What this checker does, and what it misses
This checker applies three of the most common permitted development conditions for garden buildings in England: whether the building is forward of the principal elevation, whether it exceeds 2.5 m in height within 2 m of a boundary, and whether it exceeds common overall height limits.
Those three catch most straightforward cases. They are not the full set of conditions, and a result of no obvious issue is not permission. The section below lists what the checker does not test, which is the part worth reading.
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Before you rely on it
- Permitted development rules differ across the UK. This checker reflects England; Scotland, Wales and Northern Ireland have their own regimes.
- Height is measured from the highest ground level immediately adjacent to the building, not from your patio or a levelled base.
- Permitted development rights can be removed by an Article 4 direction, by a planning condition on a newer estate, or by a covenant in your deeds.
- The final word rests with your local planning authority. A lawful development certificate is the way to get it in writing.
It means the work does not require an application, provided every condition is met. If one condition is breached the whole thing needs planning permission, and enforcement can require removal. Because the conditions are numerous, a certificate of lawfulness is often worth the modest fee for anything substantial.
How this calculator works
Three tests, any of which flags a possible issue:
Forward of the principal elevation → flag
Within 2 m of a boundary and over 2.5 m high → flag
Over 4 m high → flag
No flags → no obvious issue in these checksWhat this checker does not test. Total outbuilding coverage, which must not exceed half the land around the original house. Eaves height, limited to 2.5 m. The distinction between a dual-pitched roof, limited to 4 m, and any other roof, limited to 3 m. Verandas, balconies and raised platforms above 300 mm, which are excluded entirely. Use as self-contained living accommodation, which is not permitted development. Additional restrictions on designated land — conservation areas, National Parks, Areas of Outstanding Natural Beauty, World Heritage Sites — and on listed buildings, where outbuildings need consent.
Building regulations are separate again. A garden building may be exempt, but electrics, and habitable use, generally are not.
Worked example: a 2.5 m building near a boundary
Using the default figures — 2.5 m high, 1 m from the boundary, not forward of the principal elevation:
- Forward of principal elevation: no
- Within 2 m of a boundary and over 2.5 m: no, it is exactly 2.5 m
- Over 4 m: no
- Result: no obvious issue in these basic checks
This example sits exactly on the limit, which is worth noticing. At 2.51 m it would flag. And even passing all three tests, this building could still need permission — if outbuildings already cover more than half the garden, if the roof is single-pitched and over 3 m, if it has a raised deck, or if the property is in a conservation area. A clear result narrows the question rather than answering it.
Common mistakes
- Treating a clear result as permission. Several conditions are not tested here.
- Measuring height from a levelled base. It is measured from the highest adjacent ground level.
- Forgetting the 50% coverage rule. All outbuildings count together, including existing ones.
- Assuming rules are UK-wide. They differ between the four nations.
- Overlooking covenants and Article 4 directions. Both can remove permitted development rights entirely.
Frequently asked questions
How is height measured?
From the highest point of the ground immediately adjacent to the building, to the highest point of the structure. Building up a level base in a sloping garden raises the effective height on the low side. The eaves height limit of 2.5 m applies separately and is measured the same way.
What is the 50% rule?
The total area covered by outbuildings, extensions and other buildings must not exceed half the area of land around the original house — meaning the house as first built, or as it stood in 1948. Existing sheds, garages and extensions all count towards it, which catches people who have added over time.
Do I need building regulations approval?
A detached single-storey outbuilding under 15 m² is generally exempt, and between 15 and 30 m² may be exempt if it is at least 1 m from a boundary or built of substantially non-combustible materials. Electrical work is notifiable regardless, and anything used as sleeping accommodation is not exempt.
Can I live in it or rent it out?
Not under permitted development. Using an outbuilding as self-contained living accommodation is a change of use requiring planning permission, and it engages building regulations for insulation, ventilation, fire safety and drainage. Home offices and gyms are generally fine as ancillary use; a separate dwelling is not.
How do I get certainty?
Apply to your local planning authority for a Lawful Development Certificate. It costs a fraction of a planning application, and it gives written confirmation that the work is permitted development. Buyers' solicitors ask for it, and it is far cheaper than discovering the problem at sale.
Related tools
References
- GOV.UK — permitted development rights for outbuildings, and Lawful Development Certificates
- Planning Portal — the official England and Wales guide to planning rules for outbuildings
Sources are checked at publication and can change — how I choose and check references.