Do You Need Planning for a 10ft or 20ft Cabin? Here’s How It Usually Works

I’ve had a few people recently unsure whether they’d need planning for a 10ft or 20ft cabin. Fair question. The answer just isn’t as black and white as people expect.

The short version?
Size on its own doesn’t decide it.

A 10ft cabin can need planning.
A 20ft cabin can fall under permitted development.
And sometimes it’s the other way round.

What planners actually look at

When councils assess these things, they’re not fixated on the footprint first. They’re looking at context:

– Where it’s going
– What it’s being used for
– How close it is to boundaries
– How tall it is
– Whether the property is in a conservation area
– Whether it’s residential or commercial in nature

That framework matters more than the fact it’s “only” 10ft.

If it’s going in a garden

Most garden cabins used as home offices, gyms, studios or storage fall under permitted development — assuming they meet the usual criteria.

In practice that tends to mean:

It sits behind the main front wall of the house.
It’s no more than 2.5m high if within 2m of a boundary.
Outbuildings don’t cover more than 50% of the land around the house.
The use is incidental to the main dwelling.

That last one is the part people miss.

Working from home is fine.
Running a business with regular client traffic is a different scenario.

Often it’s the use that changes the planning position, not the building itself.

If it’s for business use on land

Once you move away from residential garden use — for example onto farmland, a yard, leased land or a separate plot — planning becomes much more likely.

Even for a small 10ft unit.

Because now you’re potentially introducing:

Vehicle movements
Parking
Drainage considerations
Operational use of land
Visibility and access requirements

That’s what planners are assessing. Not just the cabin.

The “temporary” assumption

A lot of people assume that calling something temporary removes the need for planning.

That isn’t automatically the case.

If the structure materially changes how the land is used, it can still require permission — even if it’s only there for a period of time.

Temporary applications exist, but they’re not a loophole.

What about conservation areas or listed properties?

If you’re in a conservation area, or the property is listed, permitted development rights can be restricted.

That doesn’t mean it can’t be done. It just means you shouldn’t assume the normal garden rules apply.

This is usually where a quick check upfront saves a lot of frustration.

Where most confusion actually comes from

In reality, planning confusion rarely comes down to whether something is 10ft or 20ft.

It comes down to:

Use
Location
Impact

Those three carry more weight than length.

The expensive mistake isn’t applying when you didn’t strictly need to. The expensive mistake is installing a unit and then being told to remove or relocate it.

Transport, crane hire, new bases, reinstatement works — it escalates quickly.

A simple way to sense-check it

Before making a decision, ask yourself:

Is this clearly incidental to my house?
Will non-household members be regularly using it?
Is it visible from the road?
Is it within 2m of a boundary and over 2.5m tall?
Is the property in a conservation area?

If more than one of those raises doubt, it’s worth looking at properly before committing.

There isn’t a universal yes or no for 10ft or 20ft cabins. Anyone who gives you one without asking questions is guessing.

Planning is contextual. It always has been.

If you’re unsure about your own setup, you don’t need a full formal application to start with. Most situations can be assessed fairly quickly once the intended use and location are clear.

Better to work it out on paper than after a unit has been delivered