The Quick Size Limits

Under permitted development (Class E, GPDO 2015), there is no absolute maximum footprint for an outbuilding. Instead, the rules use a combination of:

• Height limits — which vary depending on roof type and distance from the boundary
• A 50% garden coverage limit — your outbuildings and extensions together cannot cover more than half the land around the original house (front and back)
• Position restrictions — outbuildings cannot be in front of the principal elevation

Within these parameters, you have significant freedom on the size and footprint of your outbuilding.

Height Rules in Detail

The eaves height restriction of 2.5 metres applies everywhere. The overall height limit then depends on the roof type. But if the outbuilding is within 2 metres of any boundary, the overall height — regardless of roof type — must not exceed 2.5 metres.

Note that height is measured from natural ground level — not from any raised base or platform. If you’re installing a deck or raised base, be careful that the combined structure doesn’t breach the height limits.

The 50% Coverage Rule

This is where many plans run into problems. The total footprint of all outbuildings and extensions combined must not exceed 50% of the curtilage of the original dwelling house (i.e., the garden when the house was built, excluding the footprint of the house itself).

What’s included in the calculation?

• All existing outbuildings — sheds, garages, greenhouses, summerhouses
• Any extensions already added to the house
• The new outbuilding you want to build
• Any garden structures with a roof (pergolas without a solid roof may not count)

What’s excluded?

• The original footprint of the house
• Patios, paths, and decking at ground level
• Open fences, walls, and gates

Real-World Size Examples

These figures assume no extensions have been added to the house (extensions also count against the 50% allowance). If you’ve already added a 30m² extension to your 200m² garden plot, only 70m² is left for outbuildings.

The 2-Metre Boundary Rule

The 2-metre boundary rule is one of the most tripping points for homeowners. If your outbuilding — or any part of it — is within 2 metres of your property boundary, the maximum height of the structure drops to 2.5 metres.

This limit applies to the overall height of the structure, including any ridge or peak. So a standard flat-roof garden room at 2.7m height would not comply if placed within 2 metres of the fence.

The 2-metre measurement is from the boundary — typically the fence line, but legally the boundary as recorded in the title register. The measurement is to the nearest part of the outbuilding (including any eaves overhang).

Exceptions and Special Cases

The rules above apply to standard houses in England. The position changes in certain circumstances:

• Conservation areas, National Parks, AONBs, World Heritage Sites: Outbuildings to the side of a house require planning permission. Limits on size and position may be tighter.
• Listed buildings: Any outbuilding requires listed building consent. The same size rules don’t apply.
• Flats and maisonettes: Class E does not apply to flats — any outbuilding would require planning permission.
• Article 4 Directions: Some councils have used Article 4 Directions to remove PD rights for outbuildings in specific areas.
• New build planning conditions: Some new developments have conditions removing PD rights — check your title deeds.