Planning permission for a garden room or log cabin

Usually not. Most garden buildings fall under Permitted Development, which means no application. What decides it is size, position and use — not what the building is called.

Use is what catches people out. A garden room, office or workshop is normally permitted. Somewhere to sleep and cook is not. An annexe used as separate living accommodation needs an application whatever its size, in all four nations. It is the most common surprise we see.

The figures below are the general limits for each nation. They are guidance, not a decision on your plot: only your council can confirm that. Send us the address and what you have in mind, and we will check it for you before you spend anything.

• Single storey, with eaves no higher than 2.5 m.
• Maximum 4 m overall with a dual-pitched roof, 3 m with any other roof.
• Anything within 2 m of a boundary: maximum 2.5 m overall.
• Behind the principal elevation of the house.
• All outbuildings and extensions together: no more than half the land around the original house.
• No verandas, balconies or raised platforms.
• In a National Park, AONB or conservation area, buildings more than 20 m from the house are limited to 10 m².
• Within the curtilage of a listed building, permission is always required.

Your local planning authority confirms your position, and most will answer an informal enquiry. We can make that check for you instead.

Source: Planning Portal — Outbuildings · figures checked August 2026.

Shaped differently from England, and two of the limits surprise people who have read the English ones.

• At the back of the house.
• Maximum 4 m at the highest point.
• Eaves no higher than 3 m — more generous than England.
• Anything within 1 m of a boundary: maximum 2.5 m — a tighter margin than England’s 2 m.
• Not half or more of the rear garden.
• Not used as a separate home.
• Listed building: 4 m² footprint. Conservation area: 8 m² — much tighter than elsewhere in the UK.

Your council confirms it, and it is worth asking early in a conservation area. Send us the address and we will check before you commit.

Source: mygov.scot — Build a shed, garage or greenhouse · figures checked August 2026.

Close to England, with one extra limit worth knowing.

• Not more than one storey, with eaves no higher than 2.5 m.
• Maximum 4 m with a dual-pitched or hipped roof, 3 m with another roof form, and 2.5 m for a flat roof.
• Anything within 2 m of a boundary: maximum 2.5 m.
• Not in front of the building line of the principal elevation.
• Outbuildings together: no more than 50% of the curtilage.
• Must be incidental to the enjoyment of the house, which excludes separate living accommodation.
• In a National Park, AONB or conservation area, buildings more than 20 m from the house are limited to 10 m².

Your council will confirm it. We are happy to do that check for you first.

Source: GOV.WALES — Planning permission: outbuildings · figures checked August 2026.

• Maximum 4 m overall.
• Eaves no higher than 2.5 m where any part is within 2 m of the boundary.
• Buildings together: no more than 50% of the curtilage, excluding the original house.
• Not in front of the principal or side elevation that faces a road.
• Not within 3.5 m of a rear boundary that adjoins a road — a rule unique to Northern Ireland.
• Domestic purposes only, not a separate dwelling.
• In a conservation area, AONB or World Heritage Site it cannot sit between the house and the boundary, and buildings more than 20 m from the house are limited to 10 m².

Your council planning office confirms it. Tell us the address and we will look at it with you.

Source: Mid and East Antrim Borough Council — Your Home and Planning Permission · figures checked August 2026.

Different people decide them, for different reasons, and you can need one without the other.

• Planning is about whether the building may exist there — size, siting, effect on neighbours.
• Building Regulations are about whether it is safe and warm enough to use — structure, insulation, fire, electrics.

A garden room usually needs neither. A habitable annexe usually needs both.

That is a step, not a stop. There are normally four routes, and we will tell you which we would take.

• Design it to fit. Usually the quickest. Drop the ridge, move it a metre off the boundary, change the roof — and the same usable space stays within Permitted Development.
• Apply. If you want more than the limits allow, an application is a normal part of the project.
• Change the use, not the building. A garden room with a shower is a different proposal from an annexe. Sometimes what you actually want is already permitted.
• Get it in writing. A Certificate of Lawful Development proves you never needed permission. Worth having when you sell.

We check your plot against all of this before you order anything — see Architectural & Planning for what that involves and what we produce.