permitted under current planning legislation;
3. Be materially comparable with the proposed development.
Establishing Lawful Fallbacks
1. Certificates of Lawful Development (LDCs)
An LDC confirms that a particular use or development is lawful at a specific point in time. For extensions and alterations, these are usually proposed LDCs (section 192), which establish that a future development would be lawful under the GPDO.
Common Examples:
• A 3m rear extension on a semi-detached house
• A rear dormer loft conversion under Class B
• A garage conversion under Class C
Strategic Use:
• Submit an LDC application for a PD-compliant extension.
• Once approved, use the LDC as a material fallback when submitting a planning application for a slightly larger or altered design.
Example:
A homeowner secures an LDC for a 3m deep rear extension under PD. They then apply for a 4m deep extension under full planning, arguing that the 4m scheme has a better design and no greater impact on neighbours than the lawful fallback.
2. Prior Approval for Larger Home Extensions
Under Class A, Part 1 of Schedule 2 of the GPDO, homeowners can build larger single-storey rear extensions of up to:
• 6m for terraced and semi-detached houses
• 8m for detached houses
This is subject to the neighbour consultation scheme (prior approval), which allows neighbours to object only on the grounds of amenity impact.
Strategic Use:
• Secure prior approval for the larger PD extension (e.g. an 8m rear extension).
• Use this as a fallback when applying for a more sympathetic or better-designed extension that still requires full planning permission.
Example:
A detached homeowner gains prior approval for an 8m rear extension but applies for a 6m extension that includes a parapet wall and glazed roof. The LPA’s policies may resist such features, but the applicant can argue that the 8m fallback is larger and has greater visual or amenity impact.
Common Householder Scenarios Using Fallbacks
1. Loft Conversions with Dormers
• A large box dormer may be allowed under Class B PD rights.
• A more architecturally sympathetic pitched dormer requiring full permission may be preferable.
• The fallback argument: “The PD dormer is lawful, but the proposed dormer is better designed and less bulky.”
2. Side and Wraparound Extensions
• A single-storey side extension and rear extension may be PD when built separately.
• A combined wraparound extension may require full planning.
• The fallback: “We could build both under PD, but this unified design reduces overall massing and visual impact.”
3. Rear Extensions on Sloping Sites
• On sloping land, PD rear extensions may have higher impact due to raised platforms or steps.
• A planning application for a sunken or level structure may be preferable, even if it exceeds PD thresholds.
• The fallback supports the argument that a worse PD outcome is avoidable by granting permission.
4. Conversions of Garages or Outbuildings
• Conversions may be PD depending on the building’s status and location.
• Planning may be needed if changes affect the appearance or use materially.
• An LDC can secure the fallback position that a basic conversion is lawful, supporting a higher-quality proposal.
Presenting the Fallback to the LPA
When using a fallback position as a planning argument:
• Include the LDC or Prior Approval notice as part of the planning application documents.
• Provide clear comparative drawings between the fallback and proposed scheme.
• Emphasise improvements in design, neighbour impact, or visual quality.
• Demonstrate intention to implement the fallback if permission is refused (e.g. through statements or early-stage works).
When Fallbacks Are Most Effective
Fallback arguments are particularly useful when:
• The LPA’s local plan policies restrict certain designs or sizes.
• The site is in a conservation area, Green Belt, or other sensitive location where PD rights still apply.
• You are seeking negotiation leverage with planning officers.
• You want to avoid appeal risks by showing that refusing permission leads to a worse outcome.
Risks and Limitations
• Fallbacks must be credible. LPAs and Inspectors will disregard hypothetical or implausible scenarios.
• Time-sensitive: Prior approval lapses if not implemented within 3 years. LDCs do not grant permission—they confirm lawfulness.
• Design may still matter: Just because something is lawful doesn’t mean a worse design will be approved — the fallback must clearly demonstrate lesser harm.
• PD rights can be restricted by Article 4 Directions or planning conditions.
Conclusion
Fallback positions are an increasingly valuable part of the householder and extension planning toolkit. By lawfully securing what could be built under PD or through a certificate, applicants can present a strong case for their preferred design—even where it exceeds local policy guidelines.
The key is to establish lawfulness, demonstrate intent, and present a clear comparison between the fallback and proposed scheme. When done correctly, this can tilt the balance toward approval and avoid costly redesigns or appeals.
Disclaimer: This article is for general informational purposes only and does not constitute legal or professional advice. Always consult relevant professionals and local authorities before undertaking any development or change of use.