Planning Rules
Outbuilding Size and Height Limits: Permitted Development Rules (2025)
Outbuildings must stay under 4m ridge height, 2.5m eaves, and 3m if flat-roofed. Here’s every height and size limit explained — including the 2m boundary rule.
⏱ 7 min read📅 Updated June 2025🏠 England only
Quick Answer
Outbuilding height limits depend on roof type, position, and whether you’re in a designated area
Under Part 1, Class E of the GPDO 2015, permitted development outbuildings must be single storey with: a maximum eaves height of 2.5m; a maximum ridge height of 4m for a dual-pitch or hipped roof; a maximum overall height of 3m for any other roof type (flat, mono-pitch, curved). If any part of the outbuilding is within 2m of the property boundary, the maximum height of the entire building is 2.5m — regardless of roof type. These limits apply to all outbuildings in the curtilage including sheds, garages, garden rooms, studios, and swimming pool enclosures.
Outbuilding Height Limits at a Glance
| Rule |
Limit |
| Eaves height (all roof types) |
Maximum 2.5m |
| Ridge height — dual-pitch or hipped roof |
Maximum 4m |
| Ridge/overall height — flat roof |
Maximum 3m |
| Ridge/overall height — mono-pitch (lean-to) roof |
Maximum 3m |
| Any roof type — if within 2m of boundary |
Maximum 2.5m total height |
| Number of storeys |
Single storey only — no upper floors, no mezzanine with sleeping accommodation |
What ‘Eaves Height’ Means
The eaves are the lowest edge of the roof — where the roof overhangs the top of the walls. Eaves height is measured from ground level to this point. The 2.5m eaves limit effectively restricts wall height to 2.5m. Above the eaves, the roof can rise to the ridge height limit (4m for pitched, 3m for flat).
For a flat-roof garden room, the eaves and the ridge are at the same height — so the maximum height is 2.5m (limited by the eaves rule, which is lower than the 3m flat-roof overall limit).
⚠️ A flat-roof garden room can only be 2.5m tall — not 3m. The 3m overall limit for flat roofs is effectively overridden by the 2.5m eaves limit, because on a flat roof the eaves and the top of the building are the same point.
The 2m Boundary Rule in Detail
If any part of the outbuilding is within 2m of the property boundary (any boundary — rear, side, or shared with another property), the maximum height of the entire building is 2.5m. This applies to:
- The walls of the building
- The roof at any point
- Any chimney, flue, or other projection
The 2m is measured from the nearest part of the building structure to the nearest point of the property boundary. Roof overhangs count toward the measurement if they project beyond the wall.
✅ To build a taller outbuilding (up to 4m ridge height), position the entire building — including any roof overhang — more than 2m from every property boundary. Even 2.05m clearance gives you access to the full height allowance.
Floor Area and Footprint Limits
Permitted development for outbuildings has no absolute floor area limit. Instead, the rules impose a coverage limit:
- The total area covered by all outbuildings and extensions (combined) must not exceed 50% of the total curtilage of the original house
- “Original house” means the house as first built, or as it stood on 1 July 1948 — not subsequent extensions
- Existing structures count — a pre-existing garage, shed, or extension all consume part of the 50% allowance
There is also no minimum size for an outbuilding — permitted development applies equally to a small garden shed and a large timber-framed garden room, provided the height and coverage limits are met.
Outbuildings in Conservation Areas and Designated Areas
In conservation areas, national parks, AONBs, and World Heritage Sites, there are additional restrictions:
- Outbuildings, enclosures, and pools to the side of the house are not permitted development — planning permission is required
- Outbuildings to the rear of the house remain permitted development (subject to the standard height and coverage limits)
- The additional restriction applies to the side of the house — defined as the land between the principal and rear elevations on either side
⚠️ ‘Side of house’ is defined by reference to the elevations of the house — not compass direction. On a corner plot, both ‘sides’ of the house may face roads. The restriction catches these cases — if a side elevation faces the road, outbuildings on that side need planning permission in designated areas.
Frequently Asked Questions
How tall can an outbuilding be without planning permission?
The maximum height for an outbuilding under permitted development is 4m to the ridge for a dual-pitch or hipped roof, and 3m for any other roof type. However, the eaves height must not exceed 2.5m in all cases — and for flat roofs, this 2.5m eaves limit is effectively the maximum height of the whole building. If any part of the outbuilding is within 2m of the property boundary, the maximum height of the entire building (including the roof) is 2.5m, regardless of roof type.
What is the maximum size of an outbuilding without planning permission?
There is no absolute floor area limit for outbuildings under permitted development. The rule is that total outbuildings and extensions cannot cover more than 50% of the total curtilage (garden area) of the original house. Existing structures (sheds, garages, previous extensions) all count toward this 50% limit. In practice, a garden room of 20-40m² is within permitted development limits for most typical suburban properties.
Can an outbuilding be two storeys?
No — all outbuildings under permitted development must be single storey. A mezzanine level within a garden room that is used as a sleeping or living area could be considered a second storey. The height limits (maximum 4m ridge, 2.5m eaves) naturally prevent two-storey construction in any case — there is not enough height for two full-height floors within these limits. A two-storey outbuilding requires planning permission.
Do outbuilding PD rules apply to flats and apartments?
No — Part 1, Class E permitted development rights for outbuildings apply only to houses, not flats or apartments. Flats have no Part 1 permitted development rights at all. If you own a ground-floor flat with a garden, any outbuilding in the garden requires planning permission from the local planning authority.
More on Permitted Development Rights
Extensions, loft conversions, outbuildings, solar panels — our complete guide covers everything you can build without planning permission.
Read the Complete PD Guide →
