How Big Can a Garden Room Be Without Planning Permission in the UK?
- Wired Media
- Jul 24
- 3 min read
If you're dreaming of extra space without the hassle of full-scale construction, a garden room is the perfect solution. But before you start sketching floorplans, you might be asking the all-important question: How big can a garden room be without planning permission in the UK?
The good news is that most garden rooms do not require planning permission — as long as you stay within a few key guidelines under Permitted Development Rights.
In this guide, we’ll walk you through exactly how large your garden room can be, what restrictions to watch out for, and when you might need to apply for permission after all.
Permitted Development: What It Means
Permitted Development (PD) allows you to build certain structures on your property without the need for full planning approval, as long as they meet specific size, use, and location rules.
Garden rooms usually qualify under PD if they are:
Single-storey
Not used as self-contained accommodation
Located at the rear or side of the house
Respectful of size and height limits (more below)
PD applies in England and Wales, though Scotland and Northern Ireland have slightly different rules.
How Big Can a Garden Room Be Without Planning Permission?
Here’s a breakdown of the main limits under current UK Permitted Development rules (as of 2025):
Factor | Limit Under Permitted Development |
Maximum height (flat roof) | 2.5 metres (if within 2m of a boundary) |
Maximum height (pitched roof) | 4 metres (at the ridge) and 2.5 metres at the eaves |
Max height near boundary | Must not exceed 2.5m if within 2 metres of any boundary |
Total area coverage | Must not take up more than 50% of your garden (excluding house footprint) |
Number of storeys | Must be single-storey only |
Basement | Not permitted without full planning permission |
Location | Cannot be built in front of the principal elevation (i.e. not in front gardens) |
Use | Must be for incidental use only (e.g. office, gym, studio, lounge) — not a dwelling |
So, in most gardens, you can build a generous garden room up to 30m² in floor space without needing planning permission — as long as it stays within the above limits.
Can You Sleep in a Garden Room?
Using a garden room as a guest bedroom or occasional sleep space is generally fine under PD rules. However, if you intend to use the space as a permanent living space or separate accommodation, this would require planning permission and likely building control approval.
What About Building Regulations?
Even if planning permission isn’t needed, your garden room may still need to comply with building regulations — especially if:
It's over 15m² and used as an office
It’s over 30m² in size
It includes sleeping accommodation
It has mains plumbing, electrics, or heating
At CS Garden Offices, our garden rooms are constructed using fully insulated panels, certified electrics, and durable foundations, meeting the relevant standards for safe year-round use.
Exceptions and Special Cases
You will need planning permission if:
Your property is listed, in a conservation area, AONB, or World Heritage Site
You want to install a balcony, veranda, or raised platform over 30cm
You’re building in the front garden or want the structure to be two-storey
If in doubt, check with your local planning authority.
How to Measure Correctly
Height is measured from the highest ground level next to the base of the building (not from inside the garden).
Area covered is the footprint of all outbuildings combined — so sheds, garages, and greenhouses all count toward the 50% rule.
Frequently Asked Questions
Q: Can I build a 3m high garden room without planning permission? Only if it’s more than 2 metres from the boundary and has a pitched roof (up to 4m ridge height). Otherwise, you must keep it at or below 2.5m.
Q: What’s the biggest size I can go? You can usually build up to 30m² without planning, provided height, location, and use remain within PD rules.
Q: Does the 50% garden rule include the house? No — the 50% calculation is based on your garden excluding the original house footprint.
Summary: How Big Can You Go?
Scenario | Planning Required? |
Garden room up to 2.5m tall, 30m², rear garden | ❌ No (under PD) |
Over 2.5m tall within 2m of boundary | ✅ Yes |
Built in front garden or used as living accommodation | ✅ Yes |
Detached annex with plumbing/sleeping | ✅ Yes (usually) |
Create the Perfect Garden Room — No Permission Needed
At CS Garden Offices, we specialise in designing and building stunning, fully insulated garden rooms that fall within permitted development rules — so you can enjoy the space you need without the stress of applying for planning.
From compact home offices to large multi-purpose rooms, our expert team will help you design a space that’s compliant, comfortable, and built to last.
