Outbuilding & Garden Office Calculator
Check whether your proposed outbuilding meets the Class E permitted development rules before you order materials or hire a builder. This calculator checks position, height, boundary proximity, garden coverage, and designated land restrictions under the GPDO 2015.
Class E rules at a glance
- Max ridge height: 4m (dual pitched) or 3m (flat, mono-pitch, hip)
- Max eaves height: 2.5m in all cases
- Within 2m of a boundary: max overall height 2.5m (most commonly overlooked rule)
- Must not cover more than 50% of the garden (cumulative with other structures)
- Must not be forward of the principal elevation (no front garden)
- On designated land: max 10m² if more than 20m from the house; no side outbuildings
Enter your address to automatically detect whether the property is in a designated area (conservation area, AONB, National Park).
Check your outbuilding
Answer nine questions about your outbuilding and garden. You will need approximate measurements for heights, distances, and areas. The result checks each Class E rule individually.
Highest point of the roof, measured from natural ground level directly below.
Where the roof meets the wall, measured from ground level. Must not exceed 2.5m in any case.
If within 2m, the overall height limit drops to 2.5m regardless of roof type.
External floor area of the proposed outbuilding.
Total curtilage area (front, side, and rear) excluding the footprint of the original house.
Total footprint of all existing sheds, garages, outbuildings, and extensions already on site. Enter 0 if none.
On designated land, outbuildings over 10m² more than 20m from the house, and side outbuildings, need planning permission.
Building regulations to consider
Exempt buildings
Under 15m² with no sleeping accommodation: usually exempt. Between 15–30m²: exempt if at least 1m from any boundary or non-combustible. Over 30m²: full building regulations apply.
Electrical work (Part P)
Any electrical work in an outbuilding is notifiable under Part P, regardless of floor area. It must be done by a registered electrician who can self-certify, or inspected by building control.
Plumbing and drainage
If your garden office includes a WC, kitchenette, or fixed plumbing, building regulations may apply for drainage connections even if the floor area is under 15m².
Sleeping accommodation
Outbuildings used as self-contained living accommodation are never permitted development. A granny annexe, rental unit, or bedroom requires full planning permission and building regulations.