UK Planning states that an outbuilding must remain below 2.5m in height, otherwise planning permission is required.

My problem is that the ground is uneven, but the roof would be flat, so where do I measure this height? Should it be an average of the tall side and short side, or should it be the tallest side alone?


  • Any chance you could level the ground? Does the law say the building can only be 2.5m tall, or that it can only be 2.5m above grade? Are you planning to make the floor sloped with the grade?
    – Tester101
    Oct 15 '13 at 10:53
  • well i'm going to build a raised base that blends to the floor at the front edge. leveling the floor would mean raising the back to the level of the front, so i would still have the same problem, really! Oct 15 '13 at 11:05
  • 2
    So the roof is level, the floor is level, but the ground is sloped? OR the roof is level, the ground is sloped, and the floor is the ground?
    – Tester101
    Oct 15 '13 at 16:31
  • 2
    How about a picture/drawing?
    – DA01
    Oct 15 '13 at 17:45
  • 2
    Why not give your local government a quick call, and ask them how they measure?
    – Tester101
    Oct 16 '13 at 9:49

Edit to answer new question:

It appears that currently you'd measure the height from "the highest part of the adjoining land.", which would mean that you'd measure from the up side of the slope. Source.

So your building; as planned, is in compliance.

Height’ - references to height (for example, the heights of the eaves on a house extension) is the height measured from ground level. Ground level is the surface of the ground immediately adjacent to the building in question. Where ground level is not uniform (e.g. if the ground is sloping), then the ground level is the highest part of the surface of the ground next to the building. Source

Original answer:

The verbiage of the laws is very important. After some research, I think I've found what you're referring to.

Outbuildings are considered to be permitted development, not needing planning permission, subject to the following limits and conditions:

  • Outbuildings and garages to be single storey with maximum eaves height of 2.5 metres and maximum overall height of four metres with a dual pitched roof or three metres for any other roof.

Which means for a flat roof shed, you can have an overall height of 3m, with an eaves height of 2.5m.


If you want to put up small detached buildings such as a garden shed or summerhouse in your garden, building regulations will not normally apply if the floor area of the building is less than 15 square metres and contains NO sleeping accommodation.

If the floor area of the building is between 15 square metres and 30 square metres, you will not normally be required to apply for building regulations approval providing that the building contains NO sleeping accommodation and is either at least one metre from any boundary or it is constructed of substantially non-combustible materials.

Building a detached garage of less than 30 square metres floor area would not normally need building regulations approval if:

  • the floor area of the detached garage is less than 15 square metres.
  • the floor area of the garage is between 15 square metres and 30 square metres, provided the garage is at least one metre from any boundary, or it is constructed from substantially non-combustible materials.

Quoted text comes from the Outbuildings section, of the Planning Portal.

NOTE: Check with the appropriate government agencies before starting this, or any other project.


All the scrolling of the interweb has led me to believe that the height of an out building is determined by the ground immediately adjacent to the original property. I have only researched ground that falls away from the property, so it won't be relevant if your garden is on a rise Without going into heights of an out-building under permitted development, your out-building can be at the maximum height permitted from the highest point of ground immediately adjacent to the dwelling. So for the picture diagram as of the beginning of this thread, if your property is to the right of the diagram (2.5 meters) then building a level Foundation which would mean a height of 2.8 meters at the far end would be perfectly acceptable, but it is suggested that you check with your local planning authority before carrying out any work. I'm guessing that if your property was at the 2.8 meter side then you would have to dig out at the back, but again this is restricted by the height of a permitted development retaining wall, which I am led to believe is no greater than 1 meter

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