Extensions
Two-Storey Extension Permitted Development Rules (2025 Guide)
Two-storey extensions face tighter rules than single-storey — but in some cases they don’t need planning permission. Here’s exactly what’s allowed under permitted development.
⏱ 6 min read
📅 Updated June 2025
🏠 England only
Quick Answer
Sometimes permitted development — but with strict conditions
A two-storey rear extension can be permitted development if it projects no more than 3 metres beyond the original rear wall, doesn’t exceed the original ridge height, uses matching materials, and the eaves and ridge heights don’t exceed those of the original house. Side extensions of two storeys always need planning permission. Properties in conservation areas, AONBs, or with Article 4 Directions will almost always need planning permission.
The Rules for Two-Storey Extensions Under PD
Under Class A of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015, a two-storey rear extension is permitted development provided all of the following conditions are met:
| Condition |
Limit |
| Maximum projection beyond original rear wall |
3 metres |
| Maximum eaves height |
Must not exceed the eaves height of the original house |
| Maximum ridge height |
Must not exceed the ridge height of the original house |
| Roof pitch |
Must match the roof pitch of the original house |
| Materials |
Must be similar in appearance to the original house |
| Windows on upper-floor side elevations |
Must be obscure-glazed and non-opening below 1.7m from floor |
| Distance from rear boundary |
Must be at least 7 metres from the rear boundary |
| Position |
Rear only — not to the side or front |
Note that the 3-metre rear projection limit for two-storey extensions is significantly more restrictive than for single-storey extensions (which can extend 4 metres for a detached house, or 3 metres for a terraced/semi-detached house, under standard PD — or further under the Larger Home Extension Scheme).
Why Rear-Only Matters
The permitted development rules for extensions only apply to additions at the rear of the house. “Rear” means the elevation that does not face the highway (the road or public right of way).
This means:
- A two-storey addition at the back of the house: can be PD (if conditions met)
- A two-storey side extension: always needs planning permission — there is no PD right for two-storey side extensions
- A two-storey wraparound (side and rear): always needs planning permission
- A two-storey front extension: always needs planning permission
⚠️ Side extensions of any height need planning permission
If any part of your two-storey addition extends to the side of the house — even if most of it is at the rear — you will likely need planning permission. The PD rules are strict on this point.
Boundary and Neighbour Rules
The 7-metre rear boundary rule is one of the most commonly misunderstood conditions. It means the extension (measured from the rear wall of the extension) must be at least 7 metres from the opposite boundary of the curtilage — typically the rear fence.
In practice, this means houses with smaller gardens often cannot build a two-storey rear extension under PD. For example:
- House with 10m rear garden: extension projects 3m, leaving 7m to boundary — just compliant
- House with 9m rear garden: extension projects 3m, leaving only 6m — not compliant
- House with 8m rear garden: any two-storey extension would need planning permission
The upper-floor side window requirement also matters for neighbours. Any window on the side elevation of an upper storey must be obscure-glazed to protect the privacy of adjoining properties.
When You Always Need Planning Permission
Regardless of size or design, you will need planning permission for a two-storey extension if:
- The property is a flat or maisonette: Class A PD rights do not apply to flats
- The property is listed: Listed building consent is always required
- The property is in a conservation area, AONB, National Park, or World Heritage Site: PD rights for extensions are more restricted in designated areas
- An Article 4 Direction removes Class A PD rights: Check with your local planning authority
- The extension is to the side: There are no PD rights for two-storey side extensions
- The 7m rear boundary rule cannot be met: The garden is too small
- The extension would exceed the ridge or eaves height: For example, adding to a bungalow where the current ridge is low
- Planning conditions remove PD rights: Check the original planning permission for the house
Two-Storey vs Single-Storey: Key Differences
| Rule |
Single-Storey Rear |
Two-Storey Rear |
| Max rear projection (detached) |
4m standard / 8m via LHES |
3m |
| Max rear projection (semi/terraced) |
3m standard / 6m via LHES |
3m |
| Max eaves height |
4m (3m within 2m of boundary) |
Cannot exceed original house |
| Rear boundary distance |
No minimum |
7m minimum |
| Roof pitch requirement |
No |
Must match original house |
| Side window restriction |
No |
Obscure glazing required above ground floor |
| Side extensions allowed under PD? |
Yes (single-storey) |
No |
Should You Get a Lawful Development Certificate?
For any two-storey extension, we strongly recommend getting a Lawful Development Certificate (LDC) before starting work. This is a formal written confirmation from the council that your extension is lawful under permitted development.
Why it matters more for two-storey extensions:
- The conditions are more complex and harder to verify yourself
- The 7m boundary rule requires accurate measurement
- Roof pitch matching is subjective and councils may disagree
- An LDC protects you if you sell — buyers’ solicitors will look for evidence of lawfulness
- The cost (around £206 + architect fees) is small relative to the build cost
✅ LDC is especially worthwhile here
Two-storey extensions are higher-value projects and attract more scrutiny from councils. An LDC removes uncertainty and gives you legal certainty before you spend tens of thousands on construction.
Frequently Asked Questions
Can I build a two-storey extension without planning permission?
Yes, in some cases. A two-storey rear extension can be permitted development if it projects no more than 3 metres beyond the original rear wall, stays within the original ridge and eaves height, uses a matching roof pitch, has obscure-glazed upper-floor side windows, and is at least 7 metres from the rear boundary. Side extensions of two storeys always need planning permission.
How far can a two-storey extension go back under permitted development?
A two-storey extension can project a maximum of 3 metres beyond the original rear wall of the house under permitted development. This is the same for detached, semi-detached, and terraced houses. Note this is less than what single-storey rear extensions are allowed — which can go up to 4 metres (detached) or 3 metres (other) under standard PD, or further under the Larger Home Extension Scheme.
Do I need planning permission to add a second storey to an existing extension?
It depends on the size and position of the existing extension. The rules look at the total addition from the original rear wall — so if your existing single-storey extension already projects 3 metres, adding a second storey on top of it would require planning permission (it would be a two-storey addition that projecting 3m, which is at the limit). If it projects less than 3m, there may be PD scope. An architect or planning consultant can advise based on your specific measurements.
Can I build a two-storey side extension under permitted development?
No. There are no permitted development rights for two-storey side extensions. The PD rules for Class A only allow single-storey side extensions (and even those have conditions). Any two-storey addition that extends to the side of the original house will require planning permission.
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