The permitted development size limits for conservatories are 4m rear projection for detached houses and 3m for others. Here’s every rule explained with practical examples.
Under standard permitted development rules: 4m maximum rear projection for a detached house; 3m for a semi-detached or terraced house. Maximum height 4m. Maximum eaves height 3m if within 2m of a boundary.
The size limits for a conservatory are the same as those for a single-storey rear extension, as set out in Part 1 Class A of the GPDO 2015. These limits determine whether planning permission is required.
The rear projection is the key measurement — it is the distance from the original rear wall of the house to the furthest point of the conservatory.
| House type | Maximum projection (standard PD) | Maximum projection (Neighbour Consultation Scheme) |
|---|---|---|
| Detached house | 4m | 8m |
| Semi-detached or terraced house | 3m | 6m |
Important: the measurement is from the original rear wall — the wall as first built (or as it stood on 1 July 1948). If you have already extended the house at the rear, any existing extension counts towards the limit.
The maximum height for a conservatory under permitted development is:
For a typical lean-to conservatory (single-pitch roof), the eaves height at the back (away from the house) is the relevant measurement if the conservatory is within 2m of a side or rear boundary.
Two further limits apply regardless of rear projection:
For larger conservatories (up to 8m for detached houses and 6m for semi-detached/terraced), the Neighbour Consultation Scheme (sometimes called the “prior approval” process for larger home extensions) allows you to go beyond the standard PD limits provided:
The council can refuse if there are material objections, but the bar is set at impact on adjoining properties — not general planning grounds. The application costs £240 (2025).
| Scenario | Planning position |
|---|---|
| Detached house, 3.5m rear conservatory, no previous extension | ✅ Permitted development (within 4m limit) |
| Semi-detached, 3m rear conservatory, no previous extension | ✅ Permitted development (exactly 3m) |
| Semi-detached, 3.5m rear conservatory, no previous extension | ❌ Exceeds 3m — needs Neighbour Consultation Scheme or planning permission |
| Terraced, 2m previous extension + 1m conservatory = 3m total | ✅ Permitted development (3m total from original wall) |
| Detached, 5m rear conservatory, no previous extension | ❌ Exceeds 4m standard PD — requires Neighbour Consultation Scheme (within 8m) or full planning |
| Semi-detached, conservatory on side of house | ❌ Side extension — needs planning permission (side PD rules are stricter) |
Extensions, loft conversions, outbuildings, solar panels — our complete guide covers everything you can build without planning permission.
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