Extension Depth Rules: Rear Extension Limits And Planning Permission
Read this when an extension proposal is growing in size and you need to understand when depth becomes the planning problem rather than just another design detail.
Read This Answer In The Order That Saves You Time
What This Answer Is Designed To Resolve
Searches this page matches
Useful when the real question sounds like What size extension can I build without permission? and you want the shortest route to a practical answer.
What it settles fastest
A practical answer-first guide to extension depth and the limits that usually matter first.
Checks to keep in view
- Rear extension depth is one of the quickest ways to move from a simple permitted development question into a formal planning application.
- Storey count, existing site history and the side effects on neighbours all matter alongside pure measurement.
- A scheme can be acceptable in principle but still need a better design response to privacy, daylight or scale.
The Short Answer, The Main Tripwires And The Safest Next Move
What usually applies
Read this when an extension proposal is growing in size and you need to understand when depth becomes the planning problem rather than just another design detail.
What often changes it
- Rear extension depth is one of the quickest ways to move from a simple permitted development question into a formal planning application.
- Storey count, existing site history and the side effects on neighbours all matter alongside pure measurement.
- A scheme can be acceptable in principle but still need a better design response to privacy, daylight or scale.
Best next step
Use the detailed sections below as a briefing note, then move into the related guidance if your situation turns on one project type, one local authority or one rule.
When This FAQ Answer Is Usually Enough And When To Escalate
Usually enough when
- The question is about process, evidence, timing or one narrow planning definition.
- You need a practical briefing note before opening a project guide or local authority page.
- The proposal is not obviously close to a hard planning threshold.
Go further when
- One exact project type, council area, conservation area or listed-building issue is already driving the answer.
- The financial or timing consequences are large enough that a summary answer is not a safe stopping point.
- The route still feels mixed after reading the key checks below.
What usually settles it faster
- Rear extension depth is one of the quickest ways to move from a simple permitted development question into a formal planning application.
- Storey count, existing site history and the side effects on neighbours all matter alongside pure measurement.
- A scheme can be acceptable in principle but still need a better design response to privacy, daylight or scale.
If This Answer Turns Into A Bigger Planning Question
These are the next pages most likely to help if the answer needs to turn into a project guide, a local rule check or a more formal route decision.
House Extensions
Browse the main extension planning hub.
Open pageSingle Storey Extensions
Go deeper into the project type that most often raises depth questions.
Open pageDistance From Boundary
Boundary relationship often decides how a deep extension feels in practice.
Open pageWhy Depth Is Such A Key Trigger
Extension proposals often start modestly and then expand during design. Depth matters because it is a simple measurable way of controlling neighbour impact, garden dominance and the cumulative size of additions to the original house.
That is why rear and side extension questions are often resolved by depth long before more complex design issues are considered.
What Else Depth Connects To
A deep extension can also amplify other planning concerns, including overshadowing, overbearing impact, poor relationship with neighbouring windows and an overall sense of overdevelopment.
The more a proposal stretches depth, the more the quality of drawings and the local context tend to matter.
- Depth should be checked alongside height and boundary relationship.
- Two-storey schemes deserve extra neighbour-impact scrutiny.
- Large extensions are stronger when the design reads as part of the house rather than a bolt-on volume.
Questions People Usually Ask Next
Is rear extension depth the same rule for every house?
No. Property type, storey count and the detailed permitted development framework can change the position.
Can an extension be within depth limits but still be refused?
Yes. Design quality and neighbour impact can still be planning issues, especially on applications.
Should I reduce depth or redesign the form?
Either can help. The right answer depends on whether the main problem is pure size, neighbour impact or the overall appearance of the proposal.
Need A More Case-Specific Steer By Email?
If this FAQ answers the broad process question but your own case still turns on the details of the project, the property or the local authority area, send over the facts for a more tailored plain-English steer.
Best for
Borderline, location-sensitive or awkwardly specific cases where a broad page is useful, but not quite enough on its own.
What the reply aims to do
Best when a broad guide has narrowed the issue but the live answer still depends on the details of your site, design or local authority area.
What to include
Property type, council area, location, the change you want to make, approximate dimensions, relevant heritage or flat-related details, previous additions and the main concern.
Important: Replies are informational personalised guidance based on the details you provide and publicly available information. They are not formal legal, architectural, surveying or council advice. Site-specific or borderline cases may still need checking with the local authority or a qualified specialist before drawings, applications or contractor spend move ahead.
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When This Page Helps Most And When To Go Further
Best when
This page works best when the uncertainty is about process, evidence, permissions or one narrow planning definition rather than a full project design.
Go local when
Conservation areas, listed status, Article 4 or one specific council are the reasons the answer may change in practice.
Escalate when
If the proposal is close to a hard limit or the consequences matter financially, use the matching guide, tool or formal check rather than relying on a summary answer alone.
Related Guidance
Keep these as follow-ups after the main answer above. They are useful when the issue branches into a project, a local route or a more formal planning check.
Show more related guidance and deeper follow-up pages
Use This Answer Properly
Planning answers change when a proposal is close to a limit, the property has special controls or the site history has already used development allowances. Use this page as a practical briefing note, not as a final permission decision, and verify the position formally if the financial, timing or design consequences of being wrong are meaningful.